An Overview of Fish Disease Diagnosis and Treatment in Aquaculture in Bangladesh

Abstract

Aquaculture has rapidly become a vital sector for ensuring global food security by meeting the growing demand for animal protein. Bangladesh, one of the world’s leading aquaculture producers, recorded a production of 4.91 million MT in 2022–2023, largely driven by inland farming systems. Despite this remarkable growth, the sector is highly vulnerable to disease outbreaks, which are aggravated by different factors. Pathogens such as bacteria, viruses, fungi, and parasites cause significant losses, while conventional disease diagnosis in Bangladesh still depends mainly on visual assessment and basic laboratory techniques, limiting early detection. This narrative review highlights recent advances in diagnostics as molecular tools, immunodiagnostics, nanodiagnostics, machine learning, and next-generation sequencing (NGS) that are widely applied globally but remain limited in Bangladesh due to infrastructure gaps, lack of skilled manpower, and resource constraints. Current treatment strategies largely rely on antibiotics and aquaculture medicinal products (AMPs), often misused without proper diagnosis, contributing to antimicrobial resistance (AMR). Promising alternatives, including probiotics, immunostimulants, vaccines, and enhanced biosecurity, require greater adoption and farmer awareness. The near-term priorities for Bangladesh include standardized disease and AMR surveillance, prudent antibiotic stewardship, phased adoption of validated rapid diagnostics, and investment in diagnostic and human capacity. Policy-level actions, including a national aquatic animal health strategy, stricter antimicrobial regulation, strengthening diagnostic infrastructure in institution, are crucial to achieve sustainable disease management and ensure long-term resilience of aquaculture in Bangladesh.

1. Introduction

The rapid expansion of the global human population, increasing urbanization, and modern technology are transforming the world at a rapid pace and significantly increasing pressure on food production systems [1]. As a result, aquaculture has become a vital source of protein, responding effectively to this rising global demand [2,3,4]. Currently, aquaculture stands as the fastest-growing and most productive segment within the food production sector, exhibiting substantial potential to significantly boost fish output to meet future global nutritional requirements. Since 1990, global aquaculture production has risen dramatically by over 650%, highlighting its growing significance [5,6]. In 2022, worldwide aquaculture production achieved a record high of 130.9 million tonnes, marking a 6.6% increase from 2020, with 94.4 million tonnes specifically from aquatic animals. Asia led global aquaculture with 91.4% of the total production, while other regions contributed considerably less: Latin America and the Caribbean (3.3%), Europe (2.7%), Africa (1.9%), North America (0.5%), and Oceania (0.2%). Remarkably, in 2022, aquaculture production of aquatic animals (51%) exceeded capture fisheries for the first time [5]. The global trade in aquatic products reached an unprecedented value of USD 195 billion, a 19% increase compared to pre-pandemic levels [5]. Therefore, there is an urgent need to expand aquaculture production sustainably to meet the food demands of a projected global population exceeding 9.6 billion by 2050 [7], forecasting aquaculture production to reach 109 million MT by 2030 and 140 million MT by 2050 [8]. Within this global context, Bangladesh has emerged as a significant contributor to global fish production, achieving a production output of 4.91 million MT in 2022–2023, of which aquaculture represented 58.03% [9]. Over the past three decades, aquaculture has consistently been the fastest-growing agro-food sector in Bangladesh, particularly inland aquaculture, which has more than doubled from 1.006 million MT in 2007–08 to 2.852 million MT in 2022–23 [9]. Prominent species driving this growth include Indian major carps (Rohu, Catla, Mrigal, Kalibaus, Bata, Gonia), exotic carps (Silver carp, Grass carp, Common carp), Tilapia (Oreochromis niloticus), Pangasius (Pangasius pangasius), and crustaceans such as Penaeus monodon (bagda) and Macrobrachium rosenbergii (golda). Major carp alone contributed 22.06% of national production, followed by Tilapia (8.57%), Pangasius (8.21%), and Shrimp/Prawn (5.52%) [9]. Penaeus monodon and Macrobrachium rosenbergii notably represent Bangladesh’s primary aquaculture export commodities, cultivated in intensive or semi-intensive systems to meet international demand [9]. Despite the rapid growth worldwide, global aquaculture faces significant challenges. The intensification of culture systems, essential to meet increasing global demand, frequently results in issues such as overstocking, reduced water quality, increased fish stress, and greater susceptibility to infectious diseases [10]. Disease outbreaks now represent one of the primary limitations hindering further aquaculture expansion, causing global annual economic losses estimated between USD 1.05 and USD 9.58 billion [11,12]. In countries such as China, India, and Vietnam, disease outbreaks account for more than 30% of total aquaculture production losses [13]. Various pathogens, including bacteria, viruses, fungi, and parasites, pose a significant threat to aquaculture sustainability worldwide. Significant bacterial infections include Aeromonas septicemia, Pseudomonas septicemia, Edwardsiella tarda, Flavobacterium columnare, Streptococcus spp., Flavobacterium branchiophilum, and Vibrio spp. [14,15,16,17]. Parasitic diseases, particularly those caused by protozoan ciliates, monogenetic trematodes (Gyrodactylus spp. and Dactylogyrus spp.), and ectoparasites such as Lernaea spp. and Argulus spp. significantly impact freshwater aquaculture, leading to substantial economic losses globally [18]. Prominent viral diseases affecting aquatic species include infectious haematopoietic necrosis, viral hemorrhagic septicaemia, spring viraemia of carp, koi herpesvirus infection, channel catfish virus, infectious pancreatic necrosis, white spot syndrome, taura syndrome, yellow head, and tilapia lake virus [19,20,21,22,23,24]. Additionally, fungal diseases like saprolegniasis, branchiomycosis, and larval mycosis pose critical risks, causing sudden mortality among aquatic organisms [25,26,27]. As a major hotspot for aquaculture activity, dense and diverse farming systems of Bangladesh also make it highly susceptible to the emergence and spread of aquatic animal diseases. Consequently, disease outbreaks are common and pose serious threats to key cultured species such as carps, tilapia, pangasius, and shrimp. Different types of bacterial, viral, parasitic, and fungal diseases predominantly affect species in the different regions of Bangladesh [28,29,30]. Frequent outbreaks of these diseases result in significant economic losses due to inadequate health management practices and limited biosecurity measures. In Bangladesh, environmental degradation, inadequate feed quality, and limited health management exacerbate disease susceptibility in aquaculture systems [31,32,33]. Increased stocking densities and reliance on artificial feed, enhanced by additives and growth promoters, significantly elevate disease outbreak risks and economic losses due to mass mortalities [34,35,36]. Due to the absence of vaccination programs and inadequate health management facilities, disease control remains an unresolved challenge, resulting in substantial economic losses in Bangladesh [37]. Farmers widely use AMPs, often unmonitored, complicating disease management and potentially posing human health risks in Bangladesh [38,39,40,41]. Worldwide, research and technological advancements have enabled the development of different effective diagnostic tools, including molecular techniques (e.g., PCR, qPCR), immunoassays (e.g., ELISA), image-processing technology, fluorescence in situ hybridization (FISH), fluorescent antibody method, and confocal laser microscopic techniques for the early detection and accurate identification of these pathogens [42,43,44,45,46,47]. Treatment protocols in developed aquaculture systems emphasize the responsible use of antibiotics, vaccine development, improved feed formulations incorporating immunostimulants, and strict biosecurity protocols to reduce pathogen transmission and antimicrobial resistance. In Bangladesh, information regarding fish disease management practices and the extent of biosecurity adoption remains largely underexplored. Diagnosis at the farm level largely relies on visual observation and basic laboratory techniques, while advanced diagnostics are limited to a few research institutions and specialized centers. Treatment is often based on the widespread, and at times unregulated, use of antibiotics, chemicals, and other AMPs, which raises concerns about efficacy, environmental contamination, and public health risks [41,48]. Effective disease prevention and management are essential for ensuring sustainable aquaculture production and maintaining food safety. This can be achieved by implementing comprehensive health management strategies aimed at preventing pathogen intrusion at the farm, regional, and national levels [49]. This article reviews recent advances in fish disease diagnostics and treatment practices in Bangladesh, highlights key diseases impacting aquaculture, discusses therapeutic strategies, and identifies ongoing challenges. Recommendations for improved disease management practices, supporting sustainable aquaculture growth and enhanced fish health outcomes, are also provided.

2. Methods

This review employed a narrative synthesis approach, similar to that used by [50] to compile and analyze the literature on the prevalence of fish diseases and recent advancements in their diagnosis and treatment within Bangladesh’s aquaculture sector. Before that, the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) framework was followed to ensure transparency, efficiency, and reproducibility in the collection, screening, and selection of relevant studies (Figure 1). A comprehensive literature search was conducted across multiple databases, including Scopus and Web of Science, using combinations of keywords such as “fish disease,” “aquaculture health,” “fish disease in Bangladesh,” “molecular diagnostics,” “fish vaccines,” “biosecurity,” “PCR,” “ELISA,” “nanodiagnostics,” and “antibiotic resistance.” The search encompassed peer-reviewed journal articles, review papers, technical reports, theses, government publications, conference proceedings, and institutional research related to the diagnosis, treatment, and management of diseases affecting cultured fish species in Bangladesh. Inclusion criteria emphasized relevance to disease prevalence, diagnostic innovations, therapeutic approaches, and policy-level interventions within the Bangladeshi aquaculture context. Altogether 65 journal articles and 10 reports were reviewed to gather the required information. The included literature, which underwent a narrative review, was thematically analyzed to identify prevailing trends, technological gaps, and emerging strategies related to diagnostics, treatment, and governance of fish health in Bangladesh’s aquaculture industry. This study is limited by its reliance on secondary data and the absence of empirical field research (

Table 1. The study’s eligibility and exclusion criteria (followed by [51,52]).

Criterion	Description
	Inclusion	Exclusion
Time frame	After 2000	Before 2000
Type of Language	English	Non-English
Type of Literature	Peer-reviewed literature, government, and organizational reports	Non-peer-reviewed literature
Area of Content	Fish disease, disease diagnosis, and treatment methods in aquaculture	Non-aquaculture sectors
Publication Status	Published and available online	Published but not accessible
Geographic Coverage	Focus on Bangladesh, where aquaculture has a significant role	None
General Topics	Prevalence of fish diseases, diagnostic methods, treatment and management approaches, biosecurity, and policy interventions	None
Methodologies	Studies employing experimental trials, field surveys, laboratory validation, diagnostic tool development, or review/synthesis on diagnostics and treatments	Studies lacking methodological clarity or without a focus on the diagnosis and treatment of aquaculture diseases

). As such, conclusions are based on the synthesis of existing data rather than primary research.

3. Common Fish and Shellfish Diseases in Bangladesh

A disease can generally be characterized as either infectious or non-infectious. Pathogenic organisms cause infectious diseases, while non-infectious diseases result from genetic, environmental, or nutritional factors [53]. In aquatic systems, the risk of pathogen exposure is particularly high, as fish are constantly in contact with waterborne pathogens that may be endemic or introduced [54]. The dynamic interaction among the pathogen, the host, and the environment influences the development and severity of fish diseases. Notably, stressful conditions such as high stocking density, temperature fluctuations, and hypoxia can accelerate the spread of pathogens and lead to severe disease outbreaks [55] (Figure 2). Disease is the most serious constraint that causes damage to the livelihood of farmers, loss of jobs, reduced incomes, and food insecurity. Studies showed that almost 50% of production loss is due to diseases that are more severe in developing countries. This is because the vast majority of aquaculture farms are concentrated in developing countries [10]. As a developing country, fish diseases in Bangladesh represent a major constraint to aquaculture productivity. Bacterial infections caused by Aeromonas spp. and Edwardsiella spp. are prevalent and often lead to ulcerative symptoms and high mortality. Parasitic infestations, including Ichthyophthirius (white spot) and Argulus (fish lice), are commonly observed in pond systems, especially during seasonal transitions [33]. Additionally, fungal infections such as Saprolegnia frequently affect fish eggs and injured fish [56].

Multiple studies have documented the prevalence and distribution of fish diseases across different regions of Bangladesh (Table 2). For instance, the most prevalent disease symptoms observed by farmers included epizootic ulcerative syndrome (EUS) (31.33%), red spot disease (21.33%), fin and gill rot (16.7%), grayish white spots (6%), external parasites (5%), gulping for air (4%), and dropsy (4%) [57]. Regionally, the highest average disease prevalence was recorded in Rajshahi (27%), followed by Mymensingh (24.6%) and Sylhet (18.3%). Similarly, in northeastern Bangladesh, environmental problems were the most frequently reported cause of disease (100%), followed by argulosis and dropsy (68%), fin and tail rot (45%), and infections caused by Streptococcus spp. (28%), EUS (23%), and nutritional disorders (15%) [52]. These environmental issues were largely attributed to high stocking densities, excessive feeding, poor pond design, and limited water exchange. The highest disease incidence was noted in Sunamganj (32%), followed by Sylhet (24%), Habiganj (23%), and Maulvibazar (21%). In the southwestern coastal districts, including Jessore, Narail, Khulna, Satkhira, Bagerhat, Barisal, and Patuakhali. Aftabuddin et al. [58] identified EUS as the most common disease (18.72%), followed by tail and fin rot (13.19%), red spot disease (11.49%), gill rot (9.36%), and parasitic infestations (8.93%). Shellfish diseases, such as broken prawn antennae (7.23%) and various environmental and nutritional disorders, were also frequently observed. These findings emphasize the importance of improving water quality management and farm-level biosecurity practices, especially in stress-prone areas.

More recently, Haque et al. [59] categorized the fish and shellfish diseases reported in different regions into bacterial, viral, parasitic, and other types (including fungal and nutritional). The study revealed that bacterial infections affected over 33% of farms, while nearly 40% of farms experienced diseases beyond the major infectious categories. Bacterial diseases were particularly dominant in Jashore, Khulna, and Rangamati, whereas viral infections prevailed in Satkhira, with 50% of farms affected. Parasitic diseases were reported across all surveyed regions. More specifically, the commonly reported diseases included EUS (12.30%), dropsy, argulosis, and gill rot (each 10.77%). Lernaeasis, red spot, and tail and fin rot were also prevalent, each affecting 7.69% of farms. EUS, referred to locally as “ulcer,” was especially problematic in Rangamati and Madaripur, while gill rot was also significant in Madaripur. Dropsy was widely reported in Bhola, Rangamati, and Jashore.

For shellfish, the most dominant disease identified was white spot disease (35.71%), followed by antennae degeneration or breakage (16.96%), soft shell disease (13.40%), and yellow head disease in prawns (7.15%). Notably, half of the shrimp farms in Satkhira reported cases of white spot disease. In Khulna, the predominant shellfish issues were antennae degeneration in prawns and white spot disease in shrimp. Non-infectious fish diseases, although less frequently reported than infectious ones in Bangladesh, are increasingly recognized as an emerging concern in aquaculture systems. These conditions primarily stem from nutritional deficiencies, environmental imbalances, and genetic anomalies, which are often underreported due to the absence of structured research and limited field-level diagnostic capacity. For instance, nutritional disorders such as deficiencies in vitamin C, vitamin E, and essential fatty acids have been linked to various pathological symptoms in farmed fish, including spinal deformities, muscular degeneration, and fatty liver [53,60]. Environmental stress-related conditions, such as hypoxia, acidosis, alkalosis, and gas bubble disease, often arise from fluctuations in dissolved oxygen levels, pH, or gas saturation, particularly in static or poorly managed aquatic systems [61]. In addition, genetic disorders resulting from inbreeding and the use of poor-quality broodstock practices commonly observed in hatcheries can lead to skeletal deformities, stunted growth, and reproductive failure in cultured fish. Although comprehensive research on these non-infectious disorders remains limited, field-level observations indicate that such conditions are widespread and represent a hidden threat to the sustainability and productivity of aquaculture in Bangladesh [60,62].

Table 2. The most common infectious fish and shellfish disease, its causative agents, and signs and symptoms in Bangladesh.

Categories	Name of Diseases	Etiological Agents	Signs and Symptoms *	References
Bacterial diseases	Columnaris	Flavobacterium columnare	Ulcers and hemorrhagic patches are observed on the body, along with tail rot and red spots on the caudal peduncle. No visible lesions are found in the internal organs. The fish exhibits sluggish movement.	[33,63]
	Edwardsiellosis	Edwardsiella tarda	Spiraling in circles, opercula flared (gill covers extended), visible skin lesions, pale gills, eye swelling, excessive mucus on the body surface, scale erosion, and ulcers in a few cases.	[29,64]
	Motile aeromonas septicemia (MAS) or Dropsy	Aeromonas hydrophila	Distended abdomen, straw-colored fluid in the body cavity, scale protrusion (dropsy-like appearance), exophthalmia, intestinal inflammation, swelling, and vacuolation of hepatocytes (liver cells).	[53,65,66]
	Fin rot	A. salmonicida	White patches and lesions along the fin edge, fraying and breakdown of soft tissue between fin rays, complete fin loss, and damage to the caudal fin.	[53,57,66,67]
	Vibriosis	Vibrio parahaemolyticus, V. anguillarum	Lethargic behavior, impaired balance, muscle necrosis, anorexia, irregular swimming, and hemorrhages on the body surface. Lesions and ulcers on the skin, and exophthalmia.	[68,69,70,71,72]
	Gill rot	Flavobacterium spp. or Aeromonas spp.	Discolored and necrotic gill tissues, often covered with excess mucus or foul-smelling patches. Infected fish display signs of respiratory distress, gasping at the surface, and reduced activity.	[57,66]
	Streptococcosis	Enterococcus spp. Streptococcus spp.	Unusual appearances were observed, characterized by multifocal pinpoint hemorrhages, abscesses, necrosis, and ascites affecting the skin, fins, muscles, liver, spleen, kidney, blood, and interstitial fluids, particularly involving the central nervous system and brain.	[40,73,74]
	Enteric Septicemia of Catfish	E. ichtaluri	Hemorrhages, swollen abdomen, pop-eye, and “hole-in-the-head” lesions. Affected fish show lethargy and erratic swimming, with high mortality in warm, crowded conditions.	[75,76]
	Bacterial Hemorrhagic Septicemia	Pseudomonas spp.	Affected fish show signs such as hemorrhagic patches on the skin and fins, body ulcers, fin and tail rot, and a swollen abdomen. In advanced cases, internal organs may show signs of congestion and necrosis, with affected fish becoming lethargic and losing appetite.	[77,78]
	Acute Hepatopancreatic Necrosis Disease	V. parahaemolyticus	Primarily affects shrimp during the early culture period, typically within the first 30–35 days after stocking. Infected shrimp often show lethargy, anorexia, and gather near the edges of ponds. One of the most characteristic signs is a pale, shrunken, or atrophied hepatopancreas, accompanied by an empty gastrointestinal tract. In severe cases, shrimp may also exhibit soft shells, blackened gills, and high, sudden mortality.	[79]
Fungal	EUS	Aphanomyces invadans	It is characterized by the appearance of red spots, hemorrhagic patches, and deep ulcers on the skin that can extend into the underlying muscle. Infected fish often exhibit lethargy, loss of appetite, and erratic swimming behavior.	[53,66]
	Saprolegniasis	Saprolegnia paraisitca	Superficial fluffy colonies on skin and gills, hemorrhagic spots on the body, excess mucus secretion, discoloration, and damage to gill filaments.	[30,56]
	Branchiomycosis	Branchiomyces spp. Saprolegnia spp.	Grasping behavior, lethargy, anorexia, swollen opercula, frayed gill tissues, excessive mucus secretion, and damaged opercula.	[30,66]
	Achlya infection	Achlya spp.	Typically appears as white to grayish, cotton-like growths on the skin, fins, gills, or eyes. Affected fish may develop lesions, ulcers, or fin erosion around the infected areas. Behavioral symptoms include lethargy, loss of appetite, and rubbing against surfaces due to irritation. In hatcheries, Achlya can also infect fish eggs, leading to significant mortality. The disease often occurs under stress, injury, or poor water quality conditions.	[56,80]
Viral	Tilapia lake virus disease (TiLVD)	Tilapia lake virus	Eye opacification, skin lesions and discoloration, lesions on the operculum, endophthalmia, and exophthalmia (bulging eyes).	[81,82]
	Viral nervous necrosis diseases (VNND)	Viral nervous necrosis	Neural cell necrosis in the retina, necrosis in the brain, and the spinal cord. Affected fish also become lethargic, lose appetite, and may display darkened body coloration or exophthalmia.	[83]
	White spot syndrome virus (WSSV) disease	White spot syndrome virus	Rapid appearance of white spots or patches on the exoskeleton, especially on the carapace and appendages. Infected shrimp show lethargy, reduced feeding, reddish discoloration, and often high mortality.	[76,84,85]
	Infectious hypodermal and hematopoietic necrosis virus (IHHNV) disease	Infectious hypodermal and hematopoietic necrosis virus	Growth retardation, bent or deformed rostrum, and cuticular abnormalities in shrimp, particularly P. monodon and P. vannamei. Affected juveniles exhibit reddish body coloration, poor molting, and slow movement.	[86]
	Monodon Baculovirus (MBV) disease	Monodon baculovirus	Primarily affects the hepatopancreas of shrimp, particularly the P. monodon species. Infected shrimp often exhibit reduced growth, lethargy, and pale or soft shells. One of the key visible signs is the presence of white or milky fecal strings. Internally, histological examination reveals large eosinophilic occlusion bodies within the nuclei of hepatopancreatic tubule cells.	[86]
	Hepatopancreatic parvovirus (HPV) disease	Hepatopancreatic parvovirus	HPV disease in shrimp primarily affects the hepatopancreas and midgut epithelium of post-larvae and juveniles. Infected shrimp often show growth retardation, reduced feed intake, and pale or atrophied hepatopancreas. In severe cases, the disease can lead to high mortality, especially when co-infected with other pathogens.	[86]
	Yellow head virus (YHV) disease	Yellow head virus	Infected shrimp often show a pale or yellowish cephalothorax due to the yellowing of the hepatopancreas and gills. Other symptoms include reduced feed intake, soft shell, discolored gills, and lethargic swimming near the surface or pond edges. The disease typically spreads rapidly and can result in 100% mortality within a few days in affected ponds.	[87]
Parasitic diseases	Ichthyophthiriasis (Ich) disease	Ichthyophthirius multifiliis	Invades the epithelial tissue of gills, skin, or fins, causes small wounds, and forms visible white spots or nodules where the parasite encysts.	[28,40,88]
	Trichodiniasis	Trichodina spp.	Commonly infest the skin, fins, and gills. Infected fish often exhibit excessive mucus production, frayed fins, and frequent rubbing or flashing against tank or pond surfaces due to irritation. Affected fish may also show signs of respiratory distress, such as gasping at the surface, along with lethargy and reduced appetite. In severe cases, the weakened condition of the fish can lead to secondary bacterial or fungal infections.	[28,89]
	Argulosis	Argulus spp.	Fish infected with Argulus parasites typically exhibit restlessness, flashing behavior (rubbing against objects), and frequent jumping due to skin irritation. Visible round, flat parasites may be seen attached to the skin, fins, or around the eyes. Affected areas often show redness, hemorrhages, or ulcers, leading to secondary infections. Infected fish may also show reduced feeding, lethargy, and, in severe cases, mortality, especially in young or stressed fish.	[28,58,90]
	Ichthyobodosis	Ichthyobodo necatrix	Excess mucus forms a blue-gray or white film on the body and gills, lethargy and listlessness, loss of appetite, and increased mortality.	[28,88,91]
	Fluke	Dactylogyrus spp., Gyrodactylus spp.	Fish infected with flukes often show increased mucus production, especially on the gills or skin, leading to a cloudy or slimy appearance. Common symptoms include flashing or rubbing against objects, frayed fins, and respiratory distress, such as gasping at the water surface when gills are affected. Infected fish may also display lethargy, poor growth, and loss of appetite. Heavy infestations can cause tissue damage, secondary infections, and even mortality, particularly in fingerlings or under stressful conditions	[28,92,93]
	Fish leech	Piscicola geometra	Fish infested with leeches often display restlessness, erratic swimming, and frequent rubbing or flashing against surfaces. Visible leeches may be found attached to the skin, fins, or gills, often surrounded by red, inflamed, or ulcerated areas. Infected fish may show anemia, lethargy, and reduced feeding due to blood loss.	[28,94]

* Signs and symptoms are presented as part of the author’s literature review findings.

Table 2. The most common infectious fish and shellfish disease, its causative agents, and signs and symptoms in Bangladesh.

Categories	Name of Diseases	Etiological Agents	Signs and Symptoms *	References
Bacterial diseases	Columnaris	Flavobacterium columnare	Ulcers and hemorrhagic patches are observed on the body, along with tail rot and red spots on the caudal peduncle. No visible lesions are found in the internal organs. The fish exhibits sluggish movement.	[33,63]
	Edwardsiellosis	Edwardsiella tarda	Spiraling in circles, opercula flared (gill covers extended), visible skin lesions, pale gills, eye swelling, excessive mucus on the body surface, scale erosion, and ulcers in a few cases.	[29,64]
	Motile aeromonas septicemia (MAS) or Dropsy	Aeromonas hydrophila	Distended abdomen, straw-colored fluid in the body cavity, scale protrusion (dropsy-like appearance), exophthalmia, intestinal inflammation, swelling, and vacuolation of hepatocytes (liver cells).	[53,65,66]
	Fin rot	A. salmonicida	White patches and lesions along the fin edge, fraying and breakdown of soft tissue between fin rays, complete fin loss, and damage to the caudal fin.	[53,57,66,67]
	Vibriosis	Vibrio parahaemolyticus, V. anguillarum	Lethargic behavior, impaired balance, muscle necrosis, anorexia, irregular swimming, and hemorrhages on the body surface. Lesions and ulcers on the skin, and exophthalmia.	[68,69,70,71,72]
	Gill rot	Flavobacterium spp. or Aeromonas spp.	Discolored and necrotic gill tissues, often covered with excess mucus or foul-smelling patches. Infected fish display signs of respiratory distress, gasping at the surface, and reduced activity.	[57,66]
	Streptococcosis	Enterococcus spp. Streptococcus spp.	Unusual appearances were observed, characterized by multifocal pinpoint hemorrhages, abscesses, necrosis, and ascites affecting the skin, fins, muscles, liver, spleen, kidney, blood, and interstitial fluids, particularly involving the central nervous system and brain.	[40,73,74]
	Enteric Septicemia of Catfish	E. ichtaluri	Hemorrhages, swollen abdomen, pop-eye, and “hole-in-the-head” lesions. Affected fish show lethargy and erratic swimming, with high mortality in warm, crowded conditions.	[75,76]
	Bacterial Hemorrhagic Septicemia	Pseudomonas spp.	Affected fish show signs such as hemorrhagic patches on the skin and fins, body ulcers, fin and tail rot, and a swollen abdomen. In advanced cases, internal organs may show signs of congestion and necrosis, with affected fish becoming lethargic and losing appetite.	[77,78]
	Acute Hepatopancreatic Necrosis Disease	V. parahaemolyticus	Primarily affects shrimp during the early culture period, typically within the first 30–35 days after stocking. Infected shrimp often show lethargy, anorexia, and gather near the edges of ponds. One of the most characteristic signs is a pale, shrunken, or atrophied hepatopancreas, accompanied by an empty gastrointestinal tract. In severe cases, shrimp may also exhibit soft shells, blackened gills, and high, sudden mortality.	[79]
Fungal	EUS	Aphanomyces invadans	It is characterized by the appearance of red spots, hemorrhagic patches, and deep ulcers on the skin that can extend into the underlying muscle. Infected fish often exhibit lethargy, loss of appetite, and erratic swimming behavior.	[53,66]
	Saprolegniasis	Saprolegnia paraisitca	Superficial fluffy colonies on skin and gills, hemorrhagic spots on the body, excess mucus secretion, discoloration, and damage to gill filaments.	[30,56]
	Branchiomycosis	Branchiomyces spp. Saprolegnia spp.	Grasping behavior, lethargy, anorexia, swollen opercula, frayed gill tissues, excessive mucus secretion, and damaged opercula.	[30,66]
	Achlya infection	Achlya spp.	Typically appears as white to grayish, cotton-like growths on the skin, fins, gills, or eyes. Affected fish may develop lesions, ulcers, or fin erosion around the infected areas. Behavioral symptoms include lethargy, loss of appetite, and rubbing against surfaces due to irritation. In hatcheries, Achlya can also infect fish eggs, leading to significant mortality. The disease often occurs under stress, injury, or poor water quality conditions.	[56,80]
Viral	Tilapia lake virus disease (TiLVD)	Tilapia lake virus	Eye opacification, skin lesions and discoloration, lesions on the operculum, endophthalmia, and exophthalmia (bulging eyes).	[81,82]
	Viral nervous necrosis diseases (VNND)	Viral nervous necrosis	Neural cell necrosis in the retina, necrosis in the brain, and the spinal cord. Affected fish also become lethargic, lose appetite, and may display darkened body coloration or exophthalmia.	[83]
	White spot syndrome virus (WSSV) disease	White spot syndrome virus	Rapid appearance of white spots or patches on the exoskeleton, especially on the carapace and appendages. Infected shrimp show lethargy, reduced feeding, reddish discoloration, and often high mortality.	[76,84,85]
	Infectious hypodermal and hematopoietic necrosis virus (IHHNV) disease	Infectious hypodermal and hematopoietic necrosis virus	Growth retardation, bent or deformed rostrum, and cuticular abnormalities in shrimp, particularly P. monodon and P. vannamei. Affected juveniles exhibit reddish body coloration, poor molting, and slow movement.	[86]
	Monodon Baculovirus (MBV) disease	Monodon baculovirus	Primarily affects the hepatopancreas of shrimp, particularly the P. monodon species. Infected shrimp often exhibit reduced growth, lethargy, and pale or soft shells. One of the key visible signs is the presence of white or milky fecal strings. Internally, histological examination reveals large eosinophilic occlusion bodies within the nuclei of hepatopancreatic tubule cells.	[86]
	Hepatopancreatic parvovirus (HPV) disease	Hepatopancreatic parvovirus	HPV disease in shrimp primarily affects the hepatopancreas and midgut epithelium of post-larvae and juveniles. Infected shrimp often show growth retardation, reduced feed intake, and pale or atrophied hepatopancreas. In severe cases, the disease can lead to high mortality, especially when co-infected with other pathogens.	[86]
	Yellow head virus (YHV) disease	Yellow head virus	Infected shrimp often show a pale or yellowish cephalothorax due to the yellowing of the hepatopancreas and gills. Other symptoms include reduced feed intake, soft shell, discolored gills, and lethargic swimming near the surface or pond edges. The disease typically spreads rapidly and can result in 100% mortality within a few days in affected ponds.	[87]
Parasitic diseases	Ichthyophthiriasis (Ich) disease	Ichthyophthirius multifiliis	Invades the epithelial tissue of gills, skin, or fins, causes small wounds, and forms visible white spots or nodules where the parasite encysts.	[28,40,88]
	Trichodiniasis	Trichodina spp.	Commonly infest the skin, fins, and gills. Infected fish often exhibit excessive mucus production, frayed fins, and frequent rubbing or flashing against tank or pond surfaces due to irritation. Affected fish may also show signs of respiratory distress, such as gasping at the surface, along with lethargy and reduced appetite. In severe cases, the weakened condition of the fish can lead to secondary bacterial or fungal infections.	[28,89]
	Argulosis	Argulus spp.	Fish infected with Argulus parasites typically exhibit restlessness, flashing behavior (rubbing against objects), and frequent jumping due to skin irritation. Visible round, flat parasites may be seen attached to the skin, fins, or around the eyes. Affected areas often show redness, hemorrhages, or ulcers, leading to secondary infections. Infected fish may also show reduced feeding, lethargy, and, in severe cases, mortality, especially in young or stressed fish.	[28,58,90]
	Ichthyobodosis	Ichthyobodo necatrix	Excess mucus forms a blue-gray or white film on the body and gills, lethargy and listlessness, loss of appetite, and increased mortality.	[28,88,91]
	Fluke	Dactylogyrus spp., Gyrodactylus spp.	Fish infected with flukes often show increased mucus production, especially on the gills or skin, leading to a cloudy or slimy appearance. Common symptoms include flashing or rubbing against objects, frayed fins, and respiratory distress, such as gasping at the water surface when gills are affected. Infected fish may also display lethargy, poor growth, and loss of appetite. Heavy infestations can cause tissue damage, secondary infections, and even mortality, particularly in fingerlings or under stressful conditions	[28,92,93]
	Fish leech	Piscicola geometra	Fish infested with leeches often display restlessness, erratic swimming, and frequent rubbing or flashing against surfaces. Visible leeches may be found attached to the skin, fins, or gills, often surrounded by red, inflamed, or ulcerated areas. Infected fish may show anemia, lethargy, and reduced feeding due to blood loss.	[28,94]

* Signs and symptoms are presented as part of the author’s literature review findings.

4. Advances in Disease Diagnosis in Bangladesh

Fish disease identification is a critical aspect of modern aquaculture, essential for timely intervention, effective disease control, and the promotion of sustainable production systems [44]. Rapid and real-time diagnostic methods enable early and accurate treatment, reducing mortality and economic losses. In Bangladesh, disease detection has traditionally relied on conventional methods such as clinical observation and tissue dissection, which are often time-consuming, invasive, and dependent on expert interpretation [95]. However, worldwide recent years have seen the gradual adoption of advanced diagnostic technologies, including molecular techniques like PCR, RT-PCR, and immunoassays such as ELISA, has allowed for non-lethal, specific, and efficient pathogen detection [96].

These tools are now applied to identify major viral and bacterial infections in aquaculture. Moreover, emerging technologies such as image processing, nanotechnology, and rapid test kits like lateral flow assays are showing promise for field-level applications. Despite these advancements, the widespread implementation of modern diagnostic tools across the aquaculture sector in Bangladesh remains limited. To address this gap and strengthen disease surveillance, several innovative platforms are being explored and introduced. The following sections provide an overview of key advancements in fish disease diagnostics in Bangladesh, covering immunodiagnostic methods, molecular tools, image-based technologies, nano diagnostics, and NGS.

4.1. Immunodiagnostic Techniques

Immunological diagnostics play a vital role in fish health management by detecting specific antigens, antibodies, or immune cells from biological samples. These techniques are especially effective for the early detection and monitoring of infectious diseases. Among them, ELISA stands out for its high sensitivity and specificity and can detect trace amounts of particular antigens or antibodies. ELISA works by binding target antigens to a capture antibody, followed by detection through a biotinylated antibody and an enzymatic color reaction, which is quantified via spectrophotometry [97,98]. It allows for early and non-lethal detection of pathogens such as TiLV in tilapia [99], Infectious salmon anemia [100], Viral hemorrhagic septicemia [101], A. hydrophila in carp [102], and Renibacterium salmoninarum, the causative agent of bacterial kidney disease [103]. Another field-friendly immunodiagnostic tool is the lateral flow assay (LFA), also known as a rapid test strip. LFA offer quick, low-cost, and portable diagnostics, making them ideal for on-site pathogen detection [104]. These assays have been developed for several fish pathogens, including Lymphocystis disease virus, Nervous necrosis virus, Infectious pancreatic necrosis virus, Viral hemorrhagic septicemia virus, and Edwardsiella tarda [105,106,107,108]. LFA typically utilize sandwich or competitive formats depending on the nature of the target antigen [109]. Sheng et al. [110] developed an antibody microarray for LCDV that demonstrated high sensitivity (0.0686 μg/mL) and strong concordance with ELISA and IFAT, confirming its reliability for epidemiological applications. Similarly, Zhao et al. [111] introduced a colloidal gold immunochromatographic strip for CyHV-2, enabling rapid (10 min), highly specific detection in goldfish and crucian carp.

Although these immunodiagnostic innovations are well-established immunodiagnostic techniques widely used for detecting specific antigens and antibodies in aquaculture worldwide, their application for fish disease diagnosis in Bangladesh remains limited. Most ELISA-based studies in the country have focused on detecting veterinary drug residues [112], rather than diagnosing infectious pathogens. Therefore, a significant opportunity to expand the use of these for early, non-lethal detection of viral and bacterial fish diseases in Bangladeshi aquaculture.

4.2. Molecular Diagnostics and PCR-Based Tools

Molecular diagnostic techniques are vital tools in fish health management, significantly contributing to sustainable aquaculture practices [113]. These techniques facilitate early, rapid, and accurate detection of pathogens, which is essential for minimizing losses, protecting aquatic ecosystems, and ensuring the responsible management of aquatic resources. Effective diagnosis not only helps maintain healthy fish populations but also supports the long-term viability of aquaculture industries. Due to their high sensitivity, specificity, and speed, molecular approaches have become indispensable for timely intervention and disease surveillance in modern aquaculture systems [113]. Among these techniques, the PCR discovered by Kary Mullis in 1983, has revolutionized pathogen detection through its ability to amplify specific DNA sequences quickly and precisely [114]. PCR variants such as standard PCR, reverse transcription PCR (RT-PCR), multiplex PCR, and randomly amplified polymorphic DNA (RAPD) techniques allow for the detection of viruses, bacteria, and parasites, even at very low concentrations, often before clinical signs appear [113]. The typical PCR workflow involves the collection of tissue samples (e.g., gill, kidney, spleen), preservation in ethanol or freezing, followed by thermal cycling steps including denaturation (96 °C), primer annealing (55–60 °C), and DNA extension (72 °C) [115] (Figure 3). The resulting amplified products are commonly visualized via gel electrophoresis. In Bangladesh, PCR-based diagnostics have been increasingly applied to identify and manage fish and shrimp diseases. For instance, [116] developed a multiplex PCR assay to detect pathogenic bacteria, including Aeromonas spp., Salmonella spp., and Vibrio spp., from water, sediment, and shrimp samples, illustrating the utility of PCR for both disease diagnosis and water quality monitoring in shrimp aquaculture. Subsequently, Haque et al. [117] used conventional PCR with VP664 and VP28 gene-specific primers to detect WSSV in shrimp PL collected from Cox’s Bazar and Satkhira. Their study revealed a WSSV prevalence of 16.93% in the sampled PL, emphasizing the critical importance of early-stage screening before stocking to mitigate potential disease outbreaks. Building on this, Aktar et al. [118] developed a rapid and efficient single-step multiplex PCR protocol for the simultaneous detection of WSSV in shrimp using the host’s 16S rRNA as an internal positive control. They tested four combinations of WSSV- and shrimp-specific primers, all of which produced the expected amplicons. The optimized protocols proved to be faster, less resource-intensive, and highly suitable for routine screening, particularly when using the 16S rRNA + Lo F1R1 and/or 16S rRNA + Lo F2R2 combinations.

Further, Akter et al. [119] investigated the presence of TiLV in farmed O. niloticus in response to reports of unusual mortality. Using both conventional and real-time PCR, along with histopathological analysis, they examined 102 pooled organ samples from 34 ponds in 12 Upazilas. The study found no trace of TiLV, and the authors recommended expanding surveillance using viral metagenomic approaches to better understand unexplained mortalities in tilapia. In another notable application, Rahman et al. [34] used PCR targeting the 16S rRNA gene to identify Streptococcus agalactiae (Group B Streptococcus, GBS) in Nile tilapia and Vietnamese koi affected by popped eye disease. From 330 fish samples across four districts, the isolates were confirmed as S. agalactiae and showed resistance to all seven antibiotics tested. Experimental infection trials further demonstrated high virulence, with 80–90% mortality within 1–6 days, underscoring the pathogen’s threat to freshwater aquaculture. Likewise, [120] explored the host specificity of TiLV by testing 183 tilapia samples from 15 farms in six districts. While 20% of the tilapia samples tested positive for TiLV by RT-qPCR, none of the 15 co-cultured fish species or invertebrates (e.g., crustaceans and insects) tested positive. Experimental infection trials confirmed susceptibility only in Nile tilapia, which exhibited 70% mortality within 12 days. Carp and catfish species showed no signs of infection, suggesting TiLV is currently host-specific to tilapia, though continued surveillance is warranted. Additionally, Achariya et al. [121] applied PCR targeting the 16S rRNA gene (1500 bp) to identify A. veronii in biofloc-cultured Channa striata (striped snakehead) in Sylhet. Clinical signs and bacteriological analysis confirmed the presence of A. veronii. The isolate exhibited multidrug resistance and was linked to high mortality, demonstrating the diagnostic value of PCR in biofloc aquaculture systems.

4.3. Machine Learning (ML) Approaches

The application of ML, a subset of artificial intelligence (AI), is emerging as a powerful tool for advancing fish health diagnostics. ML algorithms use data-driven models to identify patterns and generate predictive insights, often surpassing human capabilities in speed and accuracy [122,123]. Recent developments in computer vision and ML have shown significant potential in the automatic detection of external fish disease symptoms. These approaches enable non-invasive, real-time assessment of fish health, thereby reducing diagnostic delays and allowing for faster decision-making in aquaculture management [124,125].

For instance, Mamun et al. [126] trained ML and deep learning models using a dataset of 1382 fish images categorized into four classes: White Spot, Black Spot, Red Spot, and Fresh Fish. The infected regions were localized using segmentation techniques, and ensemble deep learning models, specifically VGG16 and VGG19, achieved the highest classification accuracy of 99.64%, outperforming ResNet-50 (99.28%) and Random Forest (90.25%). In a related study, Nayan et al. [127] employed an ML-based approach to detect potential disease outbreaks by analyzing water quality data from real aquaculture environments in Bangladesh. Using parameters such as pH, DO, BOD, COD, TDS, EC, NH₃-N, and PO₄³⁻, they successfully predicted disease risk patterns, emphasizing the importance of water chemistry in disease dynamics. Sikder et al. [128] developed an automated image-based disease classification system using fish from Rangamati Kaptai Lake and Sunamganj Haor. Their method combined K-means and C-means fuzzy logic for image segmentation, with feature extraction performed using Gabor filters and Gray-Level Co-occurrence Matrix (GLCM). Classification was conducted using a Multi-Support Vector Machine (M-SVM), achieving 96.48% accuracy with K-means and 97.90% accuracy with C-means fuzzy logic. Similarly, Rajbongshi et al. [129] applied image pre-processing and K-means clustering to identify diseased regions in Rohu fish, followed by ANOVA for feature selection. Of the multiple models tested, the Enable Hist Gradient Boosting algorithm yielded the highest accuracy (88.81%), validating the effectiveness of feature optimization techniques in fish disease detection.

Despite technological advancements, the integration of such systems into farmer-level aquaculture in Bangladesh remains limited. While ML shows strong global potential, most tools are still at experimental or pilot stages, with issues of accessibility, scalability, and farmer adoption yet to be addressed in the Bangladeshi context. Thus, there is a pressing need for expanded research, extension services, and capacity building to facilitate the widespread application of ML- and image-based diagnostic tools. These innovations have the potential to transform fish health management in Bangladesh, but their success depends on bridging the gap between laboratory research and field-level practice.

4.4. Nanoparticles (NPs) in the Diagnosis of Fish Pathogens

NPs have been increasingly applied across various sectors in aquaculture worldwide, including disease detection, drug delivery, water treatment, and feed enhancement [130]. They have been increasingly employed in the rapid and sensitive detection of diseases through a class of technologies known as nanodiagnostics [131]. Among these, gold nanoparticles (Au-NPs) have garnered significant attention due to their exceptional versatility and applicability across a wide range of diagnostic platforms [132,133]. One of the earliest applications of Au-NPs in fish disease diagnostics involved the conjugation of Au-NPs with specific antibodies targeting A. salmonicida, enabling the precise detection of furunculosis in infected fish tissues [134]. Furthermore, Kuan et al. [135] advanced this field by developing an electrochemical DNA biosensor for the detection of Aphanomyces invadans, the causative agent of EUS in fish. This biosensor utilized Au-NPs conjugated with a DNA reporter probe and demonstrated superior detection sensitivity compared to conventional PCR techniques.

Although NPs hold significant potential across various domains of aquaculture, their application in Bangladesh remains limited. Currently, the primary use of NPs in the country is focused on dietary feed supplementation [136,137]. However, the use of nanodiagnostics, particularly for the early and sensitive detection of aquatic pathogens, has yet to be realized in field-level aquaculture practices in Bangladesh. Given the growing challenges of disease outbreaks in intensive and semi-intensive systems, there is substantial future scope for integrating NP-based biosensors and diagnostic tools into Bangladesh’s fish health management strategies.

4.5. Next-Generation Sequencing (NGS)

NGS emerged over a decade ago as a transformative technology for decoding large volumes of genomic data. Its use in clinical diagnostics has since become well established, ranging from targeted gene panels and whole-exome sequencing, also referred to as clinical exome sequencing, to whole-genome sequencing [138]. NGS has significantly advanced pathogen surveillance and disease diagnostics by enabling comprehensive sequencing of entire genomes or specific gene regions, thereby facilitating the early detection of novel, rare, or unculturable pathogens [139,140]. It involves collecting samples, extracting DNA, amplifying specific DNA fragments, sequencing, and finally analyzing genetic data to identify species or pathogens (Figure 4). In the global context of aquaculture, NGS has shown immense promise. Macedo et al. [141] highlighting the role of metagenomics in monitoring and controlling diseases in freshwater aquaculture systems, especially in developing nations.

In Bangladesh, the application of NGS in aquaculture is still at a nascent stage but is gradually gaining momentum, particularly for microbiome profiling and pathogen detection. For example, Foysal et al. [142] applied 16S rRNA gene sequencing to examine the gut microbiota of key carp species such as Labeo rohita, Catla catla, and Cirrhinus cirrhosus, revealing species-specific microbial signatures that are critical for health management and disease resistance. A recent study by Rahman et al. [143] demonstrated the diagnostic application of NGS in Bangladesh aquaculture by sequencing the genome of A. veronii isolated from ulcerative lesions in Heteropneustes fossilis. Using Illumina sequencing technology, the researchers successfully assembled and annotated the bacterial genome, revealing genes associated with virulence, antimicrobial resistance, and phylogenetic relationships. This highlights the power of NGS to decipher complex pathogen profiles and track their evolutionary trajectories during disease outbreaks. Technically, the NGS workflow involves several key steps, including DNA fragmentation, adaptor ligation, amplification via bridge or emulsion PCR, followed by high-throughput sequencing and bioinformatic analysis through genome alignment [144,145]. Despite its transformative potential, the use of NGS in Bangladeshi aquaculture remains limited. The technology requires significant development, skilled personnel, and substantial research funding resources that are currently scarce. However, there is a clear and compelling opportunity for expanding NGS-based research and diagnostics in the country. Future efforts should focus on capacity building, technician training, and investments in sequencing infrastructure to unlock the full potential of NGS in supporting disease surveillance, pathogen discovery, and precision aquaculture in Bangladesh.

5. Treatments and Disease Management Strategies

To mitigate the losses caused by infectious diseases in aquaculture, it is essential to address each health challenge using scientifically validated, locally applicable, and sustainable strategies. The increasing challenges posed by climate change, limited water resources, and the expansion of aquaculture highlight the need for robust epidemiological approaches to ensure aquatic animal health [10,146]. Effective control of fish diseases can be achieved through a combination of improved husbandry and management practices, movement restrictions, genetically resistant strains, dietary supplements, non-specific immunostimulants, vaccination, probiotics, prebiotics, medicinal plant-based treatments, biological control methods, antimicrobial compounds, and water disinfection techniques [147].

In Bangladesh, disease treatment in aquaculture largely depends on the use of chemotherapeutic agents, antibiotics, immunostimulants, and probiotics [38,41,148,149] (Table 3). Several studies have also indicated that the effectiveness or recovery rate following the application of antibiotics, probiotics, and disinfectants under field conditions ranges between 80% and 90% [150,151]. A total of 58 different antibiotics have been documented across the country [37]. Among them, commonly used ones include tetracycline, oxytetracycline, erythromycin, sulfadiazine, and ciprofloxacin. Ciprofloxacin was identified as the most effective antibiotic, achieving 100% recovery in experimentally infected Thai silver barb. In vitro sensitivity and minimum inhibitory dose analyses further confirmed ciprofloxacin as the most potent agent against A. hydrophila, P. fluorescens, and E. tarda [152]. At the farm level, approximately 71% of producers reported antibiotic use during the production cycle, with oxytetracycline, ciprofloxacin, and amoxicillin being the most frequently applied, often for both therapeutic and prophylactic purposes. Notably, antibiotic use was significantly associated with disease occurrence and was more prevalent in pond-based systems compared to enclosure culture [148]. In addition, Salma et al. [153] reported that fish farmers in the Rajshahi region routinely applied a wide range of aqua-chemicals, including antibiotics and pesticides, to mitigate disease risks. The study documented the use of nine active antibiotic ingredients under 11 different trade names, along with pesticides, disinfectants, and other aqua-chemicals in finfish aquaculture. Among these, Renamycin was identified as the most commonly used antibiotic in freshwater finfish farming. However, their unregulated and excessive use has raised serious concerns regarding AMR and the accumulation of drug residues in fish destined for human consumption [154,155]. To maintain water quality, farmers frequently apply disinfectants such as formalin and lime. These are often used without proper diagnosis, standardized guidelines, or knowledge of appropriate dosages [156]. Vaccination, while recognized as an effective disease prevention strategy globally, remains largely underutilized in Bangladesh. Only a few pilot initiatives targeting tilapia and catfish have been reported in commercial settings [157,158]. The use of probiotics and immunostimulants is gaining popularity as safer, sustainable alternatives to antibiotics. Hossain et al. [149] reported the use of 88 probiotic products marketed by 36 companies in Bangladesh’s aquaculture sector. Evidence from both laboratory-based trials and farm-level field studies consistently indicates that probiotics are highly effective under local conditions. Probiotic supplementation in pangasius (Pangasianodon hypophthalmus) significantly enhanced growth, survival, hematological parameters (RBC, WBC, glucose, hemoglobin), gut microbiota composition, and intestinal morphology, with benefits from early application persisting into the grow-out stage, confirming both immediate and long-term positive effects [159]. In tilapia, probiotic treatments improved water quality, growth performance, feed utilization, hematological indices, and intestinal microbial load and morphology, while the combined application of gut, soil, and water probiotics yielded the greatest improvements, supporting their role as an eco-friendly health management strategy [160]. Das et al. [161] reported that tilapia supplemented with probiotics achieved the highest growth, survival, yield, net profit, and lowest FCR compared to other treatments, demonstrating the potential of probiotics to enhance production performance. In catfish species, dietary supplementation with autochthonous Bacillus spp. and Lactobacillus spp. enhanced growth, survival, and feed efficiency in Clarias batrachus and H. fossilis; species-specific benefits were evident, with Bacillus showing superior effects in C. batrachus and Lactobacillus in H. fossilis, while probiotic-fed fish also exhibited greater resistance to A. veronii infection [162]. Moreover, Asha et al. [163] demonstrated that tilapia reared in biofloc systems and supplemented with probiotics showed significant improvements in growth, feed utilization, intestinal histomorphology (villi length, depth, muscle thickness), and gut microbial load, with the Bacillus spp.+Enzyme treatment performs best among all groups. These findings highlight the potential of commercial probiotics as a beneficial and eco-friendly management tool for farmed fish in BFT systems.

Additionally, while biosecurity measures are largely absent in traditional pond-based aquaculture, commercial hatcheries, especially those engaged in export-oriented production, have increasingly adopted biosecurity protocols. These include quarantine procedures, the use of pathogen-free seed, and water filtration systems to minimize the risk of disease transmission [164,165,166].

Table 3. Adopted methods for aquatic disease prevention and control in Bangladesh.

Management Practice	Type	Ingredient	Effectiveness	Purpose of Use	Degree of Implementation	References
Use of probiotics	Growth promoter	Bacillus sp., Lactobacillus sp., Rhodopseudomonas sp., Rhodobacter sp., Rhodococcuss sp., Nitrobacter sp.	Moderate to High	Primarily, enhance fish immunity and improve gut health, leading to better growth performance and disease resistance. They also help maintain water quality by reducing pathogenic microbial loads in the culture environment.	Moderate, increasing in commercial farms, limited adoption in small-scale farms	[149,167,168]
Use of antibiotics	Therapeutic and prophylactic	Tetracycline, oxytetracycline, erythromycin, azithromycin, sulphadiazine, trimethoprim, florfenicol, sulphamethoxazole, amoxicillin, ciprofloxacin, doxycycline, levofloxacin, and neomycin.	High	Primarily used in aquaculture to treat and control bacterial infections in fish and shellfish.	High, widespread during disease outbreaks, often without veterinary guidance	[41,148,153,169]
Vaccination	Preventive	Bacterial strains, especially Enterococcus faecalis, E. hirae, E. faecium, A. hydrophila, A. veronii	High	Used to prevent infectious diseases, boost fish immunity, and reduce reliance on antibiotics. It enhances survival rates and promotes sustainable fish health management, especially in intensive farming systems.	Low, mostly pilot projects and research trials, are rare in commercial farms	[157,158,170,171]
Liming	Preventive	Calcium carbonate (CaCO3), Calcium oxide (CaO), Calcium hydroxide (CaOH), Calcium magnesium carbonate (CaMg (CO3)2)	Moderate	Regulate water and soil pH, neutralize pond acidity, and enhance the availability of essential nutrients. It improves soil quality, promotes plankton growth, and creates a favorable environment for fish health and development by reducing the toxicity of harmful compounds, such as ammonia and hydrogen sulfide.	High, common practice in pond preparation and water pH regulation	[41,156,172,173]
Water quality monitoring	Preventive	N/A	Moderate to High	Prevents poor water conditions that lead to disease or mortality. Ensures optimal environment for fish health and growth and supports early detection of stress indicators (e.g., low DO, high ammonia).	Low to Moderate, regular in commercial or large farms, rare in smallholders	[65,174,175]
Biosecurity protocols	Preventive	N/A	Very High	Biosecurity protocols in aquaculture help reduce disease burden, improve farm and national fish health, and limit global disease spread. They also enhance socio-economic benefits and attract investment by ensuring safer, more sustainable aquaculture practices.	Low, practiced mainly in hatcheries, not in most grow-out farms	[24,49,164,165,166]
Use of immunostimulants	Health management	Glucans and polysaccharides, vitamins, minerals, vitamin-mineral premixes, enzymes, nucleic acids, and plant extracts. hemicellulose, mineral, amylase, amino acid, pectinase, lipase	High	To enhance immune competence and disease resistance in fish and shellfish, and related supplements help maintain overall health by reducing pathogen susceptibility and stress. They support growth, wound healing, stress response, and may influence lipid metabolism, collagen synthesis, and key cellular functions linked to neuromodulation, hormones, and the immune system	Moderate, growing interest but limited awareness among small farmers	[38,176]
Application of disinfectants	Preventive	Polgard Plus, Timsen, Virex, Biogaurd, Lenocide, Emsen, Aqua Cleaner Plus, Formalin and bleaching powder, Benzalkonium chloride (BKC), Pathonil, Micronil, Virocid, Potassium permanganate, Hydrogen peroxide, Sodium percarbonate, and chlorine.	High	Helps to eliminate pathogens and pollution, disinfect water and sediments between production cycles, and improve water quality by increasing dissolved oxygen and reducing ammonia and hardness. Additionally, they prevent bacterial, fungal, and viral infections while also maintaining hygienic conditions in ponds and equipment.	High, common during pond preparation and disease outbreaks	[38,41,153,169,177,178,179,180]
Use of pesticides	Pest removal	Ivermectin, Cypermethrin, L-ascorbic polyphosphate, Quinalphos, Deltamethrin, NaCl, Ethion, Trichlorfon 40%, CaCO3, Ca (OH)2, CaO, Active malathion, KMnO4, Oxalic Acid, Beta-glucan, Fenitrothion, Dextrose anhydrous USP 98% and ascorbic acid BP 2%	High	Primarily used to control ectoparasites like copepods and manage infestations such as Argulus. They are also effective in killing harmful aquatic insects, including backswimmers, dragonfly nymphs, and water scavenger beetles. Additionally, they help reduce fish stress, enhance disease resistance, and eliminate pathogens from cultured fish environments.	Moderate, applied selectively in farms, though regulated and discouraged	[153,181]

Table 3. Adopted methods for aquatic disease prevention and control in Bangladesh.

Management Practice	Type	Ingredient	Effectiveness	Purpose of Use	Degree of Implementation	References
Use of probiotics	Growth promoter	Bacillus sp., Lactobacillus sp., Rhodopseudomonas sp., Rhodobacter sp., Rhodococcuss sp., Nitrobacter sp.	Moderate to High	Primarily, enhance fish immunity and improve gut health, leading to better growth performance and disease resistance. They also help maintain water quality by reducing pathogenic microbial loads in the culture environment.	Moderate, increasing in commercial farms, limited adoption in small-scale farms	[149,167,168]
Use of antibiotics	Therapeutic and prophylactic	Tetracycline, oxytetracycline, erythromycin, azithromycin, sulphadiazine, trimethoprim, florfenicol, sulphamethoxazole, amoxicillin, ciprofloxacin, doxycycline, levofloxacin, and neomycin.	High	Primarily used in aquaculture to treat and control bacterial infections in fish and shellfish.	High, widespread during disease outbreaks, often without veterinary guidance	[41,148,153,169]
Vaccination	Preventive	Bacterial strains, especially Enterococcus faecalis, E. hirae, E. faecium, A. hydrophila, A. veronii	High	Used to prevent infectious diseases, boost fish immunity, and reduce reliance on antibiotics. It enhances survival rates and promotes sustainable fish health management, especially in intensive farming systems.	Low, mostly pilot projects and research trials, are rare in commercial farms	[157,158,170,171]
Liming	Preventive	Calcium carbonate (CaCO3), Calcium oxide (CaO), Calcium hydroxide (CaOH), Calcium magnesium carbonate (CaMg (CO3)2)	Moderate	Regulate water and soil pH, neutralize pond acidity, and enhance the availability of essential nutrients. It improves soil quality, promotes plankton growth, and creates a favorable environment for fish health and development by reducing the toxicity of harmful compounds, such as ammonia and hydrogen sulfide.	High, common practice in pond preparation and water pH regulation	[41,156,172,173]
Water quality monitoring	Preventive	N/A	Moderate to High	Prevents poor water conditions that lead to disease or mortality. Ensures optimal environment for fish health and growth and supports early detection of stress indicators (e.g., low DO, high ammonia).	Low to Moderate, regular in commercial or large farms, rare in smallholders	[65,174,175]
Biosecurity protocols	Preventive	N/A	Very High	Biosecurity protocols in aquaculture help reduce disease burden, improve farm and national fish health, and limit global disease spread. They also enhance socio-economic benefits and attract investment by ensuring safer, more sustainable aquaculture practices.	Low, practiced mainly in hatcheries, not in most grow-out farms	[24,49,164,165,166]
Use of immunostimulants	Health management	Glucans and polysaccharides, vitamins, minerals, vitamin-mineral premixes, enzymes, nucleic acids, and plant extracts. hemicellulose, mineral, amylase, amino acid, pectinase, lipase	High	To enhance immune competence and disease resistance in fish and shellfish, and related supplements help maintain overall health by reducing pathogen susceptibility and stress. They support growth, wound healing, stress response, and may influence lipid metabolism, collagen synthesis, and key cellular functions linked to neuromodulation, hormones, and the immune system	Moderate, growing interest but limited awareness among small farmers	[38,176]
Application of disinfectants	Preventive	Polgard Plus, Timsen, Virex, Biogaurd, Lenocide, Emsen, Aqua Cleaner Plus, Formalin and bleaching powder, Benzalkonium chloride (BKC), Pathonil, Micronil, Virocid, Potassium permanganate, Hydrogen peroxide, Sodium percarbonate, and chlorine.	High	Helps to eliminate pathogens and pollution, disinfect water and sediments between production cycles, and improve water quality by increasing dissolved oxygen and reducing ammonia and hardness. Additionally, they prevent bacterial, fungal, and viral infections while also maintaining hygienic conditions in ponds and equipment.	High, common during pond preparation and disease outbreaks	[38,41,153,169,177,178,179,180]
Use of pesticides	Pest removal	Ivermectin, Cypermethrin, L-ascorbic polyphosphate, Quinalphos, Deltamethrin, NaCl, Ethion, Trichlorfon 40%, CaCO3, Ca (OH)2, CaO, Active malathion, KMnO4, Oxalic Acid, Beta-glucan, Fenitrothion, Dextrose anhydrous USP 98% and ascorbic acid BP 2%	High	Primarily used to control ectoparasites like copepods and manage infestations such as Argulus. They are also effective in killing harmful aquatic insects, including backswimmers, dragonfly nymphs, and water scavenger beetles. Additionally, they help reduce fish stress, enhance disease resistance, and eliminate pathogens from cultured fish environments.	Moderate, applied selectively in farms, though regulated and discouraged	[153,181]

Research institutions such as the Bangladesh Fisheries Research Institute (BFRI) and academic universities have also initiated diagnostic services and training programs, although coverage remains limited. Recently, digital tools and mobile-based advisory services have been piloted to provide real-time disease diagnosis and management recommendations to farmers. Nevertheless, the national framework for disease surveillance, diagnosis, and treatment is still underdeveloped. There is an urgent need for coordinated efforts involving government agencies, research institutions, NGOs, and the private sector to establish disease surveillance networks, promote responsible use of therapeutics, and expand access to low-cost diagnostic services. Emphasis should also be placed on farmer training, awareness campaigns, and the development of standardized treatment protocols.

6. Institutional and Policy Support

Given the rising burden of fish diseases and the limited adoption of modern diagnostic and preventive strategies in Bangladesh, there is a critical need for policy-level interventions. Strengthening institutional frameworks, investing in diagnostic infrastructure, and promoting responsible aquaculture practices are essential for sustainable disease management. In this context, several key policy measures are recommended to improve fish health governance and support the long-term resilience of the aquaculture sector:

Development of a National Aquatic Animal Health Strategy: There is an urgent need for a comprehensive, government-backed policy framework that addresses aquatic animal disease surveillance, diagnosis, treatment, and reporting. This should include a coordinated plan to manage emerging diseases and antimicrobial resistance in aquaculture.

Strengthening Diagnostic Infrastructure: Investment in modern diagnostic labs equipped with PCR, ELISA, and NGS technologies should be prioritized. These labs should be integrated with the Upazilla level for timely disease identification.

Policy Support for Fish Vaccination: Government and donor agencies should fund universities for vaccine research and facilitate the local production and approval of fish vaccines.

Policies should strictly regulate the use of antibiotics and chemotherapeutic agents in aquaculture. Clear guidelines must be established, specifying approved compounds, dosage limits, and withdrawal periods to ensure food safety and minimize antimicrobial resistance. The unregulated or excessive use of these substances should be treated as a punishable offense, with routine monitoring, farm-level inspections, and enforcement mechanisms in place to ensure compliance.

Promoting Farmer Training and Awareness: Extension services must be restructured to provide regular, hands-on training for farmers on disease prevention, biosecurity protocols, and responsible use of chemicals. Public–private partnerships can play a role in delivering such programs at scale.

Biosecurity Legislation and Compliance: Mandatory biosecurity protocols should be incorporated into licensing regulations for hatcheries and commercial farms, with periodic audits and penalties for non-compliance to reduce pathogen transmission risks.

Investment in Research and Innovation: National funding bodies and donor-supported initiatives should prioritize research on nanodiagnostics, probiotics, and molecular epidemiology of aquatic pathogens. Multidisciplinary collaborations involving universities, research institutes, and the private sector should be encouraged.

Establishing a National Aquaculture Disease Database: A centralized digital database for disease outbreaks, diagnostics, and treatment outcomes should be established to inform real-time decision-making and support disease forecasting models.

Establishment of a Fisheries and Aquaculture Council: Although the BSc Fisheries (Hons.) curriculum covers fish disease diagnosis, treatment, and pharmacology, graduates are not legally authorized to prescribe drugs to farmers. This is due to the absence of a statutory body, such as a Bangladesh Fisheries and Aquaculture Council, comparable to the Bangladesh Veterinary Council. Establishing such an institution would provide a regulatory framework for licensing, professional recognition, and safe drug use in aquaculture, thereby enhancing service delivery and support for farmers.

Need for Policy Reform: The National Fisheries Policy of 1998 provided a foundational framework for aquaculture and fisheries development in Bangladesh. However, the industry has undergone significant evolution over the past two decades, with new challenges including antimicrobial resistance, emerging pathogens, environmental degradation, and the need for advanced diagnostic tools. Therefore, there is an urgent need to restructure and update the 1998 policy to incorporate modern disease surveillance systems, promote responsible use of antibiotics and other drugs, support the development of fish vaccines, and institutionalize biosecurity measures. A revised policy should also focus on farmer training, research investments, and establishing legal frameworks for sustainable health management in aquaculture.

7. Challenges and Future Prospects

In Bangladesh, aquaculture is rapidly expanding, but the management of fish health and disease diagnosis still faces significant challenges. A major constraint is the lack of trained personnel in fish pathology and field-level diagnostics, resulting in delayed or misinformed responses to disease outbreaks. Though academic programs have started incorporating fish health education, the gap in practical skills remains. Farmers, in many cases, apply medicines and chemicals without proper diagnosis, often based on peer advice or local chemical sellers, contributing to the growing concern of AMR. Studies have documented the use of over 50 antibiotic compounds, with oxytetracycline and ciprofloxacin being among the most commonly used, many of which are applied without considering withdrawal periods, dosage accuracy, or environmental impact [37]. Moreover, the adoption of vaccines in Bangladesh’s aquaculture is minimal. While research trials have shown promising results, such as vaccines developed for some species, these innovations have not yet reached commercial-scale implementation. Pond-based aquaculture systems, where most fish farming occurs, also lack proper biosecurity protocols [49,165]. In contrast, a few commercial hatcheries, particularly those linked to export production, have adopted measures like quarantine, pathogen-free broodstock, and water filtration [166]. However, such practices are not widespread at the grassroots level. On the other hand, although all hatcheries are considered to be registered, low-quality fish seed is still produced for many reasons, foremost among these being the introduction of non-screened broodstock in hatcheries, poor-quality water source, contamination intake due to a large variety in the way water was sourced by the hatcheries for their poor management practice, including substandard biosecurity and the use of nutritionally imbalanced or poor-quality feed during broodstock conditioning [182,183]. Despite these challenges, the future of disease management in Bangladesh aquaculture holds substantial promise. There is growing recognition of the need for low-cost, farmer-friendly diagnostic tools and mobile-based advisory platforms that can help detect and address diseases in real time. Enhancing vaccine development and making them affordable and accessible through public–private partnerships can significantly reduce disease prevalence. Furthermore, the increasing use of probiotics, immunostimulants, and herbal treatments is encouraging, offering safer alternatives to antibiotics. NPs based fish disease treatments, though currently underutilized in Bangladesh, hold promising potential and could be applied on a broader scale to enhance disease management and reduce dependency on conventional antibiotics. Regular training and awareness campaigns for farmers on judicious use of chemotherapeutics, disinfection practices, and biosecurity can also contribute to improved farm-level resilience. Additionally, updating the outdated National Fisheries Policy to reflect current disease challenges, including AMR, climate-induced disease dynamics, and biosecurity, is crucial. Strengthening disease surveillance, investing in regional diagnostic centers, and ensuring that good aquaculture practices (GAP) and biosecurity protocols are widely promoted can help transition the sector toward a more sustainable and health-conscious future. While the aquaculture sector in Bangladesh faces notable challenges in disease management, targeted research, regulatory reforms, and practical farm-level interventions can pave the way for healthier and more sustainable fish production systems.

8. Conclusions

The rapid growth of aquaculture in Bangladesh underscores its critical role in ensuring national food security, nutrition, and livelihoods. However, the sector’s expansion has been constrained by recurrent disease outbreaks, often exacerbated by high stocking densities, poor water quality, inadequate biosecurity, and indiscriminate use of antibiotics and chemotherapeutics. The review highlights that while Bangladesh has made some progress in adopting advanced diagnostic tools such as PCR, ELISA, LFA, and NGS, their practical application remains limited to research settings and specialized laboratories. Most small-scale farmers continue to depend on traditional visual inspections and unregulated treatments, leading to delayed diagnosis, economic losses, and heightened risks of AMR. The limited adoption of vaccines, inadequate diagnostic facilities, and insufficient farmer awareness further compound these challenges. Emerging innovations, including molecular diagnostics, nanodiagnostics, machine learning-based image recognition, and mobile advisory platforms, offer transformative potential for early disease detection and improved health management. Similarly, probiotics, immunostimulants, and biosecurity protocols present sustainable alternatives to conventional medicines and chemicals. However, a lack of skilled manpower, insufficient policy enforcement, and minimal investment in research and extension services have hindered their widespread use. The outdated National Fisheries Policy (1998) fails to address modern challenges such as AMR, climate-induced disease dynamics, and the need for advanced surveillance systems. Updating this policy framework to incorporate a comprehensive national aquatic animal health strategy is vital. Such a strategy should emphasize the advancement of diagnostic capacity, research funding, farmer training, vaccine production, and strict regulations on antibiotic use. The way forward requires a multi-pronged approach integrating policy reforms, institutional capacity building, and farmer-centered interventions. Strengthening diagnostic facilities at regional and Upazila levels, promoting public–private partnerships for vaccine development, and investing in training programs for farmers and extension workers are imperative. Establishing a national digital database for disease surveillance and outbreak reporting could greatly improve response mechanisms. Importantly, a shift toward responsible and sustainable health management practices through regulated use of therapeutics, biosecurity adoption, and promotion of monoprophylaxis will be key to enhancing sectoral resilience.

Bangladesh stands at a critical juncture where science-driven innovations, regulatory reforms, and grassroots-level capacity building can collectively reduce disease burdens, increase productivity, and enhance the global competitiveness of its aquaculture sector. By bridging the gap between research and field-level applications, the country can transition from reactive to preventive health management approaches. This will not only ensure safer aquatic food production but also strengthen the socio-economic well-being of millions dependent on aquaculture. The adoption of a holistic fish health governance framework encompassing diagnostics, treatment, policy support, and farmer awareness can make aquaculture in Bangladesh more sustainable, climate-resilient, and aligned with national and global food security goals.