Search Results (45)

Streptococcus agalactiae infections severely threaten global tilapia aquaculture, causing substantial mortality and economic damage. The “Zhuangluo 1” (ZL) strain, derived from the fast-growing GIFT Nile tilapia and refined through multiple generations of selection, uniquely combines robust resistance to S. agalactiae with improved growth traits. This study examined gene expression and regulation of gill mucus microbiota in ZL during experimental S. agalactiae challenge. 16S rRNA sequencing revealed Flavobacterium, Vogesella, Hydrogenophaga, Acidovorax, Rheinheimera, and Deinococcus as prominent genera in the gill mucus microbiome of ZL across time points. Transcriptome time-course analysis identified differentially expressed genes in gills of ZL that were predominantly enriched in cytoskeleton in muscle cells and motor protein pathways. Abundances of the dominant genera Flavobacterium and Hydrogenophaga showed significant correlations with genes regulating mucus secretion, mucin glycosylation, immune modulation, and oxidative stress response in ZL. Untargeted metabolomics of gill mucus revealed substantially higher levels of metabolites potentially linked to microbial metabolism and host–microbiota interactions in ZL. A complementary genome-wide association study for resistance in ZL further localized genes underlying these expression–microbiota associations. These findings elucidated microbiota–host interactions between ZL and gill mucus microbiota, and provide more insights into the role of mucus regulation in disease resistance. Full article

The present study aimed to evaluate whether commonly used condition indices reflect parasite load and bacterial colonization in juvenile Cyprinus carpio under natural environmental conditions in the Lower Danube River. A total of 260 specimens were examined for parasitological, microbiological, and biometric parameters, including 20 individuals analyzed for bacterial communities. Twenty-three parasite taxa belonging to eight major taxonomic groups were identified. Ectoparasites were found on the gills, skin, and fins, with monogeneans and ciliates, notably Dactylogyrus ssp. and Trichodina ssp., representing the dominant groups. Infection intensity was generally low to moderate, and histopathological examination revealed only mild epithelial alterations, including focal hemorrhage and mucus hypersecretion in more heavily infected individuals. Microbiological analysis identified six bacterial taxa associated with the skin, with Aeromonas hydrophila being the most frequently detected species. Correlation analyses showed no significant relationships between parasite abundance and condition indices (Fulton’s K, Le Cren’s Kn, scaled mass index, and BMI), although a slight reduction in Fulton’s K was observed in infected individuals. These findings indicate a stable host–parasite–microbiota equilibrium under natural environmental conditions. The results provide baseline ecological data that contribute to understanding fish health dynamics in the Lower Danube River and may support future monitoring and management strategies. Full article

The accumulated ammonia within the recirculating aquaculture systems threaten fish health, while little is known about the influences during early fish ontogeny. Using larval and juvenile yellow catfish (Pelteobagrus fulvidraco) as a model, a comprehensive experiment exposing fish to varying total ammonia nitrogen concentrations (0, 10, 20 mg/L for larvae; 0, 25, 125 mg/L for juveniles) was conducted to evaluate the effects on gill transcriptome and microbiota along with the serotonergic regulation. First, the serotonin (5-HT) signal, which controls oxygen chemoreception and ventilation, was mainly detected in the surface of the body of the larvae, and then shifted to gill filaments of juveniles, showing a transition from cutaneous to branchial respiration. Both larval and juvenile yellow catfish exhibited reduced survival, damaged gill structure, and elevated 5-HT expression after ammonia exposure, as well as upregulated tph1b, slc6a4b, scgn and lama5 expression with the increased ammonia concentration, indicating the effects on respiratory function via serotonergic regulation. Further transcriptome analysis was conducted in juveniles to identify the differentially expressed genes (DEGs) and thus, to illustrate more detailed responses after ammonia exposure; KEGG enrichment analysis of DEGs indicated the coping strategy shifted from metabolic buffering to metabolic elimination via glutamine synthesis with the increased ammonia level. The qRT-PCR experiment also identified the increased expression of genes involved in the urea cycle—such as ass1, asl and glula—with the increased ammonia level. Considering the potential contributary role of microbiome to gill health, 16S sequencing was conducted on the gill in the control and the 125 mg/L ammonia-exposed group. Ammonia exposure at 125 mg/L induced significant variation in Simpson index and a marked decline in β diversity. Notably, the abundance of opportunistic pathogens such as Pseudomonadota increased, while the abundance of Deinococcota and Deinococcus—which were renowned for exceptional stress resistance capacity—decreased after ammonia exposure. Thus ammonia exposure disrupts the transcriptomic and microecological balance within gill mucosa, which may elevate the risk of pathogenic infection. Overall, our study provided the first evidence of serotonergic regulation on early fish respiration during ammonia exposure, and also offered new theoretical insights into the involvement of microorganisms in ammonia toxicity. Full article

Background: Aeromonas veronii is an important bacterial pathogen in crucian carp and can cause serious disease outbreaks and substantial economic losses in aquaculture. Objectives: To evaluate how A. veronii infection and its inactivated vaccine modulate immune responses in Carassius auratus. Methods: 270 juveniles were allocated into three groups: a saline-injected control group (Ctrl), a vaccination group receiving an inactivated A. veronii vaccine (Vac), and an artificial infection group (AIG) subjected to stimulation. Liver, spleen, head kidney, gill, and intestine samples were collected from fish after anesthesia. The relative transcript levels of IgM, IgD, BAFF, MHCII, CD4, BCL6, MyD88, and NF-κB were quantified. For liver transcriptome analysis, the effective library concentration was determined. And the 16S rRNA gene resulting reads of fish gill symbiotic microbiota were processed for downstream bioinformatic analysis. Results: The results showed that the Vac achieved an RPS of 73.33%, and vaccination significantly upregulated multiple immune-related genes in different fish organs. With BAFF transcription across organs emerging as a robust sentinel readout. The Pearson correlation coefficient (r) of BAFF between other genes were all ≥0.8. GO and KEGG enrichment analyses indicated that AIG had more DEGs than Vac (5885 vs. 4008) and Ctrl (6910 vs. 6178), respectively. Some genes in AIG revealed significant over-representation of immune pathways, such as BCL6, MyD88, and NF-κB. The fish gill microbiota comprised a diverse set of low-abundance taxa, the phylum level was dominated by Proteobacteria and Fusobacteriota across all groups; whereas, the Vac group remained broadly closer to the Ctrl group in overall composition. Conclusions: These results indicated marked post-challenge immune–metabolic coupling in the liver, and suggested coordinated immunophysiological interplay between the liver and the spleen. Gill microecology of symbiotic bacteria was affected by vaccination or challenge reactions, which in turn affects the health of the gills or the organism itself. Full article

Hypoxia frequently triggers mass mortality events in pearl oysters during the summer months. Hypoxic preconditioning (HP), repeated exposure to sublethal low-oxygen conditions, has been proposed as a potential strategy to enhance stress resistance. Here, we investigated how HP affects hypoxia tolerance in the pearl oyster Pinctada fucata martensii, with emphasis on host apoptotic and immune regulation and the gut microbiota. Pearl oysters assigned to HP (experimental group, EG) and to a non-preconditioned control group (CG) were subjected to sustained hypoxic challenge (1.5 ± 0.1 mg/L DO for 15 days). HP significantly increased the expression of apoptosis- and immunity-related genes (MyD88, IκK, NF-κB) while suppressing JNK expression in gills after extended hypoxia (MyD88: EG 2.26 ± 0.65 vs. CG 0.96 ± 0.29, p < 0.05, ~2.3-fold increase; NF-κB: EG 1.50 ± 0.20 vs. CG 0.81 ± 0.31, p < 0.05, ~1.8-fold increase; IκK: EG 1.55 ± 0.38 vs. CG 0.65 ± 0.12, p < 0.05, ~4.0-fold increase; JNK: EG 0.49 ± 0.25 vs. CG 1.44 ± 0.51, p < 0.05, ~0.34-fold), consistent with a pre-activated yet controlled stress response. In parallel, HP markedly reshaped the intestinal microbial community under hypoxia, increasing alpha diversity (Ace, Chao, and Sobs indices) and enriching potentially beneficial bacterial phyla such as Planctomycetota, Nitrospirota, and Fusobacteriota, groups often linked to nutrient cycling and short-chain fatty acid production. Collectively, these results suggest that HP-enhanced hypoxia tolerance in P. f. martensii is associated with coordinated modulation of host apoptotic and immune signaling and concomitant shifts in gut microbiome diversity. These findings highlight the role of the host–microbiota axis in environmental acclimation and suggest that HP may be a practical tool for improving bivalve performance under hypoxic stress in aquaculture. Full article

Ocimum basilicum essential oil (OBEO) is an effective anesthetic and sedative for large yellow croaker (Larimichthys crocea) during live transport. This study aimed to assess the impact of OBEO on various physiological and biochemical parameters during live transport, thereby enhancing animal welfare and survival. Fish were exposed to 0 and 5 mg/L OBEO for 72 h during transport. Blood and liver samples were collected every 12 h after transport to evaluate blood biochemistry, tissue damage, oxidative stress-related and inflammation-related gene expression, intestinal microbiota, and liver metabolomics. The results demonstrated that the OBEO treatment significantly reduced serum cortisol levels and heat shock protein 70 (p < 0.05) while increasing the activity of liver antioxidant enzymes in large yellow croakers. Furthermore, compared to the control group, the expression of genes related to oxidative stress and inflammation was upregulated (p < 0.05), thereby enhancing the antioxidant and anti-inflammatory capacities of the fish. Microscopic examination of gill tissues revealed that OBEO alleviated morphological damage. Additionally, OBEO treatment altered the composition of intestinal microbiota, which contributed to the regulation of inflammatory responses. Moreover, liver metabolomics analysis identified key metabolic pathways, including arachidonic acid metabolism, steroid hormone biosynthesis, and amino acid metabolism, which could mitigate liver damage and enhance antioxidant and immune functions. In conclusion, OBEO effectively reduces transport stress in large yellow croakers through physiological, molecular, and metabolic mechanisms, providing a promising strategy to improve animal welfare and survival rate during live transport. Full article

Widespread in coastal environments, artificial light at night (ALAN) is suspected to disrupt organisms’ biological rhythms by altering natural light cycles and thus constitutes a growing threat to these ecosystems. This study evaluates the effects of ALAN exposure at low and realistic intensity (~1 lx) on a coastal keystone species, the oyster Crassostrea gigas. The results reveal that ALAN significantly impairs the expression of core circadian clock genes (CgClock and CgBmal1) as well as the valve opening behavior, affecting rhythmic characteristics such as its robustness and daily profile. At the same time, ALAN leads to a decrease in daily shell growth and to a disruption of the gill microbiota, associated with an obliterated day/night difference in microbial alpha diversity. A direct correlation between a decrease in daily rhythm robustness, limitation of shell growth, and some microbial strands is shown, suggesting that biological rhythm disruption caused by ALAN might have harmful physiological consequences in oysters. Full article

In this study, the synergistic effects of dietary Bacillus velezensis AAHM-BV2301, silica nanoparticles (SiNPs), and chitosan (CS) on the growth performance, innate immunity, gut microbiota, and disease resistance of Asian seabass (Lates calcarifer) fingerlings were evaluated. A total of 400 fish (11.25 ± 2.12 g) were assigned to five dietary treatments for 30 days: control, BV (1 × 10⁸ CFU/kg feed), BVSiNP (1 × 10⁸ CFU/kg + 2 mg SiNP/kg), BVCS (1 × 10⁸ CFU/kg + 15 g CS/kg), and BVSiNPCS (combined additives at the same concentrations). The growth indices (WG, SGR, RGR, and FCR) significantly increased in the fish fed BVSiNPs, whereas the level of innate immunity increased across all the supplemented groups, with BVCS and BVSiNPCS having the strongest respiratory burst and lysozyme activities. The tissue-specific modulation of immune-related genes (α2M, HSP70, Mx, and C3) was most pronounced in BVSiNP-fed fish, particularly in the gills and liver. Gut microbiome profiling revealed enrichment of Cetobacterium somerae in response to BV-based treatments, whereas BVSiNPCS induced the greatest increase in microbial richness and network connectivity. Postchallenge survival against Vibrio vulnificus was significantly greater in the BV and BVSiNP groups (p < 0.05). Overall, SiNPs acted as functional enhancers of the B. velezensis probiotic, supporting improved growth, immune activation, and microbiota restructuring. These results highlight the potential of nanoparticle-integrated synbiotics for microbiome-targeted health management in aquaculture. Full article

There is limited understanding regarding the potential toxicity of nano-silver to crayfish. This study aims to evaluate the histopathological changes, oxidative stress, transcriptomics, and intestinal microbiota changes in different tissues of crayfish after exposure to nano-silver. The results showed that exposure to nano-silver caused pathological changes in the muscles, hepatopancreas, and gills of crayfish. Damage to muscular tissue progressively worsened with increasing concentrations of nano-silver, leading to a gradual widening of the gaps between muscle fibers. Nano-silver enlarged hepatopancreatic lumen and epithelial vacuolation, while the structure of the gills became disorganized, with severe damage to the gill membranes. The activities of peroxidase (CAT), superoxide dismutase (SOD), and glutathione reductase (GSH), as well as the content of malondialdehyde (MDA) in the muscles, hepatopancreas, and gills, were altered due to nano-silver exposure. Furthermore, along with the alteration of intestinal flora, there were alterations in the diversity of intestinal microbiota, an increase in the abundance of Bacteroides and Ca_Bacilloplasma, and a decrease in the abundance of Citrobacter. The abundance of harmful bacteria increased, causing intestinal inflammatory damage. Totals of 1549 and 1305 differently expressed genes (DEG) were found in the muscles and hepatopancreas, according to transcriptome analysis. Significantly affected pathways included the PPAR signaling pathway. These findings provide valuable insights into the use of nano-silver in the aquaculture of crayfish. Full article

The application of alizarin dye for the marking of fish is a widely adopted practice in post-stocking monitoring programmes. Nevertheless, concerns regarding the welfare implications of alizarin staining persist. The present study conclusively demonstrated that ARS dye exerts instantaneous and protracted deleterious effects on the physiological parameters (gill ventilation frequency, homeostasis in the gut microbiota, total number of erythrocytes and leukocytes) and body fitness (total length, weight and Fulton’s condition factor) of S. trutta fry. The validity of the dye-marked fish stocking effectiveness studies is called into question by these findings. Full article

White-gill disease has emerged as one of the major health threats in large yellow croaker Larimichthys crocea (Richardson, 1846) aquaculture, yet its underlying microbial mechanisms remain poorly understood. In this study, we investigated the gut microbiota of healthy and white-gill diseased L. crocea across different growth stages and aquaculture locations using 16S rRNA gene amplicon sequencing and bioinformatics analysis. Across both juvenile and adult fish, as well as multiple sampling locations, diseased individuals consistently exhibited significantly reduced microbial richness and evenness compared to healthy counterparts, along with a clear divergence in community composition. Notably, the relative abundance of Photobacterium damselae subsp. damselae was markedly increased in diseased fish, especially juveniles, accompanied by a decline in beneficial genera such as Bacillus. Co-occurrence network analysis revealed simplified microbial interactions and decreased community stability in gut of diseased fish. Null model analysis further indicated that stochastic processes dominated gut microbial assembly, with a higher contribution in diseased individuals, suggesting weakened host selection pressure and enhanced random colonization under disease conditions. These findings highlight the important role of gut microbiota dysbiosis in the development of white-gill disease and provide new insights into microbiota-based diagnostics and ecological strategies for disease prevention in marine aquaculture. Full article

Antioxidant and microbiota in different mucosal sites of fish play important roles. However, relevant research is lacking for rice flower carp (Procypris merus). This study investigated antioxidant and microbiota characteristics across different mucosal sites (gill, skin, and intestine) of this fish. Antioxidant analysis revealed the following: catalase activity followed gill > intestine > skin (p < 0.05); total superoxide dismutase activity showed intestine > gill > skin (p < 0.05); malondialdehyde level in the gill significantly exceeded the skin and intestine (p < 0.05); and, superoxide anion level ranked gill > intestine > skin (p < 0.05). The intestinal microbiota had the significantly lowest α-diversity (p < 0.05). Across different mucosal sites, LEfSe analysis revealed differentially abundant genera, and microbial functional prediction (BugBase) showed significant differences in Forms Biofilms, Potentially Pathogenic, Stress Tolerant, and Gram-Positive (p < 0.05). Correlation analysis between differentially abundant genera and antioxidant indicators revealed multiple significant positive correlations (p < 0.05) but no significant negative correlations (p > 0.05) in the gill; only two significant negative correlations (p < 0.05) and no significant positive correlations (p > 0.05) in the skin; and no significant correlations (p > 0.05) in the intestine. Collectively, these findings might contribute to the microecological regulation of rice flower carp. Full article

New Zealand abalone (Haliotis iris) holds ecological, economic, and cultural value, with wild stocks supporting fisheries and an emerging aquaculture industry. Wild-caught adult abalone are often used as broodstock, but captivity can affect spawning and offspring quality. This study is the first to profile wild and farmed H. iris broodstock using histology, proximate composition, microbiome, and metabolomics analyses. Histology showed higher gonadal abnormalities in farmed abalone, while wild abalone exhibited increased ciliates in their gills, indicating richer marine–microorganism interactions. Microbiome analyses revealed a higher microbial richness and diversity in the buccal cavity of wild abalone. The core microbiota phyla across both groups included Proteobacteria, Bacteroidota, Campylobacterota, Fusobacteria, and Firmicutes. Proximate analyses showed higher muscle protein in farmed abalone, while gonadal tissue partitioned by sex showed higher fat in females and higher protein in males. Metabolomics revealed altered amino acid metabolism in the adductor muscle, carboxylic acid metabolism in the gonad, and fatty acid metabolism in the foot. This investigation expands our understanding of the physiological and microbial differences between wild and farmed abalone, showing altered gonad and muscle conditions from prolonged captivity and highlighting the need for greater microbial diversity in cultured stocks. Full article

Aquaculture plays a vital role in meeting the global demand for high-quality protein. However, the fish industry is challenged by infectious diseases, including gill conditions such as epitheliocystis. Epitheliocystis is characterized by cyst-like epithelial lesions, which occur in the gills of fish, and is associated with intracellular bacteria including Chlamydia-related bacteria. Although epitheliocystis was initially regarded as of low significance, attention is increasing due to its impact on commercially important fish species in intense farming conditions. This review evaluates the roles of aquatic chlamydiae as pathogens contributing to fish morbidity and mortality, and as members of fish microbiota. Additionally, Chlamydia-related bacteria are thought to be involved in complex gill disease (CGD), characterized by lamellar fusion, epithelial hyperplasia, and inflammation. Recent discoveries have expanded the diversity of Chlamydiota isolated from fish, with novel species such as Candidatus (Ca.) Panilichlamydia rohitae, Ca. Piscichlamydia trichopodus, and Chlamydia vaughanii identified in different fish hosts. Most causative agents of epitheliocystis have not yet been cultured in vitro, although C. vaughanii, the first Chlamydiaceae member isolated from fish, was successfully cultured. As C. vaughanii was recently shown to be able to propagate in mammalian cells, it raises concerns about its zoonotic potential, although a pathogenic role has yet to be described. Full article

This study aims to investigate the response of surface bacterial communities in Trachinotus ovatus to Cryptocaryon irritans infection at different stages of a single infection cycle (0~168 h). These samples were analyzed using high-throughput 16S rRNA sequencing. Alpha diversity analysis showed a reduction in the richness and diversity of skin microbiota during infection, with partial recovery post-detachment. Beta diversity analysis revealed distinct structural shifts in skin microbiota at early (24 h) and post-detachment (168 h) stages compared to other phases, while gill microbiota remained stable except during detachment. At the phylum level, Proteobacteria, Actinobacteriota, Bacteroidetes, and Firmicutes were dominant on the skin at different stages, whereas the gill microbiota was predominantly Proteobacteria (>90%). At the genus level, opportunistic pathogens, such as Vibrio and Nautella, increased in relative abundance on the skin with the infection progression, while gill microbiota composition barely changed. The hepatic bacterial load continued to increase with infection duration. These findings indicate that C. irritans alters microbiota composition on skin, facilitating pathogen invasion, thereby elevating the risk of secondary bacterial infections in T. ovatus. Full article