Fishes

15 pages, 3029 KB

Open AccessArticle

Correlation Analysis of Gut Microbiota of Fish in Yi’an Reservoir with Water Quality Parameters and Aquatic Environment Microbiota

by Jun Wang, Tienan Li, Pengpeng Qiu, Ning Zhang, Weiwei Guo, Shuang Liu, Tingyu Li and Ji Chen

Fishes 2026, 11(2), 77; https://doi.org/10.3390/fishes11020077 - 27 Jan 2026

Abstract

Yi’an Reservoir is located on a major tributary of the Baoquan River and hosts abundant aquatic resources, with Cyprinus carpio, Carassius auratus, and Hemiculter leucisculus as the dominant fish species. Water quality parameters significantly shape fish gut microbiota, which in turn [...] Read more.

Yi’an Reservoir is located on a major tributary of the Baoquan River and hosts abundant aquatic resources, with Cyprinus carpio, Carassius auratus, and Hemiculter leucisculus as the dominant fish species. Water quality parameters significantly shape fish gut microbiota, which in turn plays a crucial role in host physiological functions. This study aimed to characterize the water quality parameters in Yi’an Reservoir and identify the microbial communities in both the aquatic environment and fish guts (C. carpio, C. auratus, and H. leucisculus) through 16S ribosomal RNA sequencing. The objective was to examine the associations of water quality parameters and aquatic environmental microbiota with the assembly of gut microbial communities in fish inhabiting this reservoir system. The water quality parameters showed significant site-specific differences, of which temperature and dissolved oxygen were highest at Location B, while pH was highest at Location A. The Cyanobium_PCC-6307 was identified as a major differentially abundant taxon at the genera level across different sampling sites. Furthermore, the gut microbiota of the same fish species exhibited substantial variation across different sampling sites. Redundancy analysis identified distinct environmental drivers at each location. Specifically, pH, conductivity, and total dissolved solids (TDS) showed positive correlations with the gut microbiota at Location A. In contrast, temperature, dissolved oxygen (DO), and the environmental abundance of Cyanobium PCC-6307 were positively correlated with the gut microbiota at Locations B and C. This study provides important insights for the conservation and management of aquatic resources in reservoir ecosystems. Full article

(This article belongs to the Section Environment and Climate Change)

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16 pages, 1170 KB

Open AccessArticle

Effects of Water Flow Velocity on Growth and Nutritional Quality of Pacific Oysters (Crassostrea gigas)

by Yuanhao Liu, Yang Hong, Tiantian Ma, Xiaohui Wang, Jin Ni and Jian Shen

Fishes 2026, 11(2), 76; https://doi.org/10.3390/fishes11020076 - 24 Jan 2026

Abstract

This study examined the effects of hydrodynamic conditions on the growth performance and nutritional quality of Pacific oysters (Crassostrea gigas) in raceway flumes. Oysters were reared under three flow velocities—low (LV, 5 cm/s), medium (MV, 10 cm/s), and high (HV, 20 [...] Read more.

This study examined the effects of hydrodynamic conditions on the growth performance and nutritional quality of Pacific oysters (Crassostrea gigas) in raceway flumes. Oysters were reared under three flow velocities—low (LV, 5 cm/s), medium (MV, 10 cm/s), and high (HV, 20 cm/s)—using three replicate flumes per treatment, each containing 100 individuals. Results indicated that while shell morphology remained unaffected by flow rate, MV significantly enhanced soft tissue weight and meat yield compared to LV. Physiologically, HV upregulated the activities of trypsin and amylase, with trypsin levels significantly exceeding those in LV. Furthermore, MV exhibited the highest crude protein and glycogen content. Notably, both MV and HV improved the accumulation of total and essential amino acids. Fatty acid profiles showed clear separation among treatments, primarily driven by C16:0, C18:0, C20:5n3, C22:1n9, and C20:2. Collectively, moderate flow velocity (10 cm/s, MV) resulted in a well-balanced enhancement of growth, biochemical composition, and nutritional value compared to low or high velocities, highlighting the potential value of controlled hydrodynamic conditions in oyster farming. Full article

(This article belongs to the Special Issue Advances in Shellfish Aquaculture)

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19 pages, 392 KB

Open AccessArticle

Redesigning Aquafeeds: Insect, Algae, and By-Product Blends Sustain Growth and Nutritional Value in European Sea Bass Under Feeding Constraints

by Daniel Montero, Marta Carvalho, Silvia Torrecillas, Luís E. C. Conceição, Filipe Soares, Félix Acosta and Rafael Ginés

Fishes 2026, 11(2), 75; https://doi.org/10.3390/fishes11020075 - 23 Jan 2026

Abstract

Background: Adopting novel feed ingredients and aligning feeding strategies with these formulations are key to improving aquaculture sustainability. This study assessed the combined effects of alternative protein and lipid sources and feeding regime on growth, nutrient utilization, and body composition of European sea [...] Read more.

Background: Adopting novel feed ingredients and aligning feeding strategies with these formulations are key to improving aquaculture sustainability. This study assessed the combined effects of alternative protein and lipid sources and feeding regime on growth, nutrient utilization, and body composition of European sea bass (Dicentrarchus labrax) juveniles. Methods: Two isoenergetic and identical digestible protein diets (39%) were formulated: a control (conventional fishmeal/fish oil (FM/FO) and plant proteins, containing 20% FM and 6% FO) and an alternative diet replacing 50% of FM and 25% of vegetable proteins with a blend of poultry by-products, insect meal, and single-cell protein (Corynebacterium glutamicum) and totally replacing fish oil with alternative lipid sources (microalgae and by-product oils). Fish (28 g of initial body weight) were fed for 210 days either to apparent satiety (AS) or under moderate restriction (85% and 65% of AS). The number of fish used was 65 fish per 500 L tank (triplicate for each experimental group). Growth performance, feed conversion, nutrient efficiency ratios, protein retention, and proximate and fatty acid composition were measured. Results: The alternative diet significantly improved growth, feed and nutrient efficiency, and protein retention compared with the control. Whole-body fatty acid profiles of fish fed the alternative diet showed higher contents of nutritionally important fatty acids, including DHA. Restricted feeding at 65% of AS enhanced nutrient efficiency ratios and protein retention relative to 85% and AS, but reduced growth. Feeding to AS produced the highest feed intake and growth but poorer feed conversion and nutrient efficiency. No significant interaction between diet and feeding strategy was observed. Conclusions: Incorporating novel protein and lipid sources can improve sea bass performance and product nutritional value while supporting sustainability. Feeding at ~85% of AS may offer a practical compromise between growth and efficient nutrient utilization. Full article

(This article belongs to the Section Nutrition and Feeding)

28 pages, 1574 KB

Open AccessArticle

Genomic Diversity and Taxonomy of Aeromonas spp. in Aquarium Fish: Potential Role of Ornamental Fish as Hidden Carriers

by Muhammed Duman, Nihed Ajmi, Hector Carmona-Salido, Görkem Tasci, Artun Yıbar, Soner Altun, Jesús L. Romalde and Izzet Burcin Saticioglu

Fishes 2026, 11(2), 74; https://doi.org/10.3390/fishes11020074 - 23 Jan 2026

Abstract

Aquarium fish are increasingly being recognized as reservoirs of zoonotic pathogens, with Aeromonas species posing a notable risk because of their environmental resilience and opportunistic pathogenicity. This study presents the most comprehensive genome-based investigation to date of Aeromonas diversity in aquarium fish, aiming [...] Read more.

Aquarium fish are increasingly being recognized as reservoirs of zoonotic pathogens, with Aeromonas species posing a notable risk because of their environmental resilience and opportunistic pathogenicity. This study presents the most comprehensive genome-based investigation to date of Aeromonas diversity in aquarium fish, aiming to characterize their taxonomic distribution, population structure, and genomic features. A total of 64 Aeromonas isolates were collected from various aquarium fish species. Wholegenome sequencing was conducted on all isolates to facilitate comparative genomic analyses. Key approaches included multilocus sequence typing (MLST), pairwise Digital DNA-DNA hybridization (dDDH), and the construction of a phylogenomic tree for species-level classification. Furthermore, a population structure analysis was performed to explore genomic diversity and evolutionary trends among the isolates. The results identified 14 distinct Aeromonas species, with A. veronii, A. caviae, and A. hydrophila being the most common. Importantly, several isolates exhibited taxonomic ambiguity, indicating the possible presence of new species or subspecies lineages. Furthermore, antimicrobial resistance gene profiles and virulence factor distributions varied significantly across clades, indicating genomic plasticity. This study highlights the underappreciated genomic complexity of Aeromonas populations in aquarium environments and raises concerns about the public health implications of pathogen reservoirs in ornamental fish. Full article

(This article belongs to the Special Issue Infection and Detection of Bacterial Pathogens in Aquaculture)

16 pages, 812 KB

Open AccessReview

A Review of Adaptive Mechanisms in Fish Retinal Structure and Opsins Under Light Environment Regulation

by Zheng Zhang, Fan Fei, Liang Wang, Yunsong Rao, Wenyang Li, Xiaoqiang Gao, Ao Li and Baoliang Liu

Fishes 2026, 11(2), 73; https://doi.org/10.3390/fishes11020073 - 23 Jan 2026

Abstract

Light, as one of the most crucial environmental factors, plays an essential role in the growth, physiology, and evolutionary survival of fish. To cope with diverse light conditions in aquatic environments, fish adapt through photosensory systems composed of both visual and non-visual pathways. [...] Read more.

Light, as one of the most crucial environmental factors, plays an essential role in the growth, physiology, and evolutionary survival of fish. To cope with diverse light conditions in aquatic environments, fish adapt through photosensory systems composed of both visual and non-visual pathways. The retina is a key component of the visual system of fish, capable of converting external optical signals into neural electrical signals, making it crucial for visual formation. During the process of visual signal transduction, opsins serve as the molecular foundation for vision formation. They can be divided into two major categories: visual opsins and non-visual opsins. Among these, melanopsin, as a member of the non-visual opsin family, acts as a key upstream factor in the circadian phototransduction pathway of fish. In this review, we review the adaptability of fish retinal structures to light reception and introduce in detail the gene diversity and relative expression levels of fish opsins. At the same time, we comprehensively describe the molecular mechanism by which fish adapt to changes in the underwater light environment. We also concluded that melanopsin, as a non-imaging photoreceptor, possesses not only core light-sensing functions but also non-imaging visual functions such as circadian rhythm regulation, body coloration changes, and hormone secretion. This review suggests that future research should not only elucidate the physiological functions of melanopsin in fish but also comprehensively reveal the mechanisms underlying the multi-adaptive nature of fish vision across varying light environments. Through these studies, researchers can have a deeper understanding of the physiological regulation mechanism of fish in complex light environments, and then formulate fish light environment management strategies, optimize aquaculture practices, improve economic returns, and promote the development of related fields. Full article

(This article belongs to the Special Issue Adaptation and Response of Fish to Environmental Changes)

19 pages, 657 KB

Open AccessArticle

The Copepod/Artemia Trade-Off in the Culture of Long Snouted Seahorse Hippocampus guttulatus

by Jorge Palma, Ismael Hachero-Cruzado, Miguel Correia and José Pedro Andrade

Fishes 2026, 11(2), 72; https://doi.org/10.3390/fishes11020072 - 23 Jan 2026

Abstract

This study evaluated the effects of copepod use and copepod conditioning strategies on the growth and survival of long-snouted seahorse (Hippocampus guttulatus) juveniles from 1 to 60 days post-parturition (DPP). Four dietary treatments were tested: Artemia enriched for 24 h with [...] Read more.

This study evaluated the effects of copepod use and copepod conditioning strategies on the growth and survival of long-snouted seahorse (Hippocampus guttulatus) juveniles from 1 to 60 days post-parturition (DPP). Four dietary treatments were tested: Artemia enriched for 24 h with Isochrysis galbana (control), daily collected copepods, copepods unfed for 48 h, and copepods enriched for 24 h with I. galbana. Juveniles fed copepod-based diets exhibited significantly higher growth and survival (p < 0.05) than those fed enriched Artemia. Mean standard length increased from 1.3 ± 0.1 cm at release to 5.9 ± 0.2, 7.5 ± 1.4, 7.1 ± 1.2, and 7.3 ± 1.1 cm at 60 DPP for the enriched Artemia, daily collected copepods, unfed copepods, and enriched copepods treatments, respectively. Wet weight increased from 0.002 ± 0.001 g to 0.44 ± 0.07, 0.81 ± 0.40, 0.68 ± 0.30, and 0.76 ± 0.40 g, while final survival reached 20%, 60%, 33.3%, and 56%, respectively. Compared with enriched Artemia, copepod-based diets markedly enhanced juvenile performance, supporting faster growth and promoting favorable behavioral traits that contributed to improved survival. These results demonstrate that copepods constitute a superior live feed for early juvenile H. guttulatus; however, copepod conditioning strategies directly influence their nutritional quality and, consequently, seahorse growth and survival. The use of copepods throughout the first 60 DPP is therefore not only feasible but strongly recommended for optimizing juvenile H. guttulatus rearing performance. Full article

(This article belongs to the Special Issue Effects of Dietary Ingredients on Fish Nutrition and Health)

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20 pages, 2956 KB

Open AccessArticle

Effects of Dietary Strontium Supplementation on Growth Performance, Strontium Enrichment, Muscle Nutrition, and Hepatic Lipid Metabolism in Juvenile Hybrid Sturgeon (Acipenser baerii ♀ × Acipenser schrenckii ♂)

by Shilin Li, Qiang Zhao, Hang Chen, Yanhan Yang, Zhe Zhao, Jianxi Mei, Yuexin Sun, Li Peng, Hailong Ge, Fang Li and Zhijian Wang

Fishes 2026, 11(2), 71; https://doi.org/10.3390/fishes11020071 - 23 Jan 2026

Abstract

To explore a safe and effective approach for producing strontium-enriched fish, in this study, we modified the feed for juvenile hybrid sturgeon (Acipenser baerii ♀ × Acipenser schrenckii ♂) and set three different levels of strontium chloride content in their diet (0 [...] Read more.

To explore a safe and effective approach for producing strontium-enriched fish, in this study, we modified the feed for juvenile hybrid sturgeon (Acipenser baerii ♀ × Acipenser schrenckii ♂) and set three different levels of strontium chloride content in their diet (0 mg/kg (Sr0, control), 80 mg/kg (Sr80), and 160 mg/kg (Sr160)) for a period of 8 weeks, analyzing their growth performance, strontium enrichment, muscle nutrition, and hepatic physiological, biochemical, and transcriptomic characteristics. The results show that dietary strontium had no significant impact on sturgeon growth or survival rate (p > 0.05). The strontium content in tissues increased with dietary strontium levels, with the highest enrichment in bone plates (p < 0.05). However, muscle crude fat in the strontium-supplemented groups decreased significantly; the Sr160 group had higher glutamic acid, valine, docosahexaenoic acid methyl ester, lower myristic acid, palmitic acid, etc. (p < 0.05). In addition, strontium treatment alleviated hepatic lipid accumulation and mitochondrial swelling. Biochemical analyses revealed reduced plasma levels of Triglyceride (TG), Total Cholesterol (TC), Alanine Aminotransferase (ALT), and Aspartate Aminotransferase (AST), as well as decreased hepatic Malondialdehyde (MDA) content, while hepatic Glutathione (GSH) levels increased (p < 0.05). Transcriptomic data further showed that strontium downregulated the expression of fasn and tfrc and upregulated the expression of cpt1a, apoa1, cyp7a1, and slc3a2 (p < 0.05). In conclusion, dietary supplementation with 80–160 mg/kg strontium enables safe strontium enrichment in hybrid sturgeon, improves muscle nutritional quality, and protects liver function by regulating the genes related to lipid metabolism and antioxidant defense, providing a scientific basis for the development of strontium-enriched fish products. Full article

(This article belongs to the Special Issue Pivotal Roles of Feed Additives for Fish)

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20 pages, 4258 KB

Open AccessArticle

Impact of Stress Coping Styles on Serum Protein Electrophoresis Pattern Modulation in Sparus aurata Following Vibrio anguillarum Inoculation

by Mariele Staropoli, Mariano Dara, Irene Vazzana, Pierluigi Carbonara, Claudia La Corte, Luca Bisanti, Federica Bertini, Lucia Therese Marcianò, Daniela Parrinello, Maria Giovanna Parisi and Matteo Cammarata

Fishes 2026, 11(1), 70; https://doi.org/10.3390/fishes11010070 - 22 Jan 2026

Abstract

Stress coping style (SCS) is crucial for animal welfare in the context of breeding. The link between behavioural traits and physiological responses to external stimuli is increasingly recognized and could orient the selection of appropriate SCSs for welfare-oriented breeding. This study aimed to [...] Read more.

Stress coping style (SCS) is crucial for animal welfare in the context of breeding. The link between behavioural traits and physiological responses to external stimuli is increasingly recognized and could orient the selection of appropriate SCSs for welfare-oriented breeding. This study aimed to evaluate how SCS influences the physiological responses of Sparus aurata, a widely used species in aquaculture, following Vibrio anguillarum stimulation. To this end, the serum protein electrophoretic profile, analysed by capillary electrophoresis, was used as an innovative parameter to assess physiological variations. S. aurata individuals were categorized into three SCS groups—bold, shy, and intermediate —based on a risk-taking test. Serum was collected at day 0 (pre-inactivated V. anguillarum inoculation) and at 30 and 60 days post-inoculation. Analyses revealed an increase in the β₂-globulin fraction, putatively associated with molecules involved in the physiological response following inactivated pathogen inoculation, accompanied by a decrease in the γ fraction over time. This trend was particularly pronounced in bold fish, while shy ones showed a similar but less marked pattern. Overall, the results suggest that proactive individuals exhibit a more marked physiological modulation to inactivated pathogen stimulation than reactive ones, highlighting modulation of serum protein electrophoresis as a sensitive bioindicator of physiological response in S. aurata. Full article

(This article belongs to the Special Issue Welfare and Stressor in Aquaculture: Mechanisms, Management, and Sustainable Solutions)

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20 pages, 1574 KB

Open AccessArticle

Impact of Extreme Climate Risk on Chinese Freshwater Aquaculture Production

by Yingli Zhang, Hang Qu and Shunxiang Yang

Fishes 2026, 11(1), 69; https://doi.org/10.3390/fishes11010069 - 22 Jan 2026

Abstract

Against the backdrop of global warming and an increase in extreme weather events, the freshwater aquaculture industry, which is highly dependent on environmental conditions, faces severe challenges. As the world’s largest producer of freshwater aquaculture, the stability of China’s production is crucial for [...] Read more.

Against the backdrop of global warming and an increase in extreme weather events, the freshwater aquaculture industry, which is highly dependent on environmental conditions, faces severe challenges. As the world’s largest producer of freshwater aquaculture, the stability of China’s production is crucial for ensuring national food security and rural livelihoods. This study utilizes provincial panel data from China (2007–2023) and employs the HP filter separately for each province to construct a “climate-induced output” indicator. A panel data model is then established to examine the impact and transmission mechanisms of extreme climate risks on freshwater aquaculture output. The findings reveal the following: (1) Climate risks exert a significant negative impact on freshwater aquaculture production, with extreme low temperatures, droughts, and extreme rainfall having particularly pronounced effects. (2) Natural disasters play a partial mediating role between extreme climate and output, accounting for approximately 26.35% of the total effect. (3) From an overall perspective, both increased labor productivity and greater operational scale can significantly mitigate the negative impacts of climate risks. This study provides empirical evidence to inform policies on optimizing regional aquaculture layouts, enhancing climate resilience, and formulating adaptive strategies. Full article

(This article belongs to the Special Issue Impact of Climate Change and Adverse Environments on Aquaculture)

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16 pages, 1170 KB

Open AccessArticle

Geographical Traceability of Anguilla japonica from Different Habitats Successfully Achieved Using Muscle Elemental Fingerprint Analysis

by Chao Song, Chengyao Yang, Yijia Li, Dongyu Song, Xiaorong Huang, Sikai Wang, Feng Zhao and Hong Tao

Fishes 2026, 11(1), 68; https://doi.org/10.3390/fishes11010068 - 22 Jan 2026

Abstract

Anguilla japonica is a catadromous fish, and the Yangtze River Estuary serves as a crucial passage for A. japonica migrating downstream to the sea. A large number of adult A. japonica appear on the market during the peak migration period. Due to the [...] Read more.

Anguilla japonica is a catadromous fish, and the Yangtze River Estuary serves as a crucial passage for A. japonica migrating downstream to the sea. A large number of adult A. japonica appear on the market during the peak migration period. Due to the lack of effective discrimination basis, it is difficult to distinguish the source of samples in market supervision. Therefore, there is an urgent need to trace the origin of A. japonica from different water bodies. This study analyzed muscle elemental fingerprints of 21 elements to determine the geographical origin of A. japonica. The results showed that A. japonica from different habitats had distinct elemental compositions in their muscles. Specifically, A. japonica from estuary waters (EW) was characterized by significantly higher levels of V and Hg compared to other water bodies. Na was identified as a key discriminant element among different habitats, with its content significantly increasing in river waters (RW), EW, and offshore waters (OW), respectively. Discriminant analysis selected four discriminant elements (V, Hg, Na and Cu) from 21 elemental compositions, among which V, Hg, and Na were the three key distinguishing elements. Based on the composition of these four discriminant elements in the muscles of A. japonica from different habitats, hierarchical cluster analysis (HCA), orthogonal partial least squares discriminant analysis (OPLS-DA), and linear discriminant analysis (LDA) were applied and validated, successfully achieving rapid and accurate origin tracing and verification for new samples, achieving 100% classification accuracy. Therefore, the application of muscle EFA can achieve the geographical traceability of A. japonica from different habitats. The analytical method and verification process for origin tracing established in this study can be successfully applied to market supervision for tracing the origin of samples with unknown sources. Full article

(This article belongs to the Special Issue Conservation and Population Genetics of Fishes)

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20 pages, 9876 KB

Open AccessArticle

The Effects of Dietary Tributyrin Supplementation on Growth Performance, Antioxidant Capacity, Immune Function, and Intestinal Health of Fat Greenling (Hexagrammos otakii)

by Yuepeng Song, Zijun Wei, Xinghao Li, Zheng Zhang, Yong Wang, Jichuan Du, Kewei Wang, Yike Li, Xuejie Li, Dongwei Li, Wei Wang and Yan Chen

Fishes 2026, 11(1), 67; https://doi.org/10.3390/fishes11010067 - 21 Jan 2026

Abstract

The objective of the current research was to evaluate the influence of dietary tributyrin (TB) inclusion on the growth performance and physiological well-being of Hexagrammos otakii. Juvenile fish (initial weight 24.01 ± 1.35 g) were fed one of six isonitrogenous and isolipidic [...] Read more.

The objective of the current research was to evaluate the influence of dietary tributyrin (TB) inclusion on the growth performance and physiological well-being of Hexagrammos otakii. Juvenile fish (initial weight 24.01 ± 1.35 g) were fed one of six isonitrogenous and isolipidic diets containing graded levels of TB (0–1.5 g/kg) for 90 days. Supplementation significantly enhanced the weight gain and specific growth rates. The optimal level of 0.9 g/kg TB improved muscle nutritional quality, muscle texture, and intestinal morphology. This dosage also significantly increased hepatic and intestinal antioxidant capacity, elevating superoxide dismutase (SOD), catalase (CAT), and total antioxidant capacity (T-AOC), while reducing malondialdehyde (MDA) content. Furthermore, dietary TB at 0.9 g/kg reduced plasma and hepatic triglycerides and total cholesterol, and elevated key plasma immune parameters, including complement components (C3, C4) and phosphatase activities (ACP, AKP). Intestinal health was further enhanced, as evidenced by increased digestive enzyme activities (amylase, lipase, chymotrypsin) and improved microbial diversity, marked by a proliferation of beneficial bacteria. In conclusion, dietary TB supplementation at 0.9 g/kg optimally promotes growth, improves muscle and intestinal health, and enhances antioxidant and immune functions in H. otakii. Full article

(This article belongs to the Special Issue Dietary Supplementation in Aquaculture)

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15 pages, 1433 KB

Open AccessArticle

Biological Validation of Cortisol in Zebrafish Trunk, Skin Mucus, and Water as a Biomarker of Acute or Chronic Stress

by Sara Jorge, Luís Félix, Benjamín Costas, Lourenço Ramos-Pinto, Sofia R. Teixeira and Ana M. Valentim

Fishes 2026, 11(1), 66; https://doi.org/10.3390/fishes11010066 - 21 Jan 2026

Abstract

The most used technique to assess cortisol in zebrafish is trunk sampling, a terminal procedure. Extracting cortisol non-terminally in adult zebrafish remains challenging, limiting longitudinal studies, and the reduction of the number of zebrafish used in research. This study explored non-terminal methods for [...] Read more.

The most used technique to assess cortisol in zebrafish is trunk sampling, a terminal procedure. Extracting cortisol non-terminally in adult zebrafish remains challenging, limiting longitudinal studies, and the reduction of the number of zebrafish used in research. This study explored non-terminal methods for cortisol measurement in adult zebrafish under acute and chronic stress, focusing on housing water and skin mucus as alternatives to terminal trunk sampling. Oxidative stress markers (cerebral and hepatic) were also assessed to confirm stress responses. In experiment A, zebrafish were exposed to no stress, acute stress (AS), or chronic stress for 14 days (CS14) to evaluate skin mucus and trunk cortisol as biomarkers. In experiment B, in addition to CS14, a 7-day unpredictable chronic stress protocol (CS7) was tested to discard stress habituation. Results showed significant effects on cerebral oxidative stress: AS increased ROS and AChE activity, CS7 reduced GPx and AChE, and CS14 raised GPx in experiment A, while it increased protein carbonyls and decreased ATPase levels in experiment B. Trunk and skin mucus cortisol increased following AS. Under chronic stress, trunk and skin mucus cortisol levels were not significantly altered, but water cortisol increased at CS7. In conclusion, skin mucus and trunk cortisol levels are reliable biomarkers for acute stress, while water cortisol holds promise for chronic stress. Full article

(This article belongs to the Section Physiology and Biochemistry)

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12 pages, 2758 KB

Open AccessArticle

Cooperative Associations Between Fishes and Bacteria: The Influence of Different Ocean Fishes on the Gut Microbiota Composition

by Jintao Liu, Bilin Liu, Yang Liu and Yuli Wei

Fishes 2026, 11(1), 65; https://doi.org/10.3390/fishes11010065 - 21 Jan 2026

Abstract

Gut microbial communities perform a multitude of physiological functions for their hosts; however, the drivers and distribution patterns of microbiota in wild animals remain largely underexplored. Our understanding of how these microbial communities are structured across hosts in natural environments—especially within a single [...] Read more.

Gut microbial communities perform a multitude of physiological functions for their hosts; however, the drivers and distribution patterns of microbiota in wild animals remain largely underexplored. Our understanding of how these microbial communities are structured across hosts in natural environments—especially within a single host species remains limited. Here, we characterized the gut microbial communities of four species of ocean fish using 16S rRNA high-throughput sequencing to investigate the structural and functional features of these microbial communities across different fish species. By comparing the gut microbiota compositions of blue sharks (Prionace glauca), bigeye tuna (Thunnus obesus), sickle pomfret (Taractichthys steindachneri), and mackerel (Scomber japonicus), we identified several microbial taxa—including Photobacterium, Pelomonas, Ralstonia, and Rhodococcus—that were consistently detected across all samples, indicating they likely constitute a “common microbiota”. However, the relative abundances of these taxa varied significantly among species, with Photobacterium exhibiting the highest diversity. Blue sharks and bigeye tuna harbored relatively few dominant microbial species, but the abundance of these dominant bacteria was remarkably high, and inter-individual differences in microbial composition were pronounced. In contrast, mackerel and sickle pomfret contained a greater variety of dominant genera, each with low relative abundance, and inter-individual differences within the same species were minimal. Functionally, metabolic pathways, biosynthesis of secondary metabolites, and microbial metabolism represent the predominant functional categories of the intestinal microbiota in marine fish, with only minor interspecific differences observed. In contrast, biosynthesis of amino acids, ABC transporters, and two-component systems are the key functional pathways that exhibit significant variations across different fish species. Collectively, these findings reveal differences in gut microbial stability among different fish hosts. Such variations may be associated with the hosts’ energy utilization needs, and changes in the gut microbiota play a critical role in shaping the diverse survival strategies of these fish species. Full article

(This article belongs to the Section Biology and Ecology)

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14 pages, 297 KB

Open AccessArticle

Water Renewal Rate and Temperature on the Growth Performance and Physiology of Piaractus brachypomus in a Recirculating Aquaculture System (RAS)

by Pedro P. C. Pedras, Zandhor Lipovetsky, Fábio A. C. dos Santos, André de S. Souza, Luisa A. A. Silva, Gustavo S. da C. Júlio, Imaculada de M. C. Ananias, Sidney dos S. Silva, Ronald K. Luz and Gisele C. Favero

Fishes 2026, 11(1), 64; https://doi.org/10.3390/fishes11010064 - 19 Jan 2026

Abstract

This study evaluated the effects of water renewal rate and temperature on the growth performance and physiological responses of juvenile Piaractus brachypomus reared in a recirculating aquaculture system (RAS). A total of 336 fish (1.35 ± 0.24 g) were distributed in six RAS [...] Read more.

This study evaluated the effects of water renewal rate and temperature on the growth performance and physiological responses of juvenile Piaractus brachypomus reared in a recirculating aquaculture system (RAS). A total of 336 fish (1.35 ± 0.24 g) were distributed in six RAS units under two water renewal rates (42 and 128 L h⁻¹) and three temperatures (26, 29, and 32 °C) for 45 days. Temperature was the main factor affecting growth, with higher final weight and total length at 29 and 32 °C throughout the experimental period. Water renewal rate significantly influenced feeding efficiency and energy allocation. Higher renewal (128 L h⁻¹) increased dissolved oxygen and daily feed intake and resulted in higher hemoglobin levels and hepatic lipid deposition, particularly at 32 °C, indicating greater metabolic activity. Conversely, the lower renewal rate (42 L h⁻¹) was associated with better feed conversion ratios at 29 °C and higher muscle lipid content at 26 °C, suggesting reduced energy expenditure. Hematocrit, total plasma protein, and cholesterol were primarily influenced by temperature, with higher values at 29 and 32 °C, while glucose, triglycerides, and liver enzymes were unaffected. Overall, temperatures of 29–32 °C optimized growth, while water renewal rate modulated feed utilization, physiological responses, and lipid deposition. These findings highlight the importance of jointly optimizing temperature and water renewal rate in RAS to enhance growth performance and metabolic balance in juvenile P. brachypomus. Full article

(This article belongs to the Special Issue Advances in the Physiology of Aquatic Organisms)

14 pages, 2042 KB

Open AccessArticle

Effects of Different Application Strategies of Copper-Loaded Montmorillonite on Growth, Intestinal Histology, and Rearing-Water Quality in Penaeus monodon

by Jieyi Wang, Yangyang Ding, Falin Zhou, Jianzhi Shi, Qibin Yang, Yundong Li, Jianhua Huang, Lishi Yang, Xueliang Sun and Song Jiang

Fishes 2026, 11(1), 63; https://doi.org/10.3390/fishes11010063 - 18 Jan 2026

Abstract

Penaeus monodon is widely cultured in Asia; however, intensive farming practices often result in water-quality deterioration and compromised production performance. Copper-loaded montmorillonite (Cu-MMT) is a functional additive with adsorption and antimicrobial properties, yet the relative effectiveness of different application strategies remains insufficiently evaluated. [...] Read more.

Penaeus monodon is widely cultured in Asia; however, intensive farming practices often result in water-quality deterioration and compromised production performance. Copper-loaded montmorillonite (Cu-MMT) is a functional additive with adsorption and antimicrobial properties, yet the relative effectiveness of different application strategies remains insufficiently evaluated. In this study, 270 shrimp were assigned to three treatments: a control group (KZ), water application of Cu-MMT (PZ), and dietary inclusion of Cu-MMT (BZ). Juvenile Penaeus monodon with an initial body weight of 3.25 ± 0.15 g were used in the trial. Growth performance, intestinal histology, and rearing-water quality were assessed over a 56-day culture period. Shrimp in the BZ group exhibited a significantly higher weight gain rate (311.88 ± 38.17%) and survival rate (88.04%) than those in the KZ (247.45 ± 32.82%; 76.67%) and PZ (286.49 ± 29.78%; 83.33%) groups (p < 0.05). Intestinal histological observations revealed treatment-associated differences in morphology, with more pronounced intestinal enlargement observed in the PZ group, whereas the BZ group exhibited a more moderate intestinal architecture. Water-quality analyses showed that dietary Cu-MMT supplementation was associated with higher dissolved oxygen levels and lower concentrations of total ammonia nitrogen, sulfide, and dissolved iron, particularly during the later stages of the experiment. Overall, these results indicate that dietary inclusion of Cu-MMT provides more favorable outcomes than water application in improving growth performance and rearing-water quality in P. monodon culture under the experimental conditions tested. These findings highlight the importance of application strategy when evaluating functional additives in shrimp aquaculture. Full article

(This article belongs to the Special Issue Diet and Intestinal Microbiota of Fish)

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20 pages, 1461 KB

Open AccessArticle

Spatial and Economic Concentration of Offshore Mariculture in China: Insights from a Nation-Scale GIS Dataset

by Wei Yang, Yinping Hu and Kunlin Tang

Fishes 2026, 11(1), 62; https://doi.org/10.3390/fishes11010062 - 18 Jan 2026

Abstract

China is the world’s leading producer of offshore mariculture, contributing more than 60 percent of global output. Yet the provincial distribution of mariculture space and its economic concentration are still not well described at a comparable national scale. This study draws on a [...] Read more.

China is the world’s leading producer of offshore mariculture, contributing more than 60 percent of global output. Yet the provincial distribution of mariculture space and its economic concentration are still not well described at a comparable national scale. This study draws on a publicly available nation-scale GIS dataset extracted from Landsat 8 imagery from 2018 to map offshore mariculture across nine coastal provinces and to quantify spatial inequality and specialization. The mapped offshore mariculture footprint totals 733,840 ha. The distribution is sharply uneven. Fujian alone reaches 183,025 ha, nearly thirty times the area of Hainan. The Gini coefficient is 0.412, and concentration ratios show that the top three provinces account for 64.0 percent of the total area, and the top five account for 84.5 percent. Location quotient results indicate strong specialization in Fujian, Jiangsu, and Hebei, while Hainan and Guangxi remain marginal. Cluster analysis further identifies three development modes: large-scale expansion, medium-scale and relatively balanced growth, and small-scale dispersed production. Overall, the pattern is consistent with resource endowment, agglomeration effects, and path dependence. The findings point to the need for improved coastal spatial planning, stronger interprovincial technology diffusion, and differentiated governance that balances efficiency with equity and environmental sustainability. Full article

(This article belongs to the Special Issue Advances in Fisheries Economics)

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18 pages, 1938 KB

Open AccessArticle

Reproductive Dynamics of the Blonde Ray (Raja brachyura) in Portuguese Waters: Timing, Maturity and Fecundity

by Catarina Maia, Ivone Figueiredo, Bárbara Serra-Pereira, Neide Lagarto, Inês Farias and Teresa Moura

Fishes 2026, 11(1), 61; https://doi.org/10.3390/fishes11010061 - 17 Jan 2026

Abstract

Within the Rajidae family, the blonde ray (Raja brachyura) is considered one of the less resilient species to fishing pressure and other anthropogenic pressures, primarily due to its late maturity and large maximum size, which can exceed 120 cm total length. [...] Read more.

Within the Rajidae family, the blonde ray (Raja brachyura) is considered one of the less resilient species to fishing pressure and other anthropogenic pressures, primarily due to its late maturity and large maximum size, which can exceed 120 cm total length. This is the first study to provide comprehensive insights into the reproductive biology of Raja brachyura in the continental waters of Portugal, with insights into its timing, maturity, and fecundity. It was determined that egg-laying occurs from February to November, with a peak observed between April and September. Males were reproductively active throughout the year, with highest proportions of active males observed between January and May. The length at first maturity was estimated at 95.2 cm for females and 90.0 cm for males, corresponding to 85% of the maximum observed length in each sex. The potential fecundity was estimated at 115 follicles per female per year, and evidence suggests that the species has a determinate fecundity. The findings reinforce the appropriateness of current management measures in Portuguese continental waters, namely seasonal closure when overlapping with the peak of the reproductive season (May and June), and provide valuable scientific support for future conservation and management measures. Full article

(This article belongs to the Special Issue Ecology of Fish: Age, Growth, Reproduction and Feeding Habits)

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25 pages, 1443 KB

Open AccessReview

Microalgae as a Synergistic Enhancer for In Situ and Ex Situ Treatment Technologies in Sustainable Shrimp Aquaculture: A Critical Review

by Sheng Dong, Fei Huang, Xianghui Zou, Qiulan Luo and Jiancheng Li

Fishes 2026, 11(1), 60; https://doi.org/10.3390/fishes11010060 - 16 Jan 2026

Abstract

The intensification of shrimp aquaculture is crucial for global food security, but poses significant environmental challenges. This review critically assesses the strengths and bottlenecks of two main treatment paradigms: in situ systems, chiefly biofloc technology (BFT), and advanced ex situ systems, such as [...] Read more.

The intensification of shrimp aquaculture is crucial for global food security, but poses significant environmental challenges. This review critically assesses the strengths and bottlenecks of two main treatment paradigms: in situ systems, chiefly biofloc technology (BFT), and advanced ex situ systems, such as recirculating aquaculture systems (RASs), constructed wetlands (CWs), and membrane bioreactors (MBRs). Although BFT enables nutrient recycling, it suffers from nitrate accumulation and a high energy demand. Likewise, ex situ technologies can achieve a high treatment efficiency, but contend with high costs, large footprints, or membrane fouling. In this review, we propose the strategic integration of microalgae, representing a universal and synergistic solution for overcoming these disparate bottlenecks. We dissect how a microalgal co-culture can simultaneously remove nitrate and reduce the aeration costs in BFT systems. Furthermore, we explore how microalgae-based units can serve as efficient polishing steps for RASs, enhance the performance of CWs, and mitigate fouling in MBRs. This review delves into the fundamental mechanisms of the microalgal–bacterial symbiosis that underpins these enhancements. Finally, we highlight the valorization of the resulting algal biomass as a high-value aquafeed ingredient, which can transform waste management into a value-creation opportunity. This review aims to provide a comprehensive roadmap for developing next-generation, microalgae-enhanced aquaculture systems. Full article

(This article belongs to the Special Issue Advances in the Application of Microalgae in Aquaculture)

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20 pages, 3926 KB

Open AccessArticle

Hydrodynamic Performance of Cubic Artificial Reefs During Deployment Process Based on Smoothed Particle Hydrodynamics

by Wenhua Chu, Shijing Lu, Zijing Zhao, Xinyang Zhang and Yulei Huang

Fishes 2026, 11(1), 59; https://doi.org/10.3390/fishes11010059 - 16 Jan 2026

Abstract

Currently, research on the hydrodynamic characteristics of artificial reef deployment still faces challenges such as insufficient environmental coupling, but accurate simulation of the deployment process holds significant engineering importance for optimizing deployment efficiency and ensuring reef stability. This study employs the Smoothed Particle [...] Read more.

Currently, research on the hydrodynamic characteristics of artificial reef deployment still faces challenges such as insufficient environmental coupling, but accurate simulation of the deployment process holds significant engineering importance for optimizing deployment efficiency and ensuring reef stability. This study employs the Smoothed Particle Hydrodynamics (SPH) method to establish a 3D numerical model, focusing on the influence of key parameters—inflow velocity and water entry angle—on the hydrodynamic characteristics of cubic artificial reef deployment. The results indicate that under flow velocities of 0.4–0.5 m/s, pressure fluctuations are relatively minor, with peak pressure gradients below 15 kPa/m, exhibiting a gradual trend, while particle concentration remains high, and drag gradually increases. At flow velocities of 0.6–0.8 m/s, the maximum pressure at the bottom reaches up to 35 kPa, with low-pressure areas at the tail dropping to −10 kPa; particle concentration decreases compared to conditions at 0.4–0.5 m/s; settling time extends from 8.4 s to 12 s, representing a 42% increase. Under different water entry angles, drag varies nonlinearly with the angle, reaching its maximum at 20° and its minimum at 25°, with a reduction of approximately 47% compared to the maximum. The anti-sliding safety factor and anti-overturning safety factor are used to assess the stability of the cubic reef placed on the seabed. Across different inflow velocities, the anti-sliding safety factor of the cubic artificial reef significantly exceeds 1.2, whereas the anti-overturning safety factor is below 1.2 at 0.4 m/s but exceeds 1.2 at velocities of 0.5 m/s and above, indicating that the reef maintains stability under the majority of these flow conditions. Our findings provide a scientific basis for the deployment process, site selection, and geometric design of cubic artificial reefs, offering valuable insights for the precise deployment and structural optimization of artificial reefs in marine ranching construction. Full article

(This article belongs to the Special Issue Engineering Solutions for Sustainable Offshore Aquaculture and Fisheries)

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