Fish Diversity Research Articles

Restricted inclusion of wild broodstock at a large hatchery does not result in detectable genetic differentiation in a supplemented coho salmon (Oncorhynchus kisutch) population

Hatchery production is common in salmonid management for harvest and conservation. Many hatcheries employ integrated broodstock programs, where wild-origin fish are included as broodstock and uni- or bi-directional gene flow between wild and hatchery components of the population is encouraged. Such approaches often assume that opportunistically obtained wild fish meet the genetic goals of minimizing hatchery–wild differentiation and maintaining genetic diversity. This may be incorrect if fine-scale spatial genetic structure exists. Here we investigate the population genetic consequences of such hatchery operations in coho salmon ( Oncorhynchus kisutch) in a small river system featuring a large integrated broodstock program. We do so using 11 082 SNPs scored in wild-origin and hatchery-origin fish collected throughout the system. We found no evidence for genetic differentiation between hatchery-origin and wild-origin fish, no evidence of lowered genetic diversity in hatchery-origin fish, and no evidence for genetic differentiation among fish sampled throughout the river system. In addition, we did not detect inbreeding. Collectively, these results are consistent with current practices meeting integrated hatchery program goals of adequately sampling the genetic diversity present in wild-origin fish, although they may slightly reduce the effective population size of the combined population.

A brief review on effect of heavy metals in fish fauna

The variety of fish species is essential for the well-being and stability of aquatic environments. Fishes are one of the most important aquatic creatures that are directly or indirectly related to human health and wealth. With thousands of different species inhabiting various water bodies around the world, each fish contributes to the overall biodiversity and sustainability of these environments. Humans have long relied on aquatic resources for food, medicines, and materials. Fish species are adapted to a variety of environments such as freshwater lakes, rivers, reservoirs, oceans, and estuaries. The diversity of habitats available allows a variety of fish species to thrive in different environments. Fish diversity is a vital component of aquatic ecosystems, supporting ecosystem stability, economic value, and cultural significance. India's inland water resources are abundant and diverse, including reservoirs that play an important role in the country's inland fisheries sector.Biodiversity and its conservation are considered one of the key issues to enable sustainable use of natural resources. Protecting ichthyophan diversity in its natural habitat is essential and the need of the hour. By understanding the factors that influence fish diversity and the importance of preserving biodiversity, we can work towards protecting and protecting these priceless resources for upcoming generations.

Associations Between Gut Microbiota Diversity and a Host Fitness Proxy in a Naturalistic Experiment Using Threespine Stickleback Fish.

The vertebrate gut microbiota is a critical determinant of organismal function, yet whether and how gut microbial communities affect host fitness under natural conditions remains largely unclear. We characterised associations between a fitness proxy-individual growth rate-and bacterial gut microbiota diversity and composition in threespine stickleback fish introduced to large semi-natural ponds. We detected a 63% higher richness of bacterial taxa (α-diversity) in the guts of high-fitness fish compared to low-fitness fish, which might be driven by stronger bacterial dispersal among high-fitness fish according to the fit of a neutral community model. Further, microbial communities of high-fitness fish were more similar to one another (i.e., exhibited lower β-diversity) than those of low-fitness fish. The lower β-diversity found to be associated with higher host fitness is consistent with the Anna Karenina principle-that there are fewer ways to have a functional microbiota than a dysfunctional microbiota. Our study links differences in α- and β-diversity to a fitness-related trait in a vertebrate species reared under naturalistic conditions and our findings provide a basis for functional tests of the fitness consequences of host-microbiota interactions.

Exploring Fish Biodiversity and the Socioeconomic Status of Fishers in the Karatoya River, Sadar Upazila, Panchagarh District, Bangladesh

These studies were carried out to study species diversity of fishes and socio-economic conditions of the fishers of Karatoya River at Sadar upazila in Panchagarh district Bangladesh. Pertinent information was collected from 65 fishermen, who were directly engaged in catching fish around the study area for six months from December 2022 to June 2023. The results demonstrated that 41 fish species belonging to 8 orders and 15 families were found in the Karatoya River. Cypriniformes was found as the most dominant order, constituting 50.6% of the total fish population, considering species abundance, and Siluriformes constituting 12.7% and Perciformes constituting 12.0%, which were occupied the second and third position in abundance. The order Channiformes, Clupeiformes, Mastacembeliformes and Tetraodontifomres were constituted 6.6%, 6.0%, 4.8%, and 4.2%, respectively. Beloniformes constituted the lowest number of species (30%). It was observed that many fish species in the Karatoya River were severely impacted by the environmental and human-induced hazards. However, the age of the fishermen was ranged from 22 to 65 years. The Hindus (70%) were featured to be the highest percentage than the Muslims (30%), while no Christians and Buddhists were found. Various levels of education were documented in the study area, where majority of the fishermen were illiterate (69%), up to primary 18%, up to secondary 8% and the small portion (5%) were above secondary. The fishermen’s housing status was predominated by kaccha (66%), followed by semi pacca (23%) and pacca (11%). Majority of the fishers were landless (39%), whereas 15% fishers had 1-10 decimal (dec.) lands, 18% had 11-20 dec., 11% had 21-30 dec., 14% had 31-40 dec. and badly 3% of them had possessed >40 dec. lands. Among the fishermen, 45% of them were found to be involved in fishing activities, 40% in agriculture and 15% in sand business as day-to-day labour. There were 4 types of nets, 3 types of traps, 4 types of spears and 2 types of line fishing operated in this area. The study revealed that the fisheries production was not sufficient according to the demand. The reasons behind this might be due to the fact that the fishers around the Karatoya River were mainly poor, illiterate, lack of proper training and also nonexistence of consciousness of their sanitary and health care facilities. Therefore, it is very important to provide the required Organizational and Institutional help, support and extension facilities for the enhancement of fish biodiversity as well as development of sustainable livelihood of fishers in the Karatoya River as well.

New Insights into Fish Diversity in the Yellow and Bohai Seas Based on Environmental DNA Technology

Marine biodiversity is increasingly threatened by overfishing and marine pollution. A comprehensive understanding of the biodiversity in the Yellow and Bohai Seas is essential for resource conservation. This study conducted a large-scale survey of fishery resources in the Yellow and Bohai Seas to investigate fish community structure and diversity using eDNA technology. The results showed that 57 and 65 fish species were recorded in spring and summer, respectively, with 46 species identified in both seasons. A total of nine dominant species were identified in spring, mainly belonging to Perciformes, while seven dominant species were identified in summer, primarily from Clupeiformes. In different regions, no significant differences in fish α diversity were observed between spring and summer. However, significant seasonal differences were found in both α and β diversity. At the spatial level, fish species in the Yellow and Bohai Seas occupied similar ecological niches. However, at the temporal level, there are certain differences in the ecological niches of fish communities between seasons. Phylogenetic diversity showed no significant differences at the spatial scale, yet notable seasonal variations were observed at the temporal scale, with spring (661.46) significantly exceeding summer (540.30). The Mantel test indicated that nitrate and salinity were key environmental factors influencing α diversity. RDA analysis revealed that the dominant species in spring were mainly influenced by chlorophyll-a and water temperature, while those in summer were mainly affected by water depth, nitrite, water temperature, and salinity.

Alteration of the Intestinal Bacterial Community in Rainbow Trout (Oncorhynchus mykiss): The Role of Animal, Plant, and Microbial Diets

Intestinal bacterial community in rainbow trout (Oncorhynchus mykiss) is increasingly recognized as important for aquaculture and fish health. This review summarizes the current knowledge on how various feed components, including animal- and plant-derived ingredients, as well as other feed additives, influence the gut microbiota of rainbow trout. Studies using 16S rRNA gene profiling and metagenomics demonstrate how dietary changes affect the composition, diversity, and functionality of bacterial communities. The findings suggest that there is no single optimal alternative ingredient for fish feeds, but emphasize that the ratio of natural components plays a more significant role in shaping the intestinal bacterial community of trout. This balance is crucial for maintaining diversity, functionality, and overall fish health, thereby promoting growth and disease resistance, while enhancing aquaculture efficiency. The use of popular animal protein derived from the larva of Hermetia illucens increases the amount of Pseudomonadota, but the chitin they contain can prevent the absorption of nutrients. Thus, the development of optimal feed formulas requires careful selection and balancing of various natural ingredients to sustain a healthy microbiota and overall fish well-being.

Sequential migrations of diverse fish community provide seasonally prolonged and stable nutrient inputs to a river.

Animal migrations transport resources among spatially separate ecosystems, effectively linking them. In freshwater ecosystems, numerous fish species migrate between mainstream rivers or lakes and their tributaries, providing resources and nutrients during their spawning migrations. Multiple migratory species travel to the same destinations and contribute such nutrients, but knowledge remains limited about how the diversity of migratory animals influences the recipient ecosystem. We investigated how migrations of diverse fish community from Lake Biwa, Japan contribute to nutrient inputs in one of the lake's tributary rivers and how they influence the ecosystem. Sequential migration of six fish species continued for 8 months of a year, causing high-level nutrient concentration and primary production. The fish-derived resources were taken up by diverse members of the river community. Our results emphasize the extent to which migrations of diverse animals seasonally extend and stabilize the resource subsidy and how they extend pronounced effects on the recipient ecosystems.

Revealing the temporal dynamics of fish assemblage pattern, feeding guilds in relation to habitat quality parameters in a coastal wetland of the Indian Sundarban eco-region.

The present study was conducted from April 2016 to March 2017 in a freshwater-dominated coastal wetland of the Indian Sundarban ecoregion to illustrate the fish diversity, and abundance and the predictor variables determining fish assemblage structure in the wetland. A total of 27 fish species belonging to 13 orders, 16 families, and 23 genera with Cyprinidae (18.5%) as the most dominant family were recorded from the wetland. Fish species richness was found to vary noticeably across the season with the highest number of taxa during the monsoon season (25 species). The study revealed that small indigenous fish species (SIFs) were found dominating the overall species richness and abundance which accounted for 70.37% of the total fish diversity. Among SIFs, Mystus gulio dominated (33 - 42%) the total fish abundance followed by Amblypharyngodon mola (12 - 21.7%), Oryzias dancena (11 - 14.9%), Parambassis ranga (6 - 32%), Puntius sophore (5 - 10.8%), and Parambassis lala (3 - 5.9%). Thirteen fish species were found as inhabitants of truly freshwater, eight species of freshwater and brackish water, and six of freshwater, brackish, and marine form. The developed GAM model proved water turbidity to be the best predictor variable determining fish abundance and assemblages in the wetlands. Besides, turbidity, salinity, transparency, and temperature were found to influence the fish assemblages. There was no visible response to water depth, although this has a linear effect on fish abundance. Water temperatures up to about 30.5°C had a positive effect on fish abundance and the highest fish abundance in the wetland to be found in the range of 29 to 30.5°C.

Haemoglobin Gene Repertoire in Teleost and Cichlid Fishes Shaped by Gene Duplications and Genome Rearrangements.

Haemoglobin is a key molecule for oxygen transport in vertebrates. It exhibits remarkable gene diversity in teleost fishes, reflecting adaptation to various aquatic environments. In this study, we present the dynamic evolution of haemoglobin subunit genes based on a comparison of high-quality genome assemblies of 24 vertebrate species, including 17 teleosts (of which six are cichlids). Our findings indicate that teleost genomes contain a range of haemoglobin genes, from as few as five in fugu to as many as 43 in salmon, with the latter being the largest repertoire found in vertebrates. We find evidence that the teleost ancestor had at least four Hbα and three or four Hbβ subunit genes, and that the current gene diversity emerged during teleost radiation, driven primarily by (tandem) gene duplications, genome compaction, and rearrangement dynamics. We provide insights into the genomic organisation of haemoglobin clusters in different teleost species. We further show that the evolution of paralogous rhbdf1 genes flanking both teleost clusters (LA and MN) supports the hypothesis for the origin of the LA cluster by rearrangement within teleosts, rather than by the teleost specific whole-genome duplication. We specifically focus on cichlid fishes, where adaptation to low oxygen environment plays role in species diversification. Our analysis of six cichlid genomes, including Pungu maclareni from the Barombi Mbo crater lake, for which we sequenced a representative genome, reveals 18-32 copies of the Hb genes, and elevated rates of non-synonymous substitutions compared to other teleosts. Overall, this work facilitates a deeper understanding of how haemoglobin genes contribute to the adaptive potential of teleosts.

Seasonally flooded landscape connectivity and implications for fish in the Napo Moist Forest: A high-resolution mapping approach

The Amazon River Basin's fish diversity is shaped by its dynamic flood-pulse system, critical for hydrological and ecological connectivity. This study examines the Napo Moist Forest (NMF) ecoregion, mapping permanent and seasonally flooded areas from 2018 to 2021 using remote sensing and deep learning models. We aimed to map these areas at a high spatial resolution (10-m pixels) and analyse their role in maintaining lateral connectivity essential for fish diversity. Using synthetic aperture radar data from Sentinel-1 combined with deep learning algorithms, we produced high-accuracy flood maps to assess landscape connectivity between rivers and floodplains. Our methodology included creating a ground truth dataset with the Normalized Difference Water Index and integrating high-resolution optical data for model training, overcoming challenges of cloud coverage and dense vegetation. Our predictive model achieved high accuracy (mean pixel accuracy = 97 %) and consistently predicted 4801 km² of surface water, with only 3 % (130 km²) being seasonally flooded areas over four years. The Caquetá, Bajo Marañón, Napo, and Pastaza watersheds accounted for nearly 60 % of the flooded areas, highlighting their ecological importance. Connectivity analysis in three areas of interest within the NMF ecoregion revealed important seasonal and interannual fluctuations in hydrological connectivity due to changes in flooded patch characteristics. Reductions in the number and flooded patch area during low water seasons increased the distance between patches, leading to a disconnection between flooded areas, channels and rivers. Despite hydrological fluctuations, certain patches maintained consistent flooding, critical for lateral connectivity and sustaining aquatic biodiversity. These seasonally flooded areas act as connectors, influencing patch dynamics and connectivity with tributaries. Seasonal and interannual variations in hydrological connectivity are crucial for sustaining fish diversity. Conserving dynamic floodplains supports migratory fish life cycles and biodiversity. This study underscores the importance of high-resolution temporal and spatial data in conservation planning for aquatic ecosystems.

Aquaculture activities associated with the invasion of Oreochromis niloticus and changes in stream fish diversity

Aquaculture activities associated with the invasion of Oreochromis niloticus and changes in stream fish diversity

Important fish diversity maintenance status of the tributaries in a hotspot fish conservation area in the upper Yangtze River revealed by eDNA metabarcoding

This study employed Environmental DNA (eDNA) barcoding technology to delve into the influence of the tributaries and mainstem on fish diversity and spatiotemporal distribution in a hotspot fish conservation area in the upper Yangtze River. A total of 123 fish species were detected, belonging to 7 orders, 19 families, and 77 genera. The composition of fish species in tributaries is similar to that in mainstem, with higher fish community diversity in tributaries during the spring and summer. Exploration of fish ecotypes revealed significant differences between mainstem and tributaries. The fish community is mainly influenced by key environmental factors such as water temperature, dissolved oxygen, electrical conductivity, and ammonia nitrogen, with a higher impact of these factors on tributaries than on mainstem. In conclusion, while tributaries and mainstem in the Jiangjin section exhibit similarities in fish community composition, there are notable differences in community structure and diversity. Therefore, the protection of not only mainstem but also tributaries and their associated fish habitats is crucial for promoting the overall health and sustainability.

Rapid determination of fat content: Advanced spectroscopic methods across diverse fish species

The rapid estimation of fat content using spectroscopic-based sensors, irrespective of fish species (salmon, trout, sea bass, sea bream, tuna, cod, and mackerel), was primarily investigated in the present study. The fat content and fatty acid (FA) composition was quantified with reference methods. Fourier-Transform Infrared (FTIR) and Fourier-Transform Near-Infrared (FT-NIR) spectroscopy, along with multispectral imaging (MSI) instruments (both benchtop and portable), were evaluated for their ability to rapidly predict fat content in ground samples using data analysis. The performance of the PLS-R models was evaluated according to root mean square error (RMSE), coefficient of determination (R2) and residual prediction deviation (RPD). Also fish were classified as fat/low-fat and low/medium/high-fat using partial least squares discriminant analysis (PLS-DA). All fish species exhibited a consistent pattern of unsaturated fatty acids (UNFA) > monounsaturated fatty acids (MUFA) > polyunsaturated fatty acids (PUFA) > saturated fatty acids (SFA) and the range of fat content was from 22.8 (salmon) to 0.02 (cod), expressed in g/100 g of sample based on the reference methods. In terms of fat content prediction using rapid sensors the best performance indices of the test set were obtained from the benchtop-MSI (RMSE = 1.475, R2 = 0.847, RPD = 2.581) and FT-NIR (RMSE = 1.638, R2 = 0.855, RPD = 2.651) instruments, while FTIR and portable-MSI had scores of RMSE = 1.874, R2 = 0.815, RPD = 2.309 and RMSE = 1.737, R2 = 0.786, RPD = 2.191, respectively. All sensors discriminated fat from low-fat samples (accuracy = 100%). For low/medium/high fat the best results were achieved by benchtop-MSI (accuracy = 94.12%), followed by portable-MSI (accuracy = 88.24%) and FTIR (accuracy = 84.21%). Results were less satisfactory for the FT-NIR method (accuracy = 68.75%). This study demonstrates that vibrational and multispectral imaging spectroscopies, when coupled with data analysis, have potential to provide information about the nutritional quality (e.g., fat content) independent of the fish species. Such insights could contribute to the automation and potential digitalization of processes within the fields of food nutrition and the seafood industry.

Taxonomic diversity, distribution, and ecology of the freshwater fishes of the Zambezian Lowveld Ecoregion in southern Africa: A systematic review.

The Zambezian Lowveld Ecoregion (ZLE) is one of the 22 freshwater ecoregions covering southern Africa. This ecoregion covers ~520,418 km2 and extends from south of the Zambezi Delta in the north to the uMngeni River basin in the south. This study aimed to compile a comprehensive synthesis of the available information on the diversity and distribution of freshwater fishes in this ecoregion based on natural history collection holdings by reviewing the published scientific literature. In total, 105 native species belonging to 39 genera and 17 families were recorded from the ZLE. An important proportion, 20 (19%), of the species are considered to be narrow-range endemics. Nevertheless, the majority of them (81%) are considered to have broad geographic ranges, with some even extending into adjacent ecoregions. However, recent and ongoing studies indicate that the current taxonomy often underestimates the species diversity and therefore overestimates the distribution ranges of the latter group of freshwater fishes concerned. The present synthesis brings to the fore existing knowledge gaps in species diversity and distribution ranges of freshwater fishes of this ecoregion and highlights the need for the use of integrative approaches to address the prevailing taxonomic conflicts.

Combined Integrative RNA-Seq and Serological sIgE Analysis Enhances Understanding of Fish Allergen Profiles and Diagnostic Strategy for Fish Allergy.

Fish allergy is a significant health concern, with diagnosis and management complicated by diverse fish species and allergens. We conducted a comprehensive RNA-seq analysis of eight fish species to identify allergen profiles, integrating ImmunoCAP sIgE data to explore associations with allergen expression and diagnostic performance. Over 30 putative fish allergens were identified, with varying sequence similarities and expression levels, roughly classifying fish into two groups based on parvalbumin (PV) expression. Higher similarities in allergen expression correlated with stronger sIgE data relationships among fish extracts. High PV expression and conserved PV sequences were linked to elevated sIgE measurements, potentially indicating higher allergenicity. For diagnosis, species-specific extract sIgE remained the best indicator of corresponding fish allergy diagnosis, while incorporating multiple sIgE data enhanced performance. In component-resolved diagnosis (CRD), the current panel with PV alone showed comparable performance to fish extract for PV-high fish allergy, while PV-low fish may require the inclusion of more minor allergens for improved CRD accuracy. This RNA-seq allergen analysis helps reveal fish allergen profiles, classify fish groups, and predict allergenicity, potentially improving CRD design and food management in fish allergy.

Whole-genome resequencing reveals genetic diversity and selection signatures in five populations of Mandarin Fish (Siniperca chuatsi)

Mandarin fish is an important freshwater economic fish in China, and the genome of mandarin fish population may have specific selection signatures after long-term selection, and studying these selection signatures is one of the important strategies for screening functional genes. In this study, the whole genome was resequenced from five mandarin fish populations (HLJ, HN, AH, FJ, and BJ), and a total of high-quality SNPs with 1659,318 single nucleotide polymorphisms were obtained, and the genetic differentiation index and nucleotide polymorphism ratio between populations were used to detect the selected genomic regions. The results showed that all individuals were divided into two branches, with the HLJ population forming an independent cluster, and the HN, AH, FJ, and BJ populations clustering together. Selection signal analysis on the HLJ mandarin fish population and other mandarin fish populations using the FST and π HLJ/other methods. Finally, we identified 26 important candidate genes based on the enrichment pathways related to fat traits such as Glycerolipid metabolism, acyl-CoA oxidase activity, Wnt signaling pathway, and Notch signaling pathway, including notch3, pla2g12a and acox1. This study explores the genetic diversity and genetic structure of mandarin fish from a whole-genome perspective, identifies candidate genes related to fat traits, and provides references for the protection and utilization of mandarin fish genetic resources.

Diversity of fishes along the coast of Türkiye

Diversity of fishes along the coast of Türkiye

Fish diversity assessment through conventional morphological identification and recent advances in Saudi Arabia: A review

Fish identification in the Red Sea, particularly in Saudi Arabia, has a long history. Because of the vast fish diversity in Saudi Arabia, proper species identification is required. Indeed, identifying fish species is critical for biodiversity conservation, food and drug safety, and sustainable fishery management. Numerous approaches have been used to identify fish species, including conventional morphological identification, next-generation sequencing (NGS), nanopore sequencing, DNA barcoding, and environmental DNA analysis. In this review, we collected as much scientific information as possible on species identification in Saudi Arabia. Our findings suggest that the identification process has advanced and spread rapidly and broadly, as evidenced by the discovery of new fish species in Saudi Arabia. The advantages and disadvantages of each method were discussed as part of a comprehensive comparison. This study aimed to provide further scientific knowledge to promote the growth of fish diversity worldwide. Keywords: fish diversity, identification process, Saudi Arabia.

DNA barcoding and cryptic diversity in fishes from the Ili River Valley in China, Xinjiang.

The Ili River Valley, located in the northwest of China, serves as a vital repository for fish genetic resources. Its extensive water network and diverse climate have given rise to a unique fish composition and endemic species. In this study, we collected the cytochrome c oxidase subunit I (COI) sequences from 660 fish specimens in the Ili River Valley. The effectiveness of DNA barcoding in identifying fish species in the area was assessed by examining genetic distances, constructing phylogenetic trees, and performing ABGD (Automatic Barcode Gap Discovery) analyses, among other methods. In total, 20 species were identified, including one unidentified species (Silurus sp.). Except for Silurus asotus and Hypophthalmichthys molitrix (only one sample), the maximum intraspecific genetic distance among the remaining species was smaller than the minimum interspecific distance, which proves that the species exhibit obvious barcode gaps. In the Neighbor-Joining trees, 20 species formed separate monophyletic branches. According to ABGD analysis, 660 sequences were categorized into 19 Operational Taxonomic Units, with Silurus sp. and S. asotus grouped into a single OTU. The Silurus in this study exhibits shared haplotypes and significant genetic divergence, suggesting the potential presence of cryptic species. Furthermore, the nucleotide diversity across all species fell below the threshold level, indicating that the local fish population is gradually declining. In conclusion, this study has demonstrated the effectiveness of DNA barcoding in identifying fish species in the Ili River Valley, providing valuable data to support the conservation of local fish resources.

Microcystin Exposure Alters Gut Microbiota Composition in Fish: An In-Situ Analysis of Post-Bloom Effects in Hulun Lake, China

Cyanobacterial blooms are one of the most common stressors aquatic plants and animals encounter in freshwater ecosystems such as rivers and lakes. Following such outbreaks, some cyanobacteria release toxins, notably microcystins, which are highly toxic. Although numerous studies have explored the effects of microcystins on fish, their in-situ effects on the fish gut microbiome remain unexamined. Our objectives were to examine the fish gut microbiome before (Ju) and after (Au) cyanobacterial blooms and to monitor water quality. We collected Ju and Au fish gut and water samples from Hulun Lake. Using 16S rRNA full-length sequencing, we analyzed the composition, structure, and function of the fish gut microbiome. Results revealed significant disparities in microcystin concentrations between the Ju and Au water samples. In addition, the microcystin concentration in the carp gut was significantly higher than that in its muscle after the cyanobacterial bloom outbreak. Notably, the Au group demonstrated an increase in the microcystin level in water and a marked reduction in fish gut microbiota diversity compared with the Ju group. The cyanobacterial bloom decreased gut microbiome diversity in fish, with the Au group exhibiting a significantly reduced abundance of bacteria related to gut stability and microcystin degradation compared to the Ju group. Furthermore, we observed an upregulation of disease-associated bacterial metabolic functions in the Au group. In conclusion, these findings suggest that microcystins influence the composition and function of fish gut microbiota, improving our understanding of the interaction between fish gut microbiome and their environment. This study offers new perspectives on the adaptive mechanisms of aquatic organisms to cyanobacterial blooms.