Important Fish Species Research Articles

Effects of Feed Supplementation With Fulvic Acid on the Systemic and Mucosal Protective Mechanisms of Juvenile Rainbow Trout (Oncorhynchus mykiss).

Rainbow trout (Oncorhynchus mykiss) is an important fish species raised in aquaculture, but it is susceptible to stress, infections diseases. The present study aimed to determine the effects of fulvic acid feed addition on the systemic and mucosal protective mechanisms of juvenile rainbow trout and to elucidate the underlying molecular mechanisms of changes in the gut. Rainbow trout (4.30 ± 0.6 g) diet was supplemented with different levels of fulvic acid: 0% (Control), 0.5%, 1% and 2%. At the end of 8-week feeding trial, growth parameters such as final weight gained weight (%), SGR (F1%) increased, and FCR (all levels) decreased significantly compared to the control group. We found that the activity of lysozyme, glutathione peroxidase, and catalase in the serum were significantly improved, especially after the addition of 0.5% and 1% of fulvic acid. At the same time, the immunoglobulin concentration in the skin mucus was increased with 0.5% supplementation. However, the expression of tnf-α, il-6 and gpx in the intestine was strongly upregulated after supplementation with 2%, indicating oxidative stress and inflammation with this level of fulvic acid inclusion. Furthermore, the mucus lysozyme activity was reduced at this concentration, which can increase the susceptibility to pathogen invasion. The results suggest that adding 0.5%-1% of fulvic acid to the feed of juvenile rainbow trout can help to improve their immune and antioxidative defenses and thereby support the wellbeing of fish.

GILLNET SELECTIVITY PARAMETERS FOR COMMERCIALLY IMPORTANT SPECIES, <i>LABEO ROHITA</i> IN A TROPICAL RESERVOIR, KERALA, INDIA

The selectivity of fishing gear characterizes its capacity and efficiency in capturing fish. This knowledge helps in selecting the appropriate mesh size to suit the available fish population. The present study aims to estimate the gillnet selectivity parameters of a commercially important fish species, Labeo rohita, from a tropical reservoir in Meenkara, Kerala, India. The study was conducted from September 2019 to February 2020 through experimental fishing using gillnets of different mesh sizes (120, 130, 140, and 150mm) of identical design and dimensions. Selectivity parameters were estimated using Holt’s indirect method. The estimated optimum selection length of L. rohita for three different mesh sizes (120, 130, and 140mm) was 46.56, 50.44, and 54.32cm, and the common selection factor (SF) was 3.88. The estimated optimum mesh size of 127 mm was found to be ideal for the commercial exploitation of L. rohita in the Meenkara reservoir. The gillnet selectivity estimates obtained in the present study will be beneficial to increase the likelihood of capturing targeted size classes as well as better management of the L. rohita fishery in Meenkara reservoir.

Quantifying the Interactions and Cumulative Effects of Multiple Stressors on Salmonids.

The cumulative effects of human activities and natural pressures pose significant threats to ecosystem functioning and global biodiversity. Assessing the cumulative impact of multiple stressors-whether acting simultaneously or sequentially and directly or indirectly-is challenging due to their complex interactions. Consequently, these interactions may be unintentionally overlooked or disregarded in management decisions. While existing reviews have focused on coastal and freshwater ecosystems, analyses specifically targeting salmonids as a focal group are lacking. This research presents the first quantitative and qualitative assessment of stressor interactions affecting salmonid biology and physiology. A focused literature search identified 118 experimental trials with multiple stressors on salmonids. From these, 46 cases were considered suitable for the quantitative analysis. We calculated Hedges' g effect sizes to classify the interactions between multiple stressors as additive, synergistic, or antagonistic. Our findings revealed that additive effects were found most frequently (50% of interactions), followed by synergistic (30.5%) and antagonistic (19.5%) interactions. Additionally, we performed a network analysis including cases focusing on the influences of multiple stressors interactions (n = 38). Our qualitative analysis identified temperature, metals, and pesticides as the most paired stressors across the three types of interactions. The findings of this research highlight the potential vulnerabilities of salmonids and their habitats by identifying key interactions between multiple stressors, and priorities for future research. Understanding these interactions and cumulative effects, particularly in the context of climate change, can inform targeted conservation and management strategies, contributing to the preservation of these important fish species and their ecosystems, which are vital to local human communities.

Length–weight relations and condition factors of several endemic and native fish species from Anatolian freshwater

This study analyzed the length–weight relations and condition factors of 13 species belonging to three highly endemic genera: Oxynoemacheilus (6), Seminemacheilus (2) and Cobitis (5). Fish were sampled in several streams and lakes using a backpack electroshocker. Analyses were based on a total number of individuals, which was n = 304. A linear regression model was applied to determine the relationship between fish length and weight. The coefficient of determination (R2) ranged from 0.950 to 0.980 for all populations (p < 0.05). Allometric coefficient ‘b’ values ranged from 2.498 to 3.201 for Oxynoemacheilus, from 2.970 to 2.127 for Seminemacheilus, and from 2.111 to 3.076 for Cobitis populations. Fulton’s condition factor for Oxynoemacheilus, Seminemacheilus and Cobitis ranged from 0.391 to 3.080. This study addresses gaps in LWR and CF information for a number of ecologically important freshwater fish species. It is expected that the results of this research provide baseline data for further fisheries management studies and may support conservation studies of related species.

Aquatic circoviruses: emerging pathogens in global aquaculture - from discovery to disease management.

The expansion of global aquaculture has brought challenges from emerging pathogens, resulting in disease-related production losses across various regions. Among these pathogens, aquatic circoviruses-small, single-stranded DNA viruses initially detected in barbel (Barbus barbus)-have now been identified in multiple aquaculture species. These viruses have been associated with various clinical manifestations in economically important fish, crustacean, and mollusk species, including acute hemorrhage syndrome, which has shown mortality rates up to 95% in controlled laboratory infections of turbot. This review consolidates current knowledge on aquatic circoviruses, focusing on their genetic diversity, epidemiology, pathogenesis, and management strategies. The analysis encompasses observed host range patterns, documented instances of cross-species transmission, and evolutionary characteristics, such as host-specific clustering and recombination events. Research gaps are highlighted, particularly in understanding viral pathogenic mechanisms, host-pathogen interactions, and their ecological roles within aquatic ecosystems. We evaluate recent advances in diagnostic methods, including targeted vaccine design and RNA interference technology. The review outlines future research priorities, including elucidating cross-species transmission potential, developing effective treatments, and assessing the full economic impact of these viruses on aquaculture. By providing a comprehensive overview, this review aims to guide future research efforts and inform strategies to mitigate the impact of circoviruses on aquaculture sustainability.

Trace metal accumulations in commercially important fish and crab species from impacted tropical estuary, India: implications on human health risk assessment.

Despite the beneficial role of aquatic food, bioaccumulation of trace metals can increase health risk for consumers. We conducted a comprehensive study to understand the levels of various trace metals (Cd, Co, Cr, Cu, Fe, Ni, Pb, Zn and Mn) in fish (Nematalosa nasus, Gerres filamentosus, Arius arius, Gerres erythrourus, Sardinella fimbriata, Caranx ignobilis, Etroplus suratensis, Mugil cephalus, Sillago sihama, and Euryglossa orientalis) and crab (Portunus pelagicus and Scylla serrata) species collected from Netravathi-Gurupur estuary, India and evaluated the potential health risks to humans by measuring target health hazard (THQ), hazard index (HI), estimated daily (EDI) and weekly (EWI) intake and cancer risk (CR). The hierarchy of toxic metal content in studied species was Fe>Pb>Cr>Mn>Zn>Cu>Ni>Cd>Co. The concentration of heavy metals were distinctly lower than the threshold value as suggested by World Health Organization and Food Safety and Standards Authority of India, except for Cr and Pb in few species. THQ values were below the acceptable limit. However, the estimated mean HI values were >1 for children, indicating they may be vulnerable to health risk due to continuous consumption of contaminated aquatic species from the study area. In contrast, the cancer risk for Cr, Cd, and Pb was below the acceptable range. Principal component analysis (PCA) discerned nearby petrochemical industry, electroplating industry, pesticides and fertilizer from agricultural runoff, as the potential sources of metal bioaccumulation in different tissues. Although the study reveals that metal contamination in aquatic species does not pose any immediate human health effect, continuous monitoring of the study area is recommended, as some metals have demonstrated their ability to accumulate in the tissues.

Accumulation of Toxic Elements in Fish from Ohrid Lake Under the Influence of Anthropogenic Activities

Abstract Water ecosystems are under intense anthropogenic influence, which leads to an increased presence of pollutants, including a large number of toxic substances, primarily heavy metals, which requires constant monitoring. Fish are one of the most indicative factors for assessing water pollution with harmful elements, and this is important not only for environmental protection but also for the assessment of meat quality and the potential risk to the human population. The main goal of this research was to analyze the level of accumulation of heavy metals and metalloids, such as arsenic (As), iron (Fe), chromium (Cr), copper (Cu), lead (Pb) and zinc (Zn) in the muscle tissue of commercially important fish species from Ohrid Lake, to compare their concentrations in different fish species, to apply the index of heavy metal pollution in the assessment of water pollution, and to make a comparison of the concentrations of accumulated heavy metals and metalloids in the muscle tissue of the examined fish species with the maximal permitted concentrations prescribed by the legal regulations. The research area was in Ohrid Lake, Macedonia. The most important commercial fish species from Ohrid Lake, i.e. common carp, Ohrid trout, and barbel, were sampled for analysis. Statistical analysis of the data showed significant differences (P < 0.05) and significant variations in iron, chromium, copper, and zinc levels between different fish species and sampling months, highlighting the importance of considering species-specific factors such as feeding, habitat preferences, and metabolic processes in understanding the patterns of element accumulation, but also the temporal dynamics of element accumulation in fish. Based on the data on the concentrations of toxic elements (Fe, Cr, Cu, Pb, Zn) in common carp, Ohrid trout, and barbel during the examined months (May, September, December, February), it can be concluded that the obtained values are below the maximum allowed concentrations prescribed on the basis of Commission Regulation (EU) No 1881/2006. This means that the fish species analyzed are safe for consumption and comply with regulatory guidelines, thus ensuring the protection of consumer health.

Diving into the fish pathology of an important commercial fish species: the case of the European hake (Merluccius merluccius Linnaeus, 1758) in the northwest Mediterranean Sea.

The gross pathology and the histopathological alterations identified in juvenile specimens of the European hake (Merluccius merluccius), one of the most important target species of commercial fisheries in the northwest Mediterranean, are described. A qualitative and semi-quantitative histological approach was performed in specimens from 2007 and 2019. Prevalence and mean intensity of parasites and histopathological changes were calculated in both years. No macroscopic alterations were found in any organ but several parasites (e.g., copepods, nematodes, digeneans) were detected. Microscopically, alterations identified in gills included foci of inflammation and hyperplasia (present in 77.38% of hakes from both years), extensive hyperplasia (33.33%), and inflammation (16.65%) that were potentially related to the mechanical effects of monogeneans and copepods, cysts of unknown etiology (62.69%), and lamellar inflammation associated to Aporocotyle spinosicanalis eggs (8.33%). Granulomas and inflammatory focus were detected in the liver, spleen, and stomach, apparently associated with the presence of nematodes. Coelozoic myxosporean parasites were detected within the renal tubules (66.66%). Most of the pathologies detected were similar to those described in other gadoid species (i.e., Gadus morhua) and were usually related to the presence of ecto and endoparasites. The potential impact of parasites on the health of this fish species is discussed for improving the knowledge and management of these valuable fishing stocks.

Trends in the Average Weight of Fish Caught by Artisanal Fishers in the Croatian Section of the Sava River

Abstract The number of artisanal fishers and consequently their catch in the Sava River have been declining significantly for years. The aim of this study is therefore to examine how this affects the average weight of the most important fish species caught. The average weight increased significantly for bream Abramis brama (P < 0.01), pike-perch Sander lucioperca (P < 0.01) and wels catfish Silurus glanis (P < 0.05), while this was not the case for common carp Cyprinus carpio and pike Esox lucius (P > 0.05). Although recreational anglers also catch fish in the same waters, together with the two groups of fishermen from Bosnia and Herzegovina from the other bank of the river, it is expected that the average weight of the main fish caught will not decrease under the current circumstances.

Prevalence of Fibers as the Dominant Microplastic Fraction in the Digestive Tract of Three Commercially Important Fish Species (Sparus aurata Linneaeus 1758, Pagellus erythrinus Linneaeus 1758 and Chelon auratus Risso, 1810) from the Southeastern Coast of Istria, Northern Adriatic, Croatia

The exponential increase in plastic pollution, especially microplastics (MPs), is closely linked to human population growth, industrialization, and poor waste management practices. MPs have become a pervasive environmental contaminant, posing significant risks due to their ability to adsorb harmful substances and attached microorganisms. The Adriatic Sea is a critical region for studying microplastic pollution, ranking among Europe’s three most polluted seas, with plastic comprising 80% of waste. This study investigates the presence of MPs in three commercially important fish species - Gilthead seabream (Sparus aurata), Common pandora (Pagellus erythrinus), and Golden grey mullet (Chelon auratus) - collected from the northern Adriatic Sea. A total of 93 fish were analyzed, revealing that all extracted MPs were fibers, primarily black (42.4%) and blue (39.6%). The results indicate the higher MP contamination levels (80.64%) of S. aurata and C. auratus when compared to P. erythrinus (35.48%). This research contributes to a better understanding of microplastic pollution in the region and can improve the knowledge for effective monitoring and mitigation strategies. Future studies should focus on the long-term impacts of MPs on marine ecosystems and human health, particularly in commercially consumed species.

Gillnet selectivity of commercially important fish Labeo rohita, Hamilton,1822 and Catla catla, Hamilton,1822 in kosi river, Madhepura, Bihar

Application of fishing gears in fishery is the result of experiences gained over a long period of time. Every water body has a unique pattern of fishing activity. The present study was aimed to evaluate the selectivity of gillnets and the size at first maturity of commercially important fish species in Kosi river mainly the Rohu Labeo rohita and Catla Catla catla. Experimental fishing was conducted using gillnets of different mesh sizes (60, 80, 100, 120 and 140 mm) in six sampling occasions from 2023 - 2024. A total of 2671 fish specimens consisting of 1184 L. rohita and 1523 C. catla were analyzed. Gillnet selectivity parameters for each mesh sizes were estimated for each species using the SELECT method. The size at first maturity (Lm) and its 95% CI for L. rohita and C. catla were estimated at 23.9 cm (23.3 - 24.5 cm), and 32.5 cm (31.6 - 33.4 cm), respectively. Results showed that a Log-normal model best described gillnets selectivity for C. catla, while a Normal location model best described for L. rohita. Capture probability estimates indicate that the optimum length of capture (LCAP) of > 80 mm mesh size nets are smaller than the Lm of both target species, while LCAP of >120 mm mesh net selects above the Lm value for both L. rohita and C. catla. Although the 100 mm mesh selects above the size of Lm value for L. rohita, it still selects below the Lm value for C. catla. Based on the results obtained, it was concluded that gillnets of mesh size 100 and 120 cm may safely be applied in Kosi river fishery if proper level of effort is applied that ensures sustainability of both target species. This study provides the baseline scenario for formulating a sustainable fisheries management strategy since many aspects of the L. rohita and C. catla fishery are not disclosed.. KEYWORDS :Rohu, Catla, optimum length of capture, SELECT model, gonad maturity, Gillnet.

Population Genetic Diversity of Bluefish (Pomatomus saltatrix L, 1766) in Coastal of Türkiye

Bluefish, is a commercially important fish species distributed the Türkiye coastal area. The high migration rates of Bluefish may prevent indirect speciation across its broad geographic distribution. The conservation and sustainability of the Bluefish populations require knowledge of the population`s genetic structure. There are no genetic studies on Bluefish in Türkiye and there are only a few studies in the world. In this study we investigated the population structure of this species in Türkiye coastal areas. COI and 16S rRNA gene sequences were performed in Bluefish samples collected from 14 regions. All stations are displayed low number of haplotypes for COI and 16S rRNA. In the COI gene region, total of 20 haplotypes was found whereas in the 16S rRNA gene region, total of 8 haplotypes was found. The results of both COI and 16S rRNA AMOVA analysis revealed that within population variation is less than among population variation It has been observed that Aegean and Mediterranean populations are more diverse than other populations. It is seen that the genetic differentiation among Bluefish populations in coastal Türkiye is low level and there are mixed individuals in all populations.

Trends in fish diversity in Portuguese estuaries in the past decades and predictions in face of global changes

Coastal transition ecosystems like estuaries are amongst the most productive aquatic ecosystems on the planet, recognized worldwide as a fundamental component of coastal areas in terms of biological relevance and anthropogenic use. Estuaries along the Portuguese coast differ in their geomorphological and hydrological characteristics. These systems play a crucial role in terms of nursery areas for economically important fish species. Although several authors have observed high specific variability in estuarine fish communities along the Portuguese coast, few studies explore the factors that influence it. Most of these studies focus on a single estuary and, when several are addressed, only a single factor is used to assess the specific variability of the communities. The presente work aims to analyze the ecological role played by these estuaries for fish communities, namely in terms of their species richness, using a 30 year historical database provided by the Portuguese Coastal Monitoring Network Research Infrastructure (CoastNet RI). To this end, a generalized additive model (GAM) was developed to analyze the variation of species richness as a function of a set of temporal, spatial and environmental characteristics from the nine principal estuarine systems on the Portuguese coast. A total of 142 species from 45 families were identified. The Tejo, Mira, and Sado estuaries had the highest species counts (92, 72, and 64 species, respectively), while Minho and Ria de Aveiro had the lowest (26 and 27 species, respectively). The GAM model explained 35.1% of the variance in species richness and demonstrated significant differences in fish species richness in space (among the nine study estuaries) and time (at annual and monthly scales), and these differences were influenced by abiotic factors such as salinity and temperature. Species richness decreased with higher latitudes and varied yearly, showing a downward trend post-2002. Monthly variations showed increases in February–March and September–October. Higher species richness correlated with salinity levels between 25 and 37 and temperatures between 14 and 25 °C. Possible scenarios of future variations caused by the effects of climate change on the significant factors are also discussed. These GAMs could be useful as a preliminary tool to prepare long-term conservation plans for national legislation.

Deletion of the gsk-3β (Glycogen synthase kinase-3β) in zebrafish results in decreased susceptibility to Aeromonas hydrophila

Aeromonas hydrophila is a significant pathogen in the field of fish farming, resulting in substantial financial losses for the aquaculture industry. As the pathogen's resistance to commercially available antibiotics continues to rise, the identification of novel antimicrobial strategies becomes increasingly crucial. This study aims to explore the modulatory impact of gsk-3β (Glycogen synthase kinase-3β) on the intrinsic immunity against Aeromonas hydrophila in zebrafish, with the objective of uncovering a new avenue for enhancing fish antimicrobial activity through gene editing. Our investigation involved an analysis of the evolutionary patterns and protein sequence of gsk-3β, elucidating its conserved characteristics in zebrafish and fish species of economic importance. In this research, CRISPR-Cas9 technology was employed to generate a zebrafish model with a knockout of gsk-3β, resulting in a decreased resistance of zebrafish to Aeromonas hydrophila (ATCC 7966) infection. Furthermore, we conducted preliminary investigations into the potential mechanisms through which gsk-3β governs antimicrobial immunity. Our findings revealed that knockout of gsk-3β resulted in diminished activation of innate immunity, antioxidant capacity, and autophagy. Hence, the findings of this study are highly significant in improving the economic benefits of aquaculture and in effectively preventing and controlling infection caused by Aeromonas hydrophila.

Genetic diversity, population genetic structure and demographic history of the Ribbontail stingray Taeniura lymma (Fabricius, 1775) (elasmobranchii: myliobatiformes: dasyatidae) along the Tanzanian coastline

The Ribbontail stingray Taeniura lymma is an economically important fish and attractive species for the aquarium trade industry. Overfishing, habitat degradation, and pollution, however, pose a threat to this species. This study used partial mitochondrial cytochrome oxidase subunit I (COI) sequences (603 base pairs long) from 96 samples of T. lymma collected at five fish-landing sites (Deep Sea-Tanga, Malindi-Unguja, Kaole-Bagamoyo, Kivukoni-Dar es Salaam, and Bandarini-Mtwara) located along the coast of Tanzania to determine the species’ genetic diversity, population genetic structure, and demographic history. The findings revealed an average nucleotide diversity of 0.24 ± 0.16% and a haplotype diversity of 0.75 ± 0.04. Nucleotide and haplotype diversities were relatively low at Kaole-Bagamoyo compared to the other studied localities. An Analysis of Molecular Variance (AMOVA) indicated limited but statistically significant genetic differences among populations (Overall FST = 0.09, p < 0.01). Pairwise AMOVA revealed genetic difference between the Deep Sea-Tanga population and all other populations studied with exception of Malindi-Unguja. Analyses of mismatch distribution, demographic history, and a haplotype network support a scenario of historical population expansion in the studied species. Immediate effort is required to protect population exhibiting low genetic diversity in this commercially important ray.

Dietary Effect of Withania somnifera (Ashwagandha) Root Powder on Growth and Blood Parameters of Cyprinus carpio (Common Carp)

Aims: The present study evaluated the effect of different levels of Withania somnifera root powder in fish formulated diets on the growth performance of economically important freshwater fish species in Asia Cyprinus carpio and compare the hematological changes occurred in fishes fed with control feed and herbal formulated diet. Study Design: The experiment was planned with the size group of 30.0±1.0g. Fish of the respective size group of Cyprinus carpio were subjected to different herbal formulated diets at a concentration 0%, 0.5%, 1.0%, 1.5%, 2.0% of Withania somnifera root powder extract through their diet, while the control group received a standard diet without any supplementation. Duration of Study: The study was conducted over a period of 4 weeks. Methodology: During which growth parameters such as Average Daily Growth, Specific Growth Rate and Absolute Growth Rate were monitored at regular (10 days) intervals. The blood samples were collected at 4th week from each group to assess hematological parameters including Red Blood Cell count, White Blood Cell count, Hemoglobin, Total Cholesterol and Total serum protein levels. The overall results revealed that the inclusion of Withania somnifera extract in the diet of Cyprinus carpio significantly influenced both growth and blood parameters. Results: Fish exposed to Withania somnifera extract exhibited enhanced growth performance compared to the control group, with increased Average Daily Growth, Specific Growth Rate and Absolute Growth Rate. Moreover, hematological analysis revealed positive effects on the blood parameters of treated fish, including improvements in Red Blood Cell count, White Blood Cell count, Hemoglobin, Total Cholesterol and Total serum protein levels. Conclusion: The overall results revealed that the inclusion of Withania somnifera extract in the diet of Cyprinus carpio significantly influenced both growth and blood parameters.

Seasonal variations in microplastics in a coastal wetland in southwest India as well as their risks to Sillago sihama and Gerres filamentosus.

Microplastics are minute plastic particles ranging from 1µm to 5mm in size. Mangroves are crucial ecosystems with roles in carbon sequestration, shoreline protection, and habitat for diverse species. Despite their significance, the extent of microplastic pollution in mangroves, especially in India, remains inadequately understood. To address this gap, we conducted a seasonal sampling in the Kota mangrove ecosystem at different water column depths. Our analysis revealed average microplastic abundances of 0.93 (monsoon), 3.71 (post-monsoon), and 2.92 MPs/L (pre-monsoon). The average microplastic abundances were 19.88 and 15.86 microplastics/individual for Gerres filamentosus and Sillago sihama, respectively. Fibrous microplastics smaller than 1mm were dominant. Transparent microplastics dominated the water column (28.57% in monsoon, 77.45% in post-monsoon, and 49.24% in pre-monsoon), and they were also prevalent in S. sihama (49.55%) and G. filamentosus (41.51%). This points towards greater bioavailability and suggests that transparent microplastics are often mistaken for prey. Anthropogenic influence is a major factor that governs microplastic distribution than season in Kota mangroves. Fourier transform infrared spectroscopy revealed that polypropylene was the dominant polymer in both water column as well as in S. sihama and G. filamentosus. We identified aquaculture, tourism, and local activities as probable sources of microplastic pollution. The monitoring data is crucial as it provides insights into microplastics pollution in two economically important fish species that are largely consumed by the local population. Exposure to microplastics from the consumption of these fish may cause serious health issues for human beings.

Microbial Profile and Antimicrobial Resistance in Enteric Pathogens of Farmed Catfish (Pangasianodon hypophthalmus) in Tropical Freshwater Farms

Background: Recently, Pangasianodon hypophthalmus has emerged as an important fish species farmed in India, contributing to food security in the region. Understanding the bacterial flora associated with this fish is essential to ensure food safety, particularly in the Indian context where such studies have been limited. Objective: This study aims to determine the aerobic bacterial flora and antimicrobial resistance in enteric pathogens associated with farmed Pangasianodon hypophthalmus cultured in freshwater ponds in Kerala, India. Methods: The study included enumeration of aerobic plate counts, Pseudomonads, Aeromonas, Enterobacteriaceae and Staphylococcus aureus using standard methods. Bacterial identification was performed using analytical profile index 20E (APE20E) and 16s rDNA sequencing. Antimicrobial resistance was assessed in E. coli, S. aureus and Aeromonas species using disc diffusion assays. Results: The aerobic bacterial flora in catfish muscle tissue included H2S-producing bacteria, Enterobacteriaceae, Pseudomonas, Aeromonas, and B. thermosphacta. Dominant genera identified were Pseudomonas, Burkholderia, Stenotrophomonas, Aeromonas, Klebsiella, and Psychrobacter. Multidrug-resistant strains of enterotoxigenic E. coli and A. hydrophila were recovered, raising concerns about the prevalence of multidrug resistance in A. hydrophila, an etiological agent of red disease in farmed catfish. Conclusion: This study highlights the microbiological risks posed by Aeromonas spp. and enterotoxigenic E. coli in farmed catfish, emphasising their potential as vectors for pathogenic and antibiotic-resistant determinants in the food chain. Recommendations for future research should focus on the development of effective biopreservatives to control these pathogens in processed Pangasius products.

Levels and Classification of Microplastics and Their Impact on the Wellbeing of Selected Commercially Important Fish Species in Kisumu Bay, Lake Victoria.

Microplastics (MPs) are emerging pollutants of concern in aquatic ecosystems. Fish ingest MPs accidentally during normal feeding because they resemble prey or by ingesting prey that previously consumed them. Despite severe plastic pollution in Africa, some countries, including Kenya have implemented laws to curb this pollution menace. MPs have scantly been studied in African freshwaters. This study provides empirical data and describes the levels of MPs in four commercially important fish species in Lake Victoria. A total of 95 fish samples were collected from four sampling sites (inshore-offshore waters) between March and May 2022. Microscopy and Attenuated Total Reflectance Fourier Transformed Infrared (ATR-FTIR) spectroscopy methods were used to identify MPs. In this study, 62 out of 95 (65.26%) of the gastrointestinal tracts of the sampled fish contained MPs. The four species showed different proportions of detected MPs among the sampled individuals: 75.00% (Clarias gariepinus), 75.00% (Synodontis victoriae), 71.43% (Lates niloticus), and 59.26% (Oreochromis niloticus). Polystyrene (PS) and poly (perfluorobutadiene) were the main plastic polymers in the fish samples. The condition factors estimated for O. niloticus, S. victoriae, and L. niloticus were > 1 and < 1 for C. gariepinus, respectively. Positive correlations were observed between microplastic numbers and fish length and microplastic numbers and fish weight. However, the low R2 values obtained implied no strong relationship exists between these parameters. These findings provide evidence of microplastic contamination in fish in Kisumu Bay.

Early mucosal responses in common carp (Cyprinus carpio) to the infection of Aeromonas hydrophila

Common carp (Cyprinus carpio), an economically important freshwater fish species, is worldwide farmed especially in Europe and Asia. The current high-density intensive rearing way leading to a high susceptibility to various pathogens, and Aeromonas hydrophila is one of the most frequently encountered bacteria, causing huge economic losses to the common carp industry. The mucosal barrier of fish constitutes the first line of defense against various pathogens, and some level of inter-connectivity exists among teleost mucosal tissues. However, the molecular basis for a common mucosal immune response at multiple sites or response at one site but during different timepoints following stimulation remains to be studied. In this study, we examined and systematically analyzed a total of 144 transcriptome files from three primary common carp mucosal tissues at four early timepoints following the infection of A. hydrophila. A total of 410 unigenes were significantly differentially expressed in all tested mucosal tissues. Through GO enrichment and KEGG pathway analysis, 28 key genes which might played critical roles in the common mucosal immune response of common carp during the early stage of bacterial infection were identified. Further WGCNA analysis showed that, besides the common response, three mucosal tissues exhibited tissue-specific gene regulatory network. Meanwhile, candidate hub genes in each tissue were identified, including trim3, rpl14, tln2, itpr1, and others. Our results will provide a fundamental basis for understanding the molecular mechanisms of teleost mucosal immunity, and might suggest strategies for developing novel teleost mucosal vaccines in aquaculture.