Background The East Kolkata Wetlands (EKWs) are a well-known Ramsar-designated managed natural wetland that naturally treats wastewater through physical, chemical, and biological processes and supports wastewater-fed aquaculture and agriculture. The microbiome helps break down organic matter, recycle nutrients, and degrade pollutants but faces threats from urban expansion, stressors, and contaminants. This study examines the taxonomy, functions, resistance genes, potential for bioremediation, and degradation genes of the EKW sediment microbiome using whole-metagenome analysis. Results Shotgun metagenomic analysis revealed a highly diverse and functionally robust sediment microbiome from Sardar Bherry in the EKWs, dominated by bacteria. Among bacterial taxa, Proteobacteria was the most abundant phylum (70.91–73.61%), and Pseudomonas the most prevalent genus. The sewage site exhibited the highest microbial diversity and richness. KEGG orthology functional annotation indicated that about 60% of annotated genes were involved in metabolic functions, including xenobiotic degradation. These genes and microbial taxa may be involved in degrading substances such as benzoate, chlorocyclohexane, chlorobenzene, atrazine, DDT, bisphenol, and polycyclic aromatic hydrocarbons. The resistome comprised 85 antibiotic resistance gene (ARG) subtypes across 16 classes, with the highest ARG burden at the sewage site, dominated by beta-lactam-, aminoglycoside-, multidrug-, and bacitracin-resistance genes. Additionally, 43 metal-resistance and associated environmental stress-response genes, including those conferring resistance to mercury (Hg), arsenic (As), copper (Cu), and chromium (Cr), as well as those associated with oxidative stress, were detected, with the highest abundance at the inlet site. Functional profiling further identified 57 candidate biodegradation-associated microbial taxa and 71 candidate putative plastic-degradation-associated microorganisms, together with key enzymes, with the highest genetic potential for biodegradation observed in the middle zone of the wetland. However, these findings suggest potential functional links but don't confirm specific strains. Conclusion This metagenomic analysis improves understanding of microbial communities in polluted EKW wastewater. EKWs host a diverse microbiome crucial to potential biogeochemical processes, highlighting the role of natural wastewater treatment wetlands in ecosystem health and advancing understanding of biological functions. Nevertheless, further culture-based and functional research is necessary to confirm the activity and environmental significance of these predicted biodegradation pathways. Further research should focus on developing microbial consortia to combat pollution.

Bisphenol A (BPA) is a widespread environmental contaminant of growing toxicological concern, yet its cellular mechanisms of action in fish gill tissues remain inadequately defined. This study investigated the cytotoxicity and oxidative stress-mediated toxicity of BPA in zebrafish (Danio rerio) gill (DRG) cells following exposure to environmentally relevant concentrations (0.5-2.5 ppb) for up to 96 h. BPA induced a pronounced concentration- and time-dependent decline in cell viability, with an 89.7% reduction observed at 2.5 ppb after 96 h, as determined by the MTT assay. Morphological evaluation revealed progressive cellular damage, characterized by membrane disruption, cellular shrinkage, and eventual loss of structural integrity. BPA exposure triggered severe oxidative stress, evidenced by substantial increases of 152.9% in intracellular reactive oxygen species (ROS), reaching a maximum elevation of 397.9% at 2.5 ppb after 96 h, and a maximum 446.5% increase in malondialdehyde levels (lipid peroxidation) at the same condition. Antioxidant enzyme responses were differentially affected: superoxide dismutase activity showed a progressive overall temporal decline of 38.2% (mean across all treatment groups and time points), reaching a maximum inhibited of 81.6% at 2.5 ppb after 96 h. Catalase and glutathione peroxidase activities exhibited transient compensatory increases followed by significant suppression of 67% and 80.9% from their respective 12 h peak values at the highest exposure condition (2.5 ppb, 96 h). These findings demonstrate that BPA exerts potent cytotoxic effects in fish gill cells by disrupting antioxidant defense systems and exacerbating oxidative damage. The high sensitivity of gill cells to low-dose BPA exposure highlights their vulnerability as primary targets of aquatic toxicants and underscores the possible effect of BPA contamination in aquatic environments.

Cyanobacteria are widely distributed in water worldwide, and their harmful effects on water quality have become a global issue. It has long been recognized that cyanobacterial blooms in aquaculture ponds can cause sudden, large-scale fish mortalities. However, their impact on cellular and molecular responses in fish remains poorly understood. In this study, the impact of cyanobacterial blooms, which have been associated with mass mortality events in the freshwater fish Labeo rohita, was investigated by examining their detrimental effects on the host's cellular and molecular responses. The fish had a swollen abdomen and a red, enlarged anus. When gentle pressure was applied, fluid dripped from the anus, possibly due to an algal bloom in the culture system. Microscopic and molecular tests confirmed a cyanobacterial bloom caused by Microcystis sp. and Anabaena sp., likely responsible for the high fish mortality. During the infection, the fish exhibited severe histopathological alterations in the liver, kidney, and gills. The fish's immune system responded strongly through differentially expressed nonspecific and specific immune responses, involving significant effect on the inflammation (TNF-α, IL-1β, iNOS), immune activation (TLR 4, C3, MYD88, NOD 1), and innate and adaptive immune response (IFN-γ, Hsp70, Mx, IgM) genes in the L. rohita liver, kidney, and gill tissue samples. This suggests that cyanobacterial blooms influence the host immune system, creating conditions that promote immunotoxicity in fish, which can lead to infection and mortality. Here, we evaluated the effects of cyanobacterial blooms (Microcystis sp. and Anabaena sp.) on the cellular and molecular responses of fish during a severe mass mortality event. Hence, the present study may contribute to a deeper understanding of the interactions between the aquaculture water environment and the fish immune system.

Fish cell lines are indispensable in vitro systems that support diverse research areas, including virology, immunology, ecotoxicology, and biomedical science. Fish represent the most species-rich vertebrate group with remarkable genomic diversity, providing valuable resources for specialised cellular models. Since the establishment of the first fish cell line (RTG-2) in 1962, the global repository has expanded to approximately 918 authenticated cell lines derived from over 211 species. This review presents a comprehensive overview of the historical progression, global repositories, and current standards for cell line authentication. It summarises methodological advances in primary culture initiation, the development of continuous cell lines, and improvements in cryopreservation techniques. This review also critically explains the wide-ranging applications of fish cell lines in aquatic virology, vaccine development, and standardised ecotoxicological assays. The translational potential in biomedical research is also highlighted, particularly in cancer biology, regenerative medicine, and drug discovery, largely driven by the use of genetically tractable model species such as zebrafish (Danio rerio) and medaka (Oryzias latipes). Key challenges are also discussed, including mycoplasma contamination, cross-species misidentification, limitations in cryopreservation protocols for marine-derived cells, and the need for robust, open-access digital biobanking systems. Future perspectives encompass emerging technologies such as 3D organoids, organ-on-a-chip platforms, CRISPR-based genome editing, and serum-free culture systems. Integration of these innovations with omics approaches and adverse outcome pathway frameworks is expected to enhance the utility of fish cell lines, advancing research in aquaculture, environmental monitoring, and food security, while aligning with the principles of the 3Rs and the United Nations Sustainable Development Goals.

Polyethylene (PE) constitutes nearly 50% of the total microplastic (MP) waste worldwide, and their accumulation in the environment poses significant ecological concerns. PE persists in the environment for centuries, accumulating in landfills and aquatic ecosystems, where it adsorbs heavy metals and organic pollutants, entering food chains and posing severe ecological and health risks, including endocrine disruption and cellular toxicity. Bioremediation methods using microorganisms to degrade synthetic polymers has emerged as a sustainable alternative. However, only a limited number of microbes have been identified so far, primarily due to the challenges of culturing potential degraders under laboratory conditions and the highly resistant structure of PE. In this study, we isolated two strains, Proteus penneri ND-SD-4709 and Proteus vulgaris BKB-SD-13892, from urban plastic waste disposal sites and investigated their PE-degrading potential. Both strains utilized PE as a carbon source, as confirmed by weight loss (19.13+0.40% for P. penneri ND-SD-4709 and 17.30+0.55% for P. vulgaris BKB-SD-13892), polymer reduction rate (K=0.00177 day(-1)+0.00003 for P. penneri ND-SD-4709 and 0.00158 day(-1)+0.00006 for P. vulgaris BKB-SD-13892), and calculation of half-life (t(1/2)=391.80+8.69 for P. penneri ND-SD-4709 and 438.22+15.31 for P. vulgaris BKB-SD-13892) after 120 days of incubation in a carbon-free medium. Biodegradation was further validated using fourier transform infrared spectroscopy (FT-IR), which showed structural alterations, and field emission scanning electron microscopy (FE-SEM), which revealed surface erosion in PE following microbial treatment. Additionally, gas chromatography-mass spectrometry (GC-MS) identified degradation intermediates whose kinetic profiling revealed superior polyethylene degradation efficacy through biodegradation efficiency metrics. The results demonstrate that P. penneri ND-SD-4709 exhibits faster and more consistent polyethylene degradation kinetics than P. vulgaris BKB-SD-13892. Our work offers a laboratory-based comparative analysis of two different underexplored Proteus spp., followed by effective methodological framework for isolation, selection, and evaluation of specific polymer-degrading microorganisms using advanced analytical techniques. These findings have significant implications for developing PE-waste management strategies like enzyme characterization, metabolic engineering, and field-scale validation to enhance degradation kinetics.

The world grapples with the devastating loss of biodiversity, imperiling not only treasured species but also crucial genetic variation essential to food production, health, and safety. Conventional monitoring techniques struggle to detect rare species or juvenile life stages, necessitating innovative approaches. Environmental DNA (eDNA) enables non-invasive, cost-efficient biodiversity monitoring. Extracted from ancient and present materials, eDNA spans individual species identification to ecosystem-level studies, revolutionizing ecological preservation and conservation research. Technological hurdles persist despite advancements, mandating calibration and validation improvements to mitigate false positives and negatives. Enhanced understanding of eDNA’s physical and ecological constraints, synthesis, and potential modes of movement is imperative. This review summarizes commonly used protocols for eDNA-based detection of organisms in soil and water environments, the main uses of eDNA for aquatic and subterranean invasive species, and the difficulties and restrictions associated with eDNA metabarcoding. As a pivotal tool in ecological research, eDNA technology facilitates non-invasive biodiversity assessment and ecosystem monitoring amid environmental threats like habitat loss and climate change. Emphasizing historical evolution, methodological innovations, diverse applications, and conservation implications, this review underscores eDNA’s pivotal role and the ongoing need for refinement and technological advancement. Despite challenges, the widespread adoption of eDNA applications signifies its transformative potential in contemporary biomonitoring practices.

Myxobolus bengalensis is a significant fish parasite responsible for disease and economic losses in aquaculture; however, information on its pathogenicity and impact on fish health remains limited. This study aimed to identify the morphological and molecular features of Myxobolus bengalensis and investigate the immunological changes in infected Labeo catla. Symptomatic fish showed signs of disease, including extreme lethargy, a slender body with a large head (growth retardation), and pale gills with the presence of whitish cysts in the gill lamellae. The Myxozoan parasite was isolated from infected L. catla tissue samples and preliminarily identified as M. bengalensis based on morphology, 18S rRNA PCR sequencing, and phylogenetic analysis. Tissue specimens were collected and underwent examination of immune-related gene expression (in the liver and kidney). The M. bengalensis spores isolated from the gills were ellipsoidal, with ovoid polar capsules. Sequencing and phylogenetic analysis of the 18S rRNA region revealed a 1700 bp fragment, confirming the parasite's identity and placing it within the same clade as other M. bengalensis isolates. The transcription analysis of genes associated with inflammation (TNF-α, IL-1β, iNOS), immune activation (TLR 4, C3, MYD88, NOD 1), and both innate and adaptive immune responses (IFN‐γ, Hsp70, Mx, IgM) further highlights that M. bengalensis modulates the expression of genes in the liver and kidney tissue samples of infected L. catla. There is limited data available on the host–pathogen response during M. bengalensis infection; thus, this study provides key insights into the morphology, pathogenicity, and immunological impacts of M. bengalensis in L. catla.

Multidrug-resistant (MDR) bacterial pathogens represent an escalating challenge to sustainable aquaculture, particularly in high-value freshwater species such as Labeo rohita, a cornerstone of South Asian aquaculture. This study provides the first comprehensive integration of genomic, immunological, and microbiome analyses to characterize Proteus penneri as an emerging MDR pathogen associated with severe disease manifestations in L. rohita, including exophthalmia, ulceration, and hemorrhage. Robust identification through biochemical assays, 16S rRNA sequencing, and phylogenetic analysis confirms the clinical relevance of this isolate. Functional assays demonstrated pronounced virulence, evidenced by hemolysin activity, extensive histopathological damage, and dose-dependent mortality, underscoring its pathogenic capacity in vivo. The observed resistance to multiple frontline antibiotic classes, including tetracyclines, macrolides, and carbapenems, highlights a critical therapeutic limitation in aquaculture settings. Genomic analysis further revealed a diverse repertoire of antimicrobial resistance genes, virulence determinants (notably biofilm formation and secretion systems), and mobile genetic elements, suggesting a strong potential for persistence, adaptability, and horizontal gene transfer. Infection-associated gut microbiome disruption, marked by elevated MAR indices and enrichment of virulence-associated taxa, indicates that P. penneri not only exploits host tissues but also reshapes the microbial ecosystem in ways that may exacerbate disease severity and resistance dissemination. Concurrently, heightened serum cortisol, C3, and Hsp70 levels, along with transcriptional upregulation of key immune and stress-related genes (hsp70, nod, il6, sod, c3, and myd88), reflect an intense pro-inflammatory and physiological stress response. In silico docking analyses implicating myd88-lipopolysaccharide interactions provide mechanistic insight into potential immune-modulatory strategies employed by the pathogen. Collectively, these findings delineate a multifactorial basis for P. penneri virulence and MDR, emphasizing its significance as an emerging aquaculture pathogen. Future research should prioritize functional validation of key virulence and resistance genes, longitudinal surveillance to assess transmission dynamics and AMR spread, and experimental evaluation of alternative disease mitigation strategies, including probiotics, phage therapy, and immune-modulating interventions, to reduce antibiotic reliance and enhance fish health resilience in aquaculture systems.

Co-infections have a considerable influence on fish production, altering the progression and severity of various fish diseases. Despite this, the impact of co-infection on aquatic animals, including fish, has only recently received minimal attention, leaving a significant gap in research. The research examines the cause behind significant mortality in Labeo bata. Microbial pathogens were isolated from infected tissue samples of bata, with preliminary identification of the strains as Aeromonas veronii and Megasporoporia sp. This identification was based on morphology, 16S rRNA and ITS PCR sequencing, along with phylogenetic analysis. A co-infection fish model was developed to explore the cellular and molecular responses of fish amidst bacterial and fungal co-infection scenarios. Additional analysis suggested that the co-infection condition may be linked to the outbreak of the disease and the resulting mortality of L. bata, as confirmed by survival assays, histological examinations, and qPCR analysis. The findings indicated that co-infection with A. veronii and Megasporoporia sp. resulted in different degrees of cellular alterations within the muscle tissues of infected L. bata samples. Transcription analysis further reveals that co-infection influences the expression of genes associated with inflammation (TNF-α, IL-1β, iNOS), immune activation (TLR 4, C3, MYD88, NOD 1), and both innate and adaptive immune responses (IFN-γ, Hsp70, Mx, IgM) in liver, kidney, and gill tissues from infected L. bata. The insights gained from this study are invaluable for understanding co-infection dynamics and pathobiology, which are essential for risk assessment and the development of management strategies to mitigate virulence.

Enterococcus gallinarum IFEGHNEK1 is a multidrug-resistant bacterium belonging to the Enterococcaceae family isolated from bighead carp in 2023. We report the complete genome sequence of E. gallinarum (CP169314) containing a 3.15 Mb genome.

Microplastic (MP) pollution is an emergent global threat with widespread implications for ecological integrity, food security, and public health. These particles, typically smaller than 5 mm, originate from diverse sources, including the breakdown of larger plastic debris and direct emissions from products and industrial processes. This review critically examines the current understanding of MP sources, environmental distribution, detection technologies, ecotoxicological impacts, and mitigation strategies. Incorporating recent advances—including AI-enhanced detection, microbe-mediated degradation, and circular economy policies—it provides a comprehensive, multidisciplinary synthesis and proposes a roadmap toward microplastic-free ecosystems. It highlights the complex journey of microplastics through various ecosystems, driven by processes such as photolysis, weathering, and microbial activity, and their subsequent transportation via water bodies, soil, and atmospheric deposition. The review emphasizes recent innovations in detection techniques, including hyperspectral imaging, machine learning algorithms, and laser-induced breakdown spectroscopy (LIBS), which have significantly enhanced the sensitivity and accuracy of microplastic identification across complex environmental matrices. The ecotoxicological impacts of microplastics, including their physical and chemical effects on aquatic organisms and potential for bioaccumulation and trophic transfer, are explored in depth, underscoring the urgency of addressing this global issue. The review discusses advanced mitigation strategies, such as biodegradable alternatives, circular economy approaches, and stringent regulatory measures, which are essential to reduce the environmental burden of microplastics. Integrating scientific innovation with robust policy frameworks is crucial to curb the widespread dispersion of microplastics and mitigate their long-term impacts on ecosystems and human health. This review advances our understanding of microplastic pollution and serves as a call to action for coordinated global efforts to address this pressing environmental challenge.

Bacillus cereus is widely used as probiotics in aquaculture. However, present research work identified B. cereus from diseased fish (Labeo rohita) associated with mass mortality in Hooghly, West Bengal, India. The bacterium was identified based on morphological, biochemical characterization and molecular identification, which comprise 16S rRNA gene and housekeeping gene sequencing analysis. Furthermore, the pathogenic potential of the isolates was confirmed by the presence of different toxin-encoding genes viz. hemolytic enterotoxin (hblA, hblC, hblD), non-hemolytic enterotoxin (nheA, nheB, nheC), cytotoxin K (cytK) and enterotoxin FM (entFM), Diarrheal enterotoxin (bceT) and Cereolysin AB. All these toxin-encoding genes were regulated by a master virulence regulating transcription factor plcr, which is also present in this isolate. Additionally, this bacterium also secretes caseinase and lecithinase, which helps the bacteria to invade the host tissue. The intraperitoneal injection of B. cereus at a dose of 3.6x 10(6) CFU ml(-1) resulted in 100 % mortality of L. rohita. The histopathological changes revealed that the bacterium induces severe damage and necrosis in the liver and kidney of the infected fish. To understand the innate immune response once bacteria invade the host, a quantitative gene expression study was carried out using different immune-related genes and stress-related genes viz. Complement factor 3a (C3a), Toll-like receptor (TLR), Myeloid differentiation primary response 88 (Mydd88), Interleukin 6 (IL6), Nucleotide oligomerization domain (NOD)-like receptor, Catalase (CAT), Glutathione peroxidase (GPx) and Superoxide dismutase (SOD) in the hepatic and renal tissue. The over-expression of TLR, NOD and Mydd88 shared a common downstream inflammatory signaling pathway and the upregulation of antioxidant enzymes SOD, CAT and GPx was evident for combating strategies as well as safeguarding the host's cells from oxidative damage. Overall, this study showed that an isolated strain of B. cereus exhibits high pathogenicity, which may be attributed to climate change, urbanization or horizontal gene transfer. This presents a potential threat to the aquaculture industry and raises concerns about the possibility of cross-contamination within the human population.

The ability of bacteria to respond to environmental changes is critical for survival. This enables them to withstand stress, form complex communities, and trigger virulence responses during host infections. In this study, we examined the effects of repeated in vitro subculturing on the virulence and antimicrobial resistance (AMR) profiles of Gram-negative and Gram-positive fish pathogens. The fish pathogenic bacterial isolates, namely Lactococcus lactis, Enterococcus gallinarum, Proteus penneri, and Escherichia coli, underwent 56 consecutive subcultures in tryptic soy broth and were evaluated for virulence, antimicrobial susceptibility, and AMR gene expression. The results revealed a significant decrease in the virulence of Gram-positive pathogens. Both L. lactis and E. gallinarum exhibited a marked reduction in the mortality rates of Labeo rohita after repeated subculturing, ultimately achieving 0% mortality by day 56. This suggests losing key virulence factors, such as toxins and adhesins, under non-selective conditions. In contrast, Gram-negative bacteria, particularly P. penneri and E. coli, exhibited higher levels of virulence throughout the study, even though mortality rates gradually declined. The antimicrobial resistance profiles of L. lactis remained steady, demonstrating consistent resistance to a wide range of antibiotics, including rifampicin and polymyxin B. Meanwhile, E. gallinarum showed slight variations in resistance, especially to colistin, while P. penneri and E. coli experienced changes in resistance to multiple antibiotics, including polymyxin B and tetracycline, after 42 days of subculturing. Importantly, no genetic alterations were detected in AMR-related genes through quantitative PCR analysis, indicating that the observed changes in resistance were likely phenotypic rather than genetic. This study underscores the critical need for ongoing surveillance in aquaculture pathogen management, emphasizing the dynamic nature of bacterial virulence and resistance profiles that can develop from prolonged subculturing.

Gonadotropin-Releasing Hormone (GnRH) is a crucial neuropeptide that regulates reproductive functions in vertebrates. The study identifies and characterizes (GnRH) in the brain of Tenualosa ilisha, an iconic and lucrative Clupeiform fish from River Ganga, India. The current study aimed to analyze the GnRH gene in T. ilisha using an in silico study. The GnRH gene of T. ilisha comprises a full-length nucleotide sequence of 605 base pairs with an open reading frame of 312 base pairs, which encodes 103 deduced amino acids (aa), respectively. It was found that leucine (L) is the most abundant amino acid in the GnRH protein. Additionally, the ligand interactions of the GnRH were analyzed using computational approaches. The structural validation showed an excellent stereochemical quality of the GnRH protein sequence, with over 88% of residues in Ramachandran plot-favored regions. The binding site prediction revealed 6 ligand-binding pockets, with the largest pocket containing 12 amino acids. After ADME screening, 16 drug-like compounds were docked to GnRH protein. Top five ligands N-Ac-(4-Cl-Phe)-Trp-Lys-AlaNH2, LHRH_LYS (6), Seabream_GnRH, Leuprolide, and LHRH_Des-tyr (5) had binding affinities ranging from −7.5 to −5.6 kcal/mol. The stable binding site was confirmed by 100 ns molecular dynamics simulations, with RMSD values below 10 Å and key residues retaining ligand contacts. The GnRH-protein resulted in the development of a suitable peptide sequence of T. ilisha, showing similarity with the similar anadromous American shad (Alosa sapidissima). This will certainly aid in future therapeutic and captive breeding advances, thereby fostering the culture and conservation of the wild species.