This study aimed to assess the occurrence, distribution and dietary risks of seven dl-PCBs (dioxin-like PCBs) in eleven collected fish species from Chenab river, Pakistan. ∑7dl-PCBs (ng g−1, wet weight) burden was species-specific and the maximum average concentrations were found in Mastacembelus armatus (5.43), and Rita rita (5.1). Correlation of each dl-PCBs with δ15N%, indicated a food chain accumulation process of these chemicals into Chenab river, Pakistan. Species-specific toxicity of each dl-PCBs (WHO–PCBs TEQ) was calculated and higher values were found in three carnivore fish species i.e., M. armatus (2.5 pg TEQ g−1), R. rita (2.47 pg TEQ g−1), Securicola gora (2.98 pg TEQ g−1) and herbivore fish species i.e., Cirrhinus mrigala (2.44 pg TEQ g−1). The EDI (Estimated Daily Intake) values in most cases exceeded the WHO benchmark (4 pg WHO–TEQ kg−1 bw d−1) evidencing a potential health risk for consumers via fish consumption from Chenab river.

Acute (24 h) and sublethal (35 days) effects of cadmium chloride (CdCl₂) were examined in Cirrhinus mrigala using various endpoints (accumulation pattern, thyroid hormones (THs), and antioxidants). The mean concentrations of CdCl₂ for 24 and 96 h were found to be 35.974 and 22.387 mg L⁻ˡ, respectively. LC50 concentration of CdCl₂ for 24 h (35.97 mg L⁻ˡ) was used for the acute study. For the sublethal studies, fish were exposed to 3.59 mg L⁻¹ (Treatment I) and 7.19 mg L⁻¹ (Treatment II) corresponding to 1/10th and 1/5th of 24 h LC50 of the CdCl₂. During acute exposure, higher accumulation of CdCl₂ was noticed in the gill, liver, and kidney of C. mrigala, which is found in the order gill > liver > kidney tissues. Similarly, in sublethal treatments (Treatment I and II), a concentration and time-dependent increase of CdCl₂ accumulation was noticed in the order of gill > liver > kidney. GSH, GST, and GPx activities were found to be relatively lower from the treated groups in both acute and sublethal treatments. However, LPO activity was significantly increased in CdCl₂-treated fish C. mrigala. Further, plasma T₃ reduction was more pronounced than T₄ in acute study. During sublethal treatments, both T₄ and T₃ levels showed a continuous decrease as the exposure period extended. All the values in this study were statically significant (P < 0.01 and P < 0.05).

The present study assessed the impact of fingerling stocking of Indian major carps (Gibelion catla, Labeo rohita, and Cirrhinus mrigala) on fish yield in 24 small reservoirs of Central India. The time series data on fish stocking and yield were collected from the State Fisheries Department, Govt. of Chhattisgarh, for the year 2008 to 2016. The fish yield increased significantly (p < 0.05) from 87.11 to 379.13 kg/ha/year due to stocking indicating significant impact on fish production. The relationships between area, stocking density, and fish yield of reservoirs were also assessed. Stocking had a significant positive impact on fish yield (t test, p < 0.05). The important water quality parameters were also studied to have a conspicuous picture of eco-hydrological characteristics of these selected small reservoirs. The study forms a baseline for the small tropical reservoir fisheries of Central India (Chhattisgarh state) and suggests regional strategies for sustainable fisheries enhancement and management, employment generation, and nutritional security of a large number of fish-eating population.

Collagen is a promising candidate for food and pharmaceutical applications due to its excellent biocompatibility, low antigenicity, and controlled biodegradability; however, its heavy price restricts its utilization. Fish scales generated during the processing are generally regarded as waste material and an environmental pollutant, though they are a promising source of collagen. In the present study, Cirrhinus mrigala scales were demineralized and extracted for acid-soluble collagen (ASC) using acetic acid, with a collagen yield of 2.7%. UV–Vis spectra, SDS-PAGE, FTIR analyses, and amino acid composition confirmed the type I nature of the collagen extracted. The denaturation temperature of the collagen was found to be 30.09 °C using differential scanning calorimetry (DSC). The collagen was highly soluble at acidic pH and lower NaCl concentrations while its solubility was lowered in alkaline conditions and NaCl concentrations above 0.5 M. The collagen exhibited good emulsifying potential with an emulsion activity index (EAI) and emulsion stability index (ESI) of 21.49 ± 0.22 m² g⁻¹ and 15.67 ± 0.13 min, respectively. Owing to the good physicochemical characteristics of the extracted collagen, collagen-chitosan-neem extract (CCN) films were prepared subsequently which showed good antimicrobial activity against Bacillus subtilis NCIM 2635, Staphylococcus aureus NCIM 2654, Escherichia coli NCIM 2832, and Pseudomonas aeruginosa NCIM 5032, suggesting the potential of collagen in the development of antimicrobial films. These results demonstrate that the collagen from fish waste could be valorized and used effectively along with chitosan and neem extract for the synthesis of novel biodegradable films with antimicrobial efficacy.

The present study attempted to investigate the changes in temperature conducive to fish habitability during the summer months in a hydrologically modified wetland following damming over a river. Satellite image–driven temperature and depth data calibrated with field data were used to analyse fish habitability and the presence of thermally optimum habitable zones in some fishes, such as labeo rohita, cirrhinus mrigala, tilapia fish, small shrimp, and catfish. The study was conducted both at the water’s surface and at the optimum depth of survival. It is very obvious from the analysis that a larger part of the wetland has become an area that destroyed aquatic habitat during the post-dam period, and existing wetlands have suffered significant shallowing of water depth. This has resulted in a shrinking of the thermally optimum area of fish survival in relation to surface water temperature (from 100.09 to 74.24 km² before the dam to 93.97 to 0 km² after the dam) and an improvement in the optimum habitable condition in the comfortable depth niche of survival. In the post-dam period, it increased from 75.49 to 99.76%. Since the damming effect causes a 30.53 to 100% depletion of the optimum depth niche, improving the thermal environment has no effect on fish habitability. More water must be released from dams for restoration. Image-driven depth and temperature data calibrated with field information has been successfully applied in data sparse conditions, and it is further recommended in future work.

The epidermal mucus of fish performs diverse functions from prevention of mechanical abrasion to limit pathogen invasions. The current experiment was designed to extract skin mucus proteins of three freshwater fish, i.e. common carp (Cyprinus carpio), mrigal (Cirrhinus mrigala) and rohu (Labeo rohita) with organic solvent (methanol) and dissolve in different pH of Tris-HCl buffers to examine the significance of pH in the solubilisation of skin mucus proteins. The protein profiles of different pH solubilised methanol fish skin mucus extracts were determined by SDS-PAGE. The non-specific immune enzymes, alkaline phosphatase, lysozyme and protease of fish skin mucus were compared and this present study demonstrated that these enzymes differed in their activity depending on pH buffers. The higher lysozyme and protease activity were observed at the pH of 8.0 and higher alkaline phosphatase activity in the pH 9.0 of C. mrigala fish skin mucus methanol extract. In addition, the bactericidal activity was evaluated against the pathogens Proteus vulgaris and Pseudomonas aeruginosa. The pH 8.0 of C. mrigala skin mucus extract revealed better bactericidal activity than other fish species mucus pH buffers against both P. vulgaris and P. aeruginosa. In the case of protein profile from SDS-PAGE, based on pH buffers and the solubilisation of proteins, differences in the resolution of bands were observed. The higher alkaline pH of 9.0 showed smeared gel bands in all the three fish skin mucus methanol extract. The present study suggests that methanol extracted C. mrigala fish skin mucus at pH 8.0 showed better innate immune enzymes and bactericidal activity. The additional examinations of C. mrigala skin mucus methanol extract in this pH aids in identifying novel bioactive molecules. This is the study of proteome of three fish species skin mucus in the effect of pH. Further analyses are required to evaluate proteins present in fish skin mucus extracted with methanol and the influence of pH on protein solubility. These findings could be helpful in exploring natural alternatives to antibiotics in aquaculture industry against infectious pathogens.

Water pollution is gradually increasing in natural waters through anthropogenic activities. This study aimed to use fish scales as a bio-indicator of pollution, along with water quality parameters, and the assessment and detection of selected heavy metals in water samples collected from the River Chenab, including the Chakbandi drain that gathers domestic sewage waste and industrial effluents from Faisalabad and deposits it into this freshwater body. All water quality parameters (pH, total dissolved solids (TDS), total suspended solids (TSS), salinity, conductivity, biochemical oxygen demand (BOD), chemical oxygen demand (COD), phenols and sulphates) and concentrations of selected heavy metals (Cd, Cu, Mn, Pb and Cr) were found to be considerably higher than permissible limits as defined by the WHO, and therefore capable of causing ill health effects in aquatic organisms. Specimens of fish scales from selected fish were described qualitatively and observed quantitatively. In Catla catla, Labeo rohita and Cirrhinus mrigala, the scales showed several deformities in shape and different scale structures such as circuli, radii and annuli. In each of the three types of fish, considerable variation in the morphology of their scales was observed in specimens collected from polluted sites.

The eastern and southern parts of the Faisalabad city produce considerable quantities of industrial and municipal pollutants, much of which is drained into the River Chenab, reducing the productivity of fauna and flora in the river. This study was aimed to determine whether cysteine is useful as a biomarker of exposure to polluted fresh water. The amino acid profile of fish muscle was analyzed by paper chromatography in Cirrhinus mrigala and Labeo rohita from the River Chenab to determine habitat related variations due to the pollution from industrial and domestic sources. C. mrigala showed higher level of metal contamination in muscle tissues for Sn, Cr, Pb, Zn, Mn, Cu, and Cd when compared to L. rohita. Both fish species collected from polluted areas of the river Chenab showed significantly (P < 0.01) higher levels of metals in comparison to upstream and farmed fish. Farmed C. mrigala showed cysteine concentrations in the muscle tissue as 22 ± 1 mg/g dry weight, but concentrations increased to 45 ± 2 mg/g dry weight for fish from a mildly polluted section of the river, and further increased to 83 ± 2 mg/g dry weight in more heavily polluted sections. Cysteine concentration in farmed L. rohita was detected as 28 ± 2 and 25 ± 4 mg/g dry weight, respectively for farmed fish and fish from a mildly polluted section of the river, and then increased to 94 ± 3 mg/g dry weight for fish from highly polluted water. C. mrigala from a mildly polluted area of the river also had higher levels of cysteine in the muscle, along with increases in aspartic acid, glutamic acid, and alanine. Elevated concentrations of cysteine seem to be associated with a threat to these fish species in polluted sections of the river, and thus may be used as a biomarker.

The interfacial properties depicting the micellization behaviour of the cationic amphiphiles (surfactants) belonging to the class of quaternary ammonium salts varying in degree of hydrophobicity were evaluated using tensiometry, conductivity and fluorescence spectrophotometric methods at 303.15 K. The impact of the amphiphilic nature of these amphiphiles as a function of their concentration is accounted against the selective microbial strains using the well-diffusion approach. Also, its influence on the histological (shrinkage/curling of lamellae, necrosis, haemorrhage, hyperplasia of villi in gills and intestine) alterations and haematological (blood parameters) changes in fingerling of Cirrhinus mrigala (C. mrigala) offers an insight into the stern damages reported as aquatic toxicity. The lesions exhibited moderate to severe alterations that are further correlated with the semi-quantitative mean alteration value (MAV). The in vitro and in vivo findings are explained significantly in terms of amphiphilic hydrophobicity which followed the order: C₁₆TAB > C₁₂TAB. All the observed outcomes are rationalized by the structural assessment of the selected amphiphiles as specified by the computational simulation approach using density functional theory (DFT) with B3LYP method and 3-21G basis source set. This work also portrays the biodegradability of these cationic amphiphiles and their fate on the environment. Graphical abstract Molecular architecture of cationic amphiphiles integrated with their in vitro and in vivo rejoinders.

Freshwater fish Cirrhinus mrigala were exposed to tris(2-chloroethyl) phosphate (TCEP) with three different concentrations (0.04, 0.2, and 1 mg/L) for a period of 21 days. During the study period, thyroid-stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4) levels were significantly (p < 0.05) inhibited. The superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), and lipid peroxidation (LPO) levels were increased significantly (p < 0.05) in gills, liver, and kidney tissues, whereas glutathione (GSH) and glutathione peroxidase (GPx) (except liver tissue) activities were inhibited when compared to the control group. Likewise, exposure to TCEP significantly (p < 0.05) altered the biochemical (glucose and protein) and electrolyte (sodium, potassium, and chloride) levels of fish. Light microscopic studies exhibited series of histopathological anomalies in the gills, liver, and kidney tissues. The present study reveals that TCEP at tested concentrations causes adverse effects on fish and the studied biomarkers could be used for monitoring the ecotoxicity of organophosphate esters (OPEs).