Histopathological fingerprints and biochemical changes as multi-stress biomarkers in fish confronting concurrent pollution and parasitization

The current investigation examined histopathological and serum biochemical profiles to assess the interactive effects of river Saraswati's impaired physicochemical regime and parasite infection by ectoparasites (<i>Trichodina</i> sp., <i>Gyrodactylus</i> sp.) and endoparasites (<i>Eustrongylides</i> sp.) on health of fish (<i>Channa punctatus</i>). This study aimed at assessing the synergistic effects of the degraded water quality and parasitization on fish health looking through the lens of histopathology and serum biochemistry. Low dissolved O₂, high free CO₂, biochemical oxygen demand (BOD), and chemical oxygen demand (COD) indicate deteriorating water quality due to organic loading. The histopathological investigations revealed distinctive histopathological changes in gill, liver, and kidney of the fish as "signature" impairments inflicted by chronic (co)exposure to pollution and/or parasitization. Stress enzymes and altered serum biochemistry furnish excellent indicators of fish health because of their correlation with pollution and parasitization. Destined in a vicious cycle, fish health becomes adversely affected by degrading water qualities and parasitic infection in solo or combo.