Insights into the heavy metal-induced immunotoxic and genotoxic alterations as health indicators of Clarias gariepinus inhabiting a rivulet.

There is a dire need to assess the quality of fishes transported for human consumption as lately, their health is challenged because of anthropogenic activities. Heavy metals with a long environmental persistence are toxic to fishes and the humans. The study was conducted to evaluate the impact of heavy metals on Clarias gariepinus inhabiting popular Ganges rivulet at Narora (28.18° E, 78.39° N). The limnological values deviated from the international Standards (USEPA, WHO). Higher total dissolved solids (859 mg/L), total suspended solids (406 mg/L), low dissolved oxygen (5.60 mg/L), and pH (5.21) indicated the presence of contaminants. Heavy metals estimated followed the order Cd > Ni > Cu > Cr. Serum enzymes (hepatic and renal markers) viz., aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (ALP) were higher than the normal, whereas, creatine kinase (CK) was considerably low in both male and female fish. Stress induced was marked by elevation in cortisol and glucose. This had its impact on hematological parameters as well, as a decline in Total leucocyte count (TLC) & mean corpuscular volume (MCV) and increase in Mean cell hemoglobin (MCH) was observed. Erythrocytes also showed altered morphology. Marked histopathological alterations were observed in all immune organs (head-kidney, liver, spleen, thymus). Oxidative stress induced by heavy metals leads to the production of metal scavenging protein metallothionein (MT) and glutathione peroxidase (GPX). Maximum fold change in metallothionein (MT) gene expression was observed in the liver, followed by spleen, thymus, blood, and head-kidney. Glutathione peroxidase (GPX) gene expression was highest in the liver, followed by thymus, spleen, blood, and head-kidney. The gene expression studies further validated the increased level of heavy metals as potent contaminants of water and the non-condusive abiotic factors.