Exploring the toxicity of chromium on aquatic ecosystems: a comprehensive assessment of growth, physiological responses, genotoxicity, and histological alterations in Etroplus suratensis (Bloch, 1790) juveniles

The study was conducted to assess the effect of chromium on Etroplus suratensis, pearl spot juveniles under acute and chronic exposure. A 96-h acute toxicity test was conducted with eight Cr concentrations (30, 35, 40, 45, 50, 55, 60, and 65 ppm) and control. Behavioural changes such as hyperactivity, an unbalanced state, excessive mucus secretion, and an elevated rate of opercular activity were observed during the exposure. The LC₅₀ value at 96 h was found to be 41.83 mg/L. Histological alterations in the gills and liver tissues were observed to be severely degenerative with the increase in chromium concentration. Following the acute toxicity study, chronic toxicity study was conducted for 45 days. For chronic toxicity study, three sublethal concentrations of Cr such as one-tenth of LC₅₀ (4 mg/L, T1), one-fiftieth of LC₅₀ (0.8 mg/L, T2), and one-hundredth of LC₅₀ (0.4 mg/L, T3) were chosen for 45-day exposure. Significant reduction in average weight gain and specific growth rate was observed at T1 (4 mg/L) exposure. Antioxidant enzymes—SOD and catalase in the liver and gills, LPO, enzymatic parameters—glucose, AST, and ALT, and immune parameter—myeloperoxidase activity were also significantly higher at T1 followed by T2 and T3 depicting the stress response at higher chromium exposure similar to the growth and haematological attributes. Enzymatic parameters such as AChE, antioxidant enzymes like GST and GPx, and immune parameters, RBA and LYZ, have significantly decreased levels at T1, followed by T2 and T3, indicating the presence of toxicants in the environment, which caused severe damage to the cellular function. The genotoxicity assay carried out using gills revealed that the DNA damage increased in a concentration-dependent manner, in which the least genotoxic group was negative control, followed by T3. The present investigation revealed that chromium content in freshwater should be less than (0.4 mg/L) one-hundredth for Etroplus suratensis farming.