Fenugreek seed extract supplementation: a mitigating strategy against tannery effluent toxicity in Catla catla

This study investigated the harmful impacts of tannery effluent on fish and explored the effects of dietary fenugreek (Trigonella foenum-graecum) seed extract (FSE) as a remedial strategy. In the first phase, median lethal concentration (LC₅₀-9.98%/L) of tannery effluent for 96-h was determined following the probit analysis on Catla catla. In the next phase, the experiment was divided into eight treatment groups in which fish were exposed to tannery effluent stress and FSE supplemented sunflower meal-based diets simultaneously, for the period of 60 days. Each treatment was provided with different concentrations of FSE; T0-NC (negative control, no effluent/no FSE), T0-PC (positive control, effluent only), T1–T6 (effluent + 0.5–3% FSE). A total of 360 fish were fed twice daily at a rate of 5% body weight. The findings indicated that 1% FSE significantly (p < 0.05) improved survival (88.89%) and growth indices (weight gain: 22.7 g; specific growth rate: 1.53) and positively impacted the body composition of C. catla. Additionally, 1% FSE inclusion substantially (p < 0.05) improved hematological parameters, immune response, and antioxidant activity under tannery effluent stress. In contrast, FSE supplementation at 0.5% and 1.5% produced moderate effects, whereas 2–3% inclusion levels adversely affected these variables. Furthermore, histological analysis of the gills and liver revealed that 1% FSE showed the greatest protective effect against tannery effluent exposure, whereas the positive control and higher FSE concentrations exhibited marked abnormalities. The outcomes indicate that 1% FSE inclusion represents the optimal dietary level for ameliorating the tannery effluent toxicity and boosting fish health status.