Effects on enzyme activity and DNA integrity in rainbow trout Oncorhynchus mykiss exposed to fish farm effluents

Fish farm effluents are known to affect water quality and freshwater ecosystems, potentially harming non-target organisms and ecosystem processes. We studied the effect of fish farm effluents at different concentrations (3.125-100% v/v) on catalase (CAT) and glutathione S-transferase (GST) activity as well as the DNA integrity of Oncorhynchus mykiss fry over 24-120 h. Biochemical responses and DNA damage analysis were conducted to assess the impact. We found that fish farm effluent had higher conductivity, nitrate, nitrite, and total dissolved solids concentrations downstream compared to upstream of the farm. Interestingly, no antibiotics were detected in the effluent. CAT activity significantly increased in the fish liver at concentrations of 12.5, 50, and 100% of the effluent after 72 h. In the gills, a significant increase was observed at concentrations ranging from 6.25 to 100% of the effluent after both 24 and 72 h. GST activity increased significantly in the liver at a concentration of 100% of the effluent after 72 h and in the gills at concentrations of 25, 50, and 100% after 24 h, with a decrease noted at higher concentrations. DNA damage assessment revealed significant DNA strand breaks in blood cells at concentrations of 12.5, 25, 50, and 100% of the effluent after 120 h of exposure. The results demonstrate that fish farm effluents can induce oxidative stress, causing damage to DNA integrity in blood cells. Our findings emphasize the potential ecological risks posed by fish farm effluents to aquatic organisms.