Feasibility studies on the use of sewage sludge as supplementary feed for rearing tilapia II. PCBs of the treated fish, and biochemical response in the fish liver

This study investigated the levels of PCBs (polychlorinated biphenols) in the sludge cake and in tilapia, Oreochromis mossambicus fed on sludge supplemented diet, and the biochemical responses in the liver of tilapia fed the diet. A significant increase in the PCB concentrations was found in the flesh of fish fed on sludge (30%) supplemented diet. Total PCBs detected in the fish was 61.05 ng g⁻¹ (wet wt) and higher chlorinated PCB isomers were much more common than lower chlorinated PCB isomers. The sludge was found to be contaminated with PCBs. The activity of UDP-glucuronosyl-transferase (UDP-GT) was greater in treated fish at Day 5 in comparison to control fish and there was an increase in most fish during the experimental period. The sludge - supplemented diets did not impose any effect on both alanine aminotransferase (GPT) and aspartate aminotransferase (GOT) activities upto 30 days. However, the liver GOT activity was significantly increased (p<0.05) in fish receiving 10 and 30% of sludge-supplemented diets while GPT activity was significantly decreased (p<0.05) in fish receiving 30% of sludge- supplemented diet only, when compared with the control group, at the end of the experiment. The level of triglyceride of the treated fish was not significantly different (p>0.05) from fish fed the control diet. The changes in liver metabolism in fish fed with sludge diets indicated the existence of xenobiotics. Copyright © 1993 Informa UK Limited.