Effects of diet on PCB-induced changes in xenobiotic metabolism in the liver of channel catfish (Ictalurus punctatus)

Effects of nutrition on xenobiotic-metabolizing enzymes in fishes are not well known. We fed three groups of channel catfish (Ictalurus punctatus) either a synthetic, laboratory-prepared diet or one of two commercial catfish rations. After 3 mo on each diet, fish were treated with the enzyme inducer Aroclor 1254. Hepatic microsomal monooxygenase (MO) activity was lower in untreated fish fed a commercial diet than in those fed the laboratory diet. Aroclor 1254 increased MO activity to a lesser degree in fish fed that same commercial diet compared with those receiving the laboratory or other commercial diet. Hepatic microsomal UDP-glucuronosyltransferase (UDPGT) activity was similar in all control fish; however, Aroclor 1254 increased UDPGT activity to differing degrees in the three diet groups. Hepatic cytosolic glutathione S-transferase (GST) activity was increased by Aroclor 1254 to a similar extent in all diet groups; however, levels of GST activity generally were higher in fish fed the commercial diets than in those fed the laboratory ration. These data indicate that diet can affect the toxicity of xenobiotics to fishes through alterations in hepatic enzyme systems, and thus should be considered a potential source of variation in toxicological studies with fishes.