The effects of selected chemicals were studied in aquatic animals. Aquatic organisms, such as oysters, minnows, Rivulus-marmoratus, silversides, rainbow-trout, and salamanders, were treated with agents, such as 3-methylcholanthrene (56495) (MCA), benzo(a)pyrene (50328) (BaP), trifluralin (1582098), aflatoxin-B1 (1162658) (aflatoxin), benzidine-dihydrochloride (531851) (benzidine), or methylazoxymethanol-acetate (592621) (MAMAc), and assayed for pathobiological changes. BaP induced hepatocellular carcinomas and liver fibrosarcomas in rainbow-trout, but elicited no tissue responses in oysters or salamanders. MCA induced incipient perivascular blood cell proliferation in oysters. Benzidine induced no tumorigenic response in any species. MAMAc induced hepatocellular carcinomas in all treated species. Trifluralin induced focal benign vertebral growth in minnows. Aflatoxin induced liver lesions in minnows, Rivulus-marmoratus, and silversides. Mullets were pretreated with MCA or phenobarbital (50066). Liver microsomes were isolated and treated with BaP. The kinetics of BaP metabolism were studied for different incubation times and at different temperatures. Phenols and quinones were formed first. Secondary metabolites such as the dihydrodiols of BaP were either not formed or formed at very low concentrations. Formation of most of the metabolites, except phenols, was proportional to incubation time. At lower temperatures, the formation of phenols predominated. Hepatic S9 protein preparations from MCA induced or non induced fish and rats were incubated with BaP at 7 to 9 or 22 to 25 degrees- C and assayed for BaP/hydroxylase activity and metabolites. In both bullhead species and rats, 9,10, and 7,8 dihydrodiols and the 3- hydroxy derivative of BaP were predominantly formed. In goldfish, 1,6, and 3,6 dione derivatives of BaP were also formed. MCA increased BaP/hydroxylase activity 10 to 20 fold at 25 degrees; however, BaP/hydroxylase activity was completely inhibited at 7 degrees. The authors suggest that the thermal history and type of fish must be considered if hepatic enzyme activity is used as a predictor of environmental pollution.