THE TOXICOKINETICS OF BENZO[A]PYRENE IN JUVENILE COHO SALMON, ONCORHYNCHUS-KISUTCH, DURING SMOLTIFICATION

The activities of Phase I and Phase II biotransformation enzymes in th e livers of yearling coho salmon (Oncorhynchus kisutch), were measured biweekly from February until the release date from the hatchery in mi d-June, in order to observe any alterations in baseline levels during smoltification. Peak enzyme activities occurred in February and March and then declined through to June. Total cytochrome P450 levels ranged from 0.024+/-0.009 to 0.095+/-0.010 nmol mg(-1) microsomal protein, e thoxyresorufin O-deethylase activity ranged from 2.74+/-0.75 to 9.94+/ -0.85 pmol min(-1) mg(-1) microsomal protein, and glutathione S-transf erase activity ranged from 0.07+/-0.01 to 0.33+/-0.01 mu mol min(-1) m g(-1) cytosolic protein during this period. Following an intraperitone al injection of [H-3]benzo[a]pyrene (B[a]P), elimination occurred rapi dly (>71% excreted into the bile within 24h) from February to June. Al though the distribution of B[a]P in tissues changed through the sampli ng period, the highest levels of B[a]P-derived radioactivity were foun d in the liver, bile and fat. Analysis of the bile revealed that 55 to 63% of the radioactivity was Phase I metabolites, 16 to 24% glucuroni de conjugates, 8% sulfate conjugates, 7% other conjugates and 6% aqueo us-soluble metabolites. These findings suggest that the transformation from freshwater adapted coho 'parr' to 'smolts', can significantly al ter biotransformation enzyme activities and the distribution and elimi nation of xenobiotics such as benzo[a]pyrene in these fish.