Time course of xenobiotic biotransformation enzyme activities of rainbow trout caged in the River Po

Juvenile rainbow trout were exposed to River Po water in cages suspended upstream and downstream from the entry of the River Lambro, a minor and heavily polluted tributary. A third group of trout was held at the laboratory and served as a control. Fish were sampled after 7, 15 and 30 days of exposure. Benzo[a]pyrene hydroxylase (AHH), ethoxyresorufin-O-deethylase (EROD), aminopyrine-N-demethylase (APDM), UDP glucuronyl transferase (UDPGT), glutathione transferase (GST), glutathione reductase (GR) and glutathione peroxidase (GPx) activities were measured along with the contents of protein and non-protein thiols (SHP and SHNP) in trout liver. With the exception of GST activity and SHP content which remained unchanged in both the exposure groups, all the biomarkers showed significantly altered values. Fish exposed at the upstream site showed minor modifications and with the apparent contribution of a doubled flow of the River Po. On the contrary, the downstream-stretch of water induced earlier and higher responses of the biomarkers, confirming the higher degree of contamination in this area, where polycyclic aromatic hydrocarbons (PAH), or related compounds were suspected to act as inducers. Also for this group of organisms, an apparent relationship was found between the temporarily doubled river flow and the level of those biomarkers which can react more rapidly.