Influence of feeding procedure on biomarkers in caged rainbow trout (Oncorhynchus mykiss) used in environmental monitoring

Abstract

Biomarkers in feral fish can be a useful tool for environmental monitoring of aquatic ecosystems. Drawbacks, however, are that suitable fish species are not always available and that natural variations can bias the results. An alternative strategy is to use farmed fish placed in cages. There is, however, still a risk that factors other than pollution level could have an impact on the biomarkers and the observed responses in the fish. The present study evaluates the effects of feeding procedure on biomarkers in caged fish. Two feeding rations (2% and 8% weekly feeding) have been examined for a large number of biomarkers in caged rainbow trout (Oncorhynchus mykiss). Significant effects of feeding rations were found on hepatic ethoxyresorufin-O-deethylase (EROD) and catalase activity, PAH metabolites in bile, plasma ion concentrations and the presence of immature red blood cells. The influence on EROD activity and PAH metabolites seems to be caused by elevated uptake of pollutants when feeding ratios are higher. The effects on other biochemical and physiological variables are more likely caused by stress due to insufficient feeding. According to these results, valid comparison of fish groups in environmental monitoring requires standardized feeding levels.