Understanding biotransformation pathways in aquatic species is an integral part of ecological risk assessment with respect to the potential bioactivation of chemicals to more toxic metabolites. The long-range goal is to gain sufficient understanding of fish metabolic transformation reactions to be able to accurately predict fish xenobiotic metabolism. While some metabolism data exist, there are few fish exposure studies where metabolites have been identified and the metabolic pathways proposed. Previous biotransformation work has focused on studies which have the advantage of high throughput but may have limited metabolic capabilities, and studies which have full metabolic capacity but are low throughput. An aquatic model system with full metabolic capacity in which a large number of chemicals could be tested would be a valuable tool.The current study evaluated the rainbow trout liver slice model, which has the advantages of high throughput as found models and non-dedifferentiated cells and cell to cell communication found in systems. The pesticide diazinon, which has been previously tested both and in a number of mammalian and aquatic species including rainbow trout, was used to evaluate the slice model as a tool to study biotransformation pathways.While somewhat limited by the analytical chemistry method employed, results of the liver slice model, mainly that hydroxypyrimidine was the major diazinon metabolite, are in line with the results of previous rainbow trout studies.Therefore, the rainbow trout liver slice model is a useful tool for the study of metabolism in aquatic species.