Liver Enzyme Activity as a Growth Index in Wild Rainbow Trout

The relationship between fish size and the activity of certain liver enzymes was assessed in age I rainbow trout (Salrna gairdneri) from 3 Virginia streams. Total length and body weight of the trout differed significantly among streams. Activity of glutamate dehydrogenase and aspartate aminotransferase also differed significantly among fish in the streams and both were negatively correlated with fish size. Differences in size and enzyme activity probably relate to differential caloric intake of fish in the 3 streams. Condition factor and alanine aminotransferase activity of the trout did not differ among streams.