Influence of salinity and ratio of lipid to protein in diets on certain enzyme activities in rainbow trout (Salmo gairdneri Richardson).

The connection between metabolic and sea water adaptation of the rainbow trout was investigated. The rainbow trout were kept in fresh water and diluted sea water of 8 and 20 0/00 S at 16 degrees C and fed on three different diets for 51 days. Hyperosmotic salinity (20 0/00) tends to inhibit growth in rainbow trout by reducing the food conversion efficiency. A higher protein concentration in the diet can partly compensate for this effect. The liver IDH, G6PDH and 6PGDH activities of the rainbow trout are influenced only by food quality, whereas the liver G1DH, AspT and A1T activities, like the muscle A1T, are also affected by salinity. The salinity had no significant effect on the activities of the kidney enzymes we investigated (Na/K-ATPase, G1DH, A1T, AspT) or of the muscle AspT in these experiments.