Effect of dietary electrolytes and histidine on histidine metabolism and acid-base balance in rainbow trout (Salmo gairdneri)

1. Rainbow trout fingerlings were fed diets containing 1.2, 1.8 and 2.6% histidine and two mixtures of Na, K and Cl (Na + K - Cl = 0 or -200 meq/kgdiet) in a factorial design.

2. Growth and efficiency of feed conversion were not affected by histidine in the diet when it contained the −200 meq/kg electrolyte mixture, but with the 0 meq/kg level, 2.6% histidine depressed both measures of response.

3. Histidine increased plasma and muscle histidine levels, increased hepatic histidase activity, but did not affect hepatic histidine-pyruvate aminotransferase activity.

4. Muscle-free histidine concentrations were markedly higher and lysine concentrations were lower in trout receiving 0 meq/kg than those receiving the −200 meq/kg electrolyte mixture.

5. The electrolyte balance of the diet has a marked effect on the metabolism of histidine in trout.