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

Abstract

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 - C l = 0 or -200 meq / kg diet ) 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.