Metabolic effects of feeding a high protein/low carbohydrate diet as compared to a low protein/high carbohydrate diet to rainbow troutSalmo gairdneri.

Groups of trout were fed either a high protein/low carbohydrate (HP/LC) or a low protein/high carbohydrate (LP/HC) diet for 16 weeks. Fish fed the HP/LC diet had significantly higher levels of protein, ninhydrin positive material and tryptophan in plasma as well as lipid and protein in liver, but lower levels of glucose in plasma, glycogen in liver and a lower hepatosomatic index compared with fish fed the LP/HC diet. There were no differences concentrations of tryptophan or serotonin in the brain of fish fed the different diets. Fish fed the HP/LC diet had significantly lower activities of glycolytic enzymes but higher activities of gluconeogenic enzymes compared with the group fed the LP/HC diet. Those enzymes measured concerned with the TCA cycle or initiating amino acid catabolism were generally unaffected by diet although activities of threonine dehydrogenase, alanine aminotransferase and glutamate dehydrogenase were higher in those fish fed the HP/LC diet. The data suggest that rainbow trout show little adaptation in activities of amino acid catabolising enzymes to variations in dietary protein intake.