Utilization of free glycerol as a source of dietary energy in rainbow trout (Salmo gairdneri)

Abstract

Three feeding trials were conducted in which free glycerol was added at levels ranging from 1 to 12% to both high and low energy (lipid) diets to determine the utilization of free glycerol as an energy source in rainbow trout. The supplementation of free glycerol had no significant effect on the final body weight, feed: gain ratio, carcass dressing percent, liver: body weight ratio or liver glycogen content of the trout. The inclusion of free glycerol in high or low energy trout diets had no significant effect on the final carcass composition of the trout or on the efficiency of dietary protein conversion into tissue protein. Glycerol was not an effective precursor for lipogenesis nor was it stored as liver glycogen. Trout reared on 6 and 12% glycerol-supplemented diets had significantly higher blood glucose levels than control fish, indicating that the glycerol was being converted to glucose which is not an efficient energy source in rainbow trout. The feeding response in fish consuming the glycerol-supplemented diets was slow and/or sluggish in comparison to the control groups. This may be related to hyperglycaemia which was noted in these trout receiving the glycerol-supplemented diets. It was concluded that free glycerol was not an effective source of dietary energy in rainbow trout. © 1986.