The effect of dietary carbohydrates on the growth response, digestive gland glycogen and digestive enzyme activities of early spiny lobster juveniles, Jasus edwardsii

The effect of various carbohydrate sources (glucose, sucrose, agar, wheat, tapioca, maize, potato and dextrin), and inclusion levels of gelatinized maize starch (0, 70, 170, 270 g kg^-1), incorporated in semi-purified diets on the performance [growth, survival, food consumption (FC), enzyme activity and glycogen content of the digestive gland (DG)] of spiny lobster juveniles was investigated in a 12- week culture experiment. There was no difference in specific FC among diets (1.1% BW day^-1), but lobsters fed with fresh mussel grew significantly faster (specific growth rate = 1.8% BW day^-1) than on the formulated diets (0.9– 1.1% BW day^-1). None of the carbohydrate supplements tested produced a significant improvement in growth or survival over a basal control diet. However, the diet containing 270 g kg^-1 native wheat starch resulted in the highest moulting (mean = 2.1 moults per lobster), glycogen (3.3 mg g^-1) and free glucose (1.1 mg g^-1) concentrations among lobsters fed with the formulated diets, suggesting a superior utilization of this source of carbohydrate. The greater glycogen (8.0 mg g^-1 tissue) and free glucose (2.0 mg g^-1 tissue) concentrations, as well as higher specific activity of α-amylase (2.3 versus <0.7 U mg^-1 for other diets), found in the DG of lobsters fed with fresh mussel indicated a metabolism strongly directed to the utilization of glycogen.