Digestive enzyme response to natural and formulated diets in cultured juvenile spiny lobster, Jasus edwardsii

A better understanding of the nutritional requirements and digestive processes are essential for improving the consumption and growth of spiny lobsters on formulated diets used in commercial culture. Differences in the enzymatic digestive response (i.e., post-prandial changes in digestive enzyme activity, digestive fluid pH and digestive gland structure) of juvenile Jasus edwardsii fed either a natural (mussel flesh) or a formulated diet were investigated. Digestive enzyme activities (total protease, trypsin, α-amylase and α-glucosidase) and soluble protein concentration in the foregut after a single feeding event for the two dietary treatments displayed a common peak at 4h, and a second peak at 18h post-prandial for the mussel fed lobsters only. In lobsters fed the formulated diet, the lumen size of the digestive gland tubules was 88% larger, the number of B-cells per tubule at 18h post-feeding was 269% higher, and the pH of the digestive gland was lower (6.20 versus 6.34) than in lobsters fed mussel flesh. These results indicated an intensified intracellular digestion in the digestive gland on the formulated diet that could have played a role in the poor appetite revival (>18h) exhibited on this diet. Rearing of juvenile lobsters on the formulated diet for 6months resulted in a marked decrease in the digestive capacity (i.e., total and specific enzyme activity of the foregut and digestive gland) and nutritional condition of lobsters. Overall, these results suggest that difficulty in the digestive processing of formulated feeds may help to explain the bottlenecks encountered in developing more effective formulated diets for juvenile spiny lobster culture. Improvements in the dissolution of dietary ingredients upon entering the foregut, and in the digestibility of dietary carbohydrate sources, may assist in further improving the performance of formulated diets for lobsters.