Ontogenetic changes in digestive enzyme activity and biochemical indices of larval and postlarval European lobster (Homarus gammarus, L)

The currently limited knowledge on the nutritional requirements of the European lobster (Homarus gammarus) remains a major obstacle to the improvement of growth and survival rates in lobster farming. Therefore, digestive enzyme activity (trypsin, lipase, and amylase) and biochemical indices (RNA:DNA, proximate and lipid class composition) of larval (I–III) and postlarval (IV) stages of H. gammarus fed Antarctic krill (Euphausia superba) were determined to identify ontogenetic changes in digestive capacity and hence potential nutritional requirements. Activity of the three digestive enzymes was detected in all developmental stages examined, suggesting that H. gammarus is capable of exploiting a varied diet from stage I onwards. Amylase activity increased significantly in postlarvae denoting a shift towards a diet richer in carbohydrates after metamorphosis. Lipase activity increased progressively during the three larval stages but not further, pointing to a higher relevance of dietary lipids before metamorphosis. The decrease from 32 to 24% DM of protein in postlarvae was partially compensated by an increase in ash (from 21 to 29% DM), reflecting the increased contribution of the exoskeleton to their total body mass. Phosphatidylcholine (~ 20% total lipids), phosphatidylethanolamine (~ 14% total lipids), and cholesterol (~ 20% total lipids) were the most abundant lipid classes in the body composition of H. gammarus early stages, implying high dietary requirements for these compounds. The results presented here provide new insights into the metabolism and nutritional requirements of H. gammarus early stages, highlighting the importance of lipids during larval development and the increased relative importance of carbohydrates after metamorphosis.