Ontogenetic changes in digestive enzyme activity of the spiny lobster, Jasus edwardsii (Decapoda; Palinuridae)

Digestive enzyme profiles of puerulus, post-puerulus, juvenile and adult stages of the spiny lobster Jasus edwardsii Hutton were determined in order to identify ontogenetic changes in digestive capabilities and assess capacity to use dietary components and to exploit diets to meet nutritional requirements. Juvenile and adult lobsters exhibited a diverse range of enzymes, suggesting they can exploit varied diets. Proteolytic activity of trypsin, chymotrypsin and carboxypeptidase A (1.86-3.70 U mg-1 digestive gland protein) was significantly higher than carbohydrase activity of amylase, α-glucosidase, cellulase and chitinase (0.0014-0.38 U mg-1 digestive gland protein), thus showing that dietary protein was more important than carbohydrate and that the lobster is carnivorous. These conclusions are consistent with other studies that found spiny lobsters to feed predominantly on crabs, bivalves, ophiuroids and sponges. Lipase activity (0.371 U mg -1 digestive gland protein) was also relatively high, thus showing the importance of dietary lipid. Total activities (units per digestive gland) of every enzyme assayed increased significantly with lobster carapace length. There were few significant ontogenetic trends in specific enzyme activity (U mg-1 digestive gland protein). Amylase and laminarinase specific activity was significantly higher in small lobsters than large lobsters (regression analyses, respectively, F(1,23) = 9.84, P = 0.005; F (1,11) = 19.65, P = 0.001), suggesting that carbohydrates including laminarin are more important in the diet of small juveniles. Trypsin, amylase and lipase activities were detected in all non-feeding puerulus stages, suggesting that feeding is not a cue for digestive enzyme production in J. edwardsii. Significant variations in total and specific activities of amylase (F(1,3)= 14.2, P = 0.00; F(1,3) = 14.2, P = 0.00) and trypsin (F(1,3) = 8.8, P = 0.00; F(1,3) = 21.41, P = 0.00) and a declining trend in lipase total activity between non-feeding puerulus stages suggests that they may be hydrolysing endogenous energy reserves to sustain their onshore swimming activity prior to settlement. Profiles suggest carbohydrate and lipid are utilised first, followed by protein. Consistently high levels of lipase in all puerulus stages (0.24-0.7 U digestive gland -1; P > 0.05) confirm the importance of lipid as a major energy substrate.