Changes in digestive enzyme activities during early development of the American lobster Homarus americanus Milne Edwards

Abstract

Activities of digestive protease, lipase, and amylase from the foregut and midgut gland were measured during the course of early development in the American lobster Homarus americanus Milne Edwards. Total enzyme activities were very low among embryos sampled 3 days prior to hatching. Protease and amylase activities increased slightly at the time of hatching and again during larval Stage I; lipase activity did not change. Activity of the three enzymes more than doubled among Stage II larvae and although there were slight increases in enzyme activities during Stage III, they were not significant. Protease activity peaked during Stage IV, whereas lipase and amylase activities were greatest among Stage V juveniles. Different patterns were observed when specific enzyme activities (normalized on the basis of protein) are examined. Specific activities of the three enzymes were very low in embryos just prior to hatching and increased slightly during the hatching process. During Stage I, the specific activity of protease doubled, lipase specific activity increased by a factor of 10, and that of amylase increased slightly. Activities of both protease and amylase more than doubled in Stage II larvae; in general, there were no significant differences in specific activities measured in Stages II through V. Lipase specific activity did not change significantly among Stages I through V. The increase in enzyme activities among the hatching stages correlates well with morphological changes observed in the midgut gland (hepatopancreas), specifically in regard to the presence of enzyme-producing B-cells. Changes in enzyme activities among the postmetamorphic Stages IV and V may be related to changes in body form, habitat, or patterns of energy storage and utilization. Lobster larvae normally hatch during early summer but embryonic development can be accelerated in the laboratory by maintenance at high (21°C) rather than ambient temperature. Temperature conditions during embryonic development, however, had no effect on digestive enzyme activities of larvae that were induced to hatch out of season.