Changes in enzymatic activity during early development of bay scallops argopecten irradians and sea scallops Pacopecten magellanicus

Poor growth and survival of scallops is often reported during early developmental stages. Stage- and species-specific dietary requirements have been identified, but the mechanisms responsible for these differences remain largely unknown. Dietary success depends on food biochemical properties, digestive and/or assimilative capacity, as well as the animal's specific nutritional demands, which can vary over development and between species. The present study examines developmental changes in the activities of key digestive enzymes in larval and postlarval bay scallops Argopecten irradians and sea scallops Placopecten magellanicus raised on a mixed algal diet until ~4 to 5 mm in shell height (SH) and sampled at intervals encompassing major transitions in feeding organ development. Colorimetric assays measured general protease, lipase (esterase) and carbohydrase (α-amylase, cellulase and laminarinase) activities. The most pronounced changes in enzymatic activity occurred prior to scallops attaining ~1.2 mm SH in both scallop species. The esterase:protease ratio exhibited similar ontogenetic patterns in both scallop species, decreasing sharply between larval and immediate postlarval stages before increasing to an intermediate level and stabilizing around 1.2 mm SH. In contrast, mean carbohydrase activities measured over the experimental duration differed between species, with bay scallops exhibiting higher specific activities of α-amylase and cellulase but much lower activities of laminarinase than sea scallops. These findings have implications for understanding scallop utilization of the food supply in nature, as well as developing targeted diets that could enhance their growth and survival in culture.