Digestion of lipids and carbohydrates from microalgae (Chaetoceros muelleri Lemmermann and Isochrysis aff. galbana clone T-ISO) in juvenile scallops (Pecten maximus L.)

The digestion of laminaran and neutral lipids from the microalgae Chaetoceros muelleri or mixtures of C. muelleri and Isochrysis galbana clone T-ISO in 4-mm scallops Pecten maximus were studied. The microalgae were cultivated at fixed low and high growth rate (5% and 60% of mu(max)). The cultivation method clearly affected the lipid and carbohydrate contents, as well as their enzyme activity. Chaetoceros muelleri and T-ISO grown at low growth rate exhibited a considerably higher content of lipids and carbohydrates than those algae grown at high growth rate. The specific activity of laminaranase and neutral lipase was the highest in C. muelleri grown at the low growth rate. Growth rate of scallops was best when they were fed a mono-species diet of C. muelleri grown at low growth rate. The growth rate of the scallops was positively correlated to the dietary carbohydrate content as well as to the specific activity of neutral lipase and laminaranase in the diet. The capacity to digest carbohydrates (laminaran) might be limiting for the young scallops, and the content of carbohydrates and enzymatic activities of laminaran in the diet should be considered when formulating an optimal diet, both when the diet consist of live microalgae and formulated diets.