Activities of the digestive enzymes amylase and trypsin have been studied during development of Artemia (San Francisco, USA) cultured at different concentrations of phytoplankton (Tetraselmis suecica). The synthesis of the two enzymes varies independently throughout the development. Activity levels are controlled by food levels as well as by food composition. To obtain an optimum assimilation yield at a given food level, an adaptive mechanism would involve 1) modulation of ingestion rates based on physicochemical properties of food particles and 2) regulation of synthesis of digestive enzymes by ingestion and chemical composition of the food. Rates of ingestion and assimilation Vary more during development than does the yield. Maximum yield is achieved during the exponential growth phase and is related to food requirements. As such, regulation of digestive enzymes during development would optimize the use of the food available, as a function of the food requirements. [NOT CONTROLLED OCR]