The ingestion rate and the resulting assimilation calculated by means of a law taking into account activities of the digestive enzymes (amylase and trypsin) on the carbohydrates and proteins ingested, are determined in two experiments on Artemia. They are fed the same species of phytoplankton (Tetraselmis suecica), at the same concentration but with two chemical compositions. In one experiment, the cells are rich in carbohydrates and poor in proteins, and in the second one they are poor in carbohydrates, rich in proteins. Different observed ingestion rates induce a balance in proteins, and a large difference in the carbohydrates ingested. When digestive enzymes are taken into account, the assimilated carbohydrates and proteins are similar (explaining the similitude of the growth rate observed). The assimilation yield study shows that digestive enzymes induce a better digestion of chemical compounds in low concentrations in the food. That could correspond to a regulation of assimilation as a function of requirements of Artemia. Requirements would be the first internal factor that regulates the nutritional behavior. So two processes are possible for Artemia to obtain the sufficient quantity of food: regulation of ingestion rate, probably depending also on olfactory mechanisms, and regulation of assimilation by the way of digestive enzymes. The importance of these processes is discussed as a function of environmental conditions. [NOT CONTROLLED OCR]