Using axenically cultured Artemia, the mode of action of some microbiota will be studied as a remedy against pathogens using histological, histochemical and immunological techniques. The following hypotheses will be tested: some micro-organisms 1) find adhesion sites in the digestive tract where they proliferate; 2) inhibit pathogenic bacteria; 3) induce faster maturation of intestinal wall; 4) have a positive influence on water quality.