First important problems in pathology at the Centre Océanologique du Pacifique (COP) have been met during larval rearings of penaeid shrimps and Hacrobrachium rosenbergii. In penaeids, heavy mortalities during the zoea and mysis stages have led to the diagnosis of two main types of diseases: a bacterial necrosis of the appendages and a fungus disease. Two preventive treatments with antibiotics during the zoea stages and a continuous treatment with a selective herbicide (Treflan) allow a consistent production of 100 post-larvae/liter (80% survival from the nauplius stage). With Macrobrachium rosenbergii, during the larval rearing, mortalities of bacterial origin have been recorded in some experiments. The observation of appendage necrosis allows early diagnosis and treatment with antibiotics. Chlorination of the water helps to control the disease. [NOT CONTROLLED OCR]