In order to specify the limits of the high density larval rearing method (80-100 larvae per liter) in clear water with daily total exchange and to control the water quality evolution, the nitrite and total ammonia were measured. Nitrite concentrations in antibiotic treated tanks stayed law (5 ug N02-N/l) but can reached 40 ug N02-N/l after 41 days in untreated tanks, in spite of daily water exchange. Maximum concentrations of total ammonia were 1.70 ppm N during a 24-hour cycle. In the rearing conditions (pH 7.85 to 8.20, temperature 25 to 28 C) the un-ionized ammonia concentrations were 0.07 to 0.18 ppm N. At thase levels, no specifie larval stress was noted. [NOT CONTROLLED OCR]