300-600,000 nauplii were released into a black 270 1 fish tank of 50 cm depth, not including a conical bottom, in order to examine their spatial distribution. Temperature was 17°C and light at 1000 lux at the water-surface and a water exchange of 30 1 hP ’ A fine-meshed gaze at the outlet prevented wash-out of the nauplii. At regular intervals, samples were taken at several points at depth intervals of 10 cm and the number of nauplii registered.