Photographic observations on the behaviour of Japanese anchovy Engraulis japonica at night in the sea

Density, spacing and schooling behaviour of Japanese anchovy Engraulis japonica forming scattering layers during the night were investigated at sea by means of underwater stereophotography.The nearest neighbour distance showed very great variation.Mean nearest neighbour distance ranged from 62.5 cm (7.8 body lengths, BL) to 96.2 cm (12 BL).Anchovy did not swim entirely at random but swam less than 10 BL apart one b e h n d the other on the same plane.The fish exhibited a wide variation of tilt angles with a mean of about 10" head-up orientation while swimming.Mean densities ranged from 0.25 to 0.87 fish m-3 among stations and depths.It is suggested that this density vanation corresponded to differences in ambient temperature, and that the verhcal distribution was affected by the depth of the thermocline.