Light intensity and the feeding behaviour of herring,Clupea harengus

An infra-red sensitive video-recording technique was used to study the effects of darkness and light intensities from 0.0001 to 270 photopic lx on the feeding behaviour of herring (Clupea harengus L.). When offered natural zooplankton, consisting of a mixture ofCalanus finmarchicus, Euchaeta norvegica, Oithona similis, Balanus sp. nauplii, and crustacean nauplii as prey, the fish fed by biting (snapping) at light intensities above a threshold of 0.001 lx and were size-selective, taking the larger organisms first. When fed on pure cultures of CaliforniaArtemia sp. nauplii (San Francisco Bay brand), the threshold light intensity was 0.01 lx. Swimming speed increased with increasing light intensity when the fish were actively feeding by biting. When the fish were filter-feeding on high densities ofArtemia sp. nauplii in the light, they continued to school and swimming speed was not related to light intensity.