THE EFFECT OF TEMPERATURE ON THE VERTICAL-DISTRIBUTION OF LARVAL HERRING (CLUPEA-HARENGUS L)

The effect of temperature on the vertical distribution of herring (Clu pea harengus L.) larvae was investigated in a Perspex tank filled with sea water to a depth of 1.76 m. The vertical distributions of larvae subjected to artificial thermoclines were compared with those observed in homogeneous temperatures. All experiments were performed in comple te darkness and larvae were observed with an infra-red sensitive telev ision camera and light source. The activity of the larvae was restrict ed to alternating bouts of sinking and vertical swimming which resulte d in many encounters with the temperature discontinuity. The larvae sh owed a preference for the higher temperature, in the upper part of the tank, when exposed to temperatures of up to 13-degrees-C in the upper part of the tank and tended to accumulate near the thermocline.