EFFECT OF TEMPERATURE ON THE ESCAPE RESPONSES OF LARVAL HERRING, CLUPEA-HARENGUS

Herring (Clupea harengus L.) larvae from spring and autumn spawning st ocks were reared at different constant temperatures from 5-degrees to 17-degrees-C. At equivalent developmental stages, the spring larvae we re longer than the autumn larvae and the larvae reared at low temperat ures were longer than those reared at high temperatures. At hatching a nd at the end of the yolk-sac stage, the larvae were induced, by a pro be, to make C-start escape responses, which were recorded and analysed using a high-speed video recording at 400 frames s-1. The response wa s rapid and of short duration. The tail-beat frequency and swimming sp eed were measured during the burst of swimming following the C-start a t different test temperatures and in larvae with different temperature histories. The tail-beat frequency was strongly temperature-dependent , rising from 19 Hz at 5-degrees-C to 37 Hz at 17-degrees-C with no ef fect of temperature history, season or developmental stage. The burst- swimming speed ranged at hatching from 75 to 90 mm s-1 at 5-degrees-C to 110 to 160 mm s-1 at 17-degrees-C and at yolk resorption from 90-11 5 mm s-1 at 5-degrees-C to 175 190 mm s-1 at 17-degrees-C. The longer, spring-spawned larvae swam faster than the shorter autumn-spawned lar vae. When the swimming speeds were expressed as body lengths (L) s the se differences disappeared. Larvae swam from 7-9 L s-1 at 5-degrees-C to 15-20 L s-1 at 17-degrees-C at hatching, and from 8-9 L s-1 at 5-de grees-C to 15-17 L s-1 at 17-degrees-C at yolk resorption. There was, however, a significantly faster specific swimming speed by the larvae reared at 12-degrees-C in spring 1991.