EFFECT OF RAPID CHANGES OF HYDROSTATIC-PRESSURE ON THE ATLANTIC HERRING CLUPEA-HARENGUS L .1. LARVAL SURVIVAL AND BEHAVIOR

Larval Atlantic herring (Clupea harengus L.) from 11-39 mm total body length were subjected to different series of pressure changes intended to simulate passage through the cooling water of a thermal power station. This involved both acclimation and rapid pressure increases to 5 atmospheres pressure, followed by rapid decompression. Subsequent mortality, feeding and depth-compensating behaviour were checked as well as the integrity of the gas-filled auditory bulla-swimbladder system which develops between 23-35 mm. There was no evidence of increases in mortality in larvae up to about 20 mm. Larvae from about 25-29 mm showed increased mortality over controls; still larger larvae did not. Larvae which survived the pressure treatment fed as well as controls. There was strong evidence that larvae of all ages attempted to compensate for pressure changes by making appropriate vertical swimming movements. Some of the mortality of the intermediate-sized larvae may be attributed to hyperactivity in a restricted (experimental) space. The bulla membrane in some older larvae was ruptured by the pressure changes. Although this was not immediately a cause of mortality, it would impair mechanical reception in the long term. © 1979.