EFFECT OF RAPID CHANGES OF HYDROSTATIC-PRESSURE ON THE ATLANTIC HERRING CLUPEA-HARENGUS L .2. RESPONSE OF THE AUDITORY BULLA SYSTEM IN LARVAE AND JUVENILES

Rupturing of the pro-otic membrane of the Atlantic herring (Clupea harengus L.) occurs if the hydrostatic pressure is rapidly increased from 1 to 3 aim in 12 15 cm long fish. Smaller juveniles and larvae arc much less at risk. The effects of pressure depend on an adapting mechanism which involves the development of the swimbladder at a length of 30-35 mm. The swimbladder acts as a reservoir or sink of gas for the bulla. The time constants for this adaptation can be measured by observations of the external lateral recess membrane in the intact fïsh or the internal bulla membrane in intact transparent larvae or dissected older fïsh. The time constant is of the order of 0.3-1.75 min depending on which membrane is observed, whether the pressure is increased or decreased and whether the system has been 'in use' or not. This has an implication for entrainmcnt of the smaller stages which can pass the screens of power station intakes and for 'acceptable' depth ranges and rates of vertical migration for all stages. © 1979.