Effects of electric field exposure on blood pressure, cardioventilatory activity and the physiological stress response in Arctic char, Salvelinus alpinus L.

Abstract

Electric field exposure is used to stun or immobilize fish prior to slaughter in the aquaculture industry and for field sampling purposes (i.e. electrofishing), but the physiological response of fish to this exposure is incompletely understood. In this paper we report on changes in blood pressure, heart and ventilation rates, and hematological variables in chronically cannulated Arctic char (Salvelinus alpinus) in response to exposure to an electric field of 4V/cm (125Hz) for 5 and 30s. Both durations of exposure resulted in a brief (total duration: 5.2 to 6.0s, respectively) four-fold blood pressure increase above resting levels. The 5s exposure was followed by a period of cardiac and ventilatory arrest (for 35 and 176s on average, respectively), but cardioventilatory activity recovered in ten out of eleven fish. Nevertheless, signs of systemic stress responses were evident after the exposure. These included moderate hypertension, increased ventilation amplitude, increased plasma cortisol levels and altered hydromineral balance. After the 30s exposure, cardiac activity initially appeared to recover, but subsequently declined. Ventilation did not recover. It is suggested that circulatory failure due to cardiac ischemia resulting from ventilatory failure; rather than instantaneous and irrecoverable cardiac arrest from the electric field exposure per se, is the ultimate cause of death in fish that fail to recover from exposure to an electric field in water. The brief dramatic hypertension observed in char may partly explain the haemorrhages that are frequently observed in electrically stunned fish of some species.