Behavioural responses to pressure changes in cultured Atlantic cod (Gadus morhua): Defining practical limits for submerging and lifting sea-cages

摘要: Abstract Farmed Atlantic cod ( Gadus morhua ) are occasionally exposed to buoyancy changes in sea-cages, through lifting or lowering of cage nets. Physiological processes regulate the level gas closed swim bladders and thus ability control their buoyancy. Rapid net may cause positive buoyancy, leading barotrauma, while lead negative alter behaviours. We tested how groups farmed responded immediately after events from 5 different start depths equivalent 40% pressure reductions, long they took return pre-lifting levels. In addition, we immediate responses recovery times 100–300% increases. Trials were conducted with 100 1.1–1.7 kg a 63 m 3 sea-cage at lower (5 °C) upper (16 °C) water temperature limits experienced during culture. Swimming behaviours measured fixed intervals before lowering, feeding test was used assess appetite. general, increased swimming speeds 1.5–4 tail beats 2–3 fish swam an average −14° head-down angle, indicating The depth affected response as became more active shallow compared deeper depths. Appetite levels decreased for about 2 h lifting, independent depth. overall time 8 h did not depend upon temperature. Lowering appeared (1.3–2.3 times) beat frequencies (1.4–2.3 30° head-up angle. Neither nor this response. Time recover neutral 300% increases 42–90 h, but only 18–34 h 100% conclude that reduction is limit lifts healthy cod. Secondary should be done until least 10 h first lift. Cage slowly avoid potentially stressful crowding negatively buoyant on bottom, especially low temperatures.