ABSTRACT 

Welfare of farmed fish has become of increasing concern for consumers, producers, interest groups and authorities. To improve fish welfare, it is necessary to find indicators that can identify stressful situations early enough so that an intervention can take place before detrimental effects occur. By using heart rate bio-loggers in freely swimming rainbow trout (Oncorhynchus mykiss), combined with plasma cortisol levels and a range of haematological and blood chemistry parameters, we assessed the severity of stress responses induced by a range of common aquaculture practices before and during harvest. Following surgery, transportation and reintroduction with conspecifics in the sea cage, it took ~4 days for heart rate to stabilize and for a clear circadian rhythm in heart rate to emerge (i.e. average circadian fluctuation in heart rate of ~25 to 27 beats min?1 ). The presence or absence of this circadian rhythm in heart rate could inform researchers in the aquaculture industry whether or not specific farming routines induce unnecessary and prolonged stress. The elevations in heart rate caused by common farming practises such as crowding and transportation (e.g. heart rate increased by ~8 and 9 beats min?1 above what would normally be expected for that time of day, respectively) corresponded well with increases in plasma cortisol levels. Stressful farming practises or events (indicated by elevated plasma cortisol levels) such as air exposure during brailing and aquatic hypoxia triggered a hypoxic bradycardia until fish were released back into oxygenated water whereupon heart rate significantly increased to repay the accumulated oxygen debt. Repeated stress induced by multiple farming practises (i.e. combined stressors of crowding, brailing and transportation) clearly had a cumulative and long-lasting effect as heart rate peaked at ~25 beats min?1 above what would normally be expected for that time of day. Heart rate also remained significantly elevated by ~9 beats min?1 the following morning, suggesting that if rainbow trout need to be subjected to multiple stressors during consequtive days, it is recommended that sufficient time for recovery is provided between stressors. This study demonstrates that heart rate monitoring can be useful to assess stress levels of freely swimming fish in sea cages. Moreover, the use of implantable bio-loggers opens up a broad range of possible applications that will allow researchers to investigate the effects of environmental and/or anthropogenic stressors on the welfare of fish under conditions more realistic to the aquaculture industry.

養殖魚的福利越來越受到消費者、生產者、利益集團和機構的關注。為了改善魚類福利，有必要找到能夠及早識別壓力情況的指標，以便在有害影響發生之前進行干預。通過在自由游動的虹鱒魚(Oncorhynchusmykiss)中使用心率生物記錄儀，結合血漿皮質醇水平和一系列血液學和血液化學參數，我們評估了一系列常見水產養殖實踐引起的應激反應的嚴重程度在收獲前和收獲期間。在手術、運輸和在海籠中重新引入同種動物后，需要約4天的時間才能使心率穩定下來，并使心率出現清晰的晝夜節律(即心率的平均晝夜波動約25-27次/min)。心率晝夜節律的存在或不存在，可以告知水產養殖業的研究人員是否會引起不必要的長期壓力。由擁擠和交通等常見的農作活動引起的心率升高。心率增加8次和9次/min-1，比一天中的那個時候通常預期的高，分別與血漿皮質醇水平的增加相對應。應激性養殖實踐或事件(通過升高的血漿皮質醇水平來指示)，如燒烤過程中暴露于空氣和水中缺氧，引發缺氧性心動過緩，直到魚被釋放到含氧水中，心率顯著增加以償還累積的氧氣債務。多種耕作方式引起的重復壓力(即 當心率在25次/分鐘時達到峰值，比一天中正常情況下的心率高出約25次/分鐘時，就明顯產生了累積和持久的影響。第二天早上，心率也保持顯著升高，每分鐘約9次，這表明如果彩虹鱒魚在接下來的幾天里需要被多重壓力作用，建議在壓力作用之間提供足夠的恢復時間。這項研究表明，心率監測可用于評估自由游動的魚在海籠子中的應激水平。此外，使用可植入的生物記錄器開辟了廠泛的可能應用范圍，這將使研究人員能夠研究環境和/或人為壓力因素對魚類福利的影響，這些條件更接近水產養殖業的現實情況。

 Keywords: Stress Teleost Cardiovascular Hormones Telemetry

關鍵詞:壓力，輻鰭魚綱，心血管，激素，遙測