Department of Seafood Technology, SINTEF Ocean AS, Trondheim, Norway.
Fish Capture Division, Institute of Marine Research (IMR), Bergen, Norway.
J Fish Biol. 2022 Mar;100(3):738-747. doi: 10.1111/jfb.14987. Epub 2022 Jan 23.
Wild capture can be stressful for fish. Stress has the potential to induce mortality in released unwanted catches or negative flesh quality consequences in retained ones. Such effects compromise sustainable natural resource management and industry profitability. Mitigating stress during capture is therefore desirable. Biological indicators of stress can objectively inform fishers as to the functional welfare status of catches during fishing operations. If they are to be of practical use in mitigating stress during wild capture events, such indicators must be quantifiable, respond rapidly, reflect the level of induced stress and be easily observable. Atlantic mackerel (Scomber scombrus) are extensively targeted by purse seine fisheries in European waters but are particularly vulnerable to stress. Excessive crowding in the net is thought to be the principal stress mechanism. There is therefore a need to develop indicators of crowding stress for this species so that catch welfare can be improved. Here, we demonstrate that S. scombrus exhibit a skin colour change from predominately green to predominately blue when exposed to crowding stress. In sea cage trials, we induced various degrees of stress in groups of wild-caught S. scombrus by manipulating crowding density and its duration. Skin colour was quantified in air using digital photography. The colour change occurred rapidly (within the typical duration of crowding events in the fishery), and its magnitude was correlated to the severity and duration of crowding. Bluer fish were also associated with higher levels of plasma lactate. No appreciable colour change was observed in uncrowded (control) groups during the treatment period. Nonetheless, unstressed S. scombrus did turn blue <1 h after death. Together, these results indicate that skin colour change has the potential to be a useful real-time indicator of crowding stress for S. scombrus and could therefore be used to improve welfare during wild capture fishing.
野外捕捞会给鱼类带来压力。压力有可能导致被释放的不需要的渔获物死亡，或对被保留的渔获物的肉质质量产生负面影响。这些影响会损害可持续的自然资源管理和产业盈利能力。因此，在捕捞过程中减轻压力是可取的。压力的生物指标可以客观地告知渔民在捕捞作业过程中渔获物的功能福利状况。如果这些指标要在野外捕捞事件中减轻压力方面具有实际用途，那么它们必须是可量化的、快速响应的、反映诱导压力的水平，并且易于观察。大西洋马鲛（Scomber scombrus）是欧洲水域围网渔业的主要目标，但特别容易受到压力的影响。网中过度拥挤被认为是主要的应激机制。因此，需要为该物种开发拥挤应激指标，以改善渔获物的福利。在这里，我们证明当暴露于拥挤应激时，S. scombrus 的皮肤颜色从主要的绿色变为主要的蓝色。在海上笼箱试验中，我们通过操纵拥挤密度及其持续时间来诱导野生捕捞的 S. scombrus 群体产生不同程度的应激。使用数字摄影在空气中对皮肤颜色进行量化。颜色变化发生得很快（在渔业中拥挤事件的典型持续时间内），其幅度与拥挤的严重程度和持续时间相关。较蓝的鱼也与血浆乳酸水平较高相关。在处理期间，未拥挤（对照）组中未观察到明显的颜色变化。尽管如此，未受应激的 S. scombrus 在死亡后不到 1 小时就会变蓝。总之，这些结果表明，皮肤颜色变化有可能成为 S. scombrus 拥挤应激的有用实时指标，因此可以用于改善野生捕捞过程中的福利。
