ABSTRACT: Sea trout are known for seeking out sources of freshwater to rid themselves of salmon lice. However, the effect of natural haloclines in fjords on parasite dynamics is not well understood. We tagged 48 naturally infested wild sea trout with acoustic depth sensors. The fish were kept inside a small net-pen (4 × 4 × 5 m), 12 at a time, in western Norway during 4 separate time periods in spring 2017. The sea trout were relatively highly infested with sea lice (prevalence: 100%, mean ± SD: 68 ± 58 lice fish^-1), and a relatively large proportion of the individuals did not survive the trials (25% mortality). The results show that temperature and light were the 2 most important factors explaining the vertical behaviour of the surviving trout. Mobile lice also had a significant effect on depth distribution, where fish with higher abundances of lice were observed at shallower depths. During the 7 d periods in the net-pen, total sea louse abundance decreased from a mean of 68 to 35 fish^-1. Surface salinity explained this reduction better than the experienced salinity of the individual fish, suggesting that short-time exposure to very low salinities, rather than long-term exposure to moderate salinities, is the driving force behind the effect of haloclines on reduction in sea lice numbers.

中文翻译：

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充分利用糟糕的环境：鲑鱼虱对鲑鳟的深度偏好的影响

摘要：海鳟因寻找淡水来摆脱鲑鱼虱子而闻名。然而，人们对峡湾中天然盐环对寄生虫动力学的影响尚不十分了解。我们用声学深度传感器标记了48只自然出没的野海鳟鱼。在2017年春季的四个不同时间里，将鱼一次捕捞在挪威西部的一个小型网围栏（4×4×5 m）中，一次12个。海鳟鱼被海虱相对大量繁殖（盛行率：100） ％，平均值±SD：68±58虱子鱼^-1），并且有相对较大比例的个体无法在试验中幸存（死亡率为25％）。结果表明，温度和光照是解释存活鳟鱼垂直行为的两个最重要因素。流动虱子对深度分布也有重要影响，在较浅的深度观察到虱子丰度较高的鱼。在网围的7 d期间，总的海虱丰度从平均68条鱼^-1减少到35条鱼^-1。表层盐度比单独的鱼类经历的盐度更好地解释了这种减少，表明短期暴露于极低盐度而不是长期暴露于中度盐度是盐湖对减少海虱影响的驱动力。数字。