Emamectin benzoate (EB) is a prophylactic pharmaceutical used to protect Atlantic salmon (Salmo salar) smolts migrating out of rivers and into the ocean against sea lice parasites. Randomized control trials comparing the marine survival of smolts treated with EB to a control group is used to calculate the fraction of marine mortality attributable to sea lice parasitism. However, it is assumed that there is no baseline difference in survival induced by the application of EB treatment. We used a combined laboratory and field study approach to investigate the potential impacts of EB treatment on behaviour and survival of hatchery-reared Atlantic salmon in western Norway. In aquaria experiments, EB-treated salmon smolts did not differ significantly in exploratory behaviour. Fish from treated groups responded similarly to simulated predator attack with spontaneous escape and elevated gill beat rate. Three rivers in the Osterfjord system of western Norway were selected for field experiments, Dale, Modalen, and Vosso. Dale River smolts were treated with intraperitoneal EB injections and had lower probability of detection in a wolf trap downstream of the release site than control smolts. Salmon smolts raised in the Vosso River hatchery were treated with EB delivered in their food and were detected on PIT antennas at the rivermouth at lower rates than control fish, but only when released at downstream sites. Calculation of risk ratios suggested that the bias in mortality caused by treatment with EB decreased the estimated survival of treated fish from an expected 18% to 46%, reducing the observable negative impact of sea lice on Atlantic salmon smolts. The results suggest that estimates of the fraction of mortality attributable to sea lice may be underestimated due to lower baseline survival of treated fish caused by treatment and bring urgent attention towards a potential systematic underestimation of the impacts of sea lice on wild salmon.

Emamectin benzoate（EB）是一种预防性药物，用于保护大西洋鲑鱼（Salmo salar）抵御海虱寄生虫的软体动物从河流迁入大海。随机对照试验比较了用EB处理的熏鲑与对照组的海洋存活率，以计算可归因于海虱寄生的海洋死亡率。但是，假设采用EB治疗所致的生存率没有基线差异。我们使用实验室和现场研究相结合的方法来调查EB处理对挪威西部孵化场饲养的大西洋鲑鱼的行为和生存的潜在影响。在水族箱实验中，经EB处理的鲑鱼的探索行为没有显着差异。来自处理组的鱼对模拟捕食者攻击的反应类似，具有自发逃逸和g跳动率升高的情况。挪威西部Osterfjord系统中的三条河被选为Dale，Modalen和Vosso进行野外实验。Dale River熏鸭用腹膜内EB注射治疗，并且在释放点下游的狼陷阱中的检出概率比对照熏鸭低。在Vosso河孵化场中饲养的鲑鱼用食物中所含的EB进行处理，并在河口的PIT天线上以低于对照鱼的比率检出，但只有在下游地点才释放。风险比的计算表明，由EB处理导致的死亡率偏差使处理鱼的估计生存率从预期的18％降低到46％，从而减少了海虱对大西洋鲑鱼的可观察到的负面影响。