Jones Simon R M, Hargreaves N Brent
Pacific Biological Station, Fisheries and Oceans Canada, 3190 Hammond Bay Road, Nanaimo, British Columbia V9T 6N7, Canada.
Dis Aquat Organ. 2009 Apr 6;84(2):131-7. doi: 10.3354/dao02043.
A threshold of lethal infection was estimated from previous controlled laboratory exposures to be 7.5 Lepeophtheirus salmonis g(-1) for pink salmon Oncorhynchus gorbuscha averaging < 0.7 g. This threshold was used to assess the risk of mortality caused by L. salmonis among pink salmon of the same size class in the Broughton Archipelago, Canada from 2005 to 2008. Virtually all (> or = 98.9%) pink salmon collected in late March belonged to this size class, and this proportion declined to < or = 1% by early July. The proportion of these small pink salmon with infections equal to or exceeding the threshold declined from 4.5 in 2005 to 0% in 2008, coincident with an overall decline in parasite prevalence and intensity during this period. In 2005 and 2006, this proportion was greatest in March (7.8 and 1.1%, respectively) whereas in 2007, the proportion exceeding the threshold was greatest in May (2.9%). In 2008, no infections exceeded the threshold. Parasite development coincided with fish migration through the study area. The declining risk between 2005 and 2008 was possibly related to changes in ocean conditions such as temperature, to changing treatment practices for this parasite on salmon farms, or to changes in the abundance or distribution of non-farmed hosts. The concept of a threshold of L. salmonis infection density may be used to assist in the management and conservation of juvenile pink salmon in the Broughton Archipelago region.
根据之前的对照实验室暴露实验，估计对于平均体重小于0.7克的驼背大麻哈鱼（Oncorhynchus gorbuscha）而言，致死感染阈值为7.5个鲑鳟虱（Lepeophtheirus salmonis）/克。该阈值用于评估2005年至2008年期间，加拿大布劳顿群岛相同规格的驼背大麻哈鱼因感染鲑鳟虱而死亡的风险。几乎所有（≥98.9%）3月下旬采集的驼背大麻哈鱼都属于该规格，到7月初这一比例降至≤1%。这些感染程度等于或超过阈值的小规格驼背大麻哈鱼的比例从2005年的4.5%降至2008年的0%，这与同期寄生虫患病率和感染强度的总体下降相一致。在2005年和2006年，这一比例在3月最高（分别为7.8%和1.1%），而在2007年，超过阈值的比例在5月最高（2.9%）。2008年，没有感染超过阈值。寄生虫的发育与鱼类通过研究区域的洄游同步。2005年至2008年期间风险的下降可能与海洋条件变化（如温度）、鲑鱼养殖场对这种寄生虫治疗方法的改变，或非养殖宿主数量或分布的变化有关。鲑鳟虱感染密度阈值的概念可用于协助管理和保护布劳顿群岛地区的幼年驼背大麻哈鱼。
