Introduced pathogens can affect fish populations, and three main factors affect disease occurrence: the environment, host, and pathogen. Manipulating at least one of these factors is necessary for controlling disease. Myxobolus cerebralis, the parasite responsible for salmonid whirling disease, became established in Colorado during the 1990s and caused significant declines in wild Rainbow Trout Oncorhynchus mykiss populations. Attempts to re-establish Rainbow Trout have focused on manipulating salmonid host resistance. A Rainbow Trout strain known as GR × CRR was developed for stocking in Colorado by crossing a whirling-disease-resistant strain known as the German Rainbow Trout (GR) with the Colorado River Rainbow Trout (CRR). The GR × CRR fish exhibit resistance similar to that shown by GR, and survival and reproduction were expected to be similar to those of CRR. One disadvantage of stocking GR × CRR is that outcrossing and backcrossing could decrease resistance, and laboratory studies have indicated that this can occur. A potential disadvantage of stocking pure GR is lower survival due to domestication. To compare fry survival between the strains, a field experiment was conducted in 1.6-km reaches of nine Colorado streams. Each stream was stocked in August 2014 with 5,000 GR × CRR and 5,000 GR individuals. In October 2014, April 2015, and August 2015, apparent survival was assessed. Two laboratory predation experiments were also conducted. The field experiment revealed that short-term apparent survival was influenced by stream, and growth rate was influenced by strain and stream. However, after 12 months, there was no difference in apparent survival or growth rate between the GR and GR × CRR strains. Laboratory experiments showed that survival did not differ between the strains when confronted with Brown Trout Salmo trutta predation. Our results indicate that the GR strain is a viable option for stocking in streams where M. cerebralis is enzootic. Further evaluation is needed to determine whether GR fish will survive to maturity and reproduce.

中文翻译：

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野生抗旋转病虹鳟鱼苗的生存：两种菌株的比较

引入的病原体会影响鱼类种群，影响疾病发生的三个主要因素是：环境、宿主和病原体。控制这些因素中的至少一个是控制疾病所必需的。Myxobolus brainis 是导致鲑鱼旋风病的寄生虫，于 1990 年代在科罗拉多州建立，并导致野生虹鳟 Oncorhynchus mykiss 种群显着下降。重新建立虹鳟鱼的尝试集中在操纵鲑鱼宿主的抵抗力上。一种称为 GR × CRR 的虹鳟鱼品系是通过将一种称为德国虹鳟鱼 (GR) 的抗旋转病菌株与科罗拉多河虹鳟鱼 (CRR) 杂交而开发的，用于在科罗拉多州放养。GR × CRR 鱼表现出与 GR 相似的抵抗力，预计存活和繁殖与 CRR 相似。放养 GR × CRR 的一个缺点是异交和回交会降低抗性，实验室研究表明这可能发生。放养纯遗传资源的一个潜在缺点是由于驯化导致存活率较低。为了比较菌株之间的鱼苗存活率，在 9 条科罗拉多河流的 1.6 公里范围内进行了田间试验。每个流在 2014 年 8 月存有 5,000 GR × CRR 和 5,000 GR 个体。2014 年 10 月、2015 年 4 月和 2015 年 8 月，评估了表观存活率。还进行了两次实验室捕食实验。田间试验表明，短期表观成活率受溪流的影响，生长速度受株系和溪流的影响。然而，12个月后，GR 和 GR × CRR 菌株之间的表观存活率或生长率没有差异。实验室实验表明，当遇到 Brown Trout Salmo trutta 捕食时，这些菌株的存活率没有差异。我们的结果表明 GR 品系是一种可行的放养选择，可在脑 M. cereris 流行的溪流中放养。需要进一步评估以确定 GR 鱼是否能存活至成熟并繁殖。