Hatchery reared salmonid fish often have lower fitness than their natural-origin counterparts when spawning in the wild. Although this difference appears to result from rapid adaptation to captivity, it is not known what traits are under selection. We hypothesize that variation in traits that confer a growth rate advantage to some individuals in the novel hatchery environment are under strong selection because survival at sea is correlated with size at release. Here we show that full sibling families of steelhead trout ( Oncorhynchus mykiss ) show substantial variation in propensity to feed at the surface as fry, and that the more surface-oriented families grew faster under hatchery conditions. We hypothesize that surface-oriented fry gain an initial growth advantage that persists through size at release. Because surface orientation is a correlate of generalized boldness, hatcheries may inadvertently select for that phenotype, which could explain the fitness differences observed between hatchery and natural-origin fish in the wild.

中文翻译：

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硬头鱼表面饲料行为的家庭变化预测孵化场条件下的生长速度

在野外产卵时，孵化场饲养的鲑鱼通常比天然鱼类低。尽管这种差异似乎是由于对圈养的快速适应所致，但尚不清楚正在选择哪些性状。我们假设在新颖的孵化场环境中，赋予某些个体以增长速度优势的性状变异时，强烈选择，因为海上生存与释放时的大小有关。在这里，我们显示出全兄弟姐妹的硬头鳟鱼（Oncorhynchus mykiss ）显示出在水面以鱼苗为食的倾向有很大的变化，并且在孵化场条件下，面向表面的科增长更快。我们假设面向表面的鱼苗获得了最初的生长优势，该优势在释放时会一直保持大小不变​​。由于表面方向是广义胆量的相关因素，孵化场可能会无意中选择该表型，这可能解释了在野外孵化场与天然鱼类之间的适应性差异。