Food availability and thermal regimes can largely govern growth opportunities in fishes. In temperate regions, streams can exhibit summer temperatures that exceed the optima for coolwater‐adapted species relative to the amount of available food, and therefore, spring and fall may confer better growing conditions, especially for larger size classes. We examined the relationship between growth, consumption and growth efficiency across seasons in juvenile steelhead (Oncorhynchus mykiss) in their natal streams in Idaho, USA. Subyearling (0+) growth rates were higher in summer, whereas yearlings exhibited no statistically significant difference in growth between seasons. Consumption rates were overall lower in winter–spring but constituted a higher proportion of maximum consumption compared with summer and fall, indicating better food availability relative to metabolic demands. Net growth efficiencies were higher in winter–spring, but substantially more so than the proportion of maximum consumption. This suggests that overwinter growth performance was driven at least partly by higher growth efficiency, and the effect was most pronounced for yearling steelhead. The low proportions of maximum consumption for both age classes suggest that food was an overall limiting factor to growth, especially in summer when metabolic demands were highest. We discuss how temperature‐based models can overestimate growth in the warmest parts of the year and develop a simple conceptual model for the seasonal timing of juvenile growth. In anadromous populations, the outmigration of presmolts in spring can reduce the level of competition. For the individuals that remain in the river, growth in this period can be particularly important.

中文翻译：

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越冬幼鱼生长、消耗和生长效率的季节性变化

食物供应和热量状况在很大程度上可以控制鱼类的生长机会。在温带地区，相对于可用食物的数量而言，溪流的夏季温度可能超过适应冷水的物种的最佳温度，因此，春季和秋季可能会提供更好的生长条件，尤其是对于较大的尺寸等级。我们研究了美国爱达荷州幼鱼（Oncorhynchus mykiss）在其出生流中不同季节的生长、消耗和生长效率之间的关系。亚年幼 (0+) 生长率在夏季较高，而一岁幼鸽在季节之间的生长没有统计学上的显着差异。冬春季节消费率总体较低，但占最大消费量的比例高于夏秋季节，表明相对于代谢需求更好的食物供应。冬春季节的净增长效率更高，但远高于最大消费的比例。这表明越冬生长性能至少部分是由较高的生长效率驱动的，而一岁鸽的影响最为明显。两个年龄段的最大消费比例较低表明，食物是整体增长的限制因素，尤其是在代谢需求最高的夏季。我们讨论了基于温度的模型如何高估一年中最温暖地区的生长，并为幼鱼生长的季节性时间开发了一个简单的概念模型。在溯源种群中，春季前幼崽的迁出可以降低竞争水平。