The effects of domestication selection on fitness are of serious concern in hatchery‐reared anadromous salmonids, which often experience selection for rapid growth and associated deviations from natural agonistic and feeding behaviors. The high rations that are used to raise age‐1 smolts and the reduced rations that are used to produce age‐2 smolts potentially result in very different behavioral tactics and social dynamics of competition in hatchery tanks. Consequently, steelhead Oncorhynchus mykiss hatchery programs with recovery or conservation goals may need to change their aquaculture practices to minimize domestication selection. This study investigated how the feeding rate (proportion of presented food items that were successfully captured) and relative competitive ability (ability to monopolize food items in small groups) of age‐1 and age‐2 steelhead corresponded to feeding location (surface or bottom) and growth rate in hatchery rearing tanks. We raised steelhead from a common broodstock to smolt at age 1 or age 2 by manipulating their rations (age‐1 fish received the high ration, age‐2 the low ration). The fish in the age‐1 treatment had a lower feeding rate than did those in the age‐2 treatment. Feeding rate was positively correlated with both body size and with growth rate in the rearing tanks at both rations. The age‐2 steelhead were more likely to be detected at a single feeding location than were the age‐1 fish, which were more frequently detected at both locations. The more competitive age‐1 fish were more frequently detected at both feeding locations, and the less competitive fish were detected at only one location. Relative competitive ability was not associated with feeding location in the age‐2 treatment, nor was it associated with growth rate in either treatment. Age‐2 steelhead that were detected only at the bottom or at both feeding locations had higher growth rates than those that were detected only at the surface, suggesting greater scramble competition near the point of food delivery under the restricted ration. Feeding location was not associated with growth rate in the age‐1 treatment. The results indicate that ration directly affects feeding rate and that ration and relative competitive ability interact to influence feeding rate. Because feeding rate was positively associated with growth rate at both ration levels in the hatchery tanks, behaviors that are associated with feeding motivation may be an important trait under selection in salmonid hatcheries.

中文翻译：

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行为和生长对两种饲养方式的反应的可塑性及其对驯养鳟鱼的影响

在孵化场饲养的无性鲑鱼中，驯化选择对适应性的影响是令人严重关注的，因为鲑鱼经常经历选择以快速生长以及与自然激动和进食行为相关的偏离。用于养成1岁幼仔的高口粮和用于养成2岁幼仔的低口粮可能会导致孵化池竞争的行为策略和社会动态大不相同。因此，硬皮On Oncorhynchus mykiss具有恢复或保护目标的孵化场计划可能需要改变其水产养殖方式，以尽量减少驯化的选择。这项研究调查了1岁和2岁钢头的进食率（成功捕获的已呈现食物的比例）和相对竞争能力（以小群体垄断食物的能力）如何对应于进食位置（表面或底部）和孵化场饲养池的增长率。我们通过控制它们的日粮（1岁的鱼获得了高的日粮，2岁的鱼获得了低的日粮），在1岁或2岁时将硬头bro从普通亲鱼中抚养至。在1岁年龄组中，鱼的摄食率低于2岁年龄组中的鱼。两种日粮的饲喂率均与体型和饲养池中的生长率呈正相关。与1岁鱼相比，在两个喂养地点更容易发现2岁钢头鱼。在两个取食地点检测到竞争性强的1岁鱼的频率更高，而在一个地点检测到竞争性较弱的鱼。相对竞争能力与2岁年龄组的喂养位置无关，也不与两种治疗方案中的生长速度相关。仅在底部或两个进食位置检测到的2岁钢头的生长速度要比仅在表面检测到的2岁钢头的生长速度高，这表明在有限配给量下，在送餐点附近的争夺竞争加剧。喂养位置与1岁龄儿童的生长率无关。结果表明，日粮直接影响饲喂率，而日粮和相对竞争能力相互作用影响饲喂率。由于孵化池中两个定量水平的摄食率与生长率呈正相关，因此在鲑鱼孵化场的选择中，与摄食动机相关的行为可能是重要的特征。