Growth and metabolism - piscivore vs. insectivore rainbow trout

To understand the drivers of variation in digestive performance and their effects on growth, we examined relationships among food consumption, digestive metabolism, food processing efficiency, and growth rate in juveniles of fast-growing piscivore versus slow-growing insectivore ecotypes of rainbow trout reared at satiation rations of the same diet (i.e., commercial food pellets).

Relative to slow-growing insectivores with lower basal metabolism and despite a much higher food ration size, faster-growing piscivores presented an unexpected pattern of higher digestive efficiency through a reduction in the absolute costs of postprandial metabolism coupled with shorter gut residence time and higher assimilation efficiency.

These results suggest that the increase in digestive metabolism following the ingestion of larger meals can be mitigated by displacing the costs of digestion from SDA to SMR. Reducing total digestion costs (SMR+SDA) while maintaining higher assimilation efficiency may be possible through potential adaptations including 1) increased intestinal absorption capacity; 2) economies of scale that shorten gut transit time with increasing ration level; or 3) a permanently larger digestive tract that increases maintenance costs but reduces the need for cyclic upregulation and associated overhead costs.

为阐明消化性能变异的驱动因素及其对生长的调控效应，本研究以相同日粮（即商品配合饲料）饱食投喂量（satiation rations）下的两种虹鳟生态型幼鱼为研究对象，探究了快速生长的食鱼型（piscivore）与慢速生长的食虫型（insectivore）虹鳟的摄食量、消化代谢、食物加工效率与生长速率之间的内在关联。
相较于基础代谢水平更低的慢速生长食虫型个体，尽管快速生长食鱼型个体的投喂量显著更高，但其却呈现出意料之外的高消化效率特征：通过降低餐后代谢（postprandial metabolism）的绝对成本，同时缩短肠道驻留时间并提升同化效率，实现了更优的消化性能。
本研究结果表明，通过将消化成本从特殊动力作用（Specific Dynamic Action, SDA）转移至标准代谢率（Standard Metabolic Rate, SMR），可缓解大型饵料摄入后消化代谢的升高幅度。在维持较高同化效率的前提下降低总消化成本（SMR+SDA），可通过以下三类潜在适应性策略实现：1）提升肠道吸收能力；2）形成规模效应：随投喂量增加缩短肠道转运时间；3）发育永久性更大的消化道：虽会增加基础维持成本，但可减少循环性代谢上调及其相关的额外成本。