Canadian Journal of Fisheries and Aquatic Sciences, Ahead of Print.
Fish foraging and energy flow between trophic levels are predicted to decline with freshwater browning due to decreased light availability. Studies investigating these predictions have focused on juvenile and adult fishes; however, the larval stage represents a “critical period” in development. We investigated the indirect (i.e., prey availability) versus direct (i.e., visual foraging) effects of browning on zooplankton–larval fish interactions by altering water colour with SuperHume (absorbance at 440 nm = 1.6–10.8 m−1). Phytoplankton and zooplankton densities were monitored across treatments for 1 month to simulate the time leading up to fish spawning in the spring. Larval largemouth bass (Micropterus salmoides) were then introduced to assess indirect effects on fish feeding, growth, and survival. Direct effects on largemouth bass and bluegill (Lepomis macrochirus) foraging on zooplankton were determined with separate short-term experiments. Browning did not directly alter the ability of larvae to capture prey. However, indirect effects on larval fish foraging, growth, and survival were observed as phytoplankton and zooplankton abundance decreased with increased browning. Our data suggest browning may reduce energy transfer to larval fish due to a reduction in prey but not visual foraging.

中文翻译：

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淡水褐变对幼鱼觅食的间接与直接影响

加拿大渔业和水产科学杂志，提前印刷。
由于光照减少，鱼类觅食和营养级之间的能量流动预计会随着淡水褐变而下降。调查这些预测的研究集中在幼鱼和成鱼上；然而，幼虫阶段代表了发育的“关键时期”。我们通过用 SuperHume（440 nm 处的吸光度 = 1.6–10.8 m-1）改变水色，研究了褐变对浮游动物-幼鱼相互作用的间接（即，猎物可用性）与直接（即，视觉觅食）影响。对浮游植物和浮游动物密度进行了为期 1 个月的监测，以模拟春季鱼类产卵前的时间。然后引入大口黑鲈幼体（Micropterus salmoides）来评估对鱼类摄食、生长和存活的间接影响。对大口黑鲈和蓝鳃鱼（Lepomis macrochirus）对浮游动物觅食的直接影响是通过单独的短期实验确定的。布朗宁并没有直接改变幼虫捕捉猎物的能力。然而，观察到对幼鱼觅食、生长和存活的间接影响，因为浮游植物和浮游动物丰度随着褐变的增加而减少。我们的数据表明褐变可能会减少能量转移到幼鱼，因为猎物减少而不是视觉觅食。