Ecological energetics of an imperilled fish: Physiological metrics, experimental protocols and implications for...

Insights about fish physiology can be useful for population management, but collecting ecologically relevant data can be challenging, especially for imperilled and sensitive species. With the goal of identifying ecologically relevant physiological metrics, we conducted a range of experiments to characterize the metabolism, food consumption, growth, temperature tolerance and bioenergetics of Silver Shiner (Notropis photogenis) from an imperilled population in Canada. We also assessed the potential for collecting some of these metrics with non-lethal, field-based studies. Short-term (≤5-h) field-based respirometry generated estimates of standard metabolic rate (SMR) that were statistically similar to 48-h lab-based trials, though the abbreviated protocol may still differ from true SMR. A chase-to-exhaustion, single-measurement field respirometry protocol underestimated maximum metabolic rate (MMR) at warmer temperatures relative to longer (24-48 h) laboratory respirometry, possibly reflecting heightened stressor sensitivity at warm temperatures and the limitations of single-measurement protocols for capturing peak metabolic rate in this small-bodied species. Silver Shiner exhibited a eurythermal metabolism, with a broad thermal range of high aerobic scope (AS; aerobic capacity above SMR). However, bioenergetics measures including lab growth (observed) and field growth (modelled) showed greater growth potential from 12 to 21°C due to limitations in food consumption capacity >21°C. Survival was also lower above the optimal growth range, supporting links between energetics and stressor sensitivity. Across the metabolic metrics evaluated, a novel metric generated here, aerobic differential (AD = AS - SMR), which subtracts maintenance costs from aerobic capacity, was more closely related to lab and field growth than aerobic scope or factorial aerobic scope. Agitation temperatures from CT_max trials also showed some consistency with the onset of energy loss and stressor sensitivity. These findings provide insights into ecologically relevant physiological metrics and experimental designs, and have implications for managing critical habitat. In particular, aerobic differential and agitation temperature show promise as ecologically relevant indicators and have potential as non-lethal field-based assessment methods.