Digestion can make up a substantial proportion of animal energy budgets, yet our understanding of how it varies with sex, body mass and ration size is limited. A warming climate may have consequences for animal growth and feeding dynamics that will differentially impact individuals in their ability to efficiently acquire and assimilate meals. Many species, such as walleye (Sander vitreus), exhibit sexual size dimorphism (SSD), whereby one sex is larger than the other, suggesting sex differences in energy acquisition and/or expenditure. Here, we present the first thorough estimates of specific dynamic action (SDA) in adult walleye using intermittent-flow respirometry. We fed male (n=14) and female (n=9) walleye two ration sizes, 2% and 4% of individual body mass, over a range of temperatures from 2 to 20°C. SDA was shorter in duration and reached higher peak rates of oxygen consumption with increasing temperature. Peak SDA increased with ration size and decreased with body mass. The proportion of digestible energy lost to SDA (i.e. the SDA coefficient) was consistent at 6% and was unrelated to temperature, body mass, sex or ration size. Our findings suggest that sex has a negligible role in shaping SDA, nor is SDA a contributor to SSD for this species. Standard and maximum metabolic rates were similar between sexes but maximum metabolic rate decreased drastically with body mass. Large fish, which are important for population growth because of reproductive hyperallometry, may therefore face a bioenergetic disadvantage and struggle most to perform optimally in future, warmer waters.

Author contributions

Conceptualization: G.D.R.; Methodology: G.D.R.; Formal analysis: C.J.B.; Investigation: C.J.B., E.M.C.S., E.R.L.; Resources: J.W.B., G.D.R.; Data curation: C.J.B.; Writing - original draft: C.J.B.; Writing - review & editing: C.J.B., E.M.C.S., E.R.L., J.W.B., G.D.R.; Visualization: C.J.B.; Supervision: G.D.R.; Project administration: G.D.R.; Funding acquisition: J.W.B., G.D.R.

Funding

The work presented here was supported by a fisheries research grant from the Fisheries Research Program of the Great Lakes Fishery Commission (to G.D.R., J.W.B., et al.) and by a Natural Sciences and Engineering Research Council of Canada Discovery Grant (to G.D.R.). E.M.C.S. was supported by an Ontario Graduate Scholarship.

Data availability

R scripts used to analyse the respirometry data and perform statistical analyses, a final data frame, and O2 plots for each experiment are available from figshare: https://doi.org/10.6084/m9.figshare.25791975.v1.

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