Individual Variation in Bioenergetic Rates of Young‐of‐Year Rainbow Trout

Studies collecting data on bioenergetic rates in fish typically measure the rates of a large number of individuals once and then fit parameters to those data sets. Such data commonly have large amounts of variation around the mean, which is left unexplained because the study aims to address population‐level or ecosystem‐level questions. We addressed the question of whether individual fish have detectably different rates of maximum consumption and respiration rates by repeatedly measuring those rates in individually identified young‐of‐year (age‐0) rainbow trout Oncorhynchus mykiss over a range of temperatures. In experiment 1 we measured the respiration rates of two size‐classes of age‐0 rainbow trout five times at five different temperatures (9‐19°C). In experiment 2 we measured the respiration and maximum feed consumption rates of one size‐class of rainbow trout five times at four different temperatures (7‐19°C). We also use these data to develop a new parameter set for a Wisconsin bioenergetics model of maximum consumption and respiration rates for age‐0 rainbow trout. The results show that individual differences have a significant effect on their respiration and maximum feed consumption rates. The new bioenergetics parameter set differs considerably from the parameter sets developed for adult rainbow trout. The new bioenergetics model may prove useful for studies examining the growth and feed consumption of age‐0 rainbow trout. The finding of significant differences between individuals in measured rates of respiration and maximum consumption may be important in individual‐based models (IBMs) of fish populations. Specifically, IBMs have not included individual‐level differences in bioenergetic rates, but such differences may have an important effect on their predictions of fish growth, production, and population number.