Standard metabolic rate differs between Rainbow Trout (Onchorhynchus mykiss) growth forms

In variable environments, repeatable phenotypic differences between individuals provides the variation required for natural selection. The Pace Of Life Syndrome (POLS) provides a conceptual framework linking individual physiology and life histories to behaviour, where rapidly-growing individuals demonstrate higher rates of resting or ‘standard’ metabolic rate (SMR). If differences in SMR are consistent between fast and slow growing individuals, these differences may be important to capture in bioenergetic relationships used to describe their growth, energy acquisition and allocation. We compared growth rates and SMR between a domesticated and wild strain of Rainbow Trout (Oncorhynchus mykiss Walbaum 1792) using intermittent flow respirometry. Though mass scaling exponents were similar between strains, mass scaling coefficients of SMR for fast-growing Rainbow Trout were 1.25 times higher than for slower-growing fish. These observed differences in mass scaling coefficients between fast and slow growing Rainbow Trout were consistent with data extracted from several other studies. Bioenergetic estimates of consumption for domestic strain fish increased as the difference in SMR and wild strain fish increased, and increased as activity level increased. Our results indicate patterns of SMR consistent with POLS, and suggest that strain-specific SMR equations may be important for applications to active populations (i.e. field observations).