ENERGY ALLOCATION STRATEGY IN YOUNG FISH: ALLOMETRY AND SURVIVAL

Abstract

We observed substantial variation in seasonal growth rates, autumn body size, and growing-season mortality among eight experimental cohorts of age-0 rainbow trout, Oncorhynchus mykiss. Wet mass, water, lipids (storage), and lipid-free dry mass (structure) had biphasic allometries with inflexions at ∼10 cm in length. Dry:wet mass and storage:structure ratios were positively related to fish length, indicating that the relative quantities of these constituents change with body size. Lipid concentration varied according to a sigmoid relationship with wet mass which also had a growth-rate dependence. Independent assessments of the allometry of growing-season survival and winter metabolism facilitated assessment of the costs and benefits of two alternate energy allocation strategies of young fish. For cohorts with low growth rates and small autumn body size, a somatic growth rate maximization strategy is optimum, producing a 5% net survival advantage over an energy storage maximization strategy. For cohorts with intermediate growth rates and autumn mass, somatic growth and energy storage strategies lead to similar first-year survival. The fastest growing cohorts are estimated to have a net survival advantage of 7%, by adopting an energy storage maximization strategy over a growth rate maximization strategy.