Energy Allocations of Largemouth Bass (Micropterus salmoides): The Interactive Effects of Season and Ration

Abstract

Young-of-year (YOY) fish differentially allocate energy towards growth of various dimensions and tissue types. In temperate environments, several size-selective sources of mortality (e.g., overwinter starvation and predation) have driven adaptation through season-specific energy allocation strategies in YOY fish. However, the degree to which observed patterns in energy allocation are the product of ration-dependent plasticity rather than hard-wired life-history traits is largely unknown. We conducted two experiments to evaluate the role of ration and season on energy allocation of YOY largemouth bass (Micropterus salmoides). Through a controlled laboratory experiment in 2006, growth and condition of largemouth bass were monitored under four ration treatments. Repeated measures ANOVA indicated the effect of ration treatment was significant for relative weight (F3,9.41 = 9.973, p = 0.003) but not for wet weight (F3,6.41 = 2.082, p = 0.198) or total length (F3,6.41 = 0.967, p = 0.462). A second study conducted in outdoor experimental raceways in 2006 and 2007 evaluated the effects of ration (mediated by stocking density and raceway position) and season on patterns of energy allocation during summer and fall. Analyses of covariance found significant differences in length-adjusted dry weight among treatments in August and September of 2006 and 2007, but no significant difference among treatments in October of 2006 (F2,67 = 2.627, p = 0.080) and 2007 (F3,56 = 2.994, p = 0.14). These experiments demonstrate the existence of a tradeoff associated with allocating energy to structure or storage tissue and suggest that ration mediates the extent to which fish must respond to this tradeoff with seasonal shifts in energy allocation pattern.