Abstract
The ontogenetic diet shift to piscivory can be energetically beneficial for fish growth and allows larger, more energetically profitable prey to be consumed. A shift to piscivory may be easier for longer individuals within a cohort due to larger gape size, and an early shift is likely advantageous, potentially leading to increased growth rates and survival. Such length-dependent ontogenetic diet shifts may explain the intracohort variability in length that is common for age-0 walleye (Sander vitreus). The objectives of this study were to describe seasonal intracohort variability in length, identify the timing of the shift to piscivory and determine if the onset of piscivory was length-dependent in age-0 walleye. Walleye initially fed on zooplankton, but shifted to piscivory during July of 2010 and June of 2011. The onset of piscivory in age-0 walleye was associated with length-dependent differences during both years, in which longer individuals within the cohort became piscivorous earlier than shorter individuals within the same cohort. Intracohort variability in length was detected and increased postontogenetic diet shift. Age-0 walleye that experience a growth advantage could benefit from increased survival and feeding opportunities.
Highlights
Several ontogenetic diet shifts commonly occur during fishes first year of life as endogenous feeding on yolk shifts to exogenous feeding on zooplankton, other invertebrates, and fish
Individual diets and respective lengths of age-0 walleye collected on 6 July 2010 and 16–25 June 2011 were used to investigate if the shift to piscivory was length dependent
This study demonstrates the onset of piscivory within a cohort of age-0 walleye can be length-dependent
Summary
Several ontogenetic diet shifts commonly occur during fishes first year of life as endogenous feeding on yolk shifts to exogenous feeding on zooplankton, other invertebrates, and fish. The ontogenetic diet shift to piscivory can be energetically beneficial for fish development and allows larger, more energetically profitable prey to be consumed The shift to piscivory generally occurs once the predator’s gape is large enough to allow for the consumption of fish (Bremigan and Stein 1994) or when piscivory becomes energetically advantageous (Galarowicz and Wahl 2005; Graeb et al 2006). Though the shift to piscivory is known to provide an energetic advantage, the mechanisms that control the onset of piscivory are not fully understood
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