Influence of growth history on the accumulation of energy reserves and winter mortality in young fish

In seasonal environments, accumulated energy reserves are important to avoid starvation mortality during periods of low resource levels. Here we investigated patterns of energy accumulation and the importance of growth history for winter survival in young-of-the-year Eurasian perch (Perca fluviatilis). Under simulated winter conditions in aquaria, we showed that high winter mortality most likely relates to the depletion of energy reserves in small perch. Correspondingly, in a field study, using four lakes covering 3-6 lake-years each, overwinter survival within cohorts was positively related to individual size. However, average size in autumn did not explain the variation in overwinter survival between cohorts. Instead, we showed that seasonal growth history is an important factor. High growth rates late in season may increase cohort survival over winter, irrespective of average size, related to a positive growth-dependent increase in allocation to energy reserves when approaching winter. Mechanisms regulating within-season temporal dynamics of growth rates are therefore suggested to be important for overall cohort performance.