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Probability of survival in nature for underyearling brown trout is affected by individual traits that vary within a population. We found evidence for a consistent individual activity level that was positively associated with survival both at different time periods and in different streams. In fish fry, high activity may instead be of great importance for efficient foraging tactics and predator avoidance. However, further studies are needed to investigate if the positive association between activity and survival are consistent in different environmental contexts.

Fish length was positively associated with survival in one of the experiments. This was during the first experimental period which indicates a shift in selection pressure on body size. A potential explanation is that increasing fish size decreases the number of potential predators.  

Fish that experienced growth depression were not able to compensate in body structure. Since the importance of body size for survival decreased over time compensation might not be an efficient strategy for the fry due to the cost of higher growth rates. Furthermore the growth rate for the fry is already very high, possibly close to maximum, which makes growth compensation a much longer process.

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Last updated: 06/04/14