The emergence rhythm of grayling fry (Thymallus thymallus) was studied under semi-natural rearing conditions, using special traps buried in the gravel. The diel pattern of emergence proved to be mainly diurnal, with a maximum just after sunrise. The discussion emphasizes the fact that this distinguishes the grayling from other salmonids, and since eggs are buried at a reduced depth, proposes the hypothesis that light conditions during development influence the daily pattern of emergence.
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Bardonnet et al. (1990) studied this question.