Influence of photoperiod and temperature on hatching and emergence of Baltic salmon (Salmo salar L.)

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Abstract
The influence of photoperiod and temperature on hatching and emergence of Salmo salar L. was studied experimentally. Eggs were taken from a hatchery-reared Umeälven (Ume River) stock in northern Sweden (63°50′ N, 20°05′ E). Eggs kept in a light regime of 16L: 8D hatched mainly during the light period while eggs kept under conditions of no light hatched continuously over a 24-h period. Emergence of alevins from simulated redds kept under different LD regimes (light > 4 h) was well synchronized with the dark periods: the largest number of alevins left the gravel during the 1st h of darkness. In continuous darkness alevins exhibited a tendency for a persistent emergence pattern, i.e., the pattern resembled the photoperiod cycle to which they were previously exposed. Neither the length of the yolk sac phase nor the length of the emergence period among alevins was affected by photoperiod. In cold water (6.0 and 11.5 °C) emergence was mainly nocturnal. At high temperature (14.5 °C) the diel pattern of emergence switched and a major proportion of alevins left the gravel during the hours of light. In addition, at high temperatures the alevins spent a shorter time in the substrate and emerged during a short period of time compared with alevins emerging in cold water. The ecological implications of the influence of ambient temperature and photoperiod on emergence are discussed.