Temperature and family effects on muscle cellularity at hatch and first feeding in Atlantic salmon (Salmo salarL.)

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Abstract
Muscle cellularity was investigated in alevins from five families of Atlantic salmon (Salmo salar L.) reared at variable ambient temperatures averaging 4.3 °C and in water heated to ca. 8 °C. At hatch, fish reared at 8 °C had fewer muscle fibres and myonuclei per myotome and lower mean fibre cross-sectional areas than fish reared at ambient temperature. The total cross-sectional area of white muscle was 40% less in the group reared at 8 °C than in the group reared at ambient temperature. Muscle cellularity and response to temperature varied among families and there was evidence of interactions with temperature and developmental stage. The number of red and white muscle fibres approximately doubled between hatch and first feeding. At hatch, red muscle fibres stained with an antibody to fast myosin light chains, but expression was gradually switched off as development proceeded. Following hatch, alevins reared at 8 °C were more effective in translating yolk into muscle than those reared at ambient temperature, so towards the end of yolk resorption there were no significant differences in fibre number or cross-sectional area.