TEMPERATURE AND FAMILY EFFECTS ON MUSCLE CELLULARITY AT HATCH AND FIRST FEEDING IN ATLANTIC-SALMON (SALMO-SALAR L)

Muscle cellularity was investigated in alevins from five families of A tlantic salmon (Salmo salar L.) reared at variable ambient temperature s averaging 4.3 degrees C and in water heated to ca. 8 degrees C. At h atch, fish reared at 8 degrees C had fewer muscle fibres and myonuclei per myotome and lower mean fibre cross-sectional areas than fish rear ed at ambient temperature. The total cross-sectional area of white mus cle was 40% less in the group reared at 8 degrees C than in the group reared at ambient temperature. Muscle cellularity and response to temp erature varied among families and there was evidence of interactions w ith temperature and developmental stage. The number of red and white m uscle fibres approximately doubled between hatch and first feeding. At hatch, red muscle fibres stained with an antibody to fast myosin ligh t chains, but expression was gradually switched off as development pro ceeded. Following hatch, alevins reared at 8 degrees C were more effec tive in translating yolk into muscle than those reared at ambient temp erature, so towards the end of yolk resorption there were no significa nt differences in fibre number or cross-sectional area.