IS PHYSIOLOGICAL HYPOXIA THE DRIVING-FORCE BEHIND TEMPERATURE EFFECTSON MUSCLE DEVELOPMENT IN EMBRYONIC ATLANTIC SALMON (SALMO-SALAR L)

Atlantic salmon embryos raised at a higher temperature than normal exh ibit, in addition to accelerated growth and development, proportionate ly less muscle fibre hyperplasia and proportionately more fibre hypert rophy in their presumptive white muscle tissue. The egg capsule combin ed with the perivitelline fluid represents an oxygen barrier and may c ontain metabolic by-products within the egg. The effect of removing th is barrier, and thus oxygen restriction, on the development of muscle cellularity in embryonic salmon was therefore investigated in this stu dy. It was found that the presence of the chorion has a distinct effec t. Fibre hyperplasia was found to be influenced by temperature only in the presence of the egg capsule when total fibre numbers were 15% hig her at 6.5 degrees C than at 11 degrees C. Fibre hypertrophy was incre ased at the higher temperature in the chorionated embryos leading to t he average white fibre cross-sectional area being approximately 30% bi gger. The opposite effect was found in dechorionated embryos which sho wed a bigger average white fibre cross-sectional area by approximately 30% at the lower temperature. These differences in the effect of temp erature on muscle cellularity in embryonic Atlantic salmon grown withi n or without the chorion may be explained by a higher oxygen demand co mbined with restricted oxygen availability at the higher temperature. The difference may thus be due to physiological hypoxia at increased t emperatures. This is supported by findings on the immediate posthatch growth when the restriction on fibre hyperplasia at the higher tempera ture appeared to be removed. Total white muscle cross-sectional areas and fish lengths were analysed as general growth parameters.