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

Atlantic salmon embryos raised at a higher temperature than normal exhibit, in addition to accelerated growth and development, proportionately less muscle fibre hyperplasia and proportionately more fibre hypertrophy in their presumptive white muscle tissue. The egg capsule combined with the perivitelline fluid represents an oxygen barrier and may contain metabolic by-products within the egg. The effect of removing this barrier, and thus oxygen restriction, on the development of muscle cellularity in embryonic salmon was therefore investigated in this study. It was found that the presence of the chorion has a distinct effect. Fibre hyperplasia was found to be influenced by temperature only in the presence of the egg capsule when total fibre numbers were 15% higher at 6.5 degrees C than at 11 degrees C. Fibre hypertrophy was increased at the higher temperature in the chorionated embryos leading to the average white fibre cross-sectional area being approximately 30% bigger. The opposite effect was found in dechorionated embryos which showed a bigger average white fibre cross-sectional area by approximately 30% at the lower temperature. These differences in the effect of temperature on muscle cellularity in embryonic Atlantic salmon grown within or without the chorion may be explained by a higher oxygen demand combined with restricted oxygen availability at the higher temperature. The difference may thus be due to physiological hypoxia at increased temperatures. This is supported by findings on the immediate posthatch growth when the restriction on fibre hyperplasia at the higher temperature appeared to be removed. Total white muscle cross-sectional areas and fish lengths were analysed as general growth parameters.