Tw. Matschak et al., IS PHYSIOLOGICAL HYPOXIA THE DRIVING-FORCE BEHIND TEMPERATURE EFFECTSON MUSCLE DEVELOPMENT IN EMBRYONIC ATLANTIC SALMON (SALMO-SALAR L), Differentiation, 59(2), 1995, pp. 71-77
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.