OXYGEN AVAILABILITY AND TEMPERATURE AFFECT EMBRYONIC MUSCLE DEVELOPMENT IN ATLANTIC SALMON (SALMO-SALAR L)

In Atlantic salmon, muscle fibre hypertrophy (increase in fibre cross- sectional area) and muscle fibre hyperplasia (increase in muscle fibre number) are differentially affected by the incubation temperature dur ing embryonic development. This affects muscle cellularity (number and mean cross-sectional area of the fibres) at hatching and can affect p osthatch growth. When the egg capsule, an oxygen barrier, is removed t emperature has a different effect on muscle cellularity. Oxygen levels may thus play a role in the muscle development of late embryos. The e ffect of different oxygen levels (50%, 100% and 150% air saturation le vel) and temperatures (5 degrees C and 10 degrees C) during late embry onic development on the muscle cellularity at a developmental stage ju st before hatching was therefore investigated. Fibre numbers at 100% a ir saturation were 17% lower at 10 degrees C in the presence of the eg g capsule (chorionated) whereas no difference between temperature regi mes was found in its absence (dechorionated). Under low oxygen conditi ons a reduction in fibre numbers (-12%) was found at 5 degrees C in ch orionated embryos, whereas no effect was found in the dechorionated gr oups. Muscle fibre cross-sectional area was affected also by oxygen le vels with lowered O-2 leading to a reduction. An increase in temperatu re also led to a reduction in fibre cross-sectional area. Furthermore, nuclear numbers in the presumptive white muscle were strongly affecte d. Removal of the egg capsule caused an increase in nuclear numbers at both temperatures (5 degrees C: +40%, 10 degrees C: +70%). The oxygen level only affected nuclear numbers at 10 degrees C: an increase of 4 6% was found at the increased O-2 level in chorionated embryos, wherea s a reduction by 26% was observed at the low O-2 level in the dechorio nated group. O-2 levels therefore clearly affected muscle cellularity in a temperature-dependent way. Overall the results suggest that O-2 a vailability is a significant contributing factor to temperature effect s during late muscle development in Atlantic salmon embryos.