Oxygen availability and temperature affect embryonic muscle development in Atlantic salmon ( Salmo salar L.)

Abstract

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 during embryonic development. This affects muscle cellularity (number and mean cross-sectional area of the fibres) at hatching and can affect posthatch growth. When the egg capsule, an oxygen barrier, is removed temperature has a different effect on muscle cellularity. Oxygen levels may thus play a role in the muscle development of late embryos. The effect of different oxygen levels (50%, 100% and 150% air saturation level) and temperatures (5°C and 10°C) during late embryonic development on the muscle cellularity at a developmental stage just before hatching was therefore investigated. Fibre numbers at 100% air saturation were 17% lower at 10°C in the presence of the egg capsule (chorionated) whereas no difference between temperature regimes was found in its absence (dechorionated). Under low oxygen conditions a reduction in fibre numbers (–12%) was found at 5°C in chorionated embryos, whereas no effect was found in the dechorionated groups. Muscle fibre cross-sectional area was affected also by oxygen levels with lowered O 2 leading to a reduction. An increase in temperature also led to a reduction in fibre cross-sectional area. Furthermore, nuclear numbers in the presumptive white muscle were strongly affected. Removal of the egg capsule caused an increase in nuclear numbers at both temperatures (5°C: +40%; 10°C: +70%). The oxygen level only affected nuclear numbers at 10°C: an increase of 46% was found at the increased O 2 level in chorionated embryos, whereas a reduction by 26% was observed at the low O 2 level in the dechorionated group. O 2 levels therefore clearly affected muscle cellularity in a temperature-dependent way. Overall the results suggest that O 2 availability is a significant contributing factor to temperature effects during late muscle development in Atlantic salmon embryos.