INFLUENCE OF PREHATCH TEMPERATURE ON THE DEVELOPMENT OF MUSCLE CELLULARITY IN POSTHATCH ATLANTIC SALMON (SALMO-SALAR)

Previous work has shown that higher incubation temperatures produce ne wly hatched salmon (Salmo salar) with fewer but larger muscle fibres t han salmon incubated at colder temperatures. Our purpose was to study the effect of differing incubation temperatures on the development of muscle cellularity in posthatch salmon. Eggs from a single pair of Atl antic salmon were incubated at either the stream ambient temperature ( fluctuating around 5 degrees C prehatch and gradually rising to around 10 degrees C posthatch) or at 11 degrees C. From each group, samples were taken at hatching, first feeding, and at 3 weeks after first feed ing. During the period of exogenous feeding under study, the ambient g roup grew faster. The number of muscle fibres remained lower in the 11 degrees C fish but there was more muscle fibre hypertrophy in the amb ient group so that the difference in muscle fibre size seen at hatchin g was eliminated by 3 weeks after first feeding. It is suggested that reduced number of nuclei in the 11 degrees C fish at hatching may cont ribute to the relatively reduced fibre hypertrophy in these fish. The results indicate that embryonic myogenesis can affect the posthatch gr owth of salmon at least up to 3 weeks after first feeding.