Incubation of the Eggs of Atlantic Salmon, Salmo salar, at Low Temperatures

Eggs of Atlantic salmon (Salmo salar) from the River Alta in northern Norway were subjected to three experimental temperature regimes during prehatching incubation. Two of these were intended to simulate possible temperature situations in the river after hydroelectrical development of its upper reaches. The third temperature regime was that of the natural river. The results indicated that hydroelectrical development of the Alta may lead to an earlier hatch of the salmon embryos in the river. Incubation time, and perhaps also a "trigger" such as rising temperature, may be more important than the heat sum (degree-days) of the incubation period in determining the exact timing of the hatch.