LIGHT-INTENSITY AFFECTS GROWTH AND SEXUAL-MATURATION OF ATLANTIC SALMON (SALMO-SALAR) POSTSMOLTS IN SEA CAGES

The aim of the present study is to test the extent to which different intensities of continuous additional light affect somatic growth and s exual maturation in Atlantic salmon postsmolts in sea cages. Postsmolt s (9 200 individuals) were randomly distributed among four commercial sized sea cages and exposed to either natural light or natural light continuous additional light of low, medium or high intensity from Jan uary to June. In May the high light intensity group had a significantl y higher mean live body weight than the other groups, and at the end o f the experiment in June, all groups differed in mean gutted weight. T here was a positive logarithmic regression between level of light inte nsity exposure during night and mean gutted weight. A small proportion of fish matured sexually (after 1.5 years in seawater) in the natural light group, whereas no maturation was detected in the light groups. These results suggests that to affect growth and proportion of maturat ion in Atlantic salmon by additional light, there might be different t hreshold values of light intensity.