First feeding of Atlantic salmon, Salmo salar L., under different photoperiods and light intensities

Abstract

. First feeding fry of Atlantic salmon, Salmo salar L., were reared under four experimental light regimes from mid-June until mid-September. One group was reared under a simulated natural photoperiod 4 months out of phase, with initial daylength in mid-June corresponding to natural daylength in mid-February. Two groups were reared under continuous light of either low (27 lux) or high (1400 lux) intensity. The fourth group received a dual photoperiod combining a continuous, low intensity (27 lux) background illumination and a superimposed simulated natural photoperiod phase adjusted according to the natural photoperiod group. Growth rate and survival was higher during the first 3 weeks under continuous light or dual photoperiod than under the phase adjusted simulated natural photoperiod. This could partly be due to the restricted feeding time during the initial short daylength of the simulated natural photoperiod, and partly to a photostimulation of growth in groups reared under the continuous light regimes. Fish reared under a simulated natural photoperiod migrated vertically during the 24-hour cycle. The same behaviour was seen, though not as ctearly, in the fish reared under a dual photoperiod. Changes in light intensity appeared to be the primary releasing factor for the vertical migration observed. The fish reared under continuous light showed no diurnal vertical migration. Acknowledgments The authors would like to thank Dr Gunnar Naevdal and Dr Lars Petter Hansen for helpful suggestions and criticism of the manuscript. We also thank the staff at Matre Aquaculture Station for skilled assistance during the experiment. This study was financed by the Norwegian Fisheries Research Council (NFFR V.701.146).