Influence of Photoperiod on Growth of Juvenile Atlantic Salmon and Development of Salinity Tolerance during Winter–Spring

Abstract
Underyearling Atlantic salmon Salmo salar were subjected to extended day length beginning in early August or early September; the photoperiod was 18 h light and 6 h darkness (LD 18:6) during August-October (A–O), September-October (S–O), and September–November (S–N). A control group experienced simulated natural photoperiod. The LD 18:6 regimes stimulated growth and, by fate October, treatment fish were significantly larger than the controls. The 3-month S–N and A–O regimes promoted growth more effectively than the 2-month S–O regime, Stimulation of growth from August through October was not as effective as that from September through November. Thus, duration (2 versus 3 months) and time of onset of extended day length and return to simulated natural photoperiod appeared to influence photostimulation of growth. Bimodality in length-frequency distribution in the S–O and control groups was clearly developed by mid-December. Photostimulation of growth and continued entry offish into the upper modal ...

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