The reproductive cycle of reconditioned Atlantic salmon can be manipulated with light and temperature. Wild Atlantic salmon (Salmo salar) kelts held in freshwater and exposed from late December 1986 to a simulated natural photoperiod (NP) and a regime of two 6-mo seasonally accelerated light increases and decreases (2CP) reconditioned. Fifty-six percent of NP females spawned by early November 1987, 1 mo later than virgin wild females. No 2CP females spawned by December 1987. However, all 2CP females transferred in December 1987 to natural photoperiod and 7 °C water released eggs by June 1988. NP females that spawned showed seasonal peaks in cholesterol in August, triglycerides and calcium in September, and alkaline phosphatase in November; NP and 2CP females that failed to spawn showed no such changes. Alkaline phosphatase activity and calcium concentrations were linearly related to increasing oocyte diameter (but not oocyte number), and were good predictors of sex and oocyte development. Forty-two percent of 2CP males matured and released sperm in mid-August, 1 mo earlier than NP males or a virgin wild group. Twenty-three percent of 2CP males did not mature. Males showed significant differences in blood parameters between regimes and between spawners and nonspawners, but the levels were never as high as maturing females.
Atlantic salmon (Salmo salar) kelts exposed to a regime of two 6-mo seasonally accelerated light increases and decreases (2CP) in 1989 spawned in the spring of 1990 when water temperatures were above 7 °C during the winter months. Kelts exposed to water temperatures below 4 °C during the same period failed to spawn in the spring. Exposure of the nonspawning 2CP kelts to warmer water temperatures in the summer of 1990 stimulated egg development and ovulation by 17 October 1990. Kelts exposed to a simulated natural 12-mo photoperiod regime also spawned at this time. Eggs and sperm from kelts spawned in the spring were viable. Spring-spawned eggs fertilized with fresh sperm had lower survival levels to the eyed-egg stage or to hatch than did eggs from wild fall-spawned stocks. Kelts entrained to spawn in the spring with 2CP photocycles were manipulated to spawn again in the spring of the next year following exposure to a time-shifted photoperiod and elevated winter/spring water temperature.
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