Effects of Photoperiod, Temperature, and Diet on the Reconditioning Response, Blood Chemistry, and Gonad Maturation of Atlantic Salmon Kelts (Salmo salar) Held in Freshwater

Abstract

Changes in feeding behavior, rate of reconditioning, gonadal development, and maturation were investigated together with changes in plasma electrolytes, triglycerides, cholesterol, protein, and alkaline phosphatase in female Atlantic salmon kelts (Salmo salar) exposed to advanced and simulated natural photoperiods and warmer and natural water temperatures. Natural photoperiod cycles at natural and 12 °C temperatures were most stimulatory for feeding behavior, reconditioning, gonadal development, and maturation. Advancing photoperiod only slightly stimulated gametogenesis at 12 °C whereas at low temperature, vitellogenesis did not proceed and oocyte maturation did not occur. In all regimes, early reconditioning was associated with gonadal maturation. The levels of calcium, triglycerides, and alkaline phosphatase were markedly elevated in spawners and were coincident with temperature and photoperiod manipulation. No similar change occurred in nonspawners. Ovulation occurred earliest in the advanced photoperiod and 12 °C temperature regime, suggesting an effect of both temperature and photoperiod on the rate of gonadal maturation. The factors influencing egg production and maturation in Atlantic salmon kelts are also discussed.