Delayed gametogenesis and spawning in rainbow trout (Salmo gairdneri) kept under permanent light during the first and second reproductive cycles

Male and female rainbow trout in their first reproductive cycle were subjected to long days (16L : 8D; 24L : 0D and 16L : 8D shifting progressively to 24L : 0D within 6 months). All the fish were maintained at ambient temperatures of between 3 and 16°C. Mean ovulation and spermiation times were 2 months later in the long-day group than in the control group, and ovulation and onset of spermiation were spread over a long period. The quantity and quality of the sexual products obtained were comparable in all groups. In subsequent experiments with the female groups, 50% of the females kept for the first time under permanent light ovulated or were about to ovulate 1–2 months later than the controls. All females initially kept in LD during the first cycle also showed delayed ovulation but only a few ovulated. In the ovaries of ovulated and non-ovulated females, small vitellogenetic oocytes were found, indicating abnormalities in recruitment. Fish exposed for the first time to long days showed a delay in spawning but had normal ovulation.