Exposure to continuous light inhibits maturation in turbot (Scophthalmus maximus)

Abstract

Abstract Individually tagged female turbot that had been kept in captivity for 6 years were reared in two 4 m 2 tanks at 12 °C. The fish had been reared under simulated natural photoperiod (LDN) from hatching (1991) and until the start of the experiment. In March 1997, the fish were exposed to two photoperiod regimes. One group remained on LDN, and one group was transferred to continuous light (LDN/LD24:0). Female turbot reared under natural photoperiod spawned in the period between June and August the following summer (1997). Exposure to continuous light reduced the proportion of maturing females, spawning was delayed for 4 weeks, individual spawning frequency was lower (2.6 compared to 5.3 in the LDN group) and egg production was reduced by 90% (545 g compared to 5645 g in the LDN group). Maturing females in both experimental groups had significantly lower growth compared to non-maturing females. It is concluded that exposure to continuous light around spring equinox can significantly decrease and delay maturation in adult turbot.