The relation between age at first maturity and growth in Atlantic halibut (Hippoglossus hippoglossus) reared at four different light regimes

Abstract

The effect of extended photoperiods on growth and age at first maturity was investigated in 166 (79 females and 87 males) individually tagged Atlantic halibut. The halibut were reared at 11 degrees C on four different light regimes from 10 February to 6 July 1996: simulated natural photoperiod, (LDN), continuous light (LD24:0), constant 8 h light and 16 h darkness (LD8:16) and LD8:16 switched to continuous light on 4 May 1996 (LD8:16-24:0). From 6 July 1996 to 9 February 1998 the LD24:0 and LD8:16-24:0 were reared together under continuous light and the LDN and LD8:16 together under natural photoperiod. Juveniles subjected to continuous light exhibited faster growth than those experiencing a natural photoperiod or a constant short day. Moreover, the results suggest an overall growth enhancing effect of continuous light in females, but not in males. No females matured during the trial, but the proportion of mature males differed between the photoperiod groups, with significantly fewer males maturing in groups reared at continuous light. Independent of photoperiod regime and maturation status, females were significantly bigger than males from 14 April 1997 onwards. Immature males were bigger than maturing males from 23 March 1996 onwards. As continuous light reduced maturation at age 2+ in males, this could be used to reduce precocious maturation in males.