Growth and age at first maturity in turbot and halibut reared under different photoperiods |
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| Authors: | Albert K Imsland Thor M Jonassen |
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| Institution: | 1. Akvaplan-niva, Iceland Office, Akralind 4, 201, Kópavogur, Iceland
2. Stolt Sea Farm ASA, Bredalsmarken 15/17, 5836, M?hlenpris, Bergen, Norway
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| 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 Hippoglossus hippoglossus and in 114 (50 females and 64 males) individually tagged turbot Scophthalmus maximus. The halibut were reared at 11 °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 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. The turbot were reared at 16 °C on three different light
regimes: constant light (LD24:0), 16 h light:8 h darkness (LD16:8), or simulated natural photoperiod (LDN). After 6 months
on the different photoperiods, the turbot was reared together on LDN for approximately 12 months until first maturation. Juveniles
subjected to continuous light (halibut) or extended photoperiods (halibut and turbot) exhibited faster growth than those experiencing
a natural photoperiod or a constant short day. Moreover, when the photoperiod increased naturally with day-length or when
fish were abruptly switched from being reared on short-day conditions to continuous light, a subsequent increase in growth
rate was observed. This growth enhancing effect of extended photoperiods was more apparent on a short time scale in Atlantic
halibut than in turbot, but both species show significant long-term effects of extended photoperiods in the form of enhanced
growth. In both species lower maturation of males was seen in groups exposed to extended or continuous light compared to LDN
and this could be used to reduce precocious maturation in males leading to overall increase in somatic growth.
This revised version was published online in August 2006 with corrections to the Cover Date. |
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| Keywords: | Growth Halibut (Hippoglossus hippoglossus) Maturation Photoperiod Turbot (Scophthalmus maximus) |
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