Growth and age at first maturity in turbot and halibut reared under different photoperiods
A.K. Imsland, T.M.
Jonassen-2003
Aquaculture International, 11(5):
463-475
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.
(Akvaplan-niva,
Iceland Office, Akralind 4, 201 Kópavogur,
Iceland, tel: +354 562 5800; fax: +354 564 5801, e-mail: albert.imsland@akvaplan.niva.no)