Growth, feed
utilization and growth heterogeneity in juvenile turbot Scophthalmus
maximus (Rafinesque) under different photoperiod regimes
M.Ö. Stefánsson, R.D. FitzGerald, T.F.
Cross-2002
Aquaculture
Research, 33(3):
177-188
Abstract:
Juvenile turbot (45g, SE=1.3) were reared
under three photoperiods, 08L:16D, 12L:12D and 20L:04D at slightly elevated
ambient temperature for Ireland. Over the 297-day experimental period, the
overall growth rate of the 12L:12D (0.82% d-1) treatment was
higher than for both 08L:16D (0.80% d-1) and 20L:04D (0.77% d-1).
Overall relative feed intake (FI=% consumption/day) was higher for the
20L:04D (FI=0.8%/d, SE=0.06) treatment than for the 08L:16D (0.63%/d, 0.04)
and 12L:12D (0.64% d-1 0.04) treatments, whereas feed conversion
efficiency (FCE=weight gain/consumption) was lower in the 20L:04D (FCE=0.67,
SE=0.08) group when compared with the 08L:16D (0.88, 0.06) and 12L:12D
(0.88, 0.06) treatments. Present results show that the long-term extended
fixed photoperiod may act as an irritant, inducing stress, suppressing
growth and reducing feed utilization. It is hypothesized that the
progression of size-dependent hierarchies over time can be divided into two
distinct phases herein referred to as ‘hierarchy resolution’ and
‘hierarchy stabilization’ phases (or phases 1 and 2) characterized by
increasing and decreasing growth heterogeneity respectively. Growth
heterogeneity is measured as coefficient of variation of weight and rank
correlation of initial weight of a phase and corresponding growth rate.
(Aquaculture Development Centre,
Department of Zoology and Animal Ecology, National University of Ireland,
Cork, Ireland
E-mail: magnuss@iti.is)