Growth, feed utilization and growth heterogeneity in juvenile turbot Scophthalmus maximus (Rafinesque) under different photoperiod regimes |
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| Authors: | M Ö Stefánsson R D FitzGerald & T F Cross |
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| Institution: | Aquaculture Development Centre, Department of Zoology and Animal Ecology, National University of Ireland, Cork, Ireland |
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| Abstract: | Juvenile turbot (45 g, 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?1) was higher for the 20L:04D (FI = 0.81% d?1, SE = 0.06) treatment than for the 08L:16D (0.63% d?1, 0.04) and 12L:12D (0.64% d?1 0.04) treatments, whereas feed conversion efficiency (FCE = weight gain* consumption?1) 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. |
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| Keywords: | growth feed utilization dominance hierarchies photoperiod manipulation juvenile turbot Scophthalmus maximus (Rafinesque) |
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