Effects of size on optimal temperature for growth and growth efficiency of immature Atlantic halibut ( Hippoglossus hippoglossus L.)

Abstract

The aim of this study was to determine the optimal temperature for growth and growth efficiency for different size-classes of immature halibut. In experiment A, lasting for 99 days, six groups of fish of initial mean weight 8 g were reared at 7.3, 10.0, and 12.8 °C, two replicates at each temperature. In experiment B, lasting for 216 days, six groups of fish of initial mean weight 140 g were reared at 5.0, 7.4, 9.0, 11.1, 13.0, and 14.9 °C. In experiment C, lasting for 189 days, six groups of fish of initial mean weight 2.9 kg were reared at 2.4, 4.6, 7.0, 9.8, 12.6, and 15.1 °C. The halibut were fed dry feed in experiments A and B, and fish (capelin and herring) in experiment C. In all three experiments growth rate and growth efficiency peaked at intermediate temperatures. Optimal temperature for growth decreased with increasing fish size, being approximately 14 °C for 10–60 g fish, 11.4 °C for 100–500 g fish and 9.7 °C for 3–5 kg fish. Optimal temperature for growth efficiency also decreased with increasing fish size, being approximately 14 °C for 10–60 g fish, 10.6 °C for 100–500 g fish and 5.5 °C for 3–5 kg fish. The dome-shaped relationships of growth rate and growth efficiency versus temperature became flatter with increased size of fish, suggesting that thermal sensitivity close to the optimum decreases as fish size increases.