The interaction of temperature and fish size on growth of juvenile halibut

Growth rate of individually tagged juvenile halibut was influenced signific antly by the interaction of temperature and fish size. The results suggest an optimum temperature for growth of juvenile halibut in the size range 5-7 0 g between 12 and 15 degrees C. Overall growth rate was highest at 13 degr ees C (1.62% day(-1)). At c. 5 g at the beginning of the experiment, fish a t 16 degrees C had the highest growth rate (3.2% day(-1)), but reduced this rate as they grew bigger. At 9 and 11 degrees C, growth rates were equal o r only slightly lower during the later stages of the experiment, while the fish at 6 degrees C showed significantly lower overall growth rate (0.87% d ay(-1)). Optimal temperature for growth decreased rapidly with increasing s ize, indicating an ontogenetic reduction in optimum temperature for growth. Moreover, a more flattened parabolic regression curve between growth and t emperature as size increased indicated reduced temperature dependence with size. Although individual growth rates varied significantly at all times wi thin the experimental temperatures, significant size rank correlations were maintained during the experiment. This indicated an early establishment of a stable size hierarchy within the fish groups. Haematocrit was highest at the highest temperature while Na+/K+-ATPase activity was inversely related to temperature. There was no difference in plasma Na+, Cl- and K+ concentr ations among the temperature groups. (C) 1999 The Fisheries Society of the British Isles.