EFFECTS OF TEMPERATURE ON GROWTH AND METABOLISM IN JUVENILE TURBOT

The effects of constant temperatures on growth, food efficiency, and p hysiological status were studied in four different batches of juvenile turbot. The growth responses were studied in three experiments lastin g 70-85 days under 8-20 degrees C thermal conditions. There was a posi tive correlation between growth and temperature from 8 to 17 degrees C and a plateau was observed from 17 to 20 degrees C. In fish fed to sa tiety, specific growth rate was positively correlated to the food inta ke, which was double at 20 degrees C, compared with 8 degrees C. Minor changes were observed in food efficiency. Body fat deposition decreas ed as temperature increased (25% lower at 20 degrees C, compared with 8 degrees C). Apparent food conversion, PER (protein efficiency ratio) and PUC (protein utilization coefficient) ranges were 0.8-0.9, 2.1-2. 3 and 33-38% respectively. In 70-300 g fish, routine MO(2) increased ( 2.5-6.5 mu mol O-2 h(-1) g bw(-1)) with temperature up to 20 degrees C , while larger turbot (500-600 g) appeared relatively thermo-independe nt, with a lower oxygen consumption (1.5 mu mol h(-1) g(-1)). The aver age daily total ammonia nitrogen (TAN) and urea-N excretion per fish b iomass was positively related to temperature. TAN was 30% lower at 8 d egrees C, compared with 20 degrees C. Ingested nitrogen was mainly exc reted under the final form of TAN, urea-N representing 26% of the tota l amount. A post-prandial peak in TAN and a delayed peak in urea-N nit rogen were observed. The hydromineral status [osmolarity, sodium, chlo ride and potassium blood plasma, gill (Na+-K+)-ATPase activity] of tur bot was not affected by progressive changes in temperature during the acclimation period. Juvenile turbots show remarkable homeostatic capac ities and so they have a relatively thermo-independent physiology with in the range of temperature studied. (C) 1996 The Fisheries Society of the British Isles