Effect of small rises in temperature on the mortality and growth of I-group plaice (Pleuronectes platessa L.)

An investigation was carried out with I-group plaice in water with naturally fluctuating temperature and also at 10, 20, 40 and 60C above the natural temperature. In the aquarium with natural temperature, water from a depth of 20m was used, while water from 75m was used in the other aquaria. The plaice were fed daily with a surplus of mussels. The mortality in temperatures up to about 150C was very small, but increased rapidly at higher temperatures. When the natural temperature was 60C a temperature increase of 10C was enough to give a significantly greater growth rate. A temperature difference of 1-20C with a higher natural temperature did not, however, give a significantly greater growth rate in the same period. Optimal growth was found to occur at 10-120C, while maximum food consumption took place at 14-150C. At optimal growth the plaice consumed about 8g of mussel per gram growth. Above 14-150C the plaice were not able to convert fodder to growth. (JIW)