VARIATIONS IN FEED-INTAKE AND GROWTH OF BALTIC SALMON AND BROWN TROUTEXPOSED TO CONTINUOUS LIGHT AT CONSTANT LOW-TEMPERATURE

Interindividual variations in feed intake and growth were studied in B altic salmon Salmo salar and brown trout S. trutta, held under constan t low temperatures of 2, 4 or 6 degrees C and continuous light for 2 m onths. Rates of feed intake and growth were dependent upon rearing tem perature, being lowest at 2 degrees C and highest at 6 degrees C. Furt her, feed intake and growth were initially low, but increased during t he course of the experiment in both species and at all temperatures. T hese results suggest that acclimatization to the rearing conditions ma y have required several weeks. The increase in group mean feed intake with time was the result of both an increase in the proportions of fis h that fed and an increase in feed intake amongst feeding fish. At the same time as feeding and growth rates increased, interindividual vari ations in feed intake and growth tended to decrease, suggesting that i ndividual fish were acclimatizing to the new rearing conditions at dif ferent rates. Thus, the differences in group mean feed intake and grow th rates observed at a given temperature reflected interindividual var iations among fish making up the groups. This suggests that group rate s of feed intake and growth are not only temperature-dependent, but th at they are also highly influenced by variability among fish making up the group. (C) 1997 The Fisheries Society of the British Isles.