Feeding and growth of whitefish fed restricted and abundant rations: influences on growth heterogeneity and brain serotonergic activity

The whitefish, Coregonus lavaretus, is a schooling species, and it was hypo thesized that, when faced with feed restriction, the behaviours associated with a schooling habit would lead to there being less heterogeneity in feed ing and growth than has been observed in other members of the Salmonidae. T his was tested by monitoring the feeding, growth and brain serotonergic act ivity of whitefish subjected to different levels of feed restriction (full rations and regimes estimated to give a 25 and 50% reduction in growth rate ). The feed restrictions were successful in reducing rates of feeding and g rowth, but these reductions were not accompanied by any marked increases in interindividual variations in either feed intake or growth rates. Conseque ntly, the imposition of restricted feeding regimes did not result in an inc rease in the size variation of fish within rearing tanks. Further, the brai n serotonergic activity (assessed as 5-HIAA : 5-HT ratio) of individual fis h was not found to correlate with either their feed intake or growth rates. This suggests that any competition resulting from restricted feeding did n ot lead to the establishment of marked dominance-subordination relationship s. 5-HIAA:5-HT ratios were, however, higher amongst fish fed the most restr icted rations than in fish of the other groups. This may have been a reflec tion of a general nutritional stress rather than pointing to an increase in social conflict amongst the fish fed the lowest rations. When provided wit h abundant rations the fish that had been feed-restricted responded by beco ming hyperphagic and showing catch-up growth, the degree of compensation be ing related to the severity of the previous food restriction. Taken togethe r the results suggest that restricted feeding may be a suitable method for controlling rates of production of whitefish, without there being a high ri sk of a marked increase in size variation with the passage of time. (C) 199 9 The Fisheries Society of the British Isles.