Countergradient variation in growth and food conversion efficiency of juvenile turbot

Growth performance of a high latitude (Norway) population of juvenile turbot Scophthalmus maximus was superior to that of two other lower latitude populations (Scotland, France) especially at 18°and 22°C. Overall these results lend some support to the hypothesis of countergradient variation in growth. The Norwegian population had the highest estimated temperature optimum for growth (T(opt. G) ± S.E.) (23·0 ± 0·9°C) and food conversion efficiency (T(opt. Ec)) (17·5 ± 0·3), followed by the French (T(opt. G), 21·1 ± 1·0; T(opt. Ec) 16·7 ± 0·1) population, whereas the Scottish population had the lowest optimum (T(opt. G), 19·64±0·6; T(opt. Ec), 16·5 ± 0·1°C). These results have two major implications: firstly, for turbot culture, particularly in selection work focusing on growth performance; secondly, if countergradient variation in growth performance takes place within a species one cannot assume automatically that one set of physiological parameters, in this case growth-related parameters, is satisfactory to predict growth for a species throughout its range as different populations might show a difference in response towards different physiological parameters. (C) 2000 The Fisheries Society of the British Isles.