Countergradient variation in growth and food conversion efficiency of juvenile turbot


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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 (Topt.G, ±S.E.) (23·0±0·9°C) and food conversion efficiency (Topt.Ec) (17·5±0·3), followed by the French (Topt.G 21·1±1·0; Topt.Ec, 16·7±0·1) population, whereas the Scottish population had the lowest optimum (Topt.G, 19·6±0·6; Topt 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.