Countergradient variation in growth and food conversion efficiency of juvenile turbot

Growth performance of a high latitude (Norway) population of juvenile turbo t Scophthalmus maximus was superior to that of two other lower latitude pop ulations (Scotland, France) especially at 18 degrees and 22 degreesC. Overa ll these results lend some support to the hypothesis of countergradient var iation in growth. The Norwegian population had the highest estimated temper ature optimum for growth (T-opt.G +/- S.E.) (23.0 +/- 0.9 degrees C) and fo od 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 Scot tish population had the lowest optimum (T-opt.G, 19.6 +/- 0.6; T-opt.Ec, 16 .5 +/- 0.1 degreesC). These results have two major implications: firstly, f or turbot culture, particularly in selection work focusing on growth perfor mance; secondly, if countergradient variation in growth performance takes p lace within a species one cannot assume automatically that one set of physi ological parameters, in this case growth-related parameters, is satisfactor y to predict growth for a species throughout its range as different populat ions might show a difference in response towards different physiological pa rameters. (C) 2000 The Fisheries Society of the British Isles.