Comparisons of RNA/DNA ratios, growth, and metabolism in different populations of juvenile turbot Scophthalmus maximus reared at four temperatures

We compared RNA/DNA ratios, growth rind routine oxygen consumption in populations of juvenile turbot from Norway, Scotland, and France reared at low (10 C), medium (14 C, 18 C) and high (22 C) temperatures. The relationships between growth and RNA/DNA ratios differed between temperatures, although they were always positive. Growth and RNA/DNA of the Norwegian fish were higher than those of the other populations especially at the two highest temperatures (18 C and 22 C). Minor differences were found between the Scottish and French populations. Fish from the Norwegian population displayed the lowest oxygen consumption at these temperatures (146 and 270, 182 and 310, 192 and 328 mg O-2/kg per d, for 18 and 22 C, and Norwegian, French, and Scottish populations, respectively). Growth differences did not conform to a simple thermal adaptation model, but might represent an example of countergradient variation in growth. The findings have implications for turbot culture, particularly in selection focusing on growth performance.