Comparison of growth rate among different protein genotypes in Atlantic cod, Gadus morhua, under farmed conditions

A major aim of the aquaculture industry in Norway is to develop sustainable farming of Atlantic cod, Gadus morhua L. A great deal of research, including farming trials and stock enhancement, has been performed on this species in Norway during the past two decades. The success of domestication of a new species depends on the genetic variability of the wild broodstock and the selection of appropriate genotypes for the farming environment. Growth experiments under farmed conditions, including genetic analyses, were started as early as 1983 after the breakthrough of cod juvenile production in mesocosm systems. At later stages (1988 and 1992 year classes), more detailed studies were conducted under farmed conditions. Based on individual tagging and genotyping (blood and white muscle biopsy sampling), estimates of growth performance (specific growth rate, SGR) of the various genotypes within six polymorphic protein loci were obtained. In general, the SGR in the two experiments varied through the year as a function of temperature and body size. In the 1988 year-class experiment, only a few statistically significant differences (ANOVA) were detected among genotypes, measured as mean weight and SGR. The 1992 year-class experiment included two different cod stocks, Northeast Arctic (NE) and Norwegian coastal (NC) cod, which were reared for about two years in the same net pen. Further, during this experiment, only a few genotypes exhibited significantly different growth within the NE group. No consistency was found in the variation with regard to protein loci investigated, growth periods studied, and relationship with temperature variation.