GROWTH-RATE RELATED TO GENOTYPE OF 0-GROUP COD AT 3 ENVIRONMENTAL TEMPERATURES

Growth rates of cod of an initial weight of about one gram were studied at three environmental temperatures (6, 10, and 14-degrees-C) for about 70 days. Samples of all three groups of fish were genotyped for haemoglobin and several tissue enzymes by agar or starch gel electrophoresis. Size at termination of the experiment, regarded to represent individual growth rate, was studied separately for frequent genotypes within temperature groups. No clear associations between mean growth rate and genotypes of the enzymes LDH or PGI were found at any temperature. However, fish of the genotype Hb-I(2/2) showed the highest mean growth rate regardless of environmental temperature, and fish of genotype Hb-I(1/1) grew on average slowest at the two higher temperatures. This observation was partly in contrast to earlier findings indicating that the performance of the different genotypes is temperature dependent, with Hb-I(2/2) as the more efficient at lowest temperatures.