Genotypic response to photoperiod treatment in Atlantic cod (Gadus Morhua)

Interactions between environment and genotype in individually tagged Atlantic cod juveniles (initial weight 9.1 g) were studied. Juvenile cod were reared for 3 months under simulated natural photoperiod (LDN) and continuous light (LD24:0) at 10 degrees C and 13 degrees C. At the end of the trial blood samples were taken from all fish and used to classify the fish according to their haemoglobin genotypes into three groups, Hb-I(1/1), Hb-I(1/2)and Hb-I(2/2). Individual growth trajectories and specific growth rate were studied in order to investigate whether these growth responses to extended photoperiods are genotype dependent. Continuous light enhanced growth at both temperatures. However, a significant interaction between genotypes and photoperiods was found at both temperatures, demonstrated by the variation in genotype response towards photoperiod treatment. At both temperatures the highest growth rates were found for Hb-I(2/2) at LD24:0, whereas the lowest overall mean growth rates were found for the same genotype reared at LDN. Conversely, the Hb-I(1/1) genotype displayed the fastest specific growth rates in the LDN groups at both temperatures. (C) 2005 Elsevier B.V. All rights reserved.