In the present study, polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) and restriction fragment length polymorphism (RFLP) methods were compared to analyze the polymorphism of growth hormone receptor (GHR) gene in French, Iranian and Danish strains of Oncorhynchus mykiss. A monomorphic SSCP pattern of AA genotype in the French and Iranian strains and a dimorphic AA and AB genotype in the Danish strain were observed in 3' non-coding regions of GHR gene. In the Danish strain, the AB genotype polymorphism of the GHR gene with its very low frequency (5%) has no effect on the production trait. While, RFLP-Dde1 showed no polymorphism with genetic variation in the location of GHR. Moreover, comparing the condition factors (K) of three different rainbow trout strains showed a significant correlation between the French (1.312 ± 0.13), Iranian (1.245 ± 0.17) and Danish strains (0.763 ± 0.1), respectively (p<0.05). In particular, the French strain obtained a higher K compared to the two others. The length-weight relationship is shown by the following equations W= 0.013 × L2.921, W= 0.012 ×L3.023 and W= 0.007 × L3.176 for French, Iranian and Danish strains, respectively. With the mean (b= 2.921), the studied French strain exhibited a negative allometric growth b<3 while the Iranian (b=3.023) and the Danish (b=3.176) showed positive allometric growths. Regardless of the underlying mechanism(s) responsible for the different relationships, the results of this study suggested that the AA and AB genotypes polymorphism of the GHR gene are not associated with condition factor and environmental variables can influence condition factor and length-weight relationship of rainbow trout strains in this study.