We evaluated the growth and influence of environmental factors under suspended culture conditions of the mussels Perna perna L. and P. viridis L. and of an undefined variant or morphotype sharing the substrate and morphological and colorcharacteristics of both species. The animals were grown for ten months at Turpialito Bay, located in the Gulf of Cariaco, Venezuela. The three experimental populations, seeded with an initial homogeneous size (45–50 mm), showed a similar growth pattern; however, P. viridis showed significantly smaller growth rates than those of P. perna and the morphotype, with a final dorsoventral shell length of 71.2, 77.0 and 77.8 mm, respectively. Correlativity analyses of environmental and growth factors could not define the somatic growth modulation due to environmental factors, but reproductive activity, particularly when it begins for the first time, may act as a negative endogenous factor. Although the results show similar physiological responses fromthe mussels, a greater similarity was observed between P. perna and the morphotype, and there were enough differences between them and P. viridis to suggest that the first two could be more genetically related. Nevertheless, differences were found between the morphotype and P. perna in regard to the phenotypic characteristics of the shell, survival and the gonadosomatic index, which may indicate significant genetic differences. Greater gonadal production in the variant could be advantageous for aquacultural activities.