Unlike in some crops, no large heterotic effects have been observed in most farmed animals. Interestingly, significant hybrid vigour for some traits has been reported in the Pacific oyster, Crassostrea gigas. Crossbreeding between closely related taxa can be seen as an efficient way to exploit the dominance component of the genetic variance of a trait. Factorial crosses between the Portuguese oyster C. angulata (from Sado estuary, Portugal) and C. gigas (from Seudre estuary, France) were done to evaluate the aquaculture potential of hybrids. Juveniles of the different progenies were reared in Ria Formosa (Portugal) under usual farming conditions. The genetic confirmation of all progenies was done using mitochondrial and nuclear markers in order to detect contaminants and confirm the hybrid status. Abnormal mortalities were observed during the grownout phase, especially in summer months. All crosses showed similar growth rates, except C. angulata, which grew more slowly. Hybrid vigour was observed for some traits in groups presenting superior values to those of the best parental line. The results obtained suggest that the trait in which positive heterosis was observed could result from the multiplication of characteristics showing additive effects. In contrast with previous studies, no maternal effect was observed for the majority of the traits analyzed. This study also reports morphological differences between C. angulata and C. gigas for the studied population.