The growth of Epinephelus marginatus living in the Natural Marine Reserve of the Lavezzi Islands was studied using the von Bertalanffy model. The growth parameters of this model were: L_∞=135.9 cm, K=0.08, t₀=-0.80 years. The relationship between length and weight was W=12.5 10^-2 TL^2.60. Grouper lengths were similar in the Lavezzi Islands and in North Tunisia. The relative abundance of trophic resources in the Lavezzi Islands, due to a positive "reserve" effect and enhanced by a small population density of groupers, has great consequences on growth, compensating the effect of lower water temperature. A plausible explanation for the similarity between these two populations is that they belong to a single metapopulation.