The pearl oyster is one of the rare animal models that support two distinct genomes,  through the surgical graft process operated for culture pearl production. This grafted  organism is assimilated to a chimera whose physiological functioning remains poorly known.  The question of the energy expenditure comparison between chimera and non-chimera  animals arises. To answer this question, grafted and non-grafted pearl oysters were  evaluated for their energetic needs by the indirect calorimetry method. This method made it  possible to measure the energy expenditure based on the respiration rate (RR)  measurement, reflecting the basal metabolism. The results showed that the RR values for  grafted and non-grafted pearl oysters were not significantly different (p < 0.05). The  estimated cost of pearl calcification including CaCO3 and proteins synthesis was 0.237 ±  0.064 J h-1, representing 0.64 % of the total energy expenditure of grafted pearl oysters. This  study made it possible, for the first time, to see the energy cost of cultured pearl formation  in P. margaritifera and the little impact in the energetic metabolism of the chimera  organism.