Three species of oysters have been or are cultivated in Europe: Crassostrea angulata, C. gigas, and Ostrea edulis. If we follow the taxonomic critera of Grassé, the European oysters belong to the group of Mollusca, class of Lamellibranchia or Bivalves, order of Filibranchia, family Ostreidae with two genera: C. angulata (Lamarck), Portuguese, cupped oyster; C. gigas, (Thunberg), Japanese or Pacific, cupped oyster; Ostrea edulis (Linné), fiat European oyster. Some authors think that C. gigas and C. angulata belong to the same species. lndeed, Ranson stated that the characteristics of the larvae are the same, and Menzel obtained viable hybrids (F2) between these two oysters. AIso, Buroker et al. in studying the genetic variations of proteins and enzymes of the flesh, revealed a genetic similarity of 99% between C. gigas and C. angulata on 24 loci. These authors proposed the hypothesis that Japanese oysters wouId have been imported from Japan to Portugal by boats in the 16th Century or vice versa. However, these two oysters obviously show different characteristics in the metabolic rate, the filtration rate, growth performance, reproduction mode, and resistance to disease. All these latter elements combine to affirm that the Portuguese and the Japanese oysters are two species with well-defined physiological characteristics, particularly with regard to oyster culture.