Performance of Diploid and TriploidCrassostrea gigas(Thunberg, 1793) Grown in Tropical Versus Temperate Natural Environmental Conditions

This work was undertaken to assess the effects that different environmental conditions of tropical and temperate aquaculture sites have on growth, survival, and reproduction of diploid and triploid Pacific oyster Crassostrea gigas. Diploid and triploid oysters were evaluated with the purpose of determining if the triploid condition results in any advantage on growth and survival that can be exploited for aquaculture of this species in tropical environments. The evaluations were performed by comparing three sites: two tropical sites in the Gulf of California and one temperate site in the Pacific Coast of the Baja California Peninsula, Mexico. When comparing tropical versus temperate sites, C. gigas growth and survival were less at the tropical sites regardless of ploidy. This can be attributed to environmental conditions, that is, high temperatures causing low productivity, in addition to an earlier-onset and sustained reproductive condition in the tropical sites when compared with the temperate site regardless of ploidy. Analyses of gonad maturation stages and number of oocytes among triploids indicated that a larger reproductive effort occurs at the tropical sites than at the temperate site. Regardless of the lower performance of both ploidy groups in the tropical environmental conditions, triploids grew significantly better than diploids in both tropical sites, and survival was the same for both ploidy groups. This contrasts with the marginal differences observed in growth between ploidies at the temperate site, where triploids showed lower survival than diploids. Possible causes for the lower triploid survival at this site are discussed.