González-Wangüemert, MercedesPérez-Ruzafa, A.Rosique, M. J.Ortiz, A.2017-03-092017-03-0920040028-1344http://hdl.handle.net/10400.1/9029Ostrea edulis is a target species for aquaculture but its hatchery has suffered as a result of the lack of morphological differentiation between individuals with a low growth and those that reach commercial size. Two sympatric species of oysters, Ostrea edulis and Ostreola stentina, have been reported at the Mar Menor Lagoon, Spain. A third nominal species, Ostreola parenzani, is now considered a synonym of O. stentina. The external morphology of O. edulis and O. stentina is very similar and this prevents their differentiation at the morphological level, except for maximum size. Oysters were collected from 3 locations along the Mar Menor Lagoon and examined for variation at the PGI locus. Principal component analysis of allo-zyme data revealed the existence of two groups, which confirms the presence of two species: Ostrea edulis and Ostreola stentina. The genetic variability of the glucose-6-phosphate isomerase (PGI) locus was also compared in Ostrea edulis and Ostreola stentina from the Mar Menor Lagoon. Ostrea edulis has high levels of homozygosis and shows an important deviation from the Hardy-Weinberg equilibrium. Ostreola stentina shows high heterozygosis and significant differentiation among coastal lagoon samples. The allele frequencies at the PGI locus can be used as a diagnostic character at the species level.engjournal article