Growth, mortality, pathological conditions and protein expression of Mytilus edulis and M. galloprovincialis crosses cultured in the Rı́a de Arousa (NW of Spain)

Abstract In this article, the growth, mortality, pathological conditions and protein expression of hatchery obtained mussels from pure and hybrid crosses between individuals from three genetically divergent European populations were evaluated in the Ria de Arousa (NW Spain) under raft-suspended cultivation conditions. Progenitors for the crosses were obtained from a Mytilus edulis population from The Netherlands and from two M. galloprovincialis populations located on each of the two sides of a major genetic break, associated with the Almeria–Oran oceanographic front in the Iberian Peninsula. Results indicated that mussels from crosses between individuals of M. galloprovincialis populations have a significantly higher biomass production than those from hybrid crosses between individuals of M. galloprovincialis and M. edulis populations. This different performance was not due to differences in growth rate but rather to the considerably higher mortality, during the warmer season, of the mussels from hybrid crosses. This strong viability selection operating against hybrid mussels with respect to pure M. galloprovincialis crosses under raft cultivation conditions in the Ria de Arousa was very similar to that operating in natural populations of the M. edulis / M. galloprovincialis hybrid zone in SW England, reported in previous studies. Our results also show that the lower viability of hybrid mussels is clearly associated with both higher parasitization by the protistan Marteilia refringens and lower levels of the stress proteins calreticulin and heat shock protein 70. Among the mussels from the different M. galloprovincialis crosses, those from crosses between males and females of autochthonous (Galician) origin are the ones which show a better performance.