Molecular identification reveals hybrids of Mytilus coruscus x Mytilus galloprovincialis in mussel hatcheries of China

Juvenile mussel trade monitoring is becoming more and more important for mussel farms of China, which is essential for the sustainable development of mussel culture. The identification of mussel hybrids by morphological analysis is unreliable, particularly between interspecific hybrids and pure species juveniles. Mytilus coruscus are the representative local mussel species for their higher market price, which is 2-5 times of M. galloprovincialis. Therefore, in the present study, we established a methodology that allows the accurate identification of M. coruscus x M. galloprovincialis hybrid and pure juveniles using both nuclear and mitochondrial primers and analysed the mussel juveniles purchased from four different seed producers in China. Nuclear primers Myti-2 used in this study were modified from the degenerated oligonucleotide primers Myti-F/R to improve the efficiency of amplification; primers YB-16S-4 derived from female type mitochondrial DNA were found to be distinct between the two species with one single peak in high-resolution melting (HRM) analysis, which was proven to be effective in maternity determination of their hybrid progenies. For samples commercialised as M. coruscus seeds of the two farms, 88.5% juveniles were identified pure M. coruscus and 11.5% were hybrids of M. coruscus female x M. galloprovincialis male in Farm A; 5.6% juvenile were pure M. galloprovincialis and 94.4% were hybrids of M. galloprovincialis female x M. coruscus male in Farm D. Samples from Farm B and C were proven to be pure M. coruscus. The validated new identification method will be a useful tool for the surveillance of the production and trade of the two commercially important mussel species and their hybrid seeds, thereby facilitating the sustainable development of mussel farming. Hybrids detected in Farm A and D also highlighted the importance of juvenile mussel trade monitoring in the market to avoid the commercial fraud.