Assessment of larval quality of two bivalve species, Crassostrea angulata and Chamelea gallina, exposed and cryopreserved with different cryoprotectant solutions.

Marine bivalves are valuable resources, however, some shellfish populations are endangered due to factors such as anthropogenic pressure, pathologies or lack of reproduction synchrony. Portuguese oyster (Crassostrea angulata) and striped venus clam (Chamelea gallina) have high socio-economic value and their endangered natural populations require rehabilitation. Cryopreservation is a valuable method for the preservation and management of genetic resources for aquaculture and restocking. Larvae cryopreservation is particularly valuable since diploid organisms are obtained upon thawing. The objective of this work was the establishment of C. angulata and C. gallina D-larvae cryopreservation through the selection of permeant cryoprotectant in the freezing solution, namely ethylene glycol (EG) and dimethyl sulfoxide (MeSO). Cryoprotectants exposure showed that, in C. angulata, MeSO promoted significantly higher incidence of abnormalities and enhanced glutathione reductase activity when compared to control (larvae without cryoprotectant exposure) or even to EG treatment. However, for both species, EG significantly reduced D-larvae average path velocity (VAP). In C. angulata post-thaw D-larvae, EG treatment promoted significantly lower motility and velocity when compared to control and MeSO treatment. Superoxide dismutase (SOD) activity showed a reduction in C. angulata post-thaw D-larvae when compared to control, which was compensated by the enhancement of glutathione peroxidase (GPX) activity. In C. gallina post-thaw D-larvae, only motility, velocity and SOD activity were significantly lower than control. Therefore, the best treatment to cryopreserve C. angulata D-larvae was EG while for C. gallina MeSO produced better results. This work established for the first time D-larvae cryopreservation protocols for C. angulata and C. gallina.