Examining the supplementation of exogenous lipid and antioxidant to improve the survivability of post-thaw oocytes in Mediterranean mussels, Mytilus galloprovincialis

The Mediterranean mussel is one of the most important aquaculture species in the world and a key bioindicator for monitoring environmental pollution. In addition to genetic resource germplasm conservation, oocyte cryopreservation could increase opportunities for off-season seed supply and facilitate genetic improvement programs and applications that require gametes year-round, such as pollution assessments using larval development as a biomarker. This study investigated the effect of exogenous lipids and antioxidants on the survivability of post-thaw mussel oocytes by supplementing lipid, antioxidant or their combination in the base cryoprotectant agent (10% ethylene glycol and 7.5% Ficoll® PM 70). The lipids included three polyunsaturated fatty acids (PUFAs), i.e., arachidonic acid, eicosapentaenoic acid and docosahexaenoic acid, one phospholipid [1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)] and the lipid extract from Atlantic salmon (Salmo salar). The antioxidant was α-tocopherol. Results from the chemical tolerance experiment showed that all PUFAs were toxic at a concentration of 0.1 mg/mL or higher. In comparison with the base cryoprotectant agent, the supplement of 0.5 mg/mL POPC or 1 mg/mL α-tocopherol alone increased the relative survival rate of D-stage larvae by approximately 50%, whereas the combination of 0.5 mg/mL POPC and 0.5 mg/mL α-tocopherol increased the relative survival rate of D-stage larvae by approximately 100%. Adding 0.5 mg/mL salmon lipid extract resulted in the highest relative survival rate of D-stage larvae. However, it was not significantly different from the POPC and α-tocopherol combination. In addition, the salmon lipid extract treatment produced twice the number of spat compared with the base cryoprotectant agent. This study reveals that adding lipids and antioxidants could therefore open a novel strategy for improving oocyte cryopreservation success in marine bivalves.