Sea bass sperm freezability is influenced by motility variables and membrane lipid composition but not by membrane integrity and lipid peroxidation

Cryopreserved sperm quality depends on the characteristics of fresh sperm. Thus, it is necessary to establish a group of variables to predict the cryopreservation potential of the fresh samples with the aim of optimizing resources. Motility, viability, lipid peroxidation and lipid profile of European sea bass (Dicentrarchus labrax) sperm were determined before and after cryopreservation to establish which variables more accurately predict the sperm cryopreservation potential in this species. Cryopreservation compromised sperm quality, expressed as a reduction of motility (46.5 ± 2.0% to 35.3 ± 2.5%; P < 0.01) and viability (91.3 ± 0.7% to 69.9 ± 1.6%; P < 0.01), and produced an increase in lipid peroxidation (2.4 ± 0.4 to 4.0 ± 0.4 μmoles MDA/mill spz; P < 0.01). Also, significant changes were observed in the lipid composition before and after freezing, resulting in a reduction in the cholesterol/phospholipids ratio (1.4 ± 0.1 to 1.1 ± 0.0; P < 0.01), phosphatidylcholine (47.7 ± 0.8% to 44.2 ± 0.8%; P < 0.01) and oleic acid (8.7 ± 0.2% to 8.3 ± 0.2%; P < 0.05) in cryopreserved sperm, as well as an increase in lysophosphatidylcholine (4.4 ± 0.3% to 4.8 ± 0.3%; P < 0.01) and C24:1n9 fatty acid (0.5 ± 0.1% to 0.6 ± 0.1%; P < 0.05). Motility, velocity, cholesterol/phospholipids ratio, monounsaturated fatty acids and the n3/n6 ratio were positively correlated (P < 0.05) before and after freezing, whereas, viability and lipid peroxidation were not correlated. Motility and the cholesterol/phospholipids (CHO/PL) ratio were negatively correlated (P < 0.05) with each other and the CHO/PL ratio was positively correlated (P < 0.05) with lipid peroxidation. Therefore, the results demonstrated that motility and plasma membrane lipid composition (CHO/PL) were the most desirable variables determined in fresh samples to predict cryo-resistance in European sea bass sperm, taking into account the effect of both on cryopreserved sperm quality.This research was supported by the CRYOSPERM project (PTDC/MAR/64533/2006) founded by FCT national funding and AGL2011-28810 project (MICINN); S. Martínez-Páramo was supported by a FCT postdoctoral fellowship (SFRH/BPD/48520/2008) co-founded by POPH-QREN, Tipologia 4.1 (FEDER and MCTES) and E. Cabrita was supported by a Ramón and Cajal research contract (RYC-2007-01650).Peer reviewe