Cryopreservation of Yesso scallop (Patinopecten yessoensis) sperm

The germplasm of farmed Yesso scallop Patinopecten yessoensis in China has deteriorated since its introduction more than 40 years ago. The main aim of this study is to develop a sperm cryopreservation technique to assist the newly established program to manage this issue in China. This study investigated the factors important to the development of a non-programmable sperm cryopreservation technique in this species, including cryoprotectant agent [CPA; dimethyl sulfoxide (DMSO), propylene glycol (PG), ethylene glycol (EG), glycine, sucrose, glucose and trehalose], equilibration time, rack height and thawing temperature. A low post-thaw sperm fertilization rate of 27.67 +/- 2.52% was produced with the parameters optimized with the permeable CPAs (DMSO, PG and EG) only: 6% DMSO, 10 min equilibration time, 5 cm rack height and 30 degrees C thawing temperature. This rate was further improved to 44.00 +/- 2.00% by adding 3% glucose into 6% DMSO. This addition had also improved the integrities of post-thaw sperm DNA, plasma membrane and acrosome, mitochondrial membrane potential and activities of some enzymes. Results from this study also showed that the post-thaw sperm morphology and ultrastructure were intensively compromised. In addition, the sperm agglutination found in the newly spawned sperm might be one of the phenomena resulted from the so-called germplasm deterioration, especially in the stock used in this study. The further exacerbation of agglutination after cryopreservation would also compromise the post-thaw sperm performance. The sperm cryopreservation technique established in this study would provide a better option to assist in managing the genetic diversity of farmed Yesso scallops in China.