Application of sperm cryopreservation in selective breeding of the Pacific oyster, Crassostrea gigas (Thunberg)

The robustness of Pacific oyster, Crassostrea gigas (Thunberg), sperm cryopreservation in the context of selective breeding based on family lines was investigated. Irrespective of egg density, high fertilization success was achieved with cryopreserved sperm when sperm:egg ratios of 1000:1 to 10 000:1 were used. Variation among replicate runs on the same oyster batches was minimal, indicating that cryopreservation and larval rearing procedures were repeatable. Twenty independent single male-female crosses were made to assess the utility of cryopreserved sperm in selective breeding. The fertility of unfrozen sperm was generally a poor predictor of cryopreserved sperm fertility. Based on D-larval yields, 17 of the 20 crosses were likely to yield adequate spat for selective breeding (> 10(5) D-larvae from 1 million eggs), two were marginal (5 x 10(4) D-larvae) and one was inadequate (4 x 10(3) D-larvae). An alternative fertilization strategy to improve D-yield from a given number of sperm was then tested. Fertilizing 10 million eggs at a sperm:egg ratio of 200:1 increased the total D-yield when compared with fertilizing 1 million eggs at a sperm:egg ratio of 2000:1 for the same male-female pair. We conclude that, despite wide variation in fertility, cryopreserved sperm is useful for family production.