The effects of cryogenically preserved sperm on the fertilization, embryonic development and hatching success of lumpfish C. lumpus

Lumpfish (C. lumpus) are used as cleaner fish in the Atlantic salmon (Salmo salar) farming industry to remove parasitic sea lice. At present, wild lumpfish broodstock are used which puts strain on wild populations. By successfully cryopreserving lumpfish sperm, the number of wild males required will be reduced and it enables the long-term storage of sperm for use in breeding programmes. The present study compared the use of fresh sperm and sperm which was cryogenically frozen for 24 h to test whether it is a viable method of preservation. The fresh and frozen sperm from 5 males was used (in equal volumes) to fertilize eggs pooled from 5 females and the difference between fertilization success, percentage of eggs which reached the eyed stage, and the hatching success was measured. A group of 100 hatched larvae were on-grown for two weeks to test whether there was a difference weight between treatment groups. The results of the trial showed that fresh sperm produced a significantly higher percentage of fertilized eggs (fresh 92.6 ± 0.8%, frozen 77.9 ± 1.8%, mean ± SEM), a higher percentage of eggs surviving to the eyed stage (fresh 93.9 ± 0.5% and frozen 80.8 ± 1.4%) and had a more successful hatch rate (fresh 72.3 ± 6.6% and frozen 63.6 ± 5.0%). There was no difference in mean weight (± SEM) of the two-week old larvae between treatments (fresh 0.63 g ± 0.024, frozen 0.59 g ± 0.028). In conclusion, this study showed that the same volume of cryogenically preserved lumpfish sperm produced fewer viable lumpfish larvae than fresh sperm. Despite this difference, the use of cryopreserved sperm did produce relatively high results at each stage of testing.