| Summary: | This study has established a successful protocol to cryopreserve lumpfish Cyclopterus lumpus (Linnaeus, 1758) milt. Three cryosolutions were tested based on Mounib’s medium; the original medium including reduced l-glutathione (GSH), the basic sucrose and potassium bicarbonate medium without GSH, or with hen’s egg yolk (EY). Dimethyl sulphoxide (DMSO) was used as the cryoprotectant along with all three diluents in a 1–2 dilution. Cryopreservation was performed with the mentioned cryosolutions at two freezing rates. Motility percentages of spermatozoa were evaluated using ImageJ with a computer assisted sperm analyzer (CASA) plug-in. Findings revealed that spermatozoa cryopreserved in Mounib’s medium without GSH had a post-thaw motility score of 6.4 percentage points (pp) higher than those in the original Mounib’s medium, and an addition of EY to the modified Mounib’s medium lowered the post-thaw motility score by 19.3 pp. The difference in motility between both freezing rates was 13.0 pp, and samples cryopreserved on a 4.8 cm high tray resulted in a better post-thaw motility score. On average, cryopreserved milt had a 24.1 pp lower post-thaw motility score than fresh milt. There was no significant difference in fertilisation success between cryopreserved and fresh milt. Cryopreservation of lumpfish milt has, to our knowledge, never been successfully carried out before. The established protocol will be a main contributing factor in a stable production of lumpfish juveniles in future.
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