LAUSR

Abstract There is increased commercial interest in the production of lumpfish (Cyclopterus lumpus) as a biological control against sea lice infections in Atlantic salmon farming. To ensure a sustainable supply of lumpfish, reliable captive reproduction is required however, optimal husbandry and conditions for captive broodstock performance remain unknown. Artificial fertilisation of gametes remains the preferred management strategy for lumpfish, but this requires an effective milt management protocol. The present study tested several milt extender solutions for short term cold storage and validated sperm concentration assessment of lumpfish milt. Results demonstrated lumpfish sperm has a long motility survival time (motile for up to 3 h) when compared to other marine teleosts. Importantly, all extenders used in the study were non-activating on dilution of the milt. Lumpfish milt was successfully stored at 4 °C in Modified Turbot Extender (MTE), Herring Ringers Solution and Aquaboost SpermCoat (Cryogenetics, Norway) for up to 14 days post stripping. MTE performed more effectively with regards to maintenance of sperm activation time in comparison to the other tested extenders. There was a significant positive correlation between sperm concentration identified through cell counts using a haemocytometer and both packed cell volume (spermatocrit) and measured optical density at 640 nm (r2 = 97.42 ± 2.14). This suggests both packed cell volume and spectrophotometric measurements can be effective methods for rapidly assessing sperm concentration in lumpfish. This study validated several options for quantifying sperm concentration and short-term cold storage of lumpfish milt that can be used for hatchery management in lumpfish aquaculture.