Activity of the Sperm of the Bluefin Tuna Thunnus thynnus under Fresh and Preserved Conditions

Abstract

Fresh semen of Thunnus thynnus from the Mediterranean Sea was very viscous and contained spermatozoa at high densities (496-648×10⁸/ml). When diluted with sea water, spermatozoa maintained high levels of motility for about seven minutes. From these characters of the semen, the dilution of semen with sea water or physiological saline seems to facilitate teh operation of artificial insemination in this species. In experiments on the preservation of liquid semen in an ice bath, spermatozoa rapidly lost their motility and became completely inactive in four days, probably and partially due to the lowering of oxygen level in the highly viscous and dense semen. Cryopreserved semen in liquid nitrogen (cryoptective agent : glycerol or DMSO; basic medium: Mounib's medium or 10% glucose) successfully maintained its spermatozoal motility, suggesting a high possibility of cryopreservation in the artificial insemination of T. thynnus. Glycerol showed its cryoprotective effectiveness at equilibration times longer than 20 minutes, while DMSO was effective at equilibration times shorter than 20 minutes.