Seasonal changes in sperm freezability of sex-reversed female rainbow trout

Abstract

In order to obtain sex-reversed females of Salmonid fish (SRF; neomales, masculinized females) the hormonal treatment of fertilized eggs or larvae is used. As a consequence, masculinized fish possess less-developed testes without functional spermatic ducts. Therefore, the semen of sex-reversed females is generally characterized by low or highly variable quality and reflects testicular rather than ejaculated semen. The aim of our study was to evaluate the alterations in sperm freezability of sex-reversed female rainbow trout during the progression of the spawning season. Sperm concentration, seminal plasma osmolality, semen pH, gonadosomatic index (GSI) and total sperm production (TSP) were monitored in fresh semen. The sperm motility parameters, adenosine triphosphate (ATP) production and sperm viability were examined throughout the spawning season in fresh and frozen/thawed semen. The day of the spawning season did not affect sperm motility of fresh semen. During the equilibration of semen, 2–3-fold increase in the sperm motility compared to fresh semen on each day of the spawning season was recorded. A decrease in the sperm motility after cryopreservation compared to equilibrated semen on each day of the spawning season was recorded. The highest ATP concentrations in fresh semen were noted on the 21st day of the spawning season, whereas in cryopreserved semen, these values were the highest on the 16th and 21st days of the spawning season. The viability of fresh semen did not change during the spawning season; however, the highest sperm viability after cryopreservation was observed between the 11th and 21st days of the spawning season. These results should be taken into account during the planning of cryopreservation of semen of valuable SRF individuals, which will be further used for fertilization of eggs under hatchery conditions.