Potassium ions in extender differentially influence the post-thaw sperm motility of salmonid fish

Potassium ions are known to have an inhibitory effect on the sperm motility of salmonids. For this reason, the addition of K+ to the extender is frequently applied. However, the effect of the addition of K+ to the extender has not yet been tested. The aim of this study was to test the influence of potassium ion supplementation of the extender on the sperm motility parameters from five Salmonidae species (rainbow trout (Oncorhynchus mykiss), sex-reversed female rainbow trout, whitefish (Coregonus lavaretus), brown trout (Salmo trutta) and brook trout (Salvelinus fontinalis)). Semen samples were diluted in extender containing 0.18 M glucose in 9% methanol (GM) supplemented with 0, 20 or 40 mM potassium chloride. After thawing sperm were stored for 30, 60, 120 and 240 min at 4 °C. Our results demonstrated that the presence of potassium ions in the extender had a negative effect on percentage of motile sperm in four of the salmonid species. In contrast, potassium ions appeared to have a positive effect on percentage of post-thaw motile sperm in whitefish semen. However, this effect could be mimicked by changing the osmolality of the extender (which was achieved by increasing the glucose concentration to 0.22 M). The addition of potassium ions turned out to have no positive effect on post-thaw storage time. Our results suggest that osmolality, rather than potassium ions, seems to be essential for cryopreservation success of salmonids sperm. Further studies should focus on the effects of small changes in osmolality on the post-thaw quality of semen.