Background: In fish with external fertilization, two main start-up mechanisms of the path that blocks or activates the spermatozoan motility apparatus are known. The main factor managing the path is osmolality or potassium ion. In burbot from the European and North American population, contradictory findings regarding the factors influencing the onset of spermatozoa motility were reported. The objective of the current study was to determine the effect of potassium and osmolality on the spermatozoa activation of European burbot, Lota lota (Actinopterygii, Gadiformes, Lotidae). Moreover, the influence of pH, as well as sodium ion concentrations on spermatozoa motility was investigated. Seven parameters characterising motility were traced by means of computer-assisted sperm analysis (CASA).
Principal findings: The spermatozoa of European burbot are K+ ion-sensitive. A 6-mM KCl solution significantly decreased motility, and above 12-mM (50 mOsm kg-1) totally ceased spermatozoa movement. Sucrose and Na+ solutions inhibited spermatozoa movement only at concentrations > 450-480 mOsm kg-1. Greater differences in the percentage of motile sperm between individuals were noted in solutions containing high concentrations of chemicals triggering sperm motility. The optimum osmolality for spermatozoa motility is in the range of 100-200 mOsm kg-1. The burbot spermatozoa were motile over a wide range of pH values with the best activation at pH 9.
Conclusion: It was demonstrated that the spermatozoa of European burbot are inhibited by K+ ions similarly as in North American burbot. Other electrolyte and non-electrolyte solutions inhibit spermatozoa movement only if their osmolality is greater than that of the physiological osmolality of seminal plasma. The data provided on basic knowledge of burbot spermatozoa allow to ensure appropriate conditions during artificial reproduction and scientific research.