This study investigated the effect of 0.25-5 mM K(+), Ca(2+), and Mg(2+) on sperm motility in the perch, Perca fluviatilis. In 75 mM NaCl, the used motility-activating solution, motility rate, and swimming velocity decreased within the first 4 min after activation, and the rate of locally motile sperm increased. Thereafter, the motility parameters remained constant for periods >20 min. Based on the decrease in sperm motility, two types of semen samples could be distinguished. Semen samples of type I retained a high motility rate of >65 % after 20 min, and the rate of locally motile sperm was <20 %. In semen samples of type II, the motility rate decreased to values <30 % after 20 min, and the rate of locally motile sperm exceeded >50 %. Ca(2+) and Mg(2+) concentrations of 0.25-0.5 mM had no effect on the sperm motility parameters 10 s after activation, while 0.25 mM K(+) increased the swimming velocity. K(+), Ca(2+), and Mg(2+) concentrations ≥1.5 mM had suppressive effects on the sperm motility 10 s after activation. No differences were found between the two semen types. Twenty minutes after activation, type I semen was not affected by the tested cations. On the contrary, 0.25-2.5 mM K(+), 0.25 mM Mg(2+), and 0.25-2.5 mM Ca(2+) significantly increased the sperm motility rate and/or sperm velocity of type II semen. Therefore, supplementation of saline solution with cations might stabilize the motility of perch sperm, which can be a benefit for experimental purposes and for specific handling procedures in aquaculture.