Dynamics of sperm motility (sperm velocity, percentage of motility and flagellar beat frequency) and monthly variations of semen characteristics (semen volume and osmolality and sperm concentration and motility) were studied in Perca fluviatilis. This study showed that sperm velocity, percentage of motility and flagellar beat frequency significantly and rapidly decreased after the activation of sperm motility. Twelve spermiating males were randomly selected and electronically tagged to study monthly variations of semen characteristics. The semen was collected 4 times (29th November 2005, 10th January 2006, 21st February 2006, and 7th April 2006). Semen volume did not change significantly from November to February, but it significantly increased in April. Sperm concentration was higher in November and January than in February and April. The highest and the lowest osmolality of semen was observed in January and April while it decreased in February and April. At 15 s post activation, the lowest percentage of motile spermatozoa was observed in November. The semen samples collected in April showed the lowest motility of spermatozoa (24.3%) at 30 s post activation. But the percentage of motile spermatozoa collected from November to February showed more than 65% motility at 30 s post activation. At the end of motility period (60 s post activation), no motile spermatozoa were observed in April, and the highest motility was in November. Sperm velocity did not show any significant differences at 15 s post activation. The lowest sperm velocity was observed in April at 30 s post activation.