Comparative study of the reproductive characteristics of XY male and hormonally sex-reversed XX male Eurasian perch, Perca fluviatilis.

In order to compare the reproductive capacity of XY male versus XX male (neomales) Eurasian perch (Perca fluviatilis), we determined the sperm quality (sperm concentration and motility) and reproductive characteristics such as gonadosomatic index (GSI), fertilization rate and sex steroid levels (testosterone, T; 17beta-estradiol, E2 and 11-ketotestosterone, 11KT) during the reproductive season. Median GSI was not significantly different between XY males (7.9%) and XX males (7.5%). Fertilization rates ranged between 30.0 and 98.0%. Sperm concentration ranged between 27.9 x 10(9) and 42.0 x 10(9) spermatozoa ml(-1). Median level of T, 11KT and E2 levels increased in the middle of the reproductive season (2136.0, 2409.0 and 3252.0 pg ml(-1), respectively) and decreased at the end (1657.0, 2006.6 and 431.0 pg ml(-1), respectively). Sperm motility was assessed by CASA and expressed by the curvilinear velocity (VCL), straight line velocity (VSL), average path velocity (VAP), linearity (LIN), percentage of motile sperm (% MOT) and motile concentration (MOC). Overall, there were not any significant differences between XY and XX males. In conclusion, no differences of reproductive capacities were observed between XY males and XX males suggesting that the last can be crossed with females to improve the productivity of Eurasian perch by producing all-female stock.