Gonadogenesis in chub Squalius (Leuciscus) cephalus (L. 1758).

The chub is an opportunistic, rheophilic cyprinid species and popular gamefish distributed throughout almost all of Europe, South Caucasus and part of Anatolia. It is most abundant in small rivers and large streams. The process of anatomical and cytological differentiation was analyzed in chub gonads. Material used in the study was derived from artificial spawning of adult individuals caught in the Lyna River in April 2002. The results showed that gonadal sex differentiation develops faster in females than males. Morphological differentiation of gonads was noted about 98 days after hatching when fish weight varied between 0.483 g and 1.014 g and body length varied between 3.7 to 4.8 cm. Developing ovaries were spindle-shaped and male gonads were pear-shaped. Final cytological differentiation took place 154 days after hatching when single previtellogenic oocytes were observed in ovaries, contrary to males in which testes filled with spermatogonia not before the 190th day post hatching.