Reproductive biology of cyprinid hybrids [S. cephalus (L.) x A. chalcoides (G.)] in T dürge Lake (Sivas)

In present study, the different reproductive properties of hybrids of Squalius cephalus x Albur nus chalcoides which occured under natural conditions, were determined. Firstly, the sexual maturity ages for males and females were indicated. The reproductive period was defined ac cording to the monthly changes of gonadosomatic index, gonad weight, egg diameter and egg number in per gram of ovarium. Mean fecundity was determined for each age group. Both fe males and males were attained sexual maturity at II age. The values of fork length for the smallest female and male with mature gonads were measured as 123 mm and 127 mm, respec tively. The maximum value of mean gonadosomatic index for females was determined in May (9.48). However, in July the index revealed minimum values (0.92). The minimum and maxi mum egg diameters were measured as 0.23 mm and 1.72 mm, respectively. Egg number in per gram of ovarium was changed between 516 and 2665. According to the monthly changes in the gonadosomatic index, gonad weight, egg diameter, and egg number in per gram of ovarium, it was determined that the spawning in hybrids of S. cephalus x A. chalcoides in T dürge Lake began in May and continued until end of July. Mean fecundity was determined as 2238 for II age group, and as 4250 for III age group. The values of fecundity of the hybrids were quite lower than the values of S. cephalus and A. chalcoides in the same age group.