بررسي بيولوژي توليد مثل در سياه ماهي Capoeta capoeta gracilis در سواحل جنوبي درياي خزر استان مازندران (رودخانه تجن)

Biological study of reproduction in (Capoeta capeota gracilis) in south coasts of Caspian sea Mazandaran Province {Tajan River)

Black fish (Capoeta capoeta gracilis) is a valuable fish in fisheries industry, that exist in south coasts of Caspian Sea specially in Mazandaran province. In this research 180 pieces of fishes were studied about reproduction biology between 1386-1387 in Tajan River from south coasts of Caspian Sea in Mazandaran province. In this study biological factors related with reproduction for example: the variations of Gonad somatic index sex ratio, average fecundity and sex maturing stages have carried to account the main objectives. The maximum of GSI was in April and may (spawning time) and the minimum was in October, November and December .GSI in spring and summer greater than autumn and winter. Like wise with age increasing the GSI increases consequently and the increasing gradient was more in premature stages in comparison with maturity. Sex maturing stages in different months were proportional with GSI and with age increasing the amount of maturity was higher subsequently. The maximum of GSI in male fishes were at ages 3-4 years and in females were 2-3 years.