relation between gonadal hormones and sexual maturity of female kutum rutilus frisii kutum during spawning season

abstract relation between sexual maturity and levels of two main steroid hormones in gonads, 17- estradiol (e2) and testosterone (t) were studied by using histological and radioimmunoassay in female kutum rutilus frisii kutum during spawning season of the southern caspian sea. the study was carried out from february to may 2008 using 105 migrated fish specimens catched from the river sefid-rood by various tools of catching including (gillnet, cast net, seine net and sheyl or kulham). the results revealed that changes in plasma levels of gonadal steroids, (e2) and (t) were closely correlated with ovarian development and increased in gonadosomatic index (gsi) (p<0.05). gsi was increased in march and reached the highest value (29.47±4.2) in april. it was then decreased sharply in early may. the highest peak of plasma level of (t) and (e2) was during spawning season and it was associated with the gsi. the results showed that levels of (e2) and (t) in female kutum at the stage iv of sexual maturity was significantly higher than immature gonads (ovary in stages ii and iii) (p<0.01). plasma (e2) and (t) levels increased in february, the highest levels were observed in march and the early of april (105.6±75.3 and 29.2±96.6 ng/ml), respectively. it was decreased in the late of april and in the early of may during the spawning season (p<0.05).