saeed shafiei sabet - Fisheries Department, Gorgan University of Agricultural Sciences and Natural Resources, Golestan, Iran
Mohammad Reza Imanpoor - Fisheries Department, Gorgan University of Agricultural Sciences and Natural Resources, Golestan, Iran
Bagher Aminian fatideh - Fishing Technology Department, Mirza Kochak Vocation and Higher Education Center for Fisheries, Sciences and Technology,Guilan, Iran

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 frisiikutum during spawning season of the southern Caspian Sea. The study was carried out from February to May2008 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 inGonadosomatic 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 instages II and III) (P<0.01). Plasma (E2) and (T) levels increased in February, the highest levels were observedin March and the early of April (105.6±75.3 and 29.2±96.6 ng/ml), respectively. It was decreased in the late ofApril and in the early of May during the spawning season (P<0.05).

kutum, Rutilus frisii kutum (Kamenskii, 1901), sex steroid hormones, spawning season, Caspian sea