STU DY ON LE VEL S OF 17-β ESTR ADIOL AND TE STO STERONE IN FEM ALE KUTUM Rutilus frisii kutum (Kamenskii, 1901) OF SOUTHERN CASPIAN SEA

Caspian Kutum Rutilus frisii kutum is an endemic fish of Caspian Sea and one of the most economical species in natural environment. Levels of two main gonad steroid hormones, 17-β estradiol (E2) and testosterone (T) in female kutum during spawning season from the River sefid- Rood of the southern Caspian Sea were studied by using radioimmunoassay (RIA). Throughout the experimental period from February to May 2008 using 105 female fish speciment. Aspects of the reproductive physiology of kutum that were investigated included reproductive hormone profiles in serum supernatant. The results of present study revealed that changes in plasma levels of gonadal steroids, (E2) and (T) were closely correlated to ovarian development and increased in GSI (P<0.05). Gonadosomatic index (GSI) was increased in March and reached the highest value (29.47±4.2) in April then decreased sharply in early may. The highest peak of serum level of (T) and (E2) during spawning season showed associated with the highest values of GSI. The results showed that levels of (E2) and (T) in female kutum at the stage IV of sexual maturity was significantly highest compared to immature gonads (ovary in stages II and III) (P<0.01). Serum (E2) and (T) levels increased in February, highest levels was observed in March and early April (105.6±75.3 and 29.2±96.6 ng/ml, respectively), and decreased in late April and in early May during the spawning season (P<0.05). The results imply a close interaction between environmental cues and endocrine control of reproduction. The endocrine control cannot continue without the appropriate environmental cues required to stimulate reproduction.

Caspian Kutum, Rutilus frisii kutum, endemic fish, Caspian Sea,gonad steroid hormones