STU DY ON SEXUAL MATURITY AND LE VEL S OF GON AD STEROI D HORMONE S IN FEM ALE KUTUM Rutilus frisii kutum KAMEN SKII , 1901 DURIN G SPAWNIN G SEASON FROM RI VER SEFI D-RU D OF THE SOUTHERN CASPIAN SEA

Caspian kutum, Rutilus frisii kutum Kamenskii, 1901 populations generally recorded along near the coast, from the Trek River the north to the southern part in Iran coastal of the Caspian Sea (Sharyati, 1993). This species is an endemic fish of the Caspian Sea and is a migratory anadromous fish spawning in the rivers in March-April. The association of changes in gonadal development with plasma levels of gonadal steroids has proven to be a valuable tool for understanding the endocrine control of reproduction in teleosts. It is well known that, in teleosts, vitellogenesis and final oocyte maturation are regulated by gonadotropins via steroids secreted by the follicular cells surrounding the oocyte. Correlations between changes in plasma levels of gonad steroids and oocyte development have been well documented in a number of freshwater species including salmoniforms (Whitehead et al., 1983; Truscott et al., 1986), cyprinids (Kobayashi et al., 1986; Santos et al., 1986), and catfish Heteropneustes fossilis (Lamba et al., 1983). To investigate gonadal development during natural spawning season female kutum R. frisii kutum fish were collected monthly from February to May in 2008. The ovaries were dissected out and weighed, the condition factor (CF) and Gonadosomatic index (GSI) were determined. For bleeding, fish were anaesthetized with clove (Syzyglum aromaticum) oil (75-115 ppm), taken from the caudal vessels by using heparinized disposable syringes centrifuged for 10 min at 3000 rpm. Serum levels of 17-β estradiol (E2) and testosterone (T) were measured by radioimmunoassay. Ovaries were fixed in Bouin’s solution, embedded in paraffin after dehydration and infiltration, sectioned at 5 mm and stained with Mayer’s hematoxylin and eosin for histological examination under binocular microscope. Results declare that Changes in serum levels of gonadal steroids, 17 β estradiol (E2) and testosterone (T) were closely correlated to ovarian development and increases in Gonadosomatic index GSI (P<0.05). (GSI) began to increase in March and reached the highest value (29.47±4.2) in April and then decreased sharply in early may. Serum level of testosterone and 17 β estradiol showed a clear peak in the spawning season, when the GSI reached the maxima. The results showed that levels of 17-β estradiol and testosterone in female kutum at the stage IV of sexual maturity are significantly higher than the individuals with immature gonads (ovary in stages II and III) (P<0.01). Serum estradiol and testosterone levels increased in February, reached their highest levels in March and early April (105.6±75.3 and 29.2±96.6 ng/ml, respectively), and then decreased in late April and in early May during the spawning season (P<0.05). 17 β estradiol (E2) has been reported to stimulate vitellogenesis in teleosts and many of these studies showed changes in plasma levels of sex steroid hormones during gonadal maturation (Smith and Haley, 1988). This author have reported an increase in plasma estradiol levels once spawning commences and that it remains high throughout the period of oocyte growth. (Rosenblum et al. 1987) have shown that a good correlation between circulating estradiol and calcium levels in female teleosts., Increases in plasma estradiol in female Tilapia Oreochromis mossambicus paralleled increases in both GSI and calcium levels (Cornish, 1993), this study thereby confirming a role for 17 β estradiol in vitellogenesis. In general, the results recorded for kutum R. frisii kutum, correspond with those for most teleosts fish and vertebrates.

Caspian Sea, endemic fish, anadromous fish, spawning, gonadal development