Variations in Plasma Sex Steroid Hormones of the Wild Caspian Cyprinid Fish, Kutum (Rutilus Frisii Kutum)

Steroid hormones in plasma play an important role in reproductive cycles of animals especially during the final maturation stages. steroid hormones synchronize gonad developments depending to fish species reproductive strategies. the wild cyprinid fish, kutum (rutilus frisii kutum) is an ecologically and economically important fish species which inhabit in southern coastline of the caspian sea in iran. over the past few decades, natural reproduction of this species dramatically impaired due to the urbanization, civilization close to the land and shallow water in south western of the caspian sea. therefore annual sex steroid hormones and gonads development were measured to assess the annual reproductive biology of female kutum. in this study for the first time, our aims were to determine the annual variations in sex steroid hormones; 17 β estradiol (e2), progesterone (p) and testosterone (t) and gonad development of female kutum. our results showed that plasma steroid levels in females manifested in two phases in annual reproductive cycle; the resting phase (june - february) being characterized with the lowest level of steroid hormones and the peak reproduction activity phase (march–may) with simultaneously a significant increase in level of e2, p and t in plasma. interestingly, comparing with other teleost fish species the baseline level of e2 in plasma of kutum during the resting phase to some extent was also huge. increase in concentration of plasma e2 was in accordance with an increase of gonadosomatic index during spawning season. our results contribute to our knowledge about the reproductive biology of kutum and calls further long-term investigation.