Sex steroid levels, reproductive indices and histological examination of gonads in adult male and female Caspian shemaya, Alburnus chalcoides

Reproductive status of Alburnus chalcoides adults from Anzali Wetland was investigated by histological examination of gonads, assessment of sex steroids (i.e. Progesterone (P), Estradiol-17ß (E2), Testosterone (T)) and reproductive indices (i.e. absolute fecundity, oocyte diameter, hepatosomatic index (%HSI) and gonadosomatic index (%GSI)). Totally, 42 females and 16 males were captured during March to May 2014 by gill net and divided into two age groups including 2 year olds and 3 year olds. In each age group, fish were classified into two groups depending on maturation stage i.e. matured and maturing fish. According to the results obtained, in each age group, there were no significant differences between matured and maturing  males and females in terms of absolute fecundity (p>0.05). In each age group, oocyte diameter was higher in matured fish than in maturing individuals (p<0.05). In 2 year old males and In 3 year old females, higher HIS values were recorded in maturing fish compared to matured fish. In females, the plasma levels of E2, T as well as P were significantly higher and lower in maturing fish and matured individual, respectively. In males, only plasma T was higher in matured fish compared to maturing fish and other assayed steroids did not show significant differences. Also, the histological examination of gonads from 10 males and females showed that all fish were in the final maturation stages