ساختار سني ماهي سفيد مهاجر (Rutilus frisii kutum kamensky, 1901) به رودخانه تنكابن

Comparative survey of some sexual steroid hormones levels of blood Serum in immature and mature breeders of grey mullet (Liza auratus) in Caspian Sea

A study was conducted to determine age structure of Kutum Rutilus frisii kutum during its migration to Tonekabon River in spring 2006. A total of 156 specimens were examined. Males and females included 4 age groups, 3+ to 6+ in males and to 7+ in females. The overall sex ratio was 1:1.33 in favour of males. The age groups of 3+ and T were dominant in male and female respectively. In both sexes, standard deviation of weight was higher than of length. Furthermore, there was a significant increase in standard deviation of weight besides increasing in age. Condition factor was the highest at age 6+ years in male and 7+ in female. Growth model was allometric (positive for females and negative for males) for both sexes. Back-calculation estimated by Fraser-Lee equation showed that for all age groups of both sexes, the back- calculated lengths were less than observed lengths. The parameters Loo, k and t0 of von Bertalanffy growth equations were computed as 130.62cm, 0.06 year"1, -0.21 and 79.87cm, 0.11 year"1, -0.38 for female and male respectively. The results provided basic information on age structure of Kutum in Tunekabon river, in addition, offer evidence that need more in-depth studies of all migratory populations in rivers of south of Caspian Sea.