Abstract

This study is aimed at evaluating when sex could be determined in beluga by examining levels of plasma steroids. Blood was taken from beluga from two stations (Shahid Rajaee: SR, Sari farm: SI) which were kept at 19°C at the age of 24 and 36 months and plasma testosterone (T), 11-ketotestosterone (KT) and estradiol (E2) concentrations and plasma calcium were determined. The results revealed that, plasma T and KT levels were significantly higher in males than females in both stations at the age of 24 and 36 months (P<0.05). There were no differences in E2 and calcium concentrations between males and females at both ages. In addition, the results showed that, plasma T increased significantly in both locations, with increasing age from 24 to 36 months. Histological analysis of gonads revealed that all but six of the SI farm fish at the age of 24 months had well differentiated testes with spermatogonia undergoing mitosis in cysts (Stage 2). The six of the population in SI farm, which had no differentiated gonad, had also the lowest weight in comparison to differentiated fish. It also appears that proliferation of spermatogonia is necessary for production of androgens and growth rate is influenced by water temperature. The results of this study revealed that, plasma T and KT can be used as good markers to determine the sex in the early life stage of beluga.

Key words: Sturgeon, cultured beluga, sex determination, sex steroids.

Abbreviation

T, Testosterone; KT, 11-ketotestosterone; E2, estradiol; SR,Shahid Rajaee; SI, Sari; H and E, Hematoxilin-Eosin.