Effects of different estradiol implants on gonadal development of cultured great sturgeon Huso huso in pre-vitellogenic stage

Puberty in sturgeon is a long process. Regard to this problem، nowadays several management and nutritional strategies and endocrine manipulation of the reproductive axis are used to induce sexual maturity. 17-β Estradiol (E2) is a female hormone which is known to be one of the most effective estrogenic hormones. The present study has been focused on the effects of different levels of E2 implants on gonadal development in 20 Three-year old cultured previtellogenic beluga (Huso huso). Great sturgeon were intraperitoneally implanted every 1. 5 month with capsules that were filled with 3، 6 and 12 mg/kg body weight E2 and cocoa butter as a career and the control fish received capsule that just contained career. Fish were biopsied at the end of the experiment in order to determine the gonadal stage and oocyte characteristics at day 190. The result of egg diameter at the end of experiment showed no significant differences between treatments (P >0. 05). Also there is no significant difference found in histological observation in the case of egg area and diameter، nucleus area and diameter and ratio of nucleus area/egg area. Based on histological observations and oocyte indices we have found that E2 implant can stimulate the growth and development of fish oocytes but regard to slow growth at the pre- vitellogenic stage and the limit period of its usage، no significant differences were observed.