ABSTRACT
Objective The aim of this study was to investigate the masculinizing effects of progesterone ( PRO) exposure at different concentrations on the morphology of female mosquitofish (Gambusia affinis).Methods Immature female G.affinis individuals were put into static water with 0.5, 5, 50 and 500 nmol/L progesterone (n=56), respective-ly.In addition, control group and parallel groups were set up .After 42-day-long exposure, we measured four main indexes of the G.affinis:the body length, body weight, morphological changes in the anal fin 3rd fin and the 14, 15 and 16 verte-bral ribs.We also observed the state of ovarian development .Results The body lengths (BL) of experimental groups ex-posed at concentration of 50 and 500 nmol/L progesterone for 42 d showed significant differences , respectively ( P0.05).When exposed to 500 nmol/L PRO, the L, D and L:D values of the 14th, 15th and 16th vertebral ribs of the female G.affinis had very significant difference ( P<0.01 for all ) , respectively , indicating significant changes of morphological masculinization .Histological examination revealed that the developmental status of the ovaries of G.affinis in the experimental groups were to different degrees inhibited , and the nuclei appeared swelling in stage II and III oocytes . Conclusions The results of this study indicate apparent masculinizing effects of progesterone on immature female mosquit -ofish.