ABSTRACT
Several methods have been used to accelerate previtellogenesis and vitellogenesis stages in fish, including hormonal induction, sustained-release delivery systems, and oral delivery of gonadotropin-releasing hormone (GnRH). In this study, we proposed the oral administration of GnRH analog + nanoparticles of chitosan to accelerate oogenesis in goldfish as a model fish in reproductive biology and aquaculture. In this regard, adult female goldfish were fed with six experimental groups: chitosan, 50 µg GnRHa/kg b.w., 100 µg GnRHa/kg b.w., chitosan + 50 µg GnRHa/kg b.w., and chitosan + 100 µg GnRHa/kg b.w., and diet without any additive as the control for 40 days in triplicate. Every 10 days, ovarian samples were collected, and gonadosomatic index (GSI), oocyte diameter (OD), zona radiata thickness (Zr), and diameter of the follicular layer (Fl) were measured to assess ovarian developmental stage for each treatment. Additionally, blood sampling was done to measure serum 17ß-estradiol concentration at the end of the experiment. All parameters remained unchanged during the experiment in the chitosan-fed group. In the group fed with 100 µg GnRH or chitosan nanoparticle + 100 µg GnRHa, these parameters in general were increased. However, the effects in 50 µg GnRHa or chitosan nanoparticle + 50 µg GnRHa treatments were uncertain; they affected serum E2 levels as a trend toward a significant increase was observed in goldfish treated with chitosan nanoparticle + 100 µg GnRHa. Finally, the results indicated the oral administration of chitosan + 100 µg GnRHa/kg b.w. significantly accelerated the oocyte development and growth of ovary.