Comparison of the effects of Origanum vulgare with LHRH-A2 and 17β-estradiol on the ultrastructure of gonadotroph cells and ovarian oogenesis in immature Trichogaster trichopterus

Origanum vulgare is a plant of the mint family that contains phytoestrogens. This study compared the effects of O. vulgare, LHRH-A2, and 17β-estradiol on the ultrastructure of gonadotroph cells and ovarian oogenesis in immature Trichogaster trichopterus. Fish (5.1 ± 0.032 cm and 2.1 ± 0.043 g, n = 150) were randomly divided into four treatment groups (three hormonal treatments and control) and treated intramuscularly at four levels with 17β-estradiol or O. vulgare at 10, 20, 30 and 50 mg/kg body weight and with LHRH-A2 at 0.001, 0.002, 0.003, and 0.005 mg/kg body weight. There were three control treatments: saline, ethanol and placebo. Fish were kept in 15 tanks, with 10 fish per tank, injected a total of seven doses over 13 days. Gonadosomatic index (GSI) and oocyte diameter were lower (P ≤ 0.05) in the control than in the three hormonal treatments. The highest GSI and oocyte diameter responses were observed in fish treated with 17β-estradiol (2.76 ± 0.23%, 149.8 ± 15.43 mm) followed by O. vulgare (1.86 ± 0.18%, 104.3 ± 11.5 mm) and LHRH-A2 (1.52 ± 0.12%, 91.75 ± 9.02 mm) (P ≤ 0.05). Moreover, there was a significant effect of dose level within all the hormonal treatments (P ≤ 0.05). The effect of treatment on the length and weight was likely GSI. Ovarian tissue results showed faster oogenesis of oocytes in fish treated with O. vulgare, after 17β-estradiol. Ultrastructure of gonadotroph cells demonstrated less stimulation by O. vulgare than by 17β-estradiol and LHRH-A2. This study suggests that compared with the two hormonal treatments, O. vulgare dose-dependently affects ovarian oogenesis and gonadotroph cells.