Stimulation of Molting and Ovarian Maturation by Methyl Farnesoate in Pacific White Shrimp, Litopenaeus Vannamei (Boone, 1931)

Abstract

Shrimp farming in the world has grown remarkably. Hence, hormonal manipulation of shrimp reproduction is necessary to meet growing demand and ultimately to achieve further growth. Eyestalk ablation is commonly performed for stimulating ovarian maturation of crustacean in aquaculture. And methyl farnesoate (MF) is involved in the regulation of molting and reproduction in crustacean. In order to know the effect of eyestalk ablation and MF administration on the molting and ovarian maturation of Litopenaeus vannamei, we removed single eyestalk and injected MF (0.1 and 1.0 µg). The lowest survival rate was in ESA group (50 %). 0.1 and 1.0 µg MF-treated groups' survival rate were 73.3 % and 80 % respectively. On the other hand, Molting numbers were the highest in ESA group. And 1.0 µg MF-treated group showed similar molting numbers to ESA group. To know the growth of shrimp, which was essentially associated with the molting frequency, we measured weight gain during the experimental period. Weight gains were significantly different (P < 0.01) in ESA and 1.0 µg MF-treated groups when compared to those from other groups. In order to understand the effect of ESA and MF treatments on gonadal maturation, gonadosomatic index (GSI) was analyzed after the experiment. The GSI values were significantly higher (P < 0.05) in all treated groups (ESA and MF treatments) than control group, and were significantly higher in 1.0 µg MF-treated group than 0.1 µg MF-treated group. In contrast, ESA and 1.0 µg MF-treated groups were not significantly different (P > 0.05). Histological analysis of the ovaries showed that all treated groups indicated previtellogenic stage, whereas control group remained in the immature stage throughout the experimental period. These results clearly suggest that high concentration of MF treatment has similar effects to ESA on molting, growth and ovarian maturation in Litopenaeus vannamei.