VITELLOGENIN PRODUCTION INDUCED BY EYESTALK ABLATION IN JUVENILE GIANT FRESH-WATER PRAWN MACROBRACHIUM-ROSENBERGII AND TRIAL METHYL FARNESOATE ADMINISTRATION

Juvenile Macrobrachium rosenbergii were bilaterally eyestalk-ablated a nd hemolymph-sampled at 3 to 6 day-intervals for three weeks. In males , vitellogenin appeared several days after ablation, increased slightl y for 1-2 weeks, and then decreased. Quantification by enzyme immunoas say indicated peak vitellogenin levels ranging from 0.1 to 0.8 mg/ml. Females showed a similar profile, but peak levels ranged from 0.5 to 3 .0 mg/ml; one individual was however exceptional with titers reaching nearly 30 mg/ml. Vitellogenin was not detectable in non-ablated animal s. Juvenile male and female vitellogenin was shown by SDS-PAGE/Western blotting to consist of a single polypeptide component of 199K; howeve r, in the exceptional female only, vitellogenin was composed of three polypeptides of 199, 102 and 90K as in adult female vitellogenin. Neve rtheless, all ablated juvenile females exhibited increased gonadosomat ic index and vitellogenic oocytes, as demonstrated by immunocytochemic al techniques. Subsequently, juvenile males were employed to examine t he effects of methyl farnesoate (MF) administration on vitellogenin pr oduction. In ablated animals, no significant differences in vitellogen in production were observed between the MF-injected and saline-injecte d groups. MF administration could not induce vitellogenin production i n non-ablated animals. The physiological significance of the appearanc e of vitellogenin in juveniles of both sexes in context of the above r esults is discussed.