The Effect of Eyestalk Extract on Vitellogenin Levels in the Haemolymph of the Giant Tiger Prawn Penaeus monodon

Abstract

Competitive ELISA using a combination of monoclonal antibodies specific to vitellin subunits was used to monitor the fluctuation of haemolymph vitellogenin levels in Penaeus monodon during ovarian development induced by bilateral eyestalk-ablation and to monitor the effect of eyestalk extract injection in prawn with developing ovary. The haemolymph vitellogenin levels were undetectable in the prawn with ovary at the resting stage but elevated sharply when the ovary began to develop, remained high during the ovary developing into ripe stage then fell to the low levels before spawning and spent stages. The result from injection of eyestalk extract into prawn with developing ovary revealed that haemolymph vitellogenin levels elevated sharply within 2 hr, reached the maximal levels and remained high during 4-10 hr, then declined slightly at 24 hr. This response directly depended on the amount of injected eyestalk extract and the response was species specific. The application of eyestalk extract from Metapenaeus affinis demonstrated the same stimulatory effect but was less potent whereas the eyestalk extract from Macrobrachium rosenbergii did not cause any changes in haemolymph vitellogenin levels. Therefore, the assay is specific and provides an indicator to monitor the activity of the putative gonad inhibiting hormone by assaying the alteration of vitellogenin levels.