Fluctuations in hemolymph ecdysteroid levels during the reproductive and nonreproductive molt cycles in the giant freshwater prawn Macrobrachium rosenbergii

Abstract

Hemolymph ecdysteroid levels were traced during the molt cycle in female giant freshwater prawn, Macrobrachium rosenbergii. Levels were compared between the reproductive molt cycle, accompanied by ovarian development and oviposition following ecdysis, and the non-reproductive molt cycle, marked by the absence of ovarian development, to examine the involvement of ecdysteroids in ovarian development. Total ecdysteroid levels determined by radioimmunoassay (RIA) showed similar fluctuation patterns between both molt cycles. Levels were low during postmolt stages A-B and gradually decreased to low basal levels at intermolt stages C₀-C₁. Levels then increased during premolt stages D₀-D₂, reached a large peak at the early D₃ stage, and declined sharply prior to ecdysis. In addition, ecdysteroids in the hemolymph were analyzed using high-performance liquid chromatography combined with RIA in order to identify individual ecdysteroid species. During both molt cycles, 20-hydroxyecdysone, ecdysone and high polarity immunoreactive products were detected, and 20-hydroxyecdysone was the most predominant ecdysteroid. Fluctuations in all ecdysteroid species during each type of molt cycle paralleled those of total ecdysteroid levels, and did not show significant differences between the reproductive and non-reproductive molt cycles. These results suggest that ecdysteroids are not involved in ovarian development but in the molting process only.