In vitro secretion of ecdysteroid by Y-organ during molt cycle and evidence for secretion of 3-dehydroecdysone in the giant freshwater prawn, Macrobrachium rosenbergii (Crustacea: Decapoda: Caridea)

Abstract

Summary In crustaceans, a molting gland, the Y-organ, is known to secrete ecdysteroids. In the present study, we examined the products and the in vitro secretory activity of the Y-organ in the giant freshwater prawn, Macrobrachium rosenbergii. Ecdysteroids present in the Y-organ incubation media were determined by high-performance liquid chromatography and radioimmunoassay systems. Ecdysone (E), 3-dehydroecdysone (3DE), 20-hydroxyecdysone (20E) and high polarity products (HPP) were detected. The detection of 20E and HPP is probably due to the hydroxylation and conjugation activities in the epidermal tissue introduced into the incubation medium along with the Y-organ. The predominant products were E and 3DE in M. rosenbergii. The in vitro secretory activities of the Y-organ fluctuated in a similar manner to the ecdysteroid levels in the hemolymph: the secretory activities were the highest in the late premolt stage in which hemolymph levels also peaked. The present study is the first report that determines the Y-organ products in a caridean species. The close relationships between Y-organ activities and hemolymph ecdysteroid levels suggest that the Y-organ activity directly affects the hemolymph ecdysteroid levels in M. rosenbergii.