Hemolymph ecdysteroid levels during the molt cycle in the Kuruma prawn Penaeus japonicus.

Abstract

The variations in hemolymph ecdysteroids were traced during the molt cycle in immature female Kuruma prawn Penaeus japonicus. Ecdysteroids in hemolymph were separated using high performance liquid chromatography, and their levels were measured by a double antibody radioimmunoassay (RIA) method. The RIA was validated prior to assay. The competition curves for the serially diluted hemolymph extracts of the Kuruma prawn and two freshwater prawns, Macrobrachium nipponense and Macrobrachium rosenbergii, were parallel to the standard curve. The mean recovery rates for 20-hydroxyecdysone and ecdysone were 107 and 99.9%, respectively. The intraassay coefficients of variation were 8.2, 8.3 and 7.7% at 62, 48 and 19% binding, respectively. The interassay coefficient of variation was 12.0%at 46% binding. Ecdysone and 20-hydroxyecdysone showed identical cross reactivities. The minimum detectable level was 15 pg/tube. In the postmolt and intermolt stages, ecdysterioid levels in the hemolymph of P. japonicus were found at basal levels. The levels increased in the early premolt stage, and peaked at the late premolt stage. The predominant immunoreactive ecdysteroid in P. japonicus was 20-hydroxyecdysone. Small amounts of ecdysone and ponasterone A were also detected. In addition, high polarity and low polarity ecdysteroids were eluted, but could not be identified.