The processes and ecdysteroids involved in the molting cycle of tiger shrimp, Penaeus monodon Fabricius, were studied. By observing the morphological changes of the setae and the epidermal line in the uropod, the molt cycle was divided into stages Ai, A2, B, C, DO, D1', D1", D1 "', D2, D3 and E, with stage C being very short (diecdysis). Anti-20-hydroxyecdysone-CMA-BSA rabbit antiserum was prepared, and the qualitative and quantitative changes of hemolymph ecdysteroids during the molting cycle were monitored by using radioimmunoassay (RIA) with or without prior fractionation by high performance liquid chromatography (HPLC). The total amount of hemolymph ecdysteroids was the lowest during stages A, B, and C, followed by a slight elevation during stages D0, D1 ' and D1", a dramatic increase to a prominent peak during stages D1''' and D2, and then a rapid decline at stage D3. No significant sexual differences throughout the molting cycle were observed, except for stage B (p < 0.05). Among the 5 ecdysteroids fractionated by HPLC, 20hydroxyecdysone was found to be the predominant circulating ecdysteroid in tiger shrimp, and the quantitative changes of these ecdysteroids coincided with that of total ecdysteroids measured. The other ecdysteroids, ecdysone, 5,20-dihydroxyecdysone, 2-deoxy-20-hydroxyecdysterone and 2-deoxyecdysterone were present in minute amounts with a similar profile to that of 20-hydroxyecdysone, and they were more prominent in postmolt (stage A) and intermolt (stage C).
Molt cycle, Ecdysteroids, Shrimp, Radioimmunoassay (RIA), High performance liquid chromatography (HPLC)
