NAMWONG, W.*; WITHYACHUMNARNKUL, B.; CHANG, S.A.; CHANG, E.S.; Mahidol Univ., Bangkok, Thailand; Mahidol Univ., Bangkok, Thailand; Bodega Marine Laboratory, Univ. of California-Davis; Bodega Marine Laboratory, Univ. of California-Davis: Characterization of the Molt Cycle in Relation to Hemolymph Ecdysteroid Levels in the Ridgeback Shrimp (Sicyonia ingentis)

Ridgeback shrimp (Sicyonia ingentis) are native to Southern California. In this species, we determined the molt interval and characterized morphological criteria for each molt stage. We also measured hemolymph ecdysteroid levels throughout the molt cycle. Shrimp were reared in flow-through systems, aerated, separated by partitions, and covered with clear lids; the temperature was 12-15°C, and the photoperiod was at 14 L:10 D. Setagenesis in the uropods was examined using light microscopy to determine molt staging. The molt cycle was divided into nine stages; postmolt (stages A and B), intermolt (stage C), premolt (stages D₀, D₁, D₂, D₃, and D₄), and ecdysis (stage E). The mean (±S.D.) weight of the shrimp was 19.6±1.6 g and the mean (±S.D.) molt interval was 66.9±5.7 d. The occurrence after ecdysis and duration for each molt stage was as follows: stage A, within 1 d postmolt (<1 d long); stage B, 0-2 d postmolt (6-8 d long); stage C, 7-11 d postmolt (4-9 d long); stage D₀, 10-16 d postmolt (3-7 d long); stage D₁, 12-21 d postmolt (8-14 d long); stage D₂, 20-35 d postmolt (7-14 d long); stage D₃, 40-43 d postmolt (9-15 d long); stage D₄, 51-61 d postmolt (7-13 d long); and stage E, 60-78 d postmolt (<1 d long). The hemolymph ecdysteroid levels were determined by using radioimmunoassay. As consistent with other crustaceans, the ecdysteroid levels were lowest at early postmolt (stage A), and gradually increased through intermolt and early premolt. The levels rose at premolt; stage D₄ showed the highest values. Funding was partially provided by the Commission on Higher Education, Thailand.