Effects of 20-hydroxyecdysone injection and eyestalk ablation on the moulting cycle of the shrimp, Penaeus vannamei

Abstract

1. 1. The effects of 20-hydroxyecdysone (20-OHE) injection and eyestalk ablation were investigated on the moulting cycle of the shrimp, Penaeus vannamei. 2. 2. Injection of 20-OHE into intact intermoult (stage C 1) animals shortened the duration of the intermoult and the early premoult stages but did not affect subsequent (postmoult, A, B) stages. 3. 3. 20-OHE injection also increased mortality and caused abnormal setal development. 4. 4. In contrast, eyestalk ablation of the early intermoult (stage C 1) animals reduced the durations of both the pre- and postmoult stages. 5. 5. Eyestalk ablation advanced the increase in hæmolymph ecdysteroid titres during the premoult stage, but did not affect the maximal (stage D) hzmolymph ecdysteroid levels. 6. 6. Eyestalk ablation also slightly elevated minimal (stages A, B) ecdysteroid levels during stages A and B.