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Ovarian and haemolymph ecdysteroid levels in adult female Penaeus monodon at various stages of vitellogenesis have been studied. The concentration of free ecdysteroids, predominantly 20-hydroxyecdysone, was maximal in animals with immature (stage 0) ovary, decreased gradually during early vitellogenesis (stage 0 to stage I) and fell sharply during later vitellogenesis (stage I to stage IV). 20-hydroxyecdysone 22-phosphate was identified in stage 0 ovary and in stage 0 and 1-11 haemolymph, and 20-hydroxyecdysonoic acid was observed in stage 0 ovary and haemolymph. Low levels of 20-hydroxyecdysone 22-fatty acyl esters were detected in stage 0 ovary but did not occur in the haemolymph. A major component of the stage IV haemolymph ecdysteroids was 20-hydroxyecdysone 22-acetate. The significance of the results is discussed.

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