The molting cycle of Penaeus vannamei juveniles was characterized by distinct and predictable changes in the setae of pleopods. The molt pattern was diecdysic with a relatively short intermolt period (40%) and a long proecdysial period (>53%). The levels of both total protein and ecdysteroids increased in the hemolymph during proecdysis, whereas the level of hemolymph glucose was low at metecdysis and proecdysis and maximal during anecdysis. As revealed by SDS-PAGE, the relative concentrations of two polypeptides (32 kD;

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One of the important peptide hormones that control reproduction in crustaceans is gonad‐inhibiting hormone (GIH). GIH is known to modulate gonad maturation by inhibiting synthesis of vitellogenin (Vg), the precursor of yolk proteins. In this study, a cDNA encoding a GIH (Pem‐GIH) from the eyestalk of Penaeus monodon was cloned using RT‐PCR and RACE techniques. Pem‐GIH cDNA is 861 bp in size with a single ORF of 288 bp. The deduced Pem‐GIH consists of a 17‐residue signal peptide and a mature peptide region of 79 amino acids with features typical of type II peptide hormones from the CHH family. Pem‐GIH transcript was detected in eyestalk, brain, thoracic and abdominal nerve cords of adult P. monodon. The gonad‐inhibiting activity of Pem‐GIH was investigated using the RNA interference technique. Double‐stranded RNA, corresponding to the mature Pem‐GIH sequence, can trigger a decrease in Pem‐GIH transcript levels both in eyestalk ganglia and abdominal nerve cord explant culture and in female P. monodon broodstock. The conspicuous increase in Vg transcript level in the ovary of GIH‐knockdown shrimp suggests a negative influence for Pem‐GIH on Vg gene expression, and thus implies its role as a gonad‐inhibiting hormone. This is the first report to demonstrate the use of double‐stranded RNA to elucidate the function of GIH in P. monodon.