IDENTIFICATION OF THE Y-ORGAN IN THE KURUMA PRAWN PENAEUS-JAPONICUS

Histological and biochemical studies were conducted in order to ascertain whether the ventral gland in the kuruma prawn Penaeus japonicus is the Y organ homologue or not. The location of the ventral gland was determined histologically. This gland existed as a hypertrophied strip of epidermis situated exterior to the coxopodite of the scaphognathite in the anterior branchial chamber. Glandular cells at premolt stage possessed extremely expanded mitochondria with tubular cristae. Smooth surfaced endoplasmic reticulum was observed to be poorly distributed. Ventral glands excised from intermolt and premolt individuals were incubated in vitro for 6 h. Samplings were conducted at 1-hour intervals, and ecdysteroid quantities secreted were quantified by RIA. Ecdysteroid secretion was observed to continue for 6 h in vitro. The amount released over 6 h period was 193 +/- 40 ng/g tissue and 61 +/- 16 ng/g tissue in premolt and intermolt prawns, respectively. In order to identify the ecdysteroid secreted, the medium was analyzed by HPLC-RIA. Immunoreactivity was observed at positions equal to ecdysone, 20-hydroxyecdysone-22-acetate and 2-deoxy-20-hydroxyecdysone. These results indicate that the ventral gland in the kuruma prawn is the homologue to the Y organ.