In the context of a hatchery programme for the penaeid prawns, some aspects of the biology of Penaeus merguiensis along the Orissa Coast were studied over a three year period (1983-1985) and are presented in this paper. This species is caught both by mechanised boats (trawlers) and the artisanal craft, the catamarans. Postlarval or juvenile population of this prawn were not recorded so far in any of the estuarine creeks or even in the outer channel of the Chilka Lake. Length frequency distribution of the adult prawns sampled from offshore catches showed that generally females exhibited two modes and males one mode in most of the months, during August 1984 to July 1985. The length-weight relationship calculated for females was found to be log W=—4.6612 + 2.8239 log L. This prawn was found to exhibit strong schooling movements and was active during day and night as exemplified by its catch in trawlers as well as catamarans. The size of the smallest observed mature female was 132 mm. The mean sex ratio of males to females was 1:1.5. Fully mature females were available from May/June to February! March with peak during July-August and November. Successful attempts have been made in developing hatchery techniques for this species based on the knowledge of its biology