THE IMPACT OF PARTICLE SIZE OF INGREDIENTS IN COMPOUNDED DIETS ON PELLET STABILITY AND PERFORMANCE IN PENAEl.!'S INDICUS H. MILNE EDWARDS RANI PALANISWAMY and S. AHMAD All· Central Marine Fisheries Research Institute, Cochin 3/, India. ·Present address: Narakkal Research Centre. Central Institute of Brac/.:ish ..... ater Aquaculture. Narokkal682505, Kerala.lndia ABSTRACT Th e impact of particle size of ingredients in a research diet and a practical feed in th e water stability of digestibility. growth, and food conversion ratio in the prawn Penaeus ;ndicus were investigated. The research diet consisted of casein. cod·Jiver oil, sucrose. starch. cellulose. and o th er addi ti ves while the practical feed wa" made up of prawn waste. mantis shrimp (Sqllilla), fish meal. groundnul oilcake and tapioca. Casein in the research diet and prawn waste, mantis shrimp, and groundnut oiJcake in the practical feed were prepared into panicles of 500, 420 ,300,250,2 10, 100, and 50 and dry pellets were prepared wi th ingredients in each size. The pellets of the diet co mpounded with the ingredie nt s of212 exhibited th e highest water stability (P < 0.05 ) both in th e research diet and in th e practical feed. These pellelS fed to P. indiClIs showed high digestibility. superior growth ( P< 0.05) and the beSt food conversion ratio compared to the diets prepared with all the other particle sizes. The significance of grinding the ingredients to specific panicle size in compou nded diets is discussed. The water stability of an aquatic feed plays an imponant role in detennining the overall perfonnance of the feed (Forster and Gabbol. 1971: Fannanfannaian and Lauterio, 1982). Feed pellets which disintegrate faster facilitate rapid leaching of nutrient s. especially the micronulrients, leading to non-availability to the animal. This leads to pollution of the water and also results in economic lo ss. The water stability of the feed depends primarily on the binding material used (New, 1976; Ahmad Ali, 1988 ). However, the method of preparation of the feed also contributes considerably to it s stability. In variabl y, in fonnulating research diets and practical feeds, a variety of ingredients with different propenies are used. Grinding the raw materials to a unifonn panicle size is essential for preparing a homogeneous feed mixture. The impact of particle size of these ingredients on the stability and digestibility of the feed is not known. In thi s context, the effect of particle size of ingredients on the pellet stability in the water and th e digestibility of a research (purified) diet and a practical prawn 1. Aqua. Trop., 6 ( 1991 ) 119-127 © Oxford & ISH Publishing Co. Pvt. Ltd.