Aquaculture, 112 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA ( 1993) 207-2 15 Elsevier Science Publishers B.V., Amsterdam 201 AQUA 50059 Performance of juvenile zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONM Oreochromis niloticus (L. ) reared on diets containing cowpea, Vigna catiang, and black gram, Phaseolus mungo, seeds C.N. Keembiyehetty’ and S.S. de Silva’ Dept. of Zoology and Fisheries Biology, UniversityofRuhuna, Matara, Sri Lanka (Accepted 28 August 1992) ABSTRACT Keembiyehetty, C.N. and De Silva, S.S., 1993. Performance of juvenile Oreochromis niloticus( L.) reared on diets containing cowpea, Vigna catiang, and black gram, Phaseolus mungo, seeds. Aqua- culture. 112: 207- 2 15. Sixteen isocaloric diets containing one of three protein levels (20, 25 and 30%) were prepared by partially or totally replacing fish meal with seeds of the legume Vigna catiang (cowpea) and Phaseolus mungo (black gram). Oreochromis niloticus fingerlings (mean weight of 2.60 If: 0.52 g) were fed the test diets twice daily to satiation over a 70-day period. Poor growth rates were noted when fish meal was completely replaced by each of the plant protein sources. Weight gain generally declined as the dietary level of legume seeds increased. Poor feed conversion was observed for fish fed diets with higher plant materials at 20% dietary protein. PER tended to increase with decreasing dietary protein level. Carcass lipid of fish fed 20°Ya protein diets was increased significantly except for one group. It was noted that each of the tested legume seeds could replace about 33% of the fish meal in the test diets without any adverse effect on growth rate. INTRODUCTION Protein is the most expensive dietary component because fish require more of this nutrient in the diet than terrestrial animals (Cowey and Sargent, 1979