Evaluation of crude palm oil and re®ned palm olein as dietary lipids in pelleted feeds for a tropical bagrid cat®sh Mystus nemurus (Cuvier & Valenciennes) W-K Ng 1 , M-C Tee 1 & P-L Boey 2 1 School of Biological Sciences, and 2 School of Chemical Sciences, Universiti Sains Malaysia, Penang 11800, Malaysia Correspondence: W-K Ng, School of Biological Sciences, Universiti Sains Malaysia, Penang 11800, Malaysia Abstract The effects of different dietary lipids on the growth, feedutilizationandtissuefattyacidcompositionofa tropical bagrid cat®sh Mystus nemurus (Cuvier & Valenciennes) were investigated. Eight isonitrogen- ous and isoenergetic semi-puri®ed diets were fed to triplicate groups of M. nemurus ®ngerlings for 10weeks. Diet lipid levels were ®xed at 10%, with 1% coming from residual oil in ®shmeal and the remainder from cod liver oil (CLO), corn oil (CORN), soybean oil (SBO), crude palm oil (CPO), re®ned, bleached and deodorized palm olein (RBDPO) or various combinations of these oils. Cat®sh fed diets supplemented with 9% RBDPO showed signi®cantly (P <0.05) higher growth rates compared with ®sh fed the other seven diets. No signi®cant differences in growth performance or feed ef®ciency ratio were observed between M. nemurus fed9%CLO,CORNor CPO or ®sh fed diets containing 4% CLO with either 5% CORN, SBO, CPO or RBDPO. Based upon these results, palm oil-based diets can be used effectively for M. nemurus without compromising growth or feed utilization ef®ciency. Muscle and liver fatty acid composition of M. nemurus re¯ected that of the dietary oils added in pelleted diets fed to the ®sh. Considering the lower cost and availability of palm oil (compared with imported vegetable oils and ®sh oils) in many tropical countries, its use in dietary formulations for M. nemurus, and possibly other cat®sh species, will make these ®sh feeds less expensive. Introduction Malaysia is currently the world's leading producer andexporterofpalmoil,whichisextractedfromthe fruit of the oil palm tree Elaeis guineensis. Palm oilrepresentsthesecondlargestvolumeofvegetable oilproducedintheworldtoday,justbehindsoybean oil production (Cottrell 1991). Palm oil and its re®neryproductsarenowconsumedworldwideasa cookingoil,margarineandshortening,andtheyare also incorporated into fat blends and a wide variety of food products (Pantzaris 1995). The bene®cial nutritional properties of palm oil for human consumption has been well researched and docu- mented (Chong 1989; Nesaretnam & Muhammad 1993). Crude palm oil (CPO) has a deep orange±red colour caused by the high content of carotenoids, and it is also a rich source of vitamin E, namely tocopherols and tocotrienols (Nesaretnam & Muhammad 1993). Both beta-carotenes and vita- min E are well-known nutritional antioxidants. During re®ning of CPO, apart from removing impurities in the oil, the carotenoids present are thermally destroyed to produce the desired colour for a re®ned, bleached and deodorized (RBD) palm oil (Young 1987). To widen the range of its use, RBD palm oil can be fractionated by thermomecha- nical processes to produce RBD palm olein (used mainly as cooking oil) and RBD palm stearin (used mainly in margarines and shortenings). Differences inthephysicalandchemicalpropertiesofCPO,RBD # 2000 Blackwell Science Ltd 337 Aquaculture Research, 2000, 31, 337±347