Acceptability and digestibility by tilapia Oreochromis niloticus of feeds containing cocoa husk A. E. FALAYE Department of Wildlife and Fisheries Management, University of Ibadan, Ibadan, Nigeria K. JAUNCEY Institute of Aquaculture, University of Stirling, Stirling FK9 4LA, Scotland Abstract The acceptability, digestibility and nutrient utilization of feeds containing cocoa husk were determined for tilapia Oreochromis niloticus ®ngerlings reared in a recirculation system. Three semipuri®ed isonitrogenous diets formulated to contain 0, 100 and 200 g kg )1 of cocoa husk were fed to satiation three times daily. Although the feeds containing cocoa husk were acceptable to the ®sh, as indicated by their voracious consumption and positive weight gains, there were signi®cant (P < 0.05) reductions in gross feed conversion eciency with the cocoa husk feeds. Both apparent protein and dry matter digestibility were signi®cantly (P < 0.05) reduced when 100 and 200 g kg )1 cocoa husk was fed. Speci®c growth rates of 3.51 and 3.34% per day, resulting from the two cocoa husk feeds, respectively, were signi®cantly (P < 0.05) lower than growth rates of control ®sh. Apparent net protein utilization was not signi®cantly aected (P > 0.05) by the 100 g kg )1 cocoa husk feed treatment. The consumption of the cocoa husk feeds could compensate for their low digestibility under acceptable ®sh yields and returns. KEY WORDS: KEY WORDS: Cocoa husk, ad libitum feeding, acceptance, digestibility growth response, tilapia Received 30 September 1997, accepted 14 August 1998 Correspondence: K. Jauncey, Institute of Aquaculture, University of Stirling, Stirling FK9 4LA, Scotland Introduction The tilapia Orechromis niloticus feeds eciently on natural fauna and ¯ora and can also utilize supplementary feed materials to achieve rapid growth and weight gain. The intensi®cation of tilapia culture necessitates the development of biologically eective and acceptable feeds for complete and supplementary feeding in tanks and ponds, respectively. The nutritive value of mixed rations depends on the nutrient composition of the individual feed components and the ability of the animal to digest and absorb the nutrients (Smith 1979; Kirchgessner et al. 1986). Cocoa Theobroma cacao husk is an agricultural by-product largely available in cocoa plantations in Nigeria and mostly discarded as waste. According to Opeke (1984), over 4.5 million metric tonnes of cocoa by-products, which include the cocoa pod husk, are available annually in the southern parts of Nigeria. Barnes et al. (1984) recorded low digestibility of cocoa pod husk in growing-®nishing pigs because of its high ®bre content. The ability of ®sh to digest and absorb plant materials as feed is not well understood (Buddington 1979). Little is known about the use of cocoa husk in ®sh feeds. The present study was therefore designed to evaluate the feed consumption, digestibility and growth of O. niloticus ®ngerlings that received feeds containing cocoa husk at two inclusion levels. Materials and methods The experimental feeds were made up of three isonitrogenous formulations with varying cocoa husk inclusion levels at 0, 100 and 200 g kg )1 (Table 1). Fish meal, which constituted the principal dietary protein source, was obtained from Ewos (UK) Ltd, Bathgate, UK. The test ingredient, cocoa husk, was imported from Nigeria. All experimental diets contained 5 g kg )1 chromic oxide as an exogenous inert marker. Feed ingredients were milled, mixed with feed additives and water in a Hobart A 200 (Hobart Ltd, London, UK) food mixer, and the dough was pelleted in a California pellet mill (CPM Crayfordsvill, IN, USA), with a 3.0-mm die. Resulting pellets were stored in polythene bags and frozen until used. Fifteen O. niloticus individuals with mean body weight of 0.97±0.02 g were housed in each of the nine 9.0-L circular plastic rearing tanks within a single water-recircula- tion system at Scotland's Tropical Aquarium Building, Institute of Aquaculture, University of Stirling, Stirling, UK, with a continuous supply of fresh water at the rate of 157 Aquaculture Nutrition 1999 5 ; 157^161 .............................................................................................. .............................................................................................. Ó 1999 Blackwell Science Ltd