A preliminary evaluation of cacao husks in practical diets for juvenile Nile tilapia ( Oreochromis niloticus)

An experiment was conducted to assess the use of cacao husks, an agricultural waste in the tropics, as partial substitute for more expensive ingredients in juvenile tilapia diets. In this respect, triplicate groups of 100 Nile tilapia fingerlings (1.40 g) were fed each of three isonitrogenous (28% crude protein) and isocaloric (4.80 kcal/g) diets in nine 1500 l ‘fastanks’ for 13 weeks. In the three diets, ground cacao husk was incorporated at 0 (diet cc0), 10 (diet cc10) and 20% (diet cc20) levels to replace maize flour, wheat bran and rice bran. Fish were fed to satiation, by hand, with fortnightly intermediate sampling to monitor growth. Fish fed aggressively throughout the trial, thus showing acceptance of the three experimental diets. The specific growth rates were very similar, ranging from 2.3 (cc0) to 2.5%/day (cc20). Although feed:gain ratios and protein efficiency ratios ranged, respectively, from 1.95 (cc20) to 2.08 (cc0) and from 1.66 (cc0) to 1.83 (cc20), no significant differences among dietary treatments were noticed. Likewise, carcass analysis revealed a slight decrease ( P < 0.05) in the protein content of the whole fish body from diets ccO (14.2%) to diet cc20 (13.5%). The cost analysis of diets showed a considerable reduction of the production cost of one kilogram of fish while moving from diet cc0 to diet cc20 (US$0.15). Based on growth performances, feed and nutrient retention efficiencies and economic analysis, cacao husk appears to be a viable partial dietary protein source (up to 20% of the diet, according to this preliminary appraisal) for juvenile tilapia.