Abstract.An assessment of the nutritive value of cassava as an energy source in a pelleted lilapia diet was carried out. Four isonitrogeneous diets containing 15. 30, 45 and 60 cassava were formulated and fed to groups ofOrtochromis niloucusL for 10 weeks. Good growth and food utilization efficiencies were obtained with all diets: there was a trend of improved growth and food utilization with increased cassava incorporation in the diet although there were no significant differences (P<0–05) in food conversion ratio, protein efficiency ratio or apparent net protein utilization between the experimental diets. No nutritionally related pathology was observed in fish fed high cassava levels. Increased incorporation of cassava led to an increase in the carcass fat content although it was within the acceptable limits for tilapia. Phytoplankton growth occurred in all experimental tanks due to the fertilization effects of uneaten feeds and faeces as the water within the experimental lankiyuem was not exchanged: the contribution of phytoplankton to the nutrition of the experimental fish was not quantified but was considered to be minimal since the phytoplankton biomass was approximately an order of magnitude less than in fertilized system
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