Cassava leaves can be used as a source of protein for Nile tilapia. However, as the leaves have high level of anti-nutritional factors that could reduce fish growth. The main aim of this study was to improve its nutrient contents by processing and evaluated its effects on growth performance of Nile tilapia. Fresh cassava leaves were treated with namely: air dried (AD), soaked-boiled sun dried (SBSD), Yeast (YF), Molasses (MF), Rumen-fluid (RF), Yeast-molasses (YMF), Yeast-rumen-fluid (YRF) and Molasses-rumen-fluid (MRF) fermentations.
Then nine iso-nitrogenous and iso-caloric diets were prepared for Nile tilapia. The results of the present study showed that YF resulted in the highest (p < 0.05) crude protein (CP) content (CP=30.3%) than others. Furthermore, in most nutrient parameters, rumen fermentation resulted in better nutrient contents than others. Fish fed RF, YMF and MRF based diets showed better apparent digestibility coefficient (ADC) of dry matter and ether extract than others next to the control diet. In addition, fish fed RF based diet showed comparable ADC of CP with the control diet. In most cases, fish fed RF, MRF and YMF cassava leaf-based diets showed better growth performance in terms of FBW, SGR and DWG than others next to control diet. In terms of feed utilization efficiency fish fed RF cassava leaf-based diet showed comparable FCR with fish fed control diet. Similarly fish fed RF and MRF cassava leaf-based diets had comparable PER with control diet. Fish whole body proximate compositions were also affected by the types of experimental diets except for CP content. The cost benefit ratio, gross profit margin, and return on investment were better for fish fed RF based diets than others. In conclusion, rumen-fluid fermentation method is the preferred processing method to improve nutrient value of cassava leaves resulted in better growth performance and profitability Nile tilapia farming.