Evaluation of locally available feed resources for Nile tilapia (Oreochromis niloticus) in Rwanda

Abstract

Aquaculture was introduced in Rwanda in the 1940s as an extensive pond-based system but the sector has gained in popularity during the past two decades, resulting in greater numbers of fish ponds and a corresponding increase in demand for quality fish feeds for sustainable aquaculture production. The aim of this thesis was to identify, sample and evaluate the nutritive value of some locally available feed ingredients that could be used by fish farmers producing Nile tilapia. An initial countrywide survey revealed that a semi-intensive farming system prevails (81% of total production) in Rwanda, three main fish species are cultured (Nile tilapia (Oreochromis niloticus) (most common), common carp (Cyprinus carpio) and North African catfish (Clarias gariepinus)) and around 31 feed ingredients are used, either individually or in mixtures in supplementary tilapia feeds. The nutrient content of local feed resources was evaluated. Digestibility trials in which fishmeal protein (reference diet, RD) was partly replaced with protein from spent brewer’s grain (SBG), spent brewer’s yeast (SBY), sweet potato leaf meal (SPLM), kidney bean leaf meal (KBLM) or wheat middlings (WM) showed that apparent digestibility (AD) of crude protein was highest for diets with SPLM and SBG (83%), followed by RD and SBY (78-82%) and then KBLM and WM (69-73%). Mean AD of indispensable amino acids (ADIAA) in the experimental diets was high (range 73-87%), and was above 81% for SPLM, SBG,RD and SBY. Weight gain, final body weight and specific growth rate were high and comparable to the control in fish fed SPLM, SBY, and SBG, but low in fish fed WM and KBLM. Hepato-somatic index and viscero-somatic index did not differ between diets, but red and white blood cell counts indicated a tendency for possible negative effects of KBLM on blood physiology in tilapia. These results suggest that SPLM, SBY, and SBG protein can replace fishmeal in Nile tilapia diets without compromising growth, feed utilisation or body indices, thus acting as a valuable local protein source for sustainable tilapia production.