Nutritional evaluation of some Ethiopian oilseed cakes in the diets of juvenile Nile tilapia, Oreochromis niloticus L.

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Addis Ababa University


This study evaluated the suitability of Niger seed cake (NSC) and linseed cake (LSC) inclusion as potential plant protein sources in Nile tilapia, Oreochromis niloticus, diets. A series of four experiments were conducted in a recirculation system using juvenile O. niloticus. The fish were fed diets containing the oilseed cakes at dietary inclusion levels ranging from 20% to 50%. Diets were formulated to be isonitrogenous (32g 100 g-1), isolipidic (10g 100 g-1) and isoenergetic (18 kJ g-1) and fed to juvenile Nile tilapia at 4-10% of their body weight per day for a period of 8 weeks. Niger seed cake (NSC) and linseed cake (LSC) were used individually or as mixtures to test for their effect on Nile tilapia growth and feed utilization. Also of interest was to compare digestibility and feeding values of NSC and LSC with that of soybean cake (SBC), the best plant protein source. Proximate analysis showed that Niger seed cake (NSC) and linseed cake (LSC) had 324.2 and 310.0 g kg-1 crude protein, 201.1 and 136.3 g kg-1 crude fibre and 18.1 and 18.6 kJ g-1 gross energy, respectively. Nutrient digestibility of these oilseed cakes suggested that Nile tilapia may be able to utilize NSC better as dietary protein source due to a reasonably high protein digestibility coefficient (72.6%) than linseed cake (62.4%). Of the three oilseed cakes (NSC, LSC and SBC) tested soybean cake (SBC) produced significantly (P< 0.05) the highest nutrient digestibility coefficients. When Niger seed cake (NSC) and linseed cake (LSC) were used individually as protein sources in Nile tilapia diets, depressed growth and feed efficiency were observed at dietary inclusion levels above 20%. This may be attributed to high levels of antinutritional factors (ANFs), high crude fibre content and poor essential amino acid profile. However, the use of mixtures of these two oilseed cakes (formulation 1 (F1): 50% NSC:50% LSC, Formulation 2 (F2): 33% NSC:67% LSC and Formulation 3 (F3) 67% NSC:33% LSC) was found to be marginally suitable than that of single sources, especially when the proportion of NSC in the mixture is 50% to 67%. The oilseed cake formulations with higher proportion of NSC could be included at 25% dietary inclusion without significantly reducing performance. This may have been as a result of lower levels of ANFs and improvements in the amino acid profile due to mixing. It can be concluded that there is nutritional and economic justification for using NSC and LSC as protein sources in Nile tilapia diets. Based on growth performance, nutrient utilization and economic benefits the diet with F3 formulation at 25% level of inclusion has the best prospects for use in Nile tilapia diets



Nutritional evaluation of some, Ethiopian oilseed cakes