Effect of dietary replacement of yellow corn energy with culled sweetpotato (as non traditional energy source) on growth performance, nutrients utilization and carcass traits of growing Nile Tilapia (Oreochromis niloticus)

The present study aimed to evaluate the effect of incorporation of culled inedible sweet potato root (as non-traditional energy source) to replace yellow corn energy in growing mono-sex Nile tilapia (Oreochromis niloticus) diets on the fish performance, nutrients utilization, whole body composition and carcass traits. The study was carried out in concrete ponds (7.5m length × 2.25m width × 0.70m water depth). Each pond was divided by fine nets into three equal parts (2.5 × 2.25 × 0.70m each) to represent four treatments; the control (CSP0); the 25 (CSP25); 50 (CSP50) and 100% (CSP100) culled sweet potato, respectively. Each dietary treatment was carried out in triplicates and the treatments were stocked with Nile tilapia fry (0.31 g initial weight) at a rate of 20 fish/m^3 i.e. 80 fish in each replicate. The experimental diets were formulated to be iso nitrogenus and iso caloric and contained about 33% crude protein and 4500 kcal GE/kg. The experimental diets were fed at daily rates of 30; 10; 6 and 4 % of the fish biomass for fish weight from start to 1g; 1-5g; 5-20g and 20g respectively till the end of the experiment after 22 weeks. The experimental diets were offered in equal portions at 9am; 11am; 1 pm and 3pm respectively. Results obtained are summarized in the following: 1- Culled sweet potato contained 92.5; 6.1; 1.0; 4.6; 3.87 and 76.93 % dry mater; crude protein; crude fat; ash; crude fiber and NFE, respectively. It contained 3671 kcal growth energy / kg. 2- Incorporation of culled sweet potato to replace 100% of yellow corn energy improved significantly final weight and weight gain compared to the 25 CSP and the control group. Replacement of yellow corn energy with CSP at all tested levels released no significant effects on condition factor and survival rate. 3- Incorporation of CSP at 50 and 100 % levels to replace yellow corn energy in Nile tilapia diets showed similar insignificant feed conversion ratio compared to the control group, however both levels improved significantly the protein efficiency ratio compared to the 25% replacement level. CSP at all tested levels had no significant effects on energy utilization compared to the control group. 4- Incorporation of CSP released significant effects on dressing; head; byproducts and flesh percentages compared to the control group. 5- Replacement of yellow corn energy with CSP at 25; 50 and 100% levels had no significant effects on whole body chemical composition. 6- Replacement of yellow corn energy with CSP energy reduced the costs of one kg gain in weight by 4.67 and 1.24% for the CSP50 and CSP100 compared to the control group, respectively; while CSP at 25% level increased the production costs of one kg gain in weight by 5.72 % compared to the control group. Based on the obtained results, it could be concluded that culled sweet potato can replace 50 to 100% of yellow corn energy without adverse effects on growth performance, feed utilization parameters with the advantage of reducing the costs of 1000 Kg gross energy.