Protein Digestibility Capability of Nile tilapia (Oreochromis niloticus) Fed on Local Feed, Ethiopia

The nutritional value of a feedstuff isn’t only on its chemical composition; however, it also depends on the nutrient-absorbing capacity of fish. Dietary markers must have no toxic effects, cannot be lost in digestion, cannot add considerable mass, and must be easily and equally mixed into feed. There are different types of dietary markers like ash, titanium dioxide (TiO2), and chromium oxide (Cr2O3). Most of the time chromic oxide was used in digestion trials with sheep, horses, cattle, pigs, fish, and humans. The experiment was conducted using 180 Oreochromis niloticus population with weights of 28.2 to 28.4 g, distributed in experimental randomized blocks design with five treatments and triplicates per treatment. Digestibility was estimated by the indirect method using chromic oxide at the concentration of 0.50 % of the diet as a marker. The apparent and true digestibility of the protein was estimated for noug cake, 87.1 and 89.1%; wheat bran 74.3 and 78.7%; soybean meal 88.3 and 90.0%; brewery waste 65.4 and 67.8%; fish meal 85.5 and 87.0%, respectively in siphoning technique. Similar (P > 0.05) results were observed in striping and siphoning methods in all experimental ingredients. This is the first report on protein digestibility status determined for O. niloticus in Ethiopia. This information provides an important basis for further investigation of single or mixed ingredients diet preparation or substitutions for evaluation of nutrient requirements of O. niloticus, to maximize performance and to minimize production costs and waste production. Soybean, noug cake, and fish meal had better (P < 0.05) crude protein digestible by O. niloticus than wheat bran and brewery waste. Brewery waste was the lowest digestible by O. niloticus. The fish that were consumed from brewery waste showed the lowest growth performance, which was also consistent with the ingredient's crude protein digestibility status. This suggests that O. niloticus has difficulty digesting brewery waste.