Effect of replacing soybean meal with yeast-fermented canola meal on growth and nutrient retention of Nile tilapia, Oreochromis niloticus (Linnaeus 1758)

Yeast fermentation integrated with water soaking was applied as a method to reduce the levels of some anti-nutritional factors in canola meal. The procedure completely eliminated glucosinolates and it reduced phytic acid content by 18%. It also led to increase of 9% of crude protein and 8-32% of some minerals in the meal. A 60-day feeding trial was conducted to evaluate replacement of dietary soybean meal protein with yeast-fermented canola meal for Nile tilapia at ratios of 0, 25, 50, 75 and 100% respectively. Three groups of fish with an initial weight of 10 g were fed with each diet twice a day to an apparent satiation. The results showed that there were non-significant differences (P > 0.05) in growth, survival rate, feed intake and feed conversion ratio for all fish fed with the test diets. However, replacement with 75 and 100% levels significantly reduced (P < 0.05) protein efficiency ratio and nutrient digestibility of protein, lipid, ash, Ca, Mg and P of fish compared with the lower levels. The low retention of protein, lipid, ash, Ca, Mg and P were also observed. These effects seemed to be related to an increased dietary phytic acid.