LAUSR

Abstract Increasing the inclusion rate of plant ingredients will increase the content of non-starch polysaccharides (NSP) and phytate in the fish feed. Both NSP and phytate are undesired in fish feed due to their anti-nutritional properties. The main objective of the present study was to assess the impact of exogenous enzyme supplementation on growth, body composition, digestibility and the energy, nitrogen and phosphorus balances in Nile tilapia. Four experimental diets were tested in a 2 × 2 factorial arrangement of treatments. The first factor was phytase supplementation at a dose of either 0 or 1000 FTU/kg and the second factor was xylanase supplementation at a dose of 0 or 4000 U/kg. This resulted in a control diet (CON-CON) without enzymes, phytase diet (PHY-CON), xylanase diet (CON-XYL) and a diet with both xylanase and phytase (PHY-XYL). In total 24 tanks (6 replicates/treatment) were used with 30 (mean initial body weight 42 g) fish each. Fish were restrictively (80% of expected satiation) fed the experimental diets for 38 days. Growth was significantly affected by the interaction between phytase and xylanase supplementation (P   0.05). The significant synergetic effect of the combination of phytase and xylanase on growth was not reflected on the digestibility (P > 0.05). The nitrogen balance showed that the synergism on growth was predominantly due the significant synergistic effect of phytase and xylanase on the protein retention (P = 0.005). Both xylanase and phytase showed to be an effective tool to improve the nutrient availability and growth in Nile tilapia. Fish fed the diet supplemented with both phytase and xylanase had a significantly higher growth than all other treatments.