Effects of b-xylanase and 6-phytase on digestibility, trace mineral utilisation and growth in juvenile red tilapia, Oreochromis niloticus (Linnaeus, 1758) x O. mossambicus (Peters, 1852), fed declining fishmeal diets

Abstract

In response to the global sustainability drive to lower fishmeal (FM) inclusion in aquatic feeds, exogenous enzymes can improve nutrient digestibility in monogastric plant-based diets. A 80-day experiment was conducted to evaluate the combined effects of xylanase and phytase on digestibility, trace mineral utilisation and growth in juvenile red tilapia, Oreochromis niloticus x O.mossambicus, (48.8 g±13.9;μ ± STD) fed declining FM diets. Basal diets were formulated to contain 0, 3 and 5% FM with and without xylanase (0.385 g kg−1) and phytase (0.075 g kg−1), forming six treatments. Each treatment was randomly assigned to four replicates, 20 fish tank−1; mean water temperature 28.98 ± 0.73°C. Although the size of the effects was modest, growth performances (feed intake, FCR, growth rate) decreased with lower FM levels (P<0.05) but improved with enzyme supplementation. Enzyme supplementation increased P digestibility and trace mineral uptake (P<0.05), but no effects were seen on protein digestibility and N retention. Nevertheless, tilapia fed the enzyme-supplemented 3% FM and control 5% FM diets performed comparably (P<0.05). This potentially justifies a 2% FM reduction for tilapia diets using exogenous xylanase and phytase without significant effects on digestibility, trace mineral utilisation and growth.