Effect of microbial phytase on phosphorus availabilityand growth of juvenile Clarias gariepinus fed different processed soyabean-based diets
Two experiments were carried out to investigate and compare phosphorus utilization by phytase in the diet of juvenile Clarias gariepinus using parameters of growth, phosphorus availability, and digestibility. Two groups of five isonitrogenous and isocalorific diets containing 25%, 50%, 75%, and 100 % soya bean meal (oil-extracted) and roasted soya bean meal (full fat), respectively, were formulated and supplemented with graded levels of phytase at 250 FTU/g (P1), 500 FTU/g (P2), 750 FTU/g (P3) and 1000 FTU/g (P4). In experiment 1, there was a significant reduction in mean weight gain M with increasing soyabean levels compared to fish meal diet (Tukey, P<0.05). Mean weight gain declined with phytase addition to diet, regardless of soyabean level (Tukey, P<0.05). The highest protein digestibility was recorded for 1000 FTU/g. Phosphorus digestibility improved significantly with phytase addition (500FTU/g-1000FTU/g) compared to control with no phytase (Tukey, P<0.05). Phosphorus availability by phytase ranged between 15.38%-65.38%. In experiment two, a reduction in mean weight gain with increasing fish meal substitution with soya bean was observed (Tukey, P<0.05). Phytase addition at 250 FTU/g resulted in higher mean weight gain compared to control, 500, 750 and 1000 FTU/g phytase. Phosphorus availability by phytase ranged between 20.81%-73.07%.
Keywords: Phytase, phosphorus availability, soyabean meal, Clarias gariepinus