Dietary phytase improves growth and water quality parameters for juvenile <i>Clarias gariepinus</i> fed soyabean meal-based diets

Abstract

The effect of phytase on growth, nutrient utilization of juvenile Clarias gariepinus fed soya bean using a 5 x 5 experimental design was investigated. Soya bean meal was used to substitute fish meal at 25 %, 50 %, 75 % and 100 % as basal controls with no phytase (0 FTU/g). Another set of four diets were formulated with the same composition as the basal diet, but were supplemented with phytase as follows: 250 FTU/g, 500 FTU/g, 750 FTU/g, and 1000 FTU/g. A fish meal based diet (0% soya bean), which served as control without phytase supplementation (0 FTU/g), was included in the experiment to compare growth performance. Triplicate group of fish (n=1638, 11.55 ± 0.20 g) were randomly allocated to 21 experimental diets and fed at 3% body weight. Growth performance was significant with phytase addition to diet (P < 0.05). Mean weight gain (MWG) declined with increasing substitution of fish meal by soya bean (P < 0.05), regardless of phytase level. Significant improvement in MWG of fish was observed in phytase-supplemented diets (P<0.05). The lowest MWG (26.33± 12.18 g/fish) and highest feed conversion ratio, FCR (4.48±6.47) were recorded in 500 FTU/g and control (0 FTU/g),respectively. The highest MWG (32.13±13.26 g/fish) and lowest FCR (1.85±0.91) were obtained in 250 FTU/g (P<0.05). There was no significant difference (P>0.05) in MWG of fish fed fish meal, 0% soya bean with 0 FTU/g (48.20±2.67g/fish) and 75% with 250 FTU/g (42.88±0.56g/fish). Compared to 25%, 50% and 100% soya bean, there was siginificant increase in dissolved oxygen (DO) and decrease in ammnonia and nitrate with increasing phytase supplementation in 75% soya bean, with the lowest ammnonia recorded in 250 FTU/g (P<0.05). Regardless of phytase level, survival rate increased up to 75% (P>0.05). The research has demonstrated that the performance and water quality of juvenile C gariepinus were improved with soya bean up to 75%. The optimum phytase of 486.22 FTU/g (cubic regression) was determined as the requirement for growth of juvenile C gariepinus.