Optimum Dietary Ca/P Ratio and Phytase for Growth and Bone Mineralization in Juvenile Clarias gariepinus Fed Soya Bean-Based Diet

Abstract

The research investigated the interactive effect of five phytase graded levels of 0 FTU/g (P0), 250 FTU/g (P1), 500 FTU/g (P2), 750 FTU/g (P3), 1000 FTU/g (P4) and four graded levels of roasted soya bean substitution at 25%, 50%, 75% and 100% in place of fish meal, respectively. All basal diets contained 0.20% calcium without added inorganic phosphorus, wheat and amino acids supplements so that the phosphorus, calcium, and Ca/P ratios of the five (5) were: S0 (1.31%, 1.85%, and 1.41), S1 (1.15%, 1.64%, and 1.43), S2 (1.01%, 1.28%, and 1.27), S3 (0.75%, 0.99%, and 1.30), and S4 (0.43%, 0.68%, and 1.59). 1092 fish of average weight 11.55 ± 0.2 g were randomly allocated to all experimental diet and fed 3% body for 84 days. There was no significant difference in final weight, weight gain and FCR S3P1 and S0P0 (P>0.05). Fish fed low phosphorus diet (100% soya bean) showed reduced total weight and weight gain compared to high (0%, 25%, 50%) and medium phosphorus diet (75%) with phytase addition (P<0.05). Fish fed phytase at 50-200 FTU/g and inorganic control had lower weight gain compared to S3P1 (P<0.05). Ca/P ratio correlated negatively with final weight (r=-0.439, P<0.01), weight gain (r=-0.431, P<0.01), SGR (r=-0.138, P>0.05), and PER (r=-0.210, P>0.05). Ca/P of S3P1 (1.41 ± 0.02) was not different from S0P0 (1.41 ± 0.01). Bone phosphorus, calcium and zinc were higher in 250 FTU/g compared to 0 FTU/g, 500 FTU/g, 750 FTU/g and 1000 FTU/g. In conclusion, Phytase improved growth performance (r=0.05) of juvenile Clarias gariepinus with optimum at 250 FTU/g; however, Ca/P affected performance (r=-0.431) and should range between 1.41-1.46 for optimum phytase activity.