Two experiments were carried out to investigate and compare growth, phosphorus availability, digestibility and serum status in juvenile Clarias gariepinus. Two groups of five isonitrogenous and isocalorific diets containing25, 50, 75, and 100 % soya bean meal (oil-extracted) and roasted soya bean meal, respectively, were formulated and supplemented with graded levels of phytase at 0. 250, 500, 750 and 1000 FTU/g. A fish meal control was included to compare growth performance. In experiment 1, 1092 fish of average weight 11.55+0.2g were fed the phytase diets at 3% body weight for 84 days. There significant reduction in weight gain with increasing soya bean levels, and fish fed fish meal control (S0P0E) had the highest weight gain (1219.47±47.57g) compared to phytase diets (P<0.05). Weight gain, feed intake and FCR were improved in S1P2 (vs S1P0), S2P4 (vs S2P0), S3P1, S3P2, S3P3 (vs S3P0) and S4P3 (vs S4P0). Oil-extraction improved phosphorus digestibility (r= 0.415, P<0.05), but decreased with phytase activity (r= -0.05, P>0.05). Serum phosphorus was improved by phytase (r= 0.402, P<0.01). In experiment two, 1040 fish were fed phytase treated full fat soya bean meal (roasted). Result showed there was no significant different between weight gain, feed intake and FCR of S3P1 and S0P0E (P<0.05). Phosphorus availability by phytase ranged (22.81-73.07%) is higher than oil-extracted-soya bean meal (16.66-65.38). Phosphorus digestibility, DPHOSP improved feed intake (r= 0.702, P<0.01) and weight gain (r= 0.802, P<0.01), but reduced by dietary fat (r -0.777, P<0.01) with reduced serum phosphorus (r= -0.09, P>0.05).

Keywords: Growth, phosphorus availability, phosphorus digestibility, soyabean meal, Clarias gariepinus