Abstract: Aquafeed is a major source of phosphorus (P) that results in eutrophication and pollution of water-ways. This study was conducted to investigate the effectiveness of treatments of dietary soybean mean (SBM) and phytase in improving the growth of African catfish (Clarias gariepinus) and mineral concentration; and in reducing environmental P loadings. SBM was prepared as raw (untreated), oven-dried, cooked, toasted or soaked in water. Same 8000 Units of phytase (Ronozyme P (5000) CT) kg-1 diet was added to each of the differently prepared SBM before mixing with other ingredients to prepare 40% protein diets. Diet 1 contained untreated SBM without phytase; diet 2 contained untreated SBM with phytase; diet 3 had oven-dried SBM plus phytase; diet 4 contained cooked SBM plus phytase; diet 5 contained toasted SBM with phytase, diet 6 had soaked SBM with phytase. The diets were administered to African catfish (7.0?1.09 g) at 5% of their body weight daily in two equal instalments. After 77 days of feeding, results indicate that the mean weight gain (MWG) of fish fed diets 4 and 5 was higher (p<0.05) than that of fish fed other diets. Fish administered diet 3 had higher (p<0.05) MWG than those fed diets 1, 2 and 6. The specific growth rate (SGR) followed similar trend. Food conversion ratio (FCR) was best (p<0.05) in fish fed diet 4. The FCR of the fish fed diets 5 and 3 was similar but better (p<0.05) than that of the fish fed diet 6, while the fish fed diet 1 had the worst FCR. Ca deposited in the fish fed diets 2, 3, 6 was higher (p<0.05) than the deposition in other fish. P concentration in the fish fed diets 4 and 5 was higher (p<0.05) than the concentration in fish fed diets 2, 3; whereas fish fed diets 1 and 6 had the poorest P concentration. P discharged by all the fish fed diets with phytase was less (p<0.05) than the discharges from the fish fed diet without phytase. However, all fish administered diets of treated SBM and phytase discharged less (p<0.05) P than the fish fed diet of untreated SBM and phytase.