USE OF PHYTASE TREATED CORN DISTILLER'S DRIED GRAINS WITH SOLUBLES IN CHINESE CATFISH (Silurus asotus Linnaeus 1758) DIET

This experiment reveals the effects of three supplemental levels and two methods of phytase inclusion in diets containing corn distiller's dried grains with solubles (DDGS) on the growth, whole body composition and nutrients digestibility of Chinese catfish (Silurus asotus Linnaeus 1758). Phytase was included at 0, 1000 and 5000 U kg^-1 diet by post-spray (PS0, PS1, PS5), spray on made diet, or by pretreatment (PT0, PT1, PT5), DDGS incubated with phytase before making diets. Cr₂O₃ at 1% was added to the diets as an inert marker for the digestibility study conducted for 3 weeks after a 10-week growth experiment. Fish (25.01±0.16 g) were stocked at 800 per m³ in 0.01m³ cylindrical cages accommodated in a round 2-MT fiberglass tank and fed to apparent satiation twice daily. Fish fed PT diets had higher survival rate (SR) and yield than those fed PS diets. Fish fed phytase treated diets had higher FW, WG, SGR and FI than the control fish but FCR and SR were not affected. In addition, PT-fish had respectively higher body content and apparent digestibility coefficients (ADCs) of crude protein (CP), ash and phosphorus (P) than PS-fish. However crude lipid was not affected. Generally, phytase improved the ADCs of dry matter (DM) and increasing phytase level also increased both ADCs and fish body content of CP, ash and P. The highest phytase level enhanced the protein efficiency ratio (PER), protein growth rate (PGR) and protein productive value (PPV). ADCs of nutrients were positively correlated with both body content of the same elements and the protein utilization parameters. It appears that phytase treatment can enhance growth, protein utilization and the ADCs of CP, ash and P in Chinese catfish. Consequently, the nutrient load especially P would be minimized. PT is more effective in our study than the PS.