Effects Of Phytase On Apparent Digestibility Of Nutrient And Digestive Enzyme Activities Of Tilapia

To offer the direction of application of phytase and theory of the deep study in the aquaculture, effects of phytase on digestive enzyme activities, apparent digestibility of phosphorus and protein of tilapia were studied.EXPERIMENT 1Effects of phytase on apparent digestibility of phosphorus and protein, digestive enzyme activities of tilapiaIn the experiment 600 tilapia were allotted into five groups randomly and transferred into net cages for 90 days. The first group was the control fed with basal diet, the others were the treated groups fed with basal diet added 500,1000,1500, 2000U/kg phytase respectively. Then 300 tilapia were transferred into aquariums for 30 days. Activities of protease, amylase and lipase of the fore intestine, stomach, hepatopancreas, the apparent digestibility of the nutrient and the weight gain rate were determined.The results showed ingestion of phytase increased the digestive enzyme activities and apparent digestibility of nutrient. Ingestion of phytase of 1000-1500U/kg was the optimum growth for tilapia. Compared with the control, ingestion of 1000,1500U/kg phytase were significant (P<0.05), the weight gain rate increased by 10.71% and 14.07%. Compared with the control, ingestion of 500,1000,1500, 2000U/kg phytase were significant (P<0.05), the apparent digestibility of phosphorus increased by 12.33%, 18.60%, 22.43% and 39.04%. Although the apparent digestibility of crude protein was improved, it had no significance (P>0.05) . Compared with the control, ingestion of 500,1000,1500U/kg phytase were significant (P<0.05), the apparent digestibility of total dry matter(DM) increased by 8.96%, 12.18% and 10.62%.The activities of protease of stomach of treated groups of 500,1000,1500U/kg phytase were 10.24%, 13.85% and 17.47% higher than those of the control respectively,but it was not significant (P>0.05). The activities of amylase of hepatopancreas of treated groups of 1000, 1500U/kg phytase were significant (P<0.05), which were 29.03%, 42.69% higher than those of the control, respectively. The amylase activities of hepatopancreas of groups of 500, 2000U/kg phytase were not significant (P>0.05). The activities of protease of fore intestine of treated group of1000U/kg phytase was significant(P<0.05), which was 23.57% higher than the control; the activities of protease of fore intestine treated groups of 500,1500,2000U/kg phytase were higher than those of the control respectively, but it was not significant(P>0.05). The activities of amylase of fore intestine of treated groups of 500,1000U/kg phytase were significant (P<0.05), which were 23.23%, 29.65% higher than those of the control, respectively; but the amylase activities of fore intestine of groups of 1500,2000U/kg phytase were not significant (P>0.05). The activities of lipase of fore intestine of treated groups of 500,1000,1500,2000U/kg phytase were not significant (P>0.05).EXPERIMENT 2The characteristics of digestive enzyme of tilapiaIn the experiment 12 tilapia (average initial weight, 111.81 ±6.74g) were allotted into three groups randomly. The characteristics of protease, amylase, lipase of intestine, stomach, hepatopancreas in tilapia were studied, including the optimum pH, the optimum temperature, the optimum substrate concentration of digestive enzyme. The results showed that the optimum pH for protease in tilapia(Oreochromis niloticus xO.aureus) were 2.0, 10 and 9.5~ 10.5 in stomach, hepatopancreas and intestine respectively, the optimum temperature were 55, 65 and 55℃, and the optimum substrate concentration were 0.1%, 0.08% and 0.4%. The optimum pH for amylase in intestine and hepatopancreas were 6.5-7 and 7.5 respectively, the optimum temperature were 30°C, and the optimum substrate concentration were 0.8%. The optimum pH and temperature for lipase were 7.0-7.5 and 35 ℃ respectively.