This study was conducted to investigate the influence of phytase on growth performance, apparent digestibility of nutrients, excretion of nitrogen and phosphorus in channel catfish (Ictalurus punctatus) and to determine the optimum additive amount of phytase. A total of 540 juvenile channel catfish with an average body weight of (1. 74 ±0. 02) g were randomly divided into 6 groups with 3 replicates per group and 30 fish per replicate. The fish in control group were fed a basal diet, and the fish in experimental groups were fed the basal diet supplemented with 300, 500, 1 000, 1 500 and 2 000 U/kg phytase, respectively. After a 90-day growth experiment, a total of 75 channel catfish [ average body weight of (16. 70 ±0.85) g ] in each group were randomly distributed into 3 replicates and 25 fish in each replicate, for measuring the nitrogen and phosphorus excretion. The nitrogen and phosphorus excretion experiment lasted for 72 h. The results of growth experiment showed as follows: compared with the control group, the weight gain rate, specific growth rate, protein efficiency ratio and apparent digestibility of nutrients in the groups with the diets supplemented with 500 to 2 000 U/kg phytase were significantly improved (P <0. 05) , and the feed conversation rate was significantly decreased (P<0.05) , but there was no significant difference among the groups with the diets supplemented with 1 500 to 2 000 U/kg phytase (P >0. 05). The results of nitrogen and phosphorus excretion experiment showed as follows: the excretion of ammonia nitrogen, total phosphorus and fecal phosphorus per kilogram of weight gain were decreased with the dietary phytase level increasing, and the above indices in the groups with the diets supplemented with 1 000 to 2 000 U/kg phytase were significantly lower compared with the control group (P <0. 05). Based on these findings, this study concludes that supplementation of 1 500 U/kg phytase in diets can improve the growth performance and apparent digestibility of nutrients in channel catfish, and decrease the nitrogen and phosphorus excretion into aquaculture water.%本试验旨在研究植酸酶对斑点叉尾鮰生长性能、营养物质表观消化率及氮、磷排泄的影响,以确定植酸酶在斑点叉尾鮰饲料中的适宜添加量.选取初始均重为(1.74±0.02)g的斑点叉尾鮰幼鱼540尾,随机分成6个组,每组3个重复,每个重复放养30尾鱼.对照组饲喂基础饲料,试验组分别饲喂在基础饲料中添加300、500、1 000、l 500和2 000 U/kg植酸酶的试验饲料,生长试验进行90 d.在生长试验结束后进行氮、磷排泄试验,从各组中挑选体重(16.70±0.85)g的斑点叉尾鮰75尾,每组3个重复,每个重复放养25尾鱼,试验时间为72 h.生长试验结果显示:与对照组相比,添加500 ～2 000 U/kg植酸酶的试验组的增重率、特定生长率、蛋白质效率及各营养物质表观消化率均有显著提高(P＜0.05),饲料系数显著降低(P＜0.05),但添加量在l 500 ～2 000 U/kg时组间无显著差异(P＞0.05).氮、磷排泄试验结果显示:随着植酸酶添加量的增加,氨氮、总磷和单位增重粪磷排泄量均有下降趋势,与对照组相比,添加1 500～2 000 U/kg植酸酶的试验组上述指标均显著降低(P＜0.05).综上所述,在斑点叉尾鮰饲料中添加1 500 U/kg植酸酶可改善其生长性能,促进营养物质的消化吸收,降低其向养殖水环境中的氮、磷排泄.
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