中性植酸酶替代磷酸二氢钙对黑鲷生长和磷利用的影响

Effects of replacing monocalcium phosphate with phytase on growth and phosphorus utilization in black sea bream, Acanthopagrus schlegelii

以鱼粉、豆粕、菜粕等为蛋白原料设计配方,磷酸二氢钙的添加量分别为1.5%、1.0%、0.5%和0(对应的饲料组为P1.5、PP1.0、PP0.5和PP0组),其中PP1.0、PP0.5和PP0组中均添加200 mg/kg的中性植酸酶,开展为期8周的黑鲷(Acanthopagrus schlegelii)养殖实验,以探讨中性植酸酶替代磷酸二氢钙对黑鲷生长和磷利用的影响。结果显示,黑鲷摄食实验饲料8周后,各组间成活率无显著差异(P>0.05);摄食饲料PP1.0、PP0.5和对照组(P1.5组)实验鱼的增重率无显著差异(P>0.05),但均显著高于PP0处理组,饲料系数则显著低于PP0处理组(P<0.05)。摄食不同饲料的黑鲷全鱼中蛋白质、脂肪、灰分及钙磷含量在不同组间均无显著差异(P>0.05)。添加植酸酶的各组鱼磷的表观消化率均显著高于对照组(P<0.05)。随着磷酸二氢钙添加量的降低,黑鲷对干物质和蛋白质的表观消化率呈升高的趋势,当饲料中磷酸二氢钙的添加量降到0时,黑鲷对干物质和蛋白质的表观消化率显著高于对照组(P<0.05)。以上结果说明,在本研究配方下,黑鲷正常生长对饲料有效磷的需求量≥0.51%;磷酸二氢钙可部分被植酸酶替代,当黑鲷饲料中含有20%鱼粉、32%豆粕和12%菜粕,且植酸酶添加量为200 mg/kg时,与饲料中添加1%的磷酸二氢钙相当;在不影响黑鲷生长的前提下,植酸酶部分替代磷酸二氢钙不仅可降低无机磷的添加,同时可提高饲料中磷的利用率,降低磷排放。

Because of a decrease in production and increase in the cost of fishmeal, there is increased interest in the use of plant-based feed in aquaculture. However, one of the major problems associated with the use of plant protein in fish feed is the presence of anti-nutritional factors, such as phytate, which is the primary storage form of phosphorus. Phy-tate is essentially unavailable to monogastric or agastric aquatic animals as they lack intestinal phytase that promote phytate hydrolysis during digestion. To address this issue, diets for monogastric or stomachless animals are often sup-plemented with monocalcium phosphate （MCP） to meet their phosphorus requirements. However, MCP is derived from fossils so it is a non-renewable resource. Furthermore, the cost of rock phosphorus has increased dramatically over the past several years. Alternatively, exogenous phytase can be added to hydrolyze phytate, and thus improve the use of phytate phosphorus. Thus, the addition of phytase may lower the need for MCP supplementation, thereby lower feed costs. This strategy may also lower the concentration of phosphorus excreted, resulting in lower eutrophication of the surrounding waters. We evaluated whether neutral phytase could partially replace MCP, and thus reduce the dietary in-clusion of MCP. The fish （initial body weight：11.52 ＆#177; 0.12 g） were fed one of four diets for 8 weeks：a control diet （designated P1.5） was prepared with 1.5%MCP but without phytase and three other diets （designated as PP1.5, PP1.0, and PP0.5） were supplemented with 1.5%, 1.0%, or 0.5%MCP, respectively, and 200 mg/kg （diet） phytase. Fish fed PP1.0 and PP0.5 had no significant change in weight gain rate（WGR）, specific growth rate （SGR）, protein efficiency rate （PER）, or feed conversion ratio （FCR） compared with the control （〉0.05）, whereas fish fed PP0 had significantly lower growth performance in the above parameters （〉0.05）. Phytase addition did not affect body composition. The apparent digestibility coefficients （ADCs） of crude protein and phosphorus increased when fish were fed with the diets in which MCP was replaced by phytase. Additionally, phosphorus discharge was significantly reduced in fish fed diets in which MCP was replaced by phytase. Our results suggest that the dietary phosphorus requirement for meeting normal growth in black sea bream is≥0.51%. MCP can partially be replaced by phytase without affecting the growth of black sea bream. A diet containing 200 mg/kg phytase is equivalent to 1%MCP. The partial substitution of MCP by phytase not only reduces inorganic phosphorus addition to the surrounding waters, but also improves use of phosphorus in the feed.