| Due to the decreasing production and increasing cost of global fishmeal,the use of plant-based protein feed in aquaculture will be more and more.Whereas,plant-based protein feed contains a large number of phytic acid,due to lack of phytase in the aquatic animal digestive tract,phytate phosphorus can hardly be used,so,aquatic feed was often supplemented with monocalcium phosphate(MCP)to meet the demand for phosphorus of aquatic animals.However,MCP is fossil phosphorus-source which is non-renewable,and the cost of rock phosphorus has increased dramatically over the past several years.Phytase can hydrolyze phytate,releasing inorganic phosphorus and nutrients combined with phytate,and thus improve the utilization of phytate phosphorus and other nutrients.Therefore,dietary inclusion of MCP can be reduced if phytase is added,and then the feed cost can be reduced;meantime,the phosphorus excretion may reduce into the water,then reduce the phosphorus pollution.In past,most research of phytase in aquaculture was acidic phytase,acidic phytase is suitable for the gastric fish,but is not suitable for the agastric fish which the digestive tract pH is nearly neutral.In the present study,we study the effect of replacement of MCP with neutral phytase corresponding to agastric fish on growth performance,body compositions,serum biochemistry parameters and phosphorus utilization in Carassius auratus gibelio,which providing the reference for popularization and application of neutral phytase in aquaculture.The experimental diets were divided into seven groups,D1(the positive control group,1.5%MCP),D2(the negative control group one,1.0%MCP),D3(1.0%MCP,400U/kg phytase),D4(1.0%MCP,phytase 800U/kg),D5(the negative control group two,0.5%MCP),D6(0.5%MCP,400U/kg phytase)and D7(0.5%MCP,800 U/kg phytase).Each diet was fed to triplicate tanks of fish(25 fish per tank,initial body weight:23.39±0.10 g).An 8-week feeding trial was conducted.After the feeding trial,the D5 group showed the worst growth performance and feed efficiency among the seven groups(P<0.05).The weight gain and specific growth rate of D2 gjroup and D6 group showed significantly lower compared with D1 group(control group),while the feed conversion ratio showed significantly higher.The growth performance of D3,D4 and D7 groups had no significant differences compared with control group(P>0.05).The moisture,crude protein,crude ash and phosphorus content of whole body,besides serum cholesterol concentration and alkaline phosphatase activities had no significant differences among the all groups.Serum phosphorus and triglyceride levels,in addition to the D5 group,showed no significant difference between the rest groups(P>0.05).At the same level of MCP,the phosphorus retention ratio and apparent digestibility coefficiency of phytase addition groups were significantly higher than that of no phytase addition groups,while the phosphorus discharge showed the opposite(P<0.05).The present study suggests that when the diet is supplemented 400 and 800 U/kg of neutral phytase,MCP level can be reduced by 0.5%and 1%respectively,without affecting the growth performance,body composition and serum biochemistry parameters of Carassius auratus gibelio.400 and 800 U/kg of neutral phytase can provide equivalent available phosphorus with 0.5%and 1.0%MCP respectively.Neutral phytase partial replacing MCP in Carassius auratus gibelio diet will improving the utilization of phosphorus,and reducing the phosphorus discharge,it is economically and ecologically beneficial. |
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