| To study the effects ofα-ketoglutarate(AKG)supplementation in low-phosphorous diets on growth,phosphorus metabolisms and skeletal development of Songpu mirror carp(Cyprinus carpio).The experiment fish was purchased from Hulan Experimental Station of Heilongjiang Fisheries Research Institute.The experiment was carried out in indoor aquarium with controlled water circulation system.Before the experiment,the fish were acclimatized two weeks.After the acclimation,triplicate groups of Songpu mirror carp(6.67±0.08g)were fed with practical diets containing available phosphorous(AP)0.65%(normal P)and 0.51%(low P)with graded levels of 0,0.2%,0.4%,0.6%,0.8%and 1.0%of AKG to satiation for 8 weeks,respectively.During the experiment,the water temperature controlled in 22±1℃,and dissolved oxygen is greater than 5mg/L and in the natural light.The fish was fed 4 times a day by hand to apparent satiation at 8:00,11:00,14:00 and 17:00.At the same time,recording the amount of feeding,regularly change water,disinfection,to ensure good water quality.The experiment was lasted for 8 weeks.The results showed as follows:(1)The feed coefficient(FCR)in the low phosphorus group was significantly higher and the weight gain rate(WGR),specific growth rate(SGR)was significantly lower than that of the normal phosphorus group(P<0.05),but the protein efficiency(PER),Viscerosomatic Index(VSI),Hepatosomatic Index(HI)and Condition Factor(CF)were similar between normal P and Low P group(P>0.05).Compared with low P group,FCR of 0.6%AKG group were significantly decreased(P<0.05)and the WGR,SGR,PER,VSI,HI and CF in 0.6%AKG group were significantly increased(P<0.05)respectively.(2)The content of crude fat(EE)in the low phosphorus group was significantly higher and the Ca and P contents in the fish body were significantly lower than that of the normal phosphorus group(P<0.05).Compared with the low phosphorus group,the content of fish body moisture,CP,EE,Ash,Ca,and P in 0.6%AKG group had no significant effect(P>0.05),but the protein deposition rate(PRV),fat deposition rate(LRV),and ash deposition rate(ARV)increased significantly(P<0.05).(3)The villi width of foregut and midgut and the muscular thickness of foregut in the low phosphorus group was significantly lower that of the normal P group(P<0.05).Compared with the normal P group,the villi height,villi width and muscular thickness of foregut in 0.6%AKG group were significantly increased(P<0.05),respectively.Low P had no significant effect on intestinal body length index and intestine body weight index(P>0.05),but intestinal body length index in 0.2%,0.4%,and 0.6%AKG group were significantly increased than normal P group(P<0.05).And Low P had no significant effect on the activity of intestinal digestive enzyme(P>0.05),but the activity of foregut protease,midgut protease and foregut lipase in 0.4%,0.6%,and 0.8%AKG group were significantly increased than low P group(P<0.05).And Low P had no significant effect on the activity of Na~+,K~+-ATPase(P>0.05),but compared with the low P group,the activity of Na~+,K~+-ATPase in 1%AKG group was significantly increased(P<0.05).(4)The content of calcium(Ca)and P in serum in the low phosphorus group were similar between normal P and Low P group(P<0.05),but the activity of alkaline phosphatase(ALP)was significantly decreased(P<0.05).The activity of Bone Alkaline Phosphatase(BALP),which tested by the semi-quantitative determination,was lower than the semi-quantitative value,indicating that the body calcium salt secretion is sufficient.Compared with low P group,the activity of alkaline phosphatase was significantly increased in AKG group(P<0.05).The content of growth hormone(GH)in liver in Low P group was decreased significantly(P<0.05),but the content of GH in serum had no significant effect(P>0.05).The content of GH in serum and liver of 0.4%and 0.6%AKG group were significantly increased than low P group(P<0.05).(5)The apparent digestibility of total phosphorus of Songpu mirror carp in low P diets was lower than normal P group,but it was significantly increased in different level AKG group(P<0.05).The expression of NaPi-Ⅱb mRNA of intestinal and kidney were similar between normal P and Low P group(P>0.05),but the expression of NaPi-Ⅱb mRNA of foregut and hindgut were significantly decreased in AKG group(P<0.05) while had no significant effect on the expression of NaPi-Ⅱb mRNA of midgut,kidney and vertebra(P>0.05).(6)Compared with normal P group,the deposition rate of calcium and phosphorus and the level of vertebra calcium and phosphorus were decreased significantly(P<0.05).Compared with low P group,AKG had no effect on the level of vertebra calcium(P>0.05).However,the deposition rate of calcium and phosphorus and the level of vertebra phosphorus in 0.6%AKG group were significantly higher than low P group(P<0.05).Low P diet had no significant effect on the content of vertebra collagen(P>0.05),but it was significantly increased with the AKG supplementation(P<0.05).(7)Compared with normal P group,low P diet had no significant effect on the content of amino acid(P>0.05),but the content of arginine and essential amino acid significantly increased in 0.4%AKG group(P<0.05).The content of total amino acid of the whole fish was significantly increased by 0.4%and 0.6%AKG supplementation(P<0.05).There was no significant effect on the expression of GH mRNA in the liver of juvenile carp(P>0.05),but IGF-I mRNA significantly increased(P<0.05).It is concluded that the 0.6%AKG supplementation in low phosphorus diet has a positive effect on the growth and improve nutrients retention and even reduce the feed coefficient.AKG supplementation in low phosphorus diet also enhance the activities of intestinal digestive enzyme,thus,it promotes intestinal development and can decrease the expression of NaPi-Ⅱb mRNA in intestine.The appropriate AKG supplementation in low phosphorus diet also can increase the apparent digestibility of total phosphorus,the content of vertebra phosphorus,mineral deposition and collagen.What’s more,dietary appropriate AKG levels can up-regulate the release of growth hormone in liver and serum and improve the content of arginine level in liver and promote bone development. |
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