| In this paper, grass carp is treated as the object of study while calcium dihydrogen phosphate, dicalcium phosphate and acidification as the test material, trying to explore effects of different P sources, phosphorus concentration and acidifier on grass carp's growth and physiology. This paper sets three tests: test one focuses on the appropriate range of different phosphate concentrations in grass carp's conventional feed; in order to further validate the results of test one as well as avoid the possible interference of anti-nutritional factors in conventional feed, purified feed is employed in test two; test three mainly probes into the substitution problem of calcium dihydrogen phosphate to monocalcium phosphate, in the aid of benzoic acid acidification agent. The three tests are designed as follows and then are the results:Test one:ⅠⅦexperimental groups: hard pellets are added inⅠⅤgroups with calcium dihydrogen phosphate's concentration gradient 0,5,8,12,18 g.kg-1,ⅥandⅦare fed with extruded feed, separately adding 8 and 18 g.kg-1 of calcium dihydrogen phosphate. Test used grass carp with initial average weight of (37.2±2.4) g are divided into 7 groups in the cement pool cage, each with 3 replicates, fed respectively with the above-mentioned feed, precisely and on schedule. The feeding time is 58d. The results shows that:①the specific growth rate of grass carp, feed conversion ratio, protein efficiency and protein deposition rate increased along with the increase of added dietary calcium dihydrogen phosphate (P <0.05), but the rate of fat deposition is not so affected ( P> 0.05);②phosphorus content in fish scale and calcium content in serum are more sensitive to P-level of the feed, but other factors.③P-level of the feed also have a great impact on the skeletal system and development of grass carp. The experimental group length specific growth rates were significantly different (P <0.05);③feed with the same formula can improve grass carp's growth efficiency after the swelling treatment, but has no obvious difference with the hard pellets group (P> 0.05).④P- level of the feed has no evident effects on fish's health indicators. These results show that:①the growth rate of grass carp goes with the increase of monocalcium phosphate, but when added to a certain level, the growth rate remains stable. In this experiment, grass carp's most appropriate demand dosage for phosphorus is 12 g.kg-1's monocalcium phosphate (amount to 12.36 g.kg-1's feed phosphorus).②Under such experimental condition, extruded material can improve the growth of grass carp.Test two: Design a purified test diet. As raw material, casein, soybean oil, starch, dextrin and cellulose are respectively added calcium dihydrogen phosphate 0,13,29,45,61,77 g.kg-1. Test used grass carp with initial average weight of 22.29±1.8g. Six groups in indoor culture systems, each with 3 replicates are fed with six above-mentioned feed. The feeding time is 75 d. The results show that:①P-level of the feed has a significant effect on the growth of grass carp (P <0.05). When the level reaches 7.13g.kg-1, grass carp enjoys the best growth.②P-level of the feed has a significant effect on the abnormal vertebrae. These results show that:①dietary phosphorus have a major impact on the growth of grass carp. If the phosphorus content is too high or too low, it is not conducive to the growth of grass carp. In this experiment, the optimum dietary phosphorus concentration is 7.13 11.06 g . kg-1.②In the absence of phosphorus or phosphorus deficiency, it may lead to the occurrence of fatty liver and skeletal deformities; vertebral deformity can be a sign of phosphorus deficiency.Test Three: Design six experimental groups: control group, calcium dihydrogen phosphate group, dicalcium phosphate group, 0.15% dicalcium phosphate acidifier group, DCP +0.30% acidifier group, 0.30% acidifier group. The initial weight could be 37.2±2.4g. In the cement pool cages, each with 3 replicates, are fed with six above-mentioned feed:①dietary inorganic phosphorus sources can significantly improve the growth of grass carp (P <0.05); and calcium dihydrogen phosphate is significantly better than DCP (P <0.05).②the combination of dicalcium phosphate and acidification is much better than adding either of them. However, it is less effective than the addition of calcium dihydrogen phosphate, as a source of phosphorus (P <0.05);③if acidifier is added to the feed without inorganic phosphorus source, the growth rate of grass carp is significantly lower than the control groupⅠ(P <0.05).④calcium dihydrogen phosphate in feed can significantly reduce grass carp's serum lipids and alkaline phosphatase's vitality (P <0.05). CONCLUSION:①inorganic mineral dietary phosphorus significantly helps to improve the growth and health of grass carp; calcium dihydrogen phosphate is better than DCP.②the compound use of dicalcium phosphate and acidification can improve the growth of grass carp, but not as good as the use of calcium dihydrogen phosphate.③If there is no inorganic minerals in the feed, acidifier is not conducive to the growth of grass carp. |
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