Study On The Requirements Of Phosphorus And Iron For Largemouth Bass(Micropterus Salmoides)

Exp.1 The digestible phosphorus requirement in practical diet of largemouth bass（Micropterus salmoides）based on growth and feed utilizationThis experiment investigated the effect of dietary monocalcium phosphate（MCP）on the growth performance,body composition,apparent digestibility and retention rate of nutrients,calcium and phosphorus content of vertebrae and plasma calcium and plasma phosphorus of largemouth bass to determine the optimum requirement of dietary phosphorus（p）of largemouth bass.Six iso-energetic and iso-nitrogenous diets were formulated to contain graded levels of digestible P（5.7,6.7,7.8,8.7,9.3and 10.0 g/kg）with the supplementation of MCP of 0,5,10,15,20 and 25g/kg,respectively.Each diet was randomly fed to triplicate groups of 25 juvenile fish（initial body weight,16.5±0.15 g）for 60 days.The results showed that the weight gain（WG）significantly increased,and feed conversion ratio,viscerosomatic index and hepatosomatic index decreased with the increasing P level（P<0.05）.The crude ash,P and calcium contents in whole body,apparent digestibility of P and protein retention also significantly increased with the increasing P level（P<0.05）.Vertebrae P and calcium levels and plasma P showed no significant increase when dietary digestible P reached 9.3,9.3 and 7.8 g/kg（P>0.05）,respectively.Broken-line analysis based on WG and vertebral P content indicated the digestible P requirements for largemouth bass were 8.9 and 9.6 g/kg,respectively.In conclusion,the supplementation of MCP in diet improved the growth and feed utilization of largemouth bass,and the digestible P requirement was suggested to be 8.9 g/kg.Exp.2 Effects of citric acid supplementation in diets with various phosphorus levels on largemouth bass（Micropterus salmoides）The study was conducted to evaluate the effects of citric acid supplementation in diets on the growth,nutrient utilization,and nitrogen（N）and phosphorus（P）emissions of largemouth bass（Micropterus salmoides）.Three diets were prepared with the addition of monocalcium phosphate（MCP）at 5,10,and 15 g/kg（P5,P10,P15）,then 10 g/kg of citric acid was added into P5 and P10 diets.The five diets were fed to juvenile fish（initial body weight,16.0 ± 0.16 g）for 60 days.The results showed that the weight gain（WG）,whole body P,crude protein retention P digestibility,vertebral P and plasma P significantly increased,and N excretion,whole body crude lipid decreased with the increasing MCP level（P<0.05）.The addition of citric acid in P5 diet significantly increased WG（+ 5.6%）and serum P level,and reduced feed conversion ratio（-0.05）and N excretion（P<0.05）,which reached the similar levels to the P10 group（P>0.05）.The addition of citric acid in P10 diet numeral improved the growth performance with similar levels to the P15 group（P>0.05）.In addition,the supplementation of citric acid in both P5 and P10 diets significantly promoted P digestibility and reduced P excretion（P<0.05）.In summary,the addition of 10 g/kg citric acid in low-phosphorus diets can improve the growth and the utilization of P and diet of largemouth bass.Exp.3 Study on iron requirements of largemouth bassThis experiment was conducted to evaluate the effects of different iron levels in diet on growth performance,proximate composition and blood parameters of largemouth bass.A practical diet and a semi-purified diet were designed as two basal diets with total iron content of 187.1 mg/kg and104.8 mg/kg,respectively,then inorganic iron（ferrous sulfate）was added into the two basal diets at 0,50,100,200,400 mg/kg inclusion.The 10 diets were fed to largemouth bass with initial body weight of 13.52±0.15 g for 8 weeks.In both semi-purified and practical diets,the increasing dietary iron level improved the weight gain,protein retention efficiency,hemoglobin,red blood cell number,serum iron and serum catalase activity,and decreased the feed conversion ratio.When the iron supplementation reached 100 mg/kg,the above indicators kept relatively stable.According to the broken-line analysis of weight gain,the determined suitable iron addition in practical feed and semi-purified feed were 76.6 mg/kg and 81.9mg/kg,respectively.The fish fed practical diets showed better performance than those fed semi-purified diets in terms of growth,hemoglobin and serum iron（P<0.05）.In summary,the appropriate supplementation level of inorganic iron in practical diet and semi-purified diet were 76.6 g/kg and81.9 g/kg with total iron content of 263.7 mg/kg and 186.7 mg/kg,respectively.Exp.4 Bioavailability evaluation of organic iron in the diet of largemouth bassThis experiment was conducted to evaluate the bioavailability of organic iron in the diet of largemouth bass.A semi-purified diet with casein and fish meal as the main protein sources was prepared,then inorganic iron（ferrous sulfate）and organic iron（yeast iron）were supplemented in the basal diet with 0（control diet）50,100 and 200 mg/kg,and 25,50 and 100mg/kg,respectively.The 7 diets were fed to largemouth bass（13.52±0.15 g）for 8 weeks.The results showed that both iron sources significantly affected the weight gain,feed conversion ratio（FCR）,serum catalase activity,hemoglobin,and red blood cell count（P<0.05）.When inorganic iron and organic iron supplementation reached 50 mg/kg and 25 mg/kg,the weight gain was significantly increased and FCR was significantly reduced（P<0.05）.When the inorganic iron and organic iron supplementation reached 100 mg/kg and 50 mg/kg,the hemoglobin content basically stabilized,and the number of red blood cells increased with the increasing iron supplementation.Based on the broken-line analysis of weight gain and hemoglobin,the proper iron supplementation was 92.0-104.5 mg/kg for FeSO₄ and 46.2-51.1 mg/kg for organic iron.Taking the weight gain and hemoglobin as evaluation indicators,the relative bioavailability of organic iron to inorganic iron were 197% and 218%.