| Production of grass carp (Ctenopharyngodon idella) constitutes the largestaquaculture industry of finfish in China. In2009, the production of grass carp reached4.08million tons, which was20.85%of freshwater aquaculture production in China(Ministry of Agriculture2010). A series studies were conducted to evaluate the effectof dietary phosphorus, calcium, potassium, magnesium, zinc and manganese onjuvenile grass carp (Ctenopharyngodon idella). The results obtained can be brieflysummarized as follows:1. A growth trial was conducted to estimate the optimum concentration of dietaryavailable phosphorus (P) for grass carp (Ctenopharyngodon idella) and the effect ofdietary P levels on growth performance and body composition of this fish. Triplicategroups of grass carp (5.59±0.02g) were fed diets containing graded levels (2.36,4.27,6.31,8.36,10.4and14.8g kg-1) of available P for8weeks. Grass carp fed with theP-supplemented diets had significantly higher specific growth rate, weight gain,protein efficiency ratio and feed efficiency than fish fed with the basal diet. In wholebody composition, protein content increased, while lipid content decreased with theincrease of P level in diet (P <0.05). Fish fed with the P-supplemented diets hadsignificantly higher whole body, vertebrae and scales mineralization (P <0.05), butCa/P ratios were not influenced. Crude ash, Ca and P contents in scales weresignificantly increased with the increase of dietary available P concentration to8.36gkg-1and then remained stable beyond this level (P <0.05). Similar trend was found invertebrae. The blood chemistry analysis showed that dietary available P had distincteffects on P, Ca and Mg contents, as well as contents of triacyglycerol and total cholesterol. Broken-line analysis indicated that8.49g kg-1dietary available P wasrequired for maximal tissue storage and mineralization as well as optimal growth.2. Six isonitrogenous (410g kg-1) diets with three levels of total phosphorus (P4,P10and P18g kg-1) and two levels of starch (S200and S350g kg-1) were fed totriplicate groups of30fish to evaluate whether the high level of dietary phosphoruscould improve the utilization of starch. Over8-week-growth trial, best weight gain(WG) and specific growth rate (SGR)(P <0.05) were observed in fish fed theP10/S200and P18/S200diets. WG and SGR significantly decreased as starch levelsincreased except for P4, while lipid contents of liver and whole body, hepatosomaticindex (HSI) and intraperitoneal fat ratio (IPF) significantly increased. These resultssuggested that high dietary starch will depress the growth performance and cause lipidaccumulation. Within both starch levels, fish fed-diet with P4tended to produce lower(P <0.05) WG and SGR, and had higher (P <0.05) values of IPF. The whole bodylipid, ash, calcium, phosphorus and iron contents were significantly affected bydietary phosphorus levels. Supplied phosphorus could improve the growth anddecrease the whole body lipid, but there is no more effect after the phosphorusrequirement was met at10g kg-1.3. A growth trial was conducted to estimate the optimum concentration of dietarycalcium (Ca) for grass carp (Ctenopharyngodon idella). Triplicate groups of grasscarp (4.52±0.02g) were fed diets containing graded levels (2.75,4.51,6.24,7.99,9.66and11.5g kg-1) of Ca for8weeks. Weight gain, specific growth rate, feedefficiency and protein efficiency ratio were linearly increased up to the7.99g kg-1dietary Ca and then maintained stable beyond this level (P <0.05). Dietary Ca levelshigher than7.99g kg-1significantly increased the ash contents of whole body,vertebrae and scales. Ca contents in whole body, vertebrae and scales were linearlyincreased up to the7.99g kg-1dietary Ca and then maintained stable beyond this level(P <0.05). Contrarily, dietary Ca levels higher than9.66g kg-1significantly decreasedMg contents in whole body, vertebrae, and scales. Dietary Ca levels higher than7.99g kg-1significantly increased plasma alkaline phosphatase activity. However, plasmaCa, P and Mg contents were not significantly affected by dietary Ca supplements (P>0.05). Broken-line analysis indicated that8.57g kg-1dietary Ca was required formaximal tissue storage and mineralization as well as optimal growth. 4. A growth trial was conducted to estimate the optimum concentration of dietarypotassium (K) for grass carp (Ctenopharyngodon idella). Triplicate groups of grasscarp (3.96±0.06g) were fed diets containing graded levels (0.87,2.90,5.37,7.54,9.87and12.4g kg-1) of K for8weeks. Final body weight, weight gain and feedefficiency and gill Na+-K+ATPase activity were highest in fish fed with9.87g kg-1dietary K and lowest in fish fed the basal diet (P <0.05). K contents in whole bodyand muscle were linearly increased up to the9.87g kg-1dietary K and then leveled offbeyond this level, while in scales and vertebrae up to the7.54g kg-1dietary K (P <0.05). However, dietary K levels had no significant effect on ash, Ca, P and Mgcontents in whole body, scales, vertebrae or muscle. Analysis by polynomialregression of weight gain and gill Na+-K+ATPase activity and by the broken-lineregression of whole body K concentrations indicated that the adequate dietary Kconcentration for grass carp is about9.45-9.99g kg-1diet.5. A growth trial was conducted to estimate the optimum concentration of dietaryMagnesium (Mg) for grass carp (Ctenopharyngodon idella). Triplicate groups ofgrass carp (5.56±0.02g) were fed diets containing graded levels (187,331,473,637,779and937mg kg-1) of Mg for8weeks. Weight gain, specific growth rate and feedefficiency were linearly increased up to the637mg kg-1dietary Mg and then leveledoff beyond this level. For body composition, dietary Mg levels higher than473mgkg-1significantly decreased the moisture content but increased the lipid content ofwhole body, muscle and liver. Dietary Mg levels higher than473mg kg-1significantlydecreased the ash contents of vertebrae, scales and muscle. Mg contents in wholebody, vertebrae, scales and plasma were increased up to the637mg kg-1dietary Mgand then leveled off beyond this level. However, Ca and P contents seem to beinversely related to dietary Mg. Dietary Mg levels higher than473mg kg-1significantly decreased Zn and Fe contents in whole body and vertebrae. Broken-lineanalysis indicated that687mg kg-1dietary Mg was required for maximal tissue Mgstorage, as well as satisfied for the optimal growth.6. A growth trial was conducted to estimate the optimum requirement of dietaryzinc (Zn) for grass carp (Ctenopharyngodon idella). Triplicate groups of grass carp(3.97±0.05g) were fed diets containing graded levels (13,25,34,53,89and135mg kg-1) of Zn for8weeks. Grass carp fed with dietary Zn levels higher than34mg kg-1significantly increased final body weight, weight gain and specific growth rate (P <0.05). For body composition, fish fed with dietary Zn levels higher than53mg kg-1significantly decreased the moisture contents but increased the lipid contents of wholebody and liver. Whole body, scales, vertebrae and liver mineralization were allaffected significantly (P <0.05) by dietary Zn levels. Zn contents in whole body,scales, vertebrae and plasma were linearly increased up to the53mg kg-1dietary Znand then remained stable beyond this level. Grass carp fed with dietary Zn levelshigher than53mg kg-1significantly increased TG and T-CHO contents and ALPactivity in plasma (P <0.05). Broken-line analysis indicated that55.1mg kg-1dietaryZn was required for maximal tissue storage and mineralization as well as optimalgrowth of grass carp.7. A growth trial was conducted to estimate the optimum concentration of dietaryManganese (Mn) for grass carp (Ctenopharyngodon idella). Triplicate groups of grasscarp (3.97±0.05g) were fed diets containing graded levels (4.0,8.9,13.8,18.7,23.6and33.3mg kg-1) of Mn for8weeks. Weight gain, feed efficiency and proteinefficiency ratio were linearly increased up to the18.7mg kg-1dietary Mn and thenmaintained stable beyond this level (P <0.05). For body composition, lipid contentsin whole body, muscle and liver decreased significantly with increasing dietary Mnlevel. Grass carp fed with dietary Mn levels higher than18.7mg kg-1significantlydecreased condition factor. Whole body, vertebrae and scales mineralization were allaffected significantly by dietary Mn levels. Mn contents in whole body, vertebrae andscales were linearly increased up to the18.7mg kg-1dietary Mn and then maintainedstable beyond this level. Contrarily, Ca and P contents seem to be inversely related todietary Mn. However, dietary Mn levels had no significant effect on body Fe contents.Broken-line analysis indicated that20.6mg kg-1dietary Mn was required for maximaltissue Mn storage as well as optimal growth of juvenile grass carp.
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