Effects Of2-hydroxy-4-(methylthio) Butanoic Zinc On Growth Performance, Physiological Function And Tissue Retention In Gibel Carp (Carassius Auratus Gibelio) And Common Carp(Cyprinus Carpio L.)

The present study was to study the effects of2-hydroxy-4-（methylthio） butanoic Zinc （MHA-Zn）on the growth performance, physiological function and tissues retention in gibel carp （Carassiusauratus gibelio） and common carp （Cyprinus carpio L.）, two trials were conducted to confirm theefficacy of the organic zinc. Besides, another trial of high doses of MHA-Zn in diets was conducted tostudy the tolerance in common carp. The results were summarized as follows:1. The first study was conducted in gibel carp, the initial weight was （2.73±0.01） g. A basal dietwas formulated with white fishmeal and pea protein concentrate as dietary protein sources. Fish in thecontrol group were fed the basal diet. Zinc sulfate （ZnSO₄7H₂O） was supplemented in the basal diet,and the dietary zinc levels amounted to50（Zn50group） and65mg/kg （Zn65group）, respectively;2-hydroxy-4-（methylthio） butanoic Zinc （MHA-Zn） was supplemented in the basal diet, and dietaryzinc levels amounted to37.5（MZn37.5group）,50（MZn50group）,65（MZn65group）,200（MZn200group）, respectively. Every treatment had four replicates. After56days, the results showed as follows:1)all the experimental groups showed higher survival rates than95%. FAW, SGR, WGR, PER were notaffected by zinc sulfate supplement and high dose of MHA-Zn （MZn200） supplement （P>0.05）, butwere reduced by low dose of MHA-Zn supplement （MZn37.5group, MZn50group, MZn65group）（P<0.05）. with the dietary zinc level increased, veterbrae zinc accumulation in zinc sulfate groupsshowed an increased tendency, and the accumulation in Zn65group was significantly higher than that inthe control group （P<0.05）; while MHA-Zn groups showed a Para curve tendency with the dietary zincincreased, the accumulation in MZn65group was significantly higher than that in the Zn65group（P<0.05）, calculated by a quadric regression, the vertebrae zinc accumulation reached the peak whendietary zinc level was131.3mg/kg （zinc supplemented as MHA-Zn）.3) Hepatopancres antioxidativeindex were not significantly affected （P>0.05）; AKP activities showed a decreasing tendency with thedietary zinc increased. In conclusion, when zinc content in practical diet satisfy needs for growth ofgibel carp, supplementing with more zinc sulfate has no effect on growth performance of gibel carp, butincreases the zinc accumulation in veterbrae, while supplementing with more low dose of MHA-Znreduces the growth performance, but also obviously increasesAKP and zinc accumulation in veterbrae,when the dietary zinc （as MHA-Zn） level increases up to131.3mg/kg, vertebrae zinc accumulationreaches the peak.2. The second trial was conducted in common carp; the initial weight was （10.0±0.03） g. Ahalf-purred basal diet was formulated with casein, glutin and krill meal as dietary protein sources and0.7%of sodium phytate.2-hydroxy-4-（methylthio） butanoic Zinc （MHA-Zn） and zinc sulfate（ZnSO₄7H₂O） were added to the basal diet at5,20,35,50,65mg zinc/kg diet, together with thecontrol diet, there were a total of11treatments. These diets were named as C0, Zn5, Zn20, Zn35, Zn50,Zn65, MZn5, MZn20, MZn35, MZn50, MZn65, and analyzed dietary zinc were12.8,14.1,37.9,41.8,52.5,78.4,17.1,32.7,46.2,60.2,87.3mg/kg respectively. Each treatment had6replicates, and everyreplicate had30fish. After70days, the results showed as follows:1) Fish in the control group grow well with a high survival rate of98%, no zinc deficiency symptoms were found during the experimentalperiod. Zinc supplement （independent on zinc sources） had no obvious effect on survival rate, growthperformance and somatic index （P>0.05）. Calculated by a quadric regression, WGR of MHA-Zn groupreached the peak （363.5%） when supplemented zinc level was50.5mg/kg while WGR of zinc sulfategroup reached the peak （342.1%） when supplemented zinc level was34.2mg/kg, the highest value ofWGR in MHA-Zn group was1.06times higher than that in zinc sulfate group; With supplemental zinclevel increased, zinc retention in veterbrae, intestine, liver and whole body elevated （P<0.01）, ZRRdecreased lineally （P<0.01）, serum SOD and Cu-ZnSOD increased （P<0.01）. Vertebrae zinc retentionand SOD reached the peak when zinc level from MHA-Zn was23.2and33.9mg/kg respectively whilevertebrae zinc retention of zinc sulfate group increased lineally with dietary zinc level increased, theoptimal supplemental zinc from zinc sulfate may higher than65.6and SOD reached the peak whensupplemental zinc level from zinc sulfate was38.6mg/kg. Using liner regression and a slope ratiotechnique, RBV of MHA-Zn, with zinc sulfate as the standard, was181%for serum SOD, and312%forveterbrae zinc retention. This study showed that MHA-Zn is more bioavailable to common carp thanzinc sulfate in half-purred diet with0.7%sodium phytate, and can improve growth performance, tissueaccumulation and antioxidant function of common carp.3. The third trial was also conducted in common carp. The initial weight was （10.0±0.03） g. Thebasal diet was exactly the same as the one used in the second trial.2-hydroxy-4-（methylthio） butanoicZinc （MHA-Zn） was supplemented in the basal diet, and the dietary zinc levels amounted to200（MZn200group）,2000mg/kg （MZn2000group）, the control group （C0） used the basal diet. Eachtreatment had6replicates. After70days, the results showed as follows:1) high dose of MHA-Znshowed no obvious effect on survival rate, growth performance and somatic index （P>0.05）.2)14serum biochemical parameters in MZn2000group were not different form that in C0group. TBIL inMZn200group was significantly higher than C0group （P<0.05）, while Cr in MZn200group wassignificantly lower than C0group （P<0.05）, other biochemical parameters were not different form C0group （P>0.05）.3) High dose of MHA-Zn obviously increased serum SOD and Cu-ZnSOD, whileshowed no effect on T-AOC and MDA （P>0.05）.4) High dose of MHA-Zn significantly increased zincaccumulation in veterbrae, intestine, liver and whole body （P<0.05）, while decreased ZRR （P<0.05）.This study showed that high dose of MHA-Zn is tolerant for common carp, dietary zinc as high as2000mg/kg supplemented by MHA-Zn shows no obvious effect on growth performance, and can increasezinc accumulation in veterbrae and whole body, and antioxidant function as well. At the same time,supplementing high dose of MHA-Zn may pollute the water environment. According to1224announcement of Ministry of Agriculture, the upper limit of dietary zinc （200mg/kg） from MHA-Zn,the coefficient of safety is10.