A Preliminary Study On Budget And Variation Of Organic Carbon, Nitrogen And Phosphorus Of Grass Carp In Different Polyculture Systems

Grass carp is one of the main species of freshwater aquaculture in China.However, the development of large-scale breeding of grass carp has been slowed byseveral factors including the elevation of intensive culture, organic pollution and thethreaten of diseases. To build a model of health culture is of great importance.Decreasing the deposit and accumulation of nutrient during the culture process canimprove the inner environment of aquaculture system, which makes it necessary tostudy the eco-system of aquaculture ponds. C,P and N are the main factors that affectthe water eco-system. Their utilizing rate and accumulation are important indexes toevaluate the aquaculture model and pollution level. Therefore, it is very necessary tostudy the balance of organic C,N and P in the eco-system of ponds.Grass carp was used as the main object of this study. According to the relatedliterature and experience, filter-breeding silver carp and omnivorous benthicvannamei shrimp were mixed cultured based on their niche and habits. The testmethod was land-based mesocosm. The data collected and comparatively analyzedincluded the balance of organic composition （C, N and P） and their accumulation inthe water and sediment. The results can indicate the influence of grass carp-silver carp–vannamei shrimp-mixed aquaculture system on the freshwater pond’s eco-systemand also provide theoretical basis for the application of mixed-culture system infreshwater aquaculture in Northern China. The specific results are presented asfollowings:1. A preliminary study of organic carbon budget of grass carp in different polyculturesystemsBased on enclosures, the article is mainly to research the budget of organic carbon in mesocosm polyculture ecosystem comprising with grass carp, silver carpand Litopenaeus vannamei. From Mar to Oct in2010, the samples were collectedmonthly for measurements of organic carbon balance in polyculture mode withdifferent quantitative proportions, aimed to analyzing the accumulation of organiccarbon of water and sediment in the ecosystems.Main results are as follows: Firstly, the organic carbon balance in differentpolyculture ecosystems, were principally originated from primary production ofphytoplankton and fish feed, the proportions of which were63.10～76.59%and22.56～36.54%, respectively. Secondly, the expense of organic carbon were followedsuccessively by water respiration, accumulation of sediment organic carbon,biological and sediment respiration, secondary production, cultured organismproduction, accumulation of water and the organic carbon of periphyton, with theproportions of32.17～44.90%，22.58～30.67%，11.45～21.54%，9.08～15.46%，4.07～9.46%，0.30～0.93%，0.74～1.03%. Thirdly, the content of organic carbon inwater increased to13.68±0.89～16.40±1.84mg/L when harvest, from5.79±0.62mg/Lin the early culture phase. Among them, the content of organic carbon in the grasscarp monoculture group（G）was significantly higher than that in the grass carppolyculture group （GS，GSL1，GSL2，GSL3and GSL4）（P＜0.05）. Meanwhile,the content of organic carbon in the grass carp polyculture group（GS） was slightlyhigher than other polyculture groups and the discrepancy was not apparently（P＞0.05）.Finally, the content of organic carbon in sediment increased to2.51±0.40%when harvest, from3.07±0.07%～3.61±0.63%in the early culture phase. Amongthem, the accumulation of organic carbon in the grass carp monoculture group（G）was significantly higher than that in the grass carp polyculture group （GS，GSL1，GSL2，GSL3and GSL4）（P＜0.05）. Meanwhile，the accumulation of organic carbonin the grass carp polyculture group（GS）was significantly higher than GSL3（P＜0.05）, and there were no apparently discrepancy among others（P＞0.05）.The results preliminarily indicated that the polyculture with grass carp, silvercarp and Litopenaeus vannamei, can alleviate the accumulation of organic carbonfrom water and sediment, which is a capability and feasibility polyculture mode. 2. A preliminary study of total nitrogen budget of grass carp in different polyculturesystems.Based on enclosures, the article is mainly to research the budget of total nitrogenin mesocosm polyculture ecosystem comprising with grass carp, silver carp andLitopenaeus vannamei. From Mar to Oct in2010, the samples were collected monthlyfor measurements of total nitrogen balance in polyculture mode with differentquantitative proportions, aimed to analyzing the accumulation of total nitrogen ofwater and sediment in the ecosystems.Main results are as follows: Firstly，the total nitrogen balance in differentpolyculture ecosystems, were principally originated from fish feed, the proportions ofwhich were87.03⁹0.45%respectively. Secondly, the expense of total nitrogen werefollowed successively by cultured nitrogen production，accumulation of sediment totalnitrogen, accumulation of water，the nitrogen of absorption，and the volatilization ofammonia nitrogen， with the proportions of43.82⁵7.99%,17.49²7.56%，7.77¹0.28%,1.36³.35%and0.20⁰.29%. Thirdly, the content of total nitrogen inwater increased to147.04±8.72¹87.18±12.06g.49m^-2when harvest, from56.51±1.72g.49m^-2in the early culture phase. Among them, the accumulation of totalnitrogen in the grass carp monoculture group（G） was significantly higher than that inthe grass carp polyculture group（GSL2,GSL3and GSL4）（P＜0.05），meanwhileit was slightly higher than group GS（P＞0.05）；group GS was significantly higherthan group GSL3（P＜0.05）, and there were no apparently discrepancy among others.Fourthly, the total nitrogen in sediment increased to0.65±0.04⁰.87±0.14%whenharvest, from0.19±0.02%in the early culture phase. Among them, the accumulationof total nitrogen in the grass carp monoculture group（G） was significantly higherthan that in the grass carp polyculture group（GSL2,GSL3and GSL4）（P＜0.05），group GS was significantly higher than that in the grass carp polyculture group（GSL2,GSL3and GSL4）（P＜0.05），group G was slightly higher than group GS（P＞0.05）.Finally, the utilization ratio of nitrogen in the grass carp polyculture group（GS and GSL）was significantly higher than group G （P＜0.05），and there were no apparently discrepancy among group GS and group GSL（P＞0.05）.The results preliminarily indicated that the polyculture with grass carp, silvercarp and Litopenaeus vannamei, can alleviate the accumulation of total nitrogen fromwater and sediment, improve the utilization of nitrogen，which is a capability andfeasibility polyculture mode.3. A preliminary study of total phosphorus budget of grass carp in differentpolyculture systemsBased on enclosures, the article is mainly to research the budget of totalphosphorus in mesocosm polyculture ecosystem comprising with grass carp, silvercarp and Litopenaeus vannamei. From Mar to Oct in2010, the samples were collectedmonthly for measurements of total phosphorus balance in polyculture mode withdifferent quantitative proportions.Aimed to analyzing the accumulation of totalphosphorus of water and sediment in the ecosystems.Main results are as follows: Firstly, the total phosphorus balance in differentpolyculture ecosystems, were principally originated from fish feed, the proportions ofwhich were90.06～91.13%respectively. Secondly, the expense of total phosphoruswere followed successively by accumulation of sediment total phosphorus,accumulation of water, cultured phosphorus production, and the phosphorus ofabsorption, with the proportions of76.80～92.38%,12.63～21.44%,6.05～9.83%and1.10～1.60%. Thirdly, the content of phosphorus in water increased to40.13±7.72⁶7.33±5.43g.49m^-2when harvest, from11.65±2.63g.49m^-2in the earlyculture phase. Among them, the content of total phosphorus in the grass carpmonoculture group（G）was significantly higher than that in the grass carp polyculturegroup （GSL1, GSL2, GSL3and GSL4）（P＜0.05）,meanwhile it was slightly higherthan group GS（P＞0.05）; group GS was significantly higher than group GSL3（P＜0.05）, and there were no apparently discrepancy among others. Fourthly, the contentof phosphorus in sediment increased to622.87±69.22⁶69.73±76.94g.49m^-2whenharvest, from379.6±39.58g.49m^-2in the early culture phase. Among them, theaccumulation of phosphorus group G was slightly higher than that group GS and group GSL（P>0.05）. Finally, the utilization ratio of phosphorus in the grass carppolyculture group（GSL1, GSL2and GSL3）was significantly higher than group G andgroup GS（P＜0.05）.The results preliminarily indicated that the polyculture with grass carp, silvercarp and Litopenaeus vannamei, can alleviate the accumulation of total phosphorusfrom water and sediment, improve the utilization of phosphorus，which is a capabilityand feasibility polyculture mode.4．A preliminary study of the variety of C, N and P in different grass carp polyculturesystemsBased on enclosures, the article is mainly to research the variety of C, N and P inmesocosm polyculture ecosystem comprising with grass carp, silver carp andLitopenaeus vannamei. From Mar to Oct in2011, the samples were collected monthlyfor measurements of the variety of C, N and P in polyculture mode with differentquantitative proportions.Main results are as follows: Firstly, the concentration of TAN, PO4-P-and nitrateis commonly in group G is higher than that in group GS and group GSL, group GShigher than group GSL simultaneously. Secondly, The TP and TN concentrations inwater grow along with the progressing of the research，and the situation is a lot moreobvious in group G than in group GLS（P＜0.05）. Thirdly, The DOC and POCconcentrations in water also grow along with the progressing of the research. In July,September and October, the DOC concentration in group G is markedly higher thanthat in group GSL（P＜0.05）； in August, September and October， the POCconcentration in group G is markedly higher than that in group GSL（P＜0.05）；theDOC and POC concentrations in group G an GSL differs a little in most of the time；the DOC：POC：TOC ratio changes from0.59：0.41：1at the beginning to0.44：0.56：1in the end. Fourthly, The Chl-a concentration in the model of grass carp onlygrows fast and reaches the top of293.95±18.51ug/L，while The Chl-a concentrationin group GS and GSL is relatively stable.The results preliminarily indicated that the polyculture with grass carp, silvercarp and Litopenaeus vannamei is positive to improve the aquaculture water quality.