的输出部分，为13.07%~15.23%，其中，GSC1组和GSC2组显著低于G组、GS组和GC组；GS组和GC组显著低于G组（P＜0.05）；草鲢鲤混养可以显著减少磷在水体中的积累（P＜0.05）；GSC2组和GS组磷的利用率显著高于G组、GC组和GSC1组（P＜0.05），因此，草鱼混养鲢鱼可以降低磷在水体中和底泥中的积累，GSC2组为较合理的混养模式。 3.草鱼不同混养方式池塘水质和底质的比较研究
于2012年6月~9月研究了草鱼、鲢鱼和凡纳滨对虾整池混养和分隔混养池塘水质和底质随养殖周期的变化，并比较了两种混养方式池塘水质和底质的不同。主要实验结果如下：1、6月~9月期间，9号池塘（分隔混养）水体的氨氮含量高于5号池塘（整池混养）；整池混养池塘水体中亚硝氮含量变化范围大，分隔混养池塘含量较稳定； 6月、7月分隔混养池塘水体中硝氮含量显著高于整池混养池塘（P＜0.05）； 5号池塘水体活性磷含量高于9号分隔养殖池塘；9号池塘水体中活性磷含量变化范围为0 mg/L~0.0042mg/L，波动范围较小。2、整池混养池塘水体中总氮含量变化范围为1.65 mg/L~3.57 mg/L，最大值出现在8月份，且显著高于分隔混养池塘；分隔混养池塘水体中总氮含量变化范围为0.84 mg/L~2.05 mg/L，最小值出现在8月份。整池混养池塘水体中总磷含量在7月、8月和9月份都高于分隔混养池塘。3、通过养殖水体和底泥中总氮总磷的比较看出，整池混养池塘中的总氮总磷含量显著高于分隔混养池塘（P＜0.05）。因此，从养殖环境减污的角度可以看出，分隔混养相对于整体混养来说可以显著减少对池塘水体和底泥的污染。
关键词:草鱼混养；氮收支；磷收支；分隔混养；水质；底质
A study of nitrogen and phosphorus budgets, and the comparison of water and sediment quality variation
in grass carp polyculture ponds
Abstract
Grass carp (Ctenopharyngodon idellus) is one of the main species in freshwater aquaculture in china. Though the intensive aquaculture has been technically improved, its increasingly aggravated water organic pollution leads to a frequent occurrence of all kinds of diseases , and therefore a negative effection on the healthy development of grass carp aquaculture. The polyculture of different species is crucial to achieve the sustainable development of grass carp culture, which functions not only in increasing its breeding production but also in reducing the pollution of the environment. We studied the nitrogen and phosphorus budgets of the grass carp, silver carp (Hypophythalmichthys molitrix) and carp (Cyprinus carpio) polyculture system. Meanwhile, the variation of water quality and sediments in two different culture patterns of grass carp, silver carp and prawn（Litopenaeus vannamei）(the whole pond polycuture and separatory polyculture) was also studied. The main research results were listed as follows:
1. A study of nitrogen budget in different grass carp polyculture systems
This study was conducted to investigate the total nitrogen budget in the grass carp monoculture group (G)，the grass carp and silver polyculture group (GS), the grass carp and carp polyculture group (GC), grass carp, silver carp and carp polyculture group (GSC) in land based enclosure.Results of present experimental showed were as follows : (1). fish feed was the main source of N input, and the proportion of which in total N input was 85.54%~93.38%, being highest in group G and lowest in group GSC2. No significant difference was observed in contents of N input among different treatments (P>0.05). 2. The N output of cultured organisms accounted for the most
proportion of total nitrogen output, being 62.80%~77.15%. 3.The proportion of accumulated sediments in total N output (15.19% ~ 27.60%) was only lower than that of cultured organisms, among which the GSC1 and GSC2 groups were significantly lower than G, GS and GC groups (P<0.05). Grass carp, silver carp and carp polyculture group could significantly reduce the accumulation of nitrogen in the sediments, and the N utilization of GSC2 was significantly higher than that of all the other groups, making GSC2 to be a better polyculture mode for grass carp. 2. A study of phosphorus budget in different grass carp culture systems
The method of land based enclosure experiment was chosen to study the phosphorus budget in the grass carp monoculture group (G), the grass carp and silver carp polyculture group (GS) and the grass carp, carp polyculture group (GC), grass carp, silver carp and carp polyculture group (GSC1 and GSC2). The main experimental results showed that: (1) the fish feed was the main source of total P input, and the proportion of which was 82.60%~84.26%; The phosphorus input of rainwater, water and the living organims accounted for a smaller part of the total phosphorus input, being 4.04% ~ 4.12%, 7.38% ~ 7.81% and 3.66% ~ 5.55% respectively. (2) In the total P output, the phosphorus output of accumulated sediments (76.37% ~ 79.96%) accounted for the most. The accumulated phosphorus output of water (13.07% ~ 15.23%) was only lower than that in the sediment output part. Among different treatments, GSC1 and GSC2 groups were significantly lower than other groups, while GS and GC groups were significantly lower than G group (P<0.05). Grass carp, silver carp and carp polyculture group could significantly reduce the accumulation of phosphorus in the aquaculture water. The phosphorus utilization in GSC2 and GS groups were significantly higher than that in G, GC and GSC1 groups. Based on the above information, it could be seen that the polyculture of grass carp and silver carp could reduce the accumulation of phosphorus in sediments and GSC2 was supposed to be the better polyculture mode.
3. The comparative study between water quality and sediment in two different grass carp polyculture systems
From Jun. to Sep. in 2012, we studied the variation of cultural water and sediment
with cultural cycle in the whole pond polyculture and separatory polyculture systems of the grass carp, silver carp and prawn and the difference between the two different polyculture systems were also compared. The main experimental results showed that: 1. The concentration of ammonia nitrogen in the pond number 9 (whole pond polyculture) was higher than that in the pond number 5(separatory pond polyculture) from June to September .The variation amplitudes of the nitrite nitrogen concentration were drastic were drastic in the whole pond polyculture system and steady in the separate pond polyculture. In June and July, The nitrte nitrogen contents in the water of the separatory pond polyculture was significantly higher than that in the whole pond polyculture(P＜0.05). The active phosphorus contents in the pond number 9 ranged from 0 mg/L to 0.0042 mg/L, being higher than that in the pond number 5. 2. The total nitrogen contents in the whole ployculture pond ranged from 1.65 mg/L to 3.57 mg/L, and the highest value of which was observed in August and significantly higher than that in the separatory polyculture pond(P＜0.05). The total nitrogen contents of the separatory polyculture pond ranged from 0.84 mg/L to 2.05 mg/L, with the minimum value in August. The total phosphorus contents in the separate polyculture pond were lower than that in the whole pond polyculture from July to September. 3. By comparing the total N and P contents in culture water and sediments, the whole pond polyculture had a significant higher value than the separate polyculture system (P＜0.05).Therefore, as can be seen from the aspect of reducing the pollution of cultural environment, the separate polyculture mode can significantly reduce the pollution of cultural water and sediment compared with the whole polyculture mode.
Key words: grass carp polyculture; nitrogen budget; phosphorus budget; separate polyculture; water quality; sediment quality
