Twenty thousand 1 year old freshwater mussel H yriopsis cumingii was stocked into 2 grass carp Ctenopharyngodon idellus (with body weight of 50 g) ponds of each 0 .8 hm2 and water depth of 1 .8 m at stocking density of 12 000 per pond polycultured with silver carp Hypophthalmichthys molitrix with body weight of 24—100 g at stocking density of 500 individuals per pond and bighead carp A ristichthys no-bilis with body weight of 150 g at stocking density of 100 individuals per pond ,2 same size and stocking ponds without freshwater mussel as control ponds .The species and biomass of phytoplankton were deter-mined in the ponds in a 24 day interval to look insight on effects of freshwater mussel on phytoplankton community structure .The results showed that there were the phytoplankton of 94 species ,48 genera ,6 phyla in the fish-mussel polyculture ponds ,while 91 species ,42 genera ,6 phyla were observed in the con-trol ponds ,with the dominant species accounting for 47 .8% in the fish-mussel polyculture ponds ,and 41.8% in the control ponds ,with Cyclotella and Synedra in Bacillariophyta ,besides Chlorella ,Scenedes-mus and Closterium in Chlorophyta .The Shannon-Wiener diversity index of phytoplankton was found from 1.24 to 1 .41 in the fish mussel polyculture ponds and from 1 .26 to 1 .36 in the control ponds .The density of the phytoplankton were varied from 539 .23 × 104ind/L to 1289 .53 × 104ind/L in the fish-mussel polycul-ture ponds and from 669 .57 × 104 ind/L to 1608 .50 × 104 ind/L in the control ponds ,with the biomass of 6 .68—12 .47 mg/L in the fish-mussel polyculture ponds and 8 .40—18 .62 mg/L in the control ponds .The growth and reproduction of phytoplankton was to some extent restrained in the fish mussel plyculture ponds ,indicating that fish- mussel polyculture can change phytoplankton community structure ,and en-hance the ability to automatically adjust the water ,and more conducive to aquaculture .%试验池塘4口 ,每口面积0 .8 hm2 ,水深1 .8 m ,放养体质量50 g的草鱼12000尾 ,体质量24~100 g的鲢鱼500尾 ,体质量150 g的鳙鱼100尾 ,常规管理 ,其中2口池塘放养1龄河蚌两万只 ,2口对照塘不放河蚌 ,定期采集水样 ,测定水中浮游植物种类和数(生物)量.结果表明 ,鱼蚌混养塘中有浮游植物6门48属94种 ,而对照塘中仅有6门42属91种.混养塘与对照塘水体中均以绿藻门的种类为主 ,分别占总数的47 .8% 和41 .8% .鱼蚌混养组中以绿藻为优势种群 ,出现频率较高的优势藻类为 :硅藻门的小环藻、针杆藻 ,绿藻门的小球藻、栅藻、新月藻 ;而对照组中的优势种不仅有试验组中的优势种类 ,还包含了蓝藻门的平裂藻、螺旋藻、微囊藻以及硅藻门的直链藻、舟形藻、双壁藻 ,绿藻门的梭形藻等.鱼蚌混养组与对照组中浮游植物多样性指数分别为1 .24~1 .41和1. 26~1 .36 ,鱼蚌混养组中浮游植物多样性指数均略高于对照组.鱼蚌混养组浮游植物密度为539 .23 × 104 个/L~1289 .53 × 104个/L ,生物量为6 .68~12 .47 m g/L ;对照组浮游植物密度为669 .57~1608 .50 × 104个/L ,生物量为8 .40~18 .62 m g/L ,鱼蚌混养组浮游植物的密度和生物量略低于对照塘 ,且差异显著( P< 0 .05 ).结果表明 ,鱼蚌混养模式可有效控制塘中浮游植物的繁殖与生长 ,浮游植物的多样性指数提高 ,池塘生态系统更加稳定.
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