Low crowding threshold for induction of sexual reproduction and diapause in a Patagonian rotifer

1. This study investigates the basis and ecological significance of the extremely high propensity for mixis (sexual reproduction) observed in laboratory populations of Brachionus calyciflorus from a temporary pond in Patagonia. 2. Experiments with stem females hatched from resting eggs showed that these females were exclusively amictic but produced mictic daughters even at very low population densities. In six experiments, newly hatched stem females were cultured individually in different volumes (1.5, 12, 40 and 150 mL). The percentage of mictic daughters (mixis ratio) was high in the smaller volumes (e.g. 44–83% in 1.5 mL) and lower in the largest volume (6–21% in 150 mL). A regression analysis combining the data from these experiments showed a highly significant decrease in mixis ratio with volume and indicated that the lowest population density at which mixis still occurs (mixis threshold) would be 3.4 females L^?1 (95% CL 2.9–4.0 females L^?1). This value is considerably lower than mixis thresholds for other rotifers (25–250 females L^?1 for many species and 9000–477 000 females L^?1 for some Spanish Brachionus plicatilis). 3. In three additional experiments, stem females and their amictic daughters were cultured individually in 150 mL. The percentage of mictic daughters produced by these two generations of females was not significantly different, showing that the mixis response to crowding is not inhibited in the stem‐female generation. 4. Laboratory experiments showed that two common predators of the Patagonian B. calyciflorus (the calanoid copepod Parabroteas sarsi and the backswimmer Notonecta vereertbruggheni) each ate 60–70 B. calyciflorus predator^?1 per day and cleared all rotifers from c. 250 mL per day. Thus, a very low mixis threshold and high maximal mixis ratio may ensure production of some resting eggs soon after colonisation of the pond and before complete removal from the plankton. 5. Two laboratory experiments showed that resting eggs of the Patagonian B. calyciflorus hatched at variable rates (28 and 81%) after a brief diapause when kept in the conditions under which they were produced and oviposited (20–21 °C; L: D 16: 8). Early hatching of resting eggs from pond sediment may allow multiple periods of colonisation and resting egg production in a season. This may offset the fitness cost of limited population growth through female parthenogenesis in the face of unpredictable and abrupt risk of extinction because of predators.     

萼花臂尾轮虫有性生殖、种群增长和休眠卵产量间的关系

利用种群指数增长和Logistic增长模型,通过计算机模拟研究了萼花臂尾轮虫有性生殖发生的频率,后代中的混交雌体发率对种群增长和休眠卵产量的影响。在所模拟的参数范围内,随有性生殖发生频率由100％减小到20％,获得了大休眠卵产量所需的混交雌体百分率由9％增大到69％,随密度制约作用的增大（环境容纳量K值由1000减小到100）,该混交雌体百分率由18％增大到69％,休眠卵产量由1072．10降低至133．67,种群的内禀增长率与获得最大休眠卵产量所需的混交雌体百分率间呈曲线相关。当有性生殖发生得越频繁,种群增长所受的密度制约作用较小时,后代中10％－30％的个体为混交雌体时的种群中休眠卵产量较大。     

萼花臂尾轮虫交配行为和受精作用研究

萼花臂尾轮虫的交配行类在致可分为５个阶段,除雌雄性比为１：２和１３时混交雌体的受精率为１００％外,其余性比下混交雌体的受精率皆无显著的差异。可受精的混交雌体自分率和具有精能力的雄性百分率皆降年龄的增大而下降,的有的混交雌体在出生后的４ｈ内均易于受精,以后随着雌长（Ｘ,ｈ）的增加,可受精的混交雌体百分率（Ｙ,％）呈非线性下降,Ｙ＝１６６．６３８６－１７．８１３Ｘ＋０．４８３７Ｘ＾２,当岭长达１８ｈ时     

Females from resting eggs and parthenogenetic eggs in the rotifer Brachionus calyciflorus: lipid droplets, starvation resistance and reproduction

1. In the heterogonic life cycle of monogonont rotifers, amictic (female‐producing) females develop from two types of eggs: fertilised resting (diapausing) eggs and parthenogenetic subitaneous eggs. Females hatched from resting eggs initiate clonal populations by female parthenogenesis and are called stem females. This study compares females from resting and parthenogenetic eggs that were produced under identical culture conditions and were of similar birth order. 2. Newborn stem females had many more lipid droplets in their tissues than similar‐sized, newborn females from parthenogenetic eggs. When neonates were stained with Nile Red and viewed under epifluorescent illumination, these droplets were shown to be sites of neutral‐lipid storage products. 3. Stem females had no posterolateral spines and short anterior spines, while their mothers and offspring in subsequent, parthenogenetic generations typically had long posterolateral spines and elongated anterior spines. 4. Newborn stem females survived starvation significantly longer than newborn females from parthenogenetic eggs. 5. When females from resting and parthenogenetic eggs were cultured from birth to death at a high food concentration, the reproductive potential (r day^?1) of the stem females was significantly higher (0.82–0.88 versus 0.70), primarily because of egg production at an earlier age. The mean lifetime fecundity (R_o) of stem females was significantly greater than that of females from parthenogenetic eggs. 6. Extensive lipid reserves should increase the ability of stem females to colonise new habitats. Firstly, compared with females from parthenogenetic eggs, stem females are more likely to experience starvation or food limitation. Resting eggs hatch in response to physical and chemical factors that are not directly related to food availability, and from sediments that may be far from food‐rich surface waters. Secondly, when food is abundant, stem females have a greater reproductive potential.     

内分泌干扰物氰戊菊酯和有机锡对萼花臂尾轮虫生殖的影响

25℃,投喂密度为(2～3)×106cells/ml的蛋白核小球藻,采用单"克隆"培养的方法对萼花臂尾轮虫(Brachionus calyciflorus)进行慢性毒性实验,分别比较具有环境雌性和雄性激素效应的药物氰戊菊酯(Fenvalerate)和三丁基氯化锡(TBTC)对萼花臂尾轮虫亲代单次携卵量、总产卵量和后代数、以及亲代和F1代的混交比率的影响.结果表明:氰戊菊酯处理组,亲代单次携2和3个卵的频次在浓度达400μg/L时都显著高于对照组(p<0.05),而亲代单次携1个卵的频次都显著低于对照组(p<0.05).各浓度组总产卵量都显著高于对照组(p<0.05),后代数也明显增高.氰戊菊酯在两个最低实验浓度(0.64μg/L和3.2μg/L)就会对亲代混交率和子一代混交率、MF/AF存在显著影响.TBTC处理组在浓度0.0016、0.008μg/L和1μg/L亲代单次携1个卵的频次显著高于对照组,而携3个和4个卵的频次显著低于对照组(p<0.01).亲代总产卵量和所产后代数在TBTC各处理组都显著低于对照组(0.0016μg/L除外)(p<0.05).而子一代的混交率、MF/AF等都显著低于对照组(p<0.05).实验表明氰戊菊酯和TBTC对萼花臂尾轮虫的生殖具有明显的内分泌干扰效应.     

维生素E对萼花臂尾轮虫繁殖的影响

15℃下 ,添加 Ve浓度为 2 0～ 80 ng/ m l时 ,种群密度与培养时间呈显著相关 ,其中 2 0 ng/ ml和 4 0 ng/ ml组最大种群密度分别为 76 .4 0 ind/ ml和 6 5 .2 0 ind/ ml,显著高于对照组 (最大密度 12 .0 0 ind/ ml)。最大混交雌体百分率低于 10 % ,对照组最大混交雌体比率为 4 0 %。轮虫卵雌比有不同程度的提高 ,但维生素浓度为 10 0 ng/ ml时 ,对种群增长不利 ;2 5℃下 ,对照组和各添加组最大密度依次为 6 8.0 0 ,12 2 .0 0 ,12 4 .0 0 ,16 8.0 0和 2 36 .0 0 ind/ ml。最大卵雌比依次为 1.2 1,1.2 5 ,1.2 2 ,1.4 1和 0 .6 9,混交雌体百分比分别为 2 7.6 9,19.89,18.4 2 ,17.0 2和 12 .88% ;30℃下 ,最大密度依次为 113.80 ,12 1.0 0 ,12 2 .80和 15 1.2 0 ind/ ml,最大卵雌比依次为 1.5 0 ,1.4 2 ,0 .6 4和 0 .96。混交雌体百分比分别为 1.76 ,32 .2 6 ,37.5 0和 32 .0 0 %。     

种群起始密度对萼花臂尾轮虫休眠卵形成的影响

应用群体累积培养法,研究了种群起始密度对萼花臂尾轮虫休眠卵的形成及之相关的混交雌体百分率和受精率的影响,结果表明,在连续１１ｄ的培养中,轮虫休眠卵的产量和形成效率以及种群中的平均混交雌体百分率以种群起始密度为１．０－１０．０ｉｎｄ．ｍｌ＾－１组最大,２０．０ｉｎｄ．ｍｌ＾－１组次之,５０．０ｉｎｄ．ｍｌ＾－１组最小,各组间的平均混交雌体受精率则无显著差异,对轮虫休卢卵最大形成效率及其出现的时间以及     

斜生栅藻密度对新安江萼花臂尾轮虫种群动态的影响

以浓度分别为1.0×106、2.0×106、4.0×106和8.0×106cells·mL-1的斜生栅藻(Scenedesmus obliquus)为轮虫食物,在25℃下,应用群体累积培养和单个体培养法研究了食物浓度对采自新安江水域(屯溪段)的萼花臂尾轮虫的种群动态影响。结果表明:食物浓度对轮虫的种群增长率和休眠卵产量均有显著的影响,均表现为低食物浓度下(≤4.0×106cells·mL-1)萼花臂尾轮虫的种群增长率和休眠卵产量较小且无差异,高食物浓度下(8.0×106cells·mL-1)轮虫的种群增长率和休眠卵产量较大;食物浓度对轮虫的混交雌体百分率和受精率无显著影响;在食物浓度为4.0×106cells·mL-1时萼花臂尾轮虫的净生殖率最大,世代时间最长,而其内禀增长率在食物浓度为1.0×106cells·mL-1时最小;在食物浓度为8.0×106cells·mL-1时平均寿命和生命期望最长。     

邻苯二甲酸酯类物质对萼花臂尾轮虫种群增长和有性生殖的影响

以萼花臂尾轮虫(Brachionus calyciflourus)为受试动物,以17β-雌二醇(E2)为阳性对照,运用3d种群增长和4d休眠卵产量实验方法研究了不同浓度的邻苯二甲酸二丁酯(DBP)、邻苯二甲酸二异辛酯(DEHP)和邻苯二甲酸丁苄酯(BBP)对轮虫种群增长和有性生殖的影响。结果显示,与空白对照组相比,0.05-5000μg/L的E2和500μg/L的BBP显著提高了轮虫种群增长率,而0.5和5000μg/L的DBP以及0.05和0.5μg/L的BBP使轮虫种群增长率显著降低;0.5-500μg/L的E2、50和500μg/L的DBP、0.005和500μg/L的DEHP和500μg/L的BBP显著提高了轮虫的休眠卵产量,而5000μg/L的DBP和0.05μg/L的BBP却与其相反;5和500μg/L的E2、50和500μg/L的DEHP以及500μg/L的DBP和BBP均使轮虫混交率显著上升,而0.005和0.05μg/L的E2、5000μg/L的DBP和DEHP及0.5μg/L的BBP显著降低了轮虫种群中混交雌体受精率;除5000μg/L的E2显著降低轮虫种群中的混交雌体数/非混交雌体数之外,其它所有处理组均对其无显著性影响;5、500和5000μg/L的E2、5000μg/L的DBP和5-5000μg/L的DEHP均使轮虫种群中的带卵雌体数/不带卵雌体数显著升高,而BBP对其无显著影响。在实验设置浓度范围内,轮虫种群中的混交雌体数/非混交雌体数与E2浓度间、轮虫种群中的混交雌体受精率和种群增长率与DBP浓度间、轮虫休眠卵产量与DEHP浓度间、轮虫混交率与BBP浓度间均具有显著的效应-剂量关系     

北京西海萼花臂尾轮虫（Brachionus calyciflorus）种群休眠卵库的遗传分化

利用线粒体细胞色素氧化酶Ⅰ亚基(COI)序列片段(543bp)对孵化自西海萼花臂尾轮虫休眠卵库的46个克隆进行分析,共发现6个单倍型,平均遗传距离为0.032,分别聚在2个分支.选取4个出现频率较高的克隆群,分别对其在3种食物浓度(蛋白核小球藻Chlorella pyrenoidosa,1×106 cells/ml,6×106 cells/ml,12×106 cells/ml)和3种温度(15℃,25℃,35℃;蛋白核小球藻Chlorella pyrenoidosa,6×106 cells/ml)下的适合度特征(R0和rm)以及个体大小(背甲长和背甲宽)进行比较研究.生命表实验结果显示,单倍型与食物浓度的交互作用(R0:P=0.038;rm:P=0.027)以及单倍型与温度的交互作用(R0:P=0.006;rm:P=0.000)对种群增长均有显著影响,这4个单倍型克隆群对环境条件具有不同的偏好,并且各个克隆群对于环境变化有不同的生殖反应.形态测量结果显示,单倍型与温度的交互作用(背甲长:P=0.033;背甲宽:P=0.000)以及单倍型与温度的交互作用(背甲长:P=0.027;背甲宽:P=0.000)对个体大小均有明显的影响.结合生命表及形态数据,探讨了休眠卵库中各个克隆群的生态位及形态分化以及可能对种群结构的动态变化产生的影响.     

孤雌生殖累积世代数和雌体年龄对萼花臂尾轮虫繁殖的影响

采用单个体培养方法,研究了孤雌生殖的累积世代数和雌体年龄对萼花臂尾轮虫混交雌体形成和产卵量的影响,结果表明,随着轮虫孤雌生殖累积世代数和增加,各代中的总混交雌体百分率呈减小的趋势,年轮的雌体可产生较多的混交雌体,非混交雌体所产后代中的总混交雌体百分率具有随其祖母年龄的增大而增大的趋势,孤雌生殖的累积世代数对轮对轮虫非混交雌体的平均产卵量无显著的影响,非混交雌体的年龄对其报代的平均产卵量亦无显著的影响。     

Effects of three organophosphorus pesticides on population growth and sexual reproduction of rotifer Brachionus calyciflorus Pallas

Effects of organophosphorus pesticides including dichlorvos, triazophos and chlorpyrifos on population growth and sexual reproduction of freshwater rotifer Brachionus calyciflorus were studied by 3-d population growth and 4-d resting egg production tests. The results showed that all the three organophosphorus pesticides influenced significantly the population growth rate, the ratio ovigerous females/non-ovigerous females in the rotifer populations and the resting egg production of the rotifers. Both dichlorvos and chlorpyrifos influenced markedly the mictic rate of the rotifers, but triazophos did not. Compared to the controls, both dichlorvos at 10.0–1000.0 μg/L and chlorpyrifos at 0.01–100.0 μg/L increased the population growth rate, but the reverse was also true for dichlorvos and triazophos both at 10000.0 μg/L. Chlorpyrifos at 10000.0 μg/L made the rotifers dead after 24-hr exposure. Dichlorvos and triazophos both at 10000.0 μg/L, and chlorpyrifos at 1000.0 μg/L all increased the ratio ovigerous females/non-ovigerous females. Both dichlorvos at 10000.0 μg/L and chlorpyrifos at 0.1–100.0 μg/L increased the mictic rate. Dichlorvos at 10.0 μg/L and 100.0 μg/L, and triazophos and chlorpyrifos both at 0.1–100.0 μg/L increased the resting egg production. Both population growth rate and ratio ovigerous females/non-ovigerous females are suitable endpoints for assessing the effects of dichlorvos, triazophos and chlorpyrifos, and mictic rate is a suitable endpoint for monitoring the effects of dichlorvos and chlorpyrifos on the reproduction of the rotifers. Both population growth rate and ratio ovigerous females/non-ovigerous females are more sensitive to dichlorvos and chlorpyrifos than mictic rate.     

Effects of three organophosphorus pesticides on population growth and sexual reproduction of rotifer Brachionus calyciflorus Pallas

Effects of organophosphorus pesticides including dichlorvos, triazophos and chlorpyrifos on population growth and sexual reproduction of freshwater rotifer Brachionus calyciflorus were studied by 3-d population growth and 4-d resting egg production tests. The results showed that all the three organophosphorus pesticides influenced significantly the population growth rate, the ratio ovigerous females/non-ovigerous females in the rotifer populations and the resting egg production of the rotifers. Both dichlorvos and chlorpyrifos influenced markedly the mictic rate of the rotifers, but triazophos did not. Compared to the controls, both dichlorvos at 10.0–1000.0 μg/L and chlorpyrifos at 0.01–100.0 μg/L increased the population growth rate, but the reverse was also true for dichlorvos and triazophos both at 10000.0 μg/L. Chlorpyrifos at 10000.0 μg/L made the rotifers dead after 24-hr exposure. Dichlorvos and triazophos both at 10000.0 μg/L, and chlorpyrifos at 1000.0 μg/L all increased the ratio ovigerous females/non-ovigerous females. Both dichlorvos at 10000.0 μg/L and chlorpyrifos at 0.1–100.0 μg/L increased the mictic rate. Dichlorvos at 10.0 μg/L and 100.0 μg/L, and triazophos and chlorpyrifos both at 0.1–100.0 μg/L increased the resting egg production. Both population growth rate and ratio ovigerous females/non-ovigerous females are suitable endpoints for assessing the effects of dichlorvos, triazophos and chlorpyrifos, and mictic rate is a suitable endpoint for monitoring the effects of dichlorvos and chlorpyrifos on the reproduction of the rotifers. Both population growth rate and ratio ovigerous females/non-ovigerous females are more sensitive to dichlorvos and chlorpyrifos than mictic rate.     

温度和食物浓度对三品系萼花臂尾轮虫实验种群动态的影响

应用个体培养方法,研究了温度(20、25和30℃)和藻类食物浓度(1．5×10^6、3．0×10^6、6．0×10^6和9．0×10^6cells·ml^-1)对青岛、芜湖、广州三品系萼花臂尾轮虫种群动态的影响．结果表明,温度仅对轮虫的世代时间和种群内禀增长率有显著影响,而品系对所有生命表参数均无显著影响．轮虫种群的内禀增长率随培养温度的升高而增大,世代时间则随培养温度的升高而缩短．食物浓度仅对轮虫的生命期望值和平均寿命有显著影响,品系对轮虫的净生殖率、世代时间、生命期望值和平均寿命也有显著影响．三品系间,以广州品系轮虫的净生殖率、世代时间、生命期望值和平均寿命最大,芜湖品系最短．当食物浓度为3．0×10^6cells·ml^-1时,轮虫的生命期望值和平均寿命最长,9．0×10^6cells·ml^-1时最短．各品系轮虫的净生殖率、世代时间、总生殖率、生命期望值和平均寿命均随培养温度的升高而减小,广州品系的净生殖率除外．轮虫种群的内禀增长率和广州品系轮虫的总生殖率则随培养温度的升高而增大．青岛和广州品系轮虫的各生命表参数,均与食物浓度呈曲线相关,但芜湖品系仅世代时间、平均寿命和生命期望值随食物浓度的增大而缩短．     

食物浓度和品系对萼花臂尾轮虫生殖期历时和混交雌体形成的影响

应用单个体培养方法比较研究了藻类食物浓度(2.0、5.0、8.0和11.0×106cells/mL)和品系对采自广州、青岛和芜湖等地的萼花臂尾轮虫生殖期历时、后代数和后代中混交雌体百分率的影响。结果表明,食物浓度对轮虫的生殖期历时和轮虫全部后代中的混交雌体百分率有显著的影响,但对轮虫的总后代数无显著的影响。品系对轮虫的生殖期历时、总后代数和全部后代中的混交雌体百分率均有显著影响。3品系间,广州品系轮虫的生殖期历时最长,为(4.53±0.19)d;总后代数最多达(18.75±0.26)个;全部后代中的混交雌体百分率最低,仅为4.32%±0.51%。而青岛品系轮虫全部后代中的混交雌体百分率最高,达49.90%±2.15%;其生殖期历时和总后代数与芜湖品系间均无显著的差异。食物浓度和品系间的交互作用仅对轮虫全部后代中的混交雌体百分率有显著影响。3品系中,仅芜湖品系轮虫的生殖期历时、总后代数和全部后代中的混交雌体百分率受食物浓度的显著影响;母体年龄对轮虫每天所产后代中的混交雌体百分率的影响因轮虫品系的不同和培养时所用的食物浓度的不同而异。     

Induction of sexual reproduction and resting egg production in Brachionus Plicatilis reared in sea water

Brachionus plicatilis raised in our laboratory in sea water reproduces asexually even under high crowding conditions (at least 40 individuals per ml). Amictic females were induced to produce mictic females, males and resting eggs by reducing the concentration of the sea water culture medium. Mictic females and males appeared predominantly among the progeny produced by the amictic females during 4 days following their transfer into 25% sea water. Resting eggs appeared first 5–12 days after the onset of the experiment. Following the disappearance of males, the culture consisted of amictic females.Resting eggs produced by the method described above may be preserved for at least three months at –14°C or by desiccation at room temperature. Under the appropriate experimental conditions, resting eggs hatch into amictic females. Since B. plicatilis is one of the most commonly used food sources of fish larvae in aquaculture, the methods reported here may offer an easy and versatile way of preserving rotifer culture stock to be used on demand.     

Impact of turbulence and turbidity on the grazing rate of the rotifer Brachionus calyciflorus (Pallas)

The impact of turbulence and turbidity on Brachionus calyciflorus grazing rate was determined in short feeding periods (10 min), using labelled Chlorella pyrenoïdosa. The response to water motion of B. calyciflorus depends on it physiological state: the grazing rate of recently fed amictic females stomach green (with one or two eggs) is significantly reduced in agitated environments compared with non-agitated environments. In contrast, the grazing rate of starved amictic females is not reduced by water motion, whatever its velocity (V1=0.18 m s?1 and V2=0.22 m s?1). In the presence of suspended particles (3–6-μm silica beads), a larger reduction in grazing rate is observed in agitated water at any water velocity (V1=0.18 m s?1 or V2=0.22 m s?1), than in stagnant water. A synergy between turbulence and turbidity is unfavourable to feeding of rotifers.     

A model evaluating the contribution of environmental factors to the production of resting eggs in the rotifer Brachionus plicatilis

The production of resting eggs by the rotifer Brachionus plicatilis was tested at four salinities (9, 18, 27 and 36\%) and six concentrations of the alga Chlorella stigmatophora (0.25, 0.5, 1.0, 2.0, 4.0 and 6.0 × 10⁶ cells ml^–1). The results indicated that resting eggs were produced only at two salinities (9\% and 18\%) and that their number was affected by the amount of food provided. A model consisting of two generalized linear sub-models was built to evaluate the contribution of each of the tested food concentrations at the two salinities. The sub-models were used to distinguish between two different components of resting egg production: one related to the presence or absence of resting egg production, and the other to the number of resting eggs produced, given that production had occurred. Besides indicating the best combination of salinity and food concentration for obtaining large numbers of resting eggs, they revealed the contribution of internal population factors that were not controlled in the course of the experiment. The model identified the positive contribution of the relative number of females to males, and the negative association between high rotifer densities and the production of resting eggs. The results of the present study help in defining the optimal conditions for mass production of resting eggs, which are of potential importance in aquaculture.Deceased, September 1991.     

镜湖不同湖区沉积物中轮虫休眠卵萌发的比较研究

实验室内对镜湖沉积物中的轮虫休眠卵进行了萌发,共孵出轮虫47种,隶属于10科19属;其中大湖区沉积物中萌发出的轮虫40种,小湖区41种,两湖区共同种类34种.每毫升大湖区沉积物中休眠卵萌发出的轮虫平均数量为(1.1±0.1)个,显著高于小湖区的(0.4±0.0)个.在两湖区沉积物中,以3种孵化方式所萌发出的平均密度超过4.0ind./200mL的轮虫种类总计有6种,它们是多须伪前翼轮虫(Proalides tentaculates)、裂痕龟纹轮虫(Anuraeopsis fissa)、螺形龟甲轮虫(Keratella cochlearis)、裂足臂尾轮虫(Brachionus diversicornis)、臂三肢轮虫(Filinia brachiata)和萼花臂尾轮虫(Brachionus calyciflorus);其中前三种轮虫为两湖区所共有.共有的3种轮虫的孵出情况在两湖区沉积物间也存在着差异.在小湖区沉积物中,3种孵化方式下孵出的平均密度大于0.05ind./200mL的轮虫属是臂尾轮属、伪前翼轮属、龟甲轮属和龟纹轮属,而大湖区沉积物中孵出的平均密度较高的轮虫属还包括三肢轮属、巨头轮属(Cephalodella)和异尾轮属(Trichocerca);水体营养程度较高的大湖区沉积物中孵出的臂尾轮属、伪前翼轮属和龟甲轮属轮虫的密度均高于营养程度较低的小湖区.     

几种培养方法对萼花臂尾轮虫(Brachionus calyciflorus)种群密度及其环境因子影响的比较研究

分别利用泥鳅 -藻 -轮虫和罗非鱼 -藻 -轮虫共生隔离培养的方法 ,研究萼花臂尾轮虫 ( Brachionuscalyciflorus)的种群密度和主要环境因子的变化。研究结果表明 :加入泥鳅的培养缸中 ,有 1 1 d轮虫数量超过 1 0 0 ind/ml,其中有 5d超过 2 0 0ind/ml,最高密度达 2 50 ind/ml;在罗非鱼的培养缸中 ,在整个实验过程中 ,种群密度超过 1 0 0 ind/ml以上的时间有 6d(第5～ 1 0天 ) ;单纯利用藻类培养轮虫时 ,种群密度较低 ,且维持时间较短 ,最高种群密度不足 1 0 0 ind/ml,利用藻类 -轮虫 -鱼类共存同一生态系统中 ,并使鱼类和轮虫隔离进行生态培养时 ,能提高轮虫种群密度 ,延长种群高峰期