The trophic linkage between zooplankton and benthic suspension feeders: direct evidence from analyses of bivalve faecal pellets

Using radiotracer (¹⁴C) and microscopic observation, we demonstrated that mussels (Mytilus edulis and Perna viridis) could be predators of mesozooplankton (rotifer Brachionus plicatilis). At radio-labelled rotifer densities of 0.1, 0.2, 0.5, 1.0 individual ml⁻¹, faecal pellets of mussels showed different degrees of radio signals and most of the faecal pellets were expelled 4 h after pulse feeding on rotifers. The maximum gut retention time (GRT) of ¹⁴C-labelled rotifers in the digestive diverticula did not o show any significant difference between the two mussel species or the different densities of rotifers, and the averaged GRT was 43.4±3.06 h (mean ± SE). At a rotifer density of 4.5 individual ml⁻¹, rotifer lorica pieces and rotifer bodies without eggs were found in faeces of M. edulis, while in the pseudofaeces, only complete rotifer bodies were found.     

Effect of the allelochemicals from the macrophyte Egeria densa on the competitive interactions of pelagic and littoral cladocerans

Macrophytes release allelochemicals, which affect pelagic cladocerans such as Daphnia. Using population growth experiments, we analysed the effects of allelochemicals from the macrophyte Egeria densa on the interaction between Daphnia mendotae and three littoral cladocerans (Diaphanosoma birgei, Macrothrix triserialis and Simocephalus mixtus). We found that allelochemicals from E. densa increased the abundance of all the tested cladocerans in spite of the presence of a competitor. This effect was stronger (nearly three to four times higher than in controls) for D. birgei and M. triserialis in the absence of D. mendotae. Independent of the presence of allelochemicals, S. mixtus, but not D. birgei and M. triserialis, reduced the abundance of D. mendotae as compared to controls. The rate of population increase (r) per day was significantly elevated due to the presence of Egeria’s allelochemicals (from 0.07–0.16?d^?1 without allelochemicals against 0.12–0.24?d^?1 with allelochemicals). In our competition experiments, the rates of population increase of the cladocerans were lower than those in single-species cultures when cultured in the absence of allelochemicals. However, in the presence of allelochemicals this trend was not consistent. Thus, the positive effects of Egeria’s allelochemicals over the cladoceran populations may enhance the grazing pressure on phytoplankton.     

不同藻密度下诺氟沙星对萼花臂尾轮虫生命表统计学参数的影响

诺氟沙星是一种被广泛使用的抗生素,但其对轮虫的毒性作用尚不清楚。为调查诺氟沙星对轮虫的毒性及其与藻密度之间的关系,以及各试验终点对诺氟沙星污染的相对敏感性,本文以萼花臂尾轮虫为受试生物,研究了不同斜生栅藻密度(1.0×10~6、2.0×10~6和4.0×10~6cells·m L~(-1))下不同浓度(0、5、20、35、50、65和80 mg·L~(-1))的诺氟沙星对其生命表统计学参数的影响。结果显示,与3个藻密度下的对照组相比,暴露于5～80 mg·L~(-1)诺氟沙星溶液中的轮虫生命期望和世代时间显著延长,净生殖率和种群内禀增长率显著提高。5 mg·L~(-1)的诺氟沙星使生命期望和世代时间的延长幅度随着藻密度的升高而增大,但6个处理组的平均提高幅度却随着藻密度的升高而减小; 5 mg·L~(-1)的诺氟沙星对净生殖率和种群内禀增长率的提高幅度随着藻密度的升高而增大,但6个处理组的平均提高幅度却在2.0×10~6cells·m L~(-1)的藻密度下最小,4.0×10~6cells·m L~(-1)的藻密度下最大。1.0×10~6cells·m L~(-1)的藻密度下,诺氟沙星浓度对轮虫后代混交率无显著性影响(P0.05); 2.0×10~6cells·m L~(-1)的藻密度下,暴露于5～35和80 mg·L~(-1)诺氟沙星溶液中的轮虫后代混交率显著降低; 4.0×10~6cells·m L~(-1)的藻密度下,暴露于5、35和80 mg·L~(-1)诺氟沙星溶液中的轮虫后代混交率显著降低。当藻密度为1.0×10~6和2.0×10~6cells·m L~(-1)时,诺氟沙星浓度与轮虫的生命期望、世代时间、净生殖率和种群内禀增长率之间具有显著的剂量-效应关系;当藻密度为4.0×10~6cells·m L~(-1)时,诺氟沙星浓度与轮虫的净生殖率和种群内禀增长率之间具有显著的剂量-效应关系。本研究表明,亚致死浓度的诺氟沙星促进轮虫的存活、发育、孤雌生殖和种群增长,促进作用的幅度受藻密度的显著影响。     

Mass culture of the rotifer Brachionus plicatilis and its evaluation as a food for larval anchovies

Growth rates of anchovy larvae, Engraulis mordax, reared for 19 days under constant environmental conditions on a diet of laboratory-cultured organisms, exceeded the growth rates of anchovies fed on a diet of wild plankton. The rotifer Brachionus plicatilis was found to be a nutritous food source when fed to the larvae in concentrations of 10 to 20/ml and in combination with the dinoflagellate Gymnodinium splendens (100/ml). Optimum conditions were determined for mass culture of the rotifer. A high food concentration was the most important parameter needed to assure a high yield of rotifers. Large volumes (464 I) of the unicellular flagellate Dunaliella sp. were cultured for feeding the rotifers. The rotifer culture technique described produces approximately 2.5×10⁶ organisms/day, providing a reliable food source for rearing studies. The lengths of B. plicatilis (without eggs) ranged between 99 and 281 , most rotifers being larger than 164 and less than 231 . Individuals weighed 0.16 g and contained 8×10^-4 cal.     

Identification of a sex pheromone from a rotifer

The first isolation and characterization of a sex pheromone from a zooplankter is reported. A 29 kdalton glycoprotein on the surface of females of the marine rotifer Brachionus plicatilis acts as a contact-mating pheromone. This glycoprotein (gp29) is glycosylated with oligosaccharides containing Nacetylglucosamine, mannose, and fucose residues, and these oligosaccharides are necessary for male recognition of females. Males detect this signal by contact chemoreception with receptors located in their corona. Binding of purified glycoprotein to male receptors reduces mating attempts by 93%. An antibody to the glycoprotein binds to females, reducing male mating attempts by 86%. When purified gp29 is bound to sepharose beads, it is sufficient to elicit male mating behavior. This glycoprotein is likely to play a key role in the evolution and maintenance of reproductive isolation in rotifers.     

A protein signal triggers sexual reproduction in Brachionus plicatilis (Rotifera)

The defining feature of the life cycle in monogonont rotifers such as Brachionus plicatilis (Muller) is alternation of asexual and sexual reproduction (mixis). Why sex is maintained in such life cycles is an important unsolved evolutionary question and one especially amenable to experimental analysis. Mixis is induced by a chemical signal produced by the rotifers which accumulates to threshold levels at high population densities. The chemical features of this signal were characterized using size exclusion, enzymatic degradation, protease protection assays, selective binding to anion ion exchange and C3 reversed phase HPLC columns, and the sequence of 17 N-terminal amino acids. These studies were carried out over two years beginning in 2003 using B. plicatilis Russian strain. When rotifer-conditioned medium was treated with proteinase K, its mixis-inducing ability was reduced by 70%. Proteinase K was added to medium auto-conditioned by 1 female ml⁻¹ where typically 17% of daughters became mictic and mixis was reduced to 1%. A cocktail of protease inhibitors added to conditioned medium significantly reduced degradation of the mixis signal by natural proteases. Conditioned medium subjected to ultrafiltration retained mixis-inducing activity in the >10 kDa fraction, but the <10 kDa fraction had no significant activity. The putative mixis signal bound to an anion exchange column, eluting off at 0.72 M NaCl. These fractions were further separated on a C3 reversed phase HPLC column and mixis-inducing activity was associated with a 39 kDa protein. Seventeen amino acids from the N-terminus have strong similarity to a steroidogenesis-inducing protein isolated from human ovarian follicular fluid. The 39 kDa protein is an excellent candidate for the rotifer mixis induction signal.     

Transfer of the chlorinated hydrocarbon PCB in a laboratory marine food chain

The transfer of chlorinated hydrocarbons (CHC) in a laboratory simulation of a three trophic level marine food chain was studied. The food chain consisted of the algal flagellate Dunaliella sp., the rotifer Brachionus plicatilis, and the larva of the Northern anchovy Engraulis mordax. CHC were introduced into the seawater at concentrations representative of near-shore conditions off southern California without the use of dispersing agents. Each trophic level appeared to be in a steady-state at the time of first sampling, 5 days after inoculation. Apparent partition coefficients were calculated for each trophic level. The CHC contamination in the diet of the rotifers and anchovy larvae was also calculated. Unfed anchovy larvae accumulated the same amount of CHC as fed larvae and the final concentration appeared to be dependent on the CHC concentration in the seawater. The data in this report suggest that CHC accumulation is not a food-chain phenomenon but rather the result of direct partitioning of the compounds between the seawater and the test organisms.     

Seasonal variations in zooplankton abundances in the Iturbide reservoir (Isidro Fabela, State of Mexico, Mexico)

This studywas undertaken to quantify the seasonal variations of zooplankton (rotifers, cladocerans and copepods) and selected physico-chemical variables (temperature, pH, conductivity, Secchi disc transparency, dissolved oxygen, ammonia, nitrate and phosphate concentrations) in the Iturbide dam. Monthly zooplankton samples (50 l filtered through 50 microm mesh, in duplicates from each of the 4 stations) were collected from February 2008 to January 2009. Simultaneously physico-chemical variables were measured. The zooplankton samples were fixed in 4% formalin in the field. In general, the temperature ranged from 9 to 16 degrees C, rarely exceeding 20 degrees C. Secchi transparency was nearly 100% since the reservoir was shallow (< 2 m) even during the rainy seasons. Dissolved oxygen was generally high, 13-18 mg l(-1). Nitrate levels (10 to 170 microg l(-1)) were low while phosphates were relatively high (9 to 35 microg l(-1)). The Iturbide reservoir was dominated by rotifer species. We encountered in all, 55 taxa of rotifers, 9 cladocerans and 2 copepods. The rotifer families Trichocercidae and Notommatidae had the highest number of species (7 each) followed by Colurellidae and Lecanidae (6 and 5 species, respectively). Trichocerca elongata, Ascomorpha ovalis, K. americana, K. cochlearis, Lepadella patella and Pompholyx sulcata were the dominant rotifers during the study period. On an annual average, rotifer density ranged between 50-200 ind.(-1). Among crustaceans Chydorus brevilabris and Macrothrix triserialis were most abundant. The maximal density of these cladocerans was about 50 ind. l(-1). Copepods were much lower in numbers (< 20 ind. l(-1)). In general the density of zooplankton was higher during summer months (April to July) than during winter. Shannon-Wiener diversity index varied from 1.0 to 4.3 depending on the site and the sampling period. Based on the data of Secchi transparency and nutrient concentrations, the Iturbide reservoir appeared to be mesotrophic.     

Food selectivity of the rotifer Brachionus plicatilis feeding on phytoplankton

Food selectivity was examined in amictic female rotifers, Brachionus plicatilis, fed Chlamydomonas sp. and Olisthodiscus sp. Filtering and ingestion rates of the rotifers in a single food suspension were higher with Chlamydomonas sp. than with Olisthodiscus sp. In every mixture of two food species, the apparent filtering rate on Chlamydomonas sp. was much higher than that on Olisthodiscus sp. Total filtering rate and apparent filtering rate in food suspensions containing Chlamydomonas sp. decreased with increasing cell concentration of Chlamydomonas sp. Total and apparent filtering rates were calculated from the decrease in total food concentration as well as from decreases in concentrations of each of the two food algae, respectively. B. plicatilis ingested Olisthodiscus sp. at an extremely low constant rate in all mixtures. The degree of food selectivity of the rotifers fed Chlamydomonas sp. (i.e., selective filtration) from the mixture of two food algae decreased with increasing cell concentration of Chlamydomonas sp. Filtering and ingestion rates of rotifers fed senescent Chlamydomonas sp. were relatively lower than those fed Chlamydomonas sp. in the exponential phase. This indicates that Brachionus plicatilis displays selectivity in regard to condition of cells as well as type of food.     

水生生物水质基准研究中轮虫、水螅、涡虫类受试生物的筛选

轮虫、水螅、涡虫是水生生态系统的重要生物类群。因其对水体污染较敏感,所以对水生生物基准研究有重要意义。依据我国生物区系资料及毒性数据丰度,筛选出8种代表性本土轮虫、水螅、涡虫类生物。参照美国水生生物基准技术指南,搜集、筛选了这8种代表性生物的急性毒性数据,通过数据分析,筛选出对各物种毒性最大的污染物,主要包括重金属、农药、有机锡化物、表面活性剂、吡啶胺类杀菌剂。分析污染物的物种敏感度分布,依据累积概率对代表性生物的物种敏感性进行分类,结果为:萼花臂尾轮虫(Brachionus calyciflorus)、绿水螅(Hydra viridissima)、普通水螅(Hydra vulgaris)对重金属铜的累积概率为6.5%、8.5%和10.4%,普通水螅(Hydra vulgaris)对重金属汞的累积概率为6.3%;龟甲轮虫(Keratella cochlearis)和四齿腔轮虫(Lecane quadridentata)对五氯酚钠的累积概率为5.1%和7.6%;褐水螅(Hydra oligactis)和绿水螅(Hydra viridissima)对三丁基氧化锡的累积概率为6.9%和13.8%,萼花臂尾轮虫(Brachionus calyciflorus)对氟啶胺的累积概率为6.7%,日本三角涡虫(Dugesia japonica)对四氯化碳、十二烷基苯磺酸钠的累积概率分别为6.7%和7.1%。上述结果表明:萼花臂尾轮虫、绿水螅对重金属铜敏感;普通水螅对重金属铜和汞敏感;龟甲轮虫和四齿腔轮虫对农药敏感;褐水螅和绿水螅对有机锡化物敏感;萼花臂尾轮虫对吡啶胺类杀菌剂敏感;日本三角涡虫对四氯化碳、表面活性剂敏感。这7种代表性生物可作为相关污染物的水生生物基准受试物种。     

环境DNA(eDNA)宏条形码技术对枝角类浮游动物物种鉴定及其生物量监测研究

环境DNA(eDNA)宏条形码(Metabarcoding)技术越来越多地被应用于环境中物种定性识别,但如何定量监测物种在环境中的丰度尚未得到解决。本研究以太湖流域常见的5种浮游动物拟同形溞、大型溞、蚤状溞、多刺裸腹溞、老年低额溞为研究对象,建立了一种基于eDNA宏条形码技术的物种定量方法,并与实时荧光定量PCR(qPCR)相比较,研究了eDNA宏条形码技术多物种定量的准确性。结果表明,PCR引物对eDNA宏条形码的物种检测和定量影响显著。313 bp COI313引物对浮游动物物种覆盖度高,但是物种间DNA扩增的偏好性大,不适用于eDNA宏条形码定量检测。基于COI序列重新设计的短COI116引物能够同时检测出所有5个物种。荧光定量PCR(qPCR)物种拷贝数与物种相对占比呈正相关。eDNA宏条形码所检出每个物种的序列数与qPCR定量拷贝数高度一致。综上,eDNA宏条形码技术可实现对浮游动物物种的半定量检测,在生物多样性监测和生物完整性评价有显著的应用价值。     

富营养化对浅水湖泊轮虫种群结构影响研究

石臼湖和固城湖是长江中下游两个浅水湖泊,富营养化问题日益突出。为探索湖泊富营养化对轮虫的影响,于2012年平水期和枯水期对这两个湖泊轮虫种群结构进行了调查,并检测水体理化因子,分析轮虫分布与水环境因子及水体富营养状况的关系。水质检测结果显示,平水期石臼湖除个别点水体综合营养状态指数（TLI）〉50为轻度富营养状态外,大多数站点TLI50,处于轻度-中度富营养化状态。水生生物调查检出轮虫35种,其中石臼湖33种,固城湖27种,平水期种类多于枯水期。出现的轮虫以臂尾轮虫（Brachionus）和异尾轮虫（Trichocerca）居多,优势种主要有螺形龟甲轮虫（Keratella cochlearis）、广生多肢轮虫（Polyarthra vulgaris）、疣毛轮虫（Trichocerca sp.）、沟痕泡轮虫（Pompholyx sulcata）、异尾轮虫属和臂尾轮虫属等。轮虫平均密度3023.19 ind·L-1,平均生物量745.72μg·L-1。现存量季节变动明显,大部分站点平水期大于枯水期。轮虫多样性指数也是平水期大于枯水期,石臼湖轮虫多样性大于固城湖。水体综合营养状态指数（TLI）与轮虫种类数和多样性成显著负相关,随着富营养化加剧,轮虫种类减少,多样性降低。典范对应分析（Canonical Correspondence Analysis,CCA）表明,影响轮虫种群分布的主要环境因子为NH4＋-N、TN、TP和CODMn。按轮虫丰度分布与水环境因子的关系排序,2次调查的24个站点可大致分成3个组。轮虫种群结构受水体富营养状态影响,每组站点的代表性种类对水体营养状态有较好的指示作用。组1的代表性种类为曲腿龟甲轮虫,指示营养级别O-β;组2代表性种类萼花臂尾轮虫,指示的营养级别为β-α;组3以O营养级种类为主。     

Utilization of a new bdelloid rotifer (Philodina acuticornis odiosa) assay to evaluate the effect of salinity on the toxicity of chlorothalonil

Acute (24 h) toxicity tests were conducted to determine the toxicity of the fungicide chlorothalonil towards the freshwater bdelloid rotifer (Philodina acuticornis odiosa). Since rotifers are the dominant zooplankton species in many inland freshwater lakes in Australia, the influence of salinity on chlorothalonil toxicty was also assessed. The rotifers used in this study appeared to be reasonably tolerant to changes in salinity, with little mortality observed at 3760 µS cm^?1, increasing thereafter at higher salinity. The bdelloid rotifers were, however, found to be highly sensitive to chlorothalonil (24 h LC50, 3.2 µg L^?1) with results also suggesting that as salinity increases, so does toxicity (e.g., 24 h LC50 at 5000 µS cm^?1, 0.5 µg L^?1).     

Acute toxicity of sugarcane vinasse to aquatic organisms before and after pH adjustment

The purpose of this study was to investigate the toxicity of vinasse to cladocerans and fish before and after pH adjustment using an acute toxicity test. Linear and quadratic regression models were adjusted to demonstrate the concentration–response relationship between vinasse and the endpoints evaluated. The median lethal concentrations (LC_50–48h) of vinasse before pH adjustment for Ceriodaphnia dubia and Daphnia magna were 0.67% and 0.80% respectively, and the median lethal concentrations (LC_50–96h) for Danio rerio was 2.62%. After pH adjustment, the values increased for all organisms, demonstrating a decrease in toxicity. This study reported marked toxicity for vinasse to aquatic organisms with toxicity reduction after pH adjustment.     

Effects on larval crabs of exposure to algal toxin via ingestion of heterotrophic prey

We tested whether ingesting toxic algae by heterotrophic prey affected their nutritional value to crab larval predators, using toxic algal strains that are either ingested directly by larval crabs or rejected by them. Ingestion of toxic strains of the dinoflagellates Alexandrium andersoni and A. fundyense by the rotifer Brachionus plicatilis was confirmed. Rotifers having ingested either algal type for five days were fed to freshly hatched larvae of three crab species, with larval survival and stage durations determined. For both algal/rotifer treatments in all three crab species, larvae fed algae directly died during the first zoeal stage, while those fed rotifers that had been fed either algal strain survived to the experiment’s end (zoeal stage 3). Survival was lower, and stage duration longer, for larvae fed rotifers cultured on toxic algae when compared to those fed non-toxic algae. The role of toxic algae in the planktonic food web may be influenced by its direct or indirect ingestion by larval crabs.     

塔玛亚历山大藻对褶皱臂尾轮虫实验种群动态的影响

采用单个体培养方法研究有毒赤潮藻塔玛亚历山大藻（Alexandrium tamarense）的细胞再悬浮液、细胞破碎液及其与亚心形扁藻（Platymonas subcordiformis）的混合藻液对褶皱臂尾轮虫（Brachionus plicatilis）实验种群动态的影响．结果表明，塔玛亚历山大藻及其细胞破碎液延缓了褶皱臂尾轮虫的生长发育，使轮虫的生殖前期延长，生殖期及寿命缩短，特定年龄出生率降低，产卵量减少，从而导致轮虫生殖力下降，种群增长受阻．其中以塔玛亚历山大藻细胞再悬浮液对轮虫的影响最为显著，rm仅为0．1832d^-1，图1表2参18     

壬基酚对多刺裸腹溞连续世代的毒性效应

为探讨典型环境激素壬基酚(nonylphenol,NP)对枝角类浮游动物多刺裸腹溞连续世代的毒性效应,在实验室条件下,暴露连续3个世代(F0、F1、F2)多刺裸腹溞于0.02~0.10 mg·L-1的NP。15 d后测定成体死亡率、首胎繁殖时间、后代数目、成体蜕皮次数以及终点体长。研究结果表明,NP对F0代多刺裸腹溞具有很高的致死率;随着世代的增加,在相同NP质量浓度暴露下,与母代成体的死亡率相比,子代多刺裸腹溞成体的死亡率增高,致死毒性放大;NP对多刺裸腹溞连续3个世代的繁殖力都有显著抑制作用(P0.05),并随着世代递增,NP对子代繁殖力的抑制增强;在NP暴露下,多刺裸腹溞F0首胎繁殖时间明显推迟,NP暴露浓度与延迟程度呈正相关,呈现出剂量-效应关系,首胎繁殖时间延迟的趋势也存在于F1、F2世代中且存在放大效应;但是连续3个世代多刺裸腹溞成体的蜕皮次数都不受NP暴露影响;F0和F1世代多刺裸腹溞终点体长降低,并呈现明显的剂量-效应关系,但与F1相比,F2低浓度处理组受试个体终点体长呈增加趋势。对结果进行分析,认为多刺裸腹溞在NP暴露后的母代DNA或DNA完整性遭到破坏导致子代在相同NP质量浓度暴露下更容易受到NP致死性的影响;NP化合物具有的苯酚结构抑制枝角类体内葡萄糖、硫酸盐与类固醇的结合,从而引起体内荷尔蒙水平异常,最终对诸如生殖等生理行为造成不利影响;多刺裸腹溞成体的蜕皮次数都不受NP暴露影响表明蜕皮激素系统未受到干扰,且NP对生长的影响显然存在蜕皮外的其他作用机制。     

The effects of zooplankton swimming behavior on prey-capture kinematics of red drum larvae, <Emphasis Type="Italic">Sciaenops ocellatus</Emphasis>

Most marine fishes undergo a pelagic larval phase, the early life history stage that is often associated with a high rate of mortality due to starvation and predation. We present the first study that examines the effects of prey swimming behavior on prey-capture kinematics in marine fish larvae. Using a digital high-speed video camera, we recorded the swimming velocity of zooplankton prey (Artemia franciscana, Brachionus rotundiformis, a ciliate species, and two species of copepods) and the feeding behavior of red drum (Sciaenops ocellatus) larvae. From the video recordings we measured: (1) zooplankton swimming velocity in the absence of a red drum larva; (2) zooplankton swimming velocity in the presence of a red drum larva; and (3) the excursion and timing of key kinematic events during prey capture in red drum larvae. Two-way ANOVA revealed that: (1) swimming velocity varied among zooplankton prey; and (2) all zooplankton prey, except rotifers and ciliates, increased their swimming velocity in the presence of a red drum larva. The kinematics of prey capture differed between two developmental stages in S. ocellatus larvae. Hyoid-stage larvae (3–14 days old) fed on slow swimming B. rotundiformis (rotifers) while hyoid-opercular stage larvae (15 days and older) ate fast moving A. franciscana. Hyoid-opercular stage red drum larvae had a larger gape, hyoid depression and lower jaw angle, and a longer gape cycle duration relative to their hyoid-stage conspecifics. Interestingly, the feeding repertoire within either stage of red drum development was not affected by prey type. Knowledge of the direct relationship between fish larvae and their prey aids in our understanding of optimal foraging strategies and of the sources of mortality in marine fish larvae.     

Salinity dependence of sexual and asexual reproduction in the rotifer Brachionus plicatilis

A salinity dependent mictic response was observed in a clone of Brachionus plicatilis cultured in the 2 to 4 salinity range. This response was related to asexual exponential reproduction rates (G) and could be divided into three categories: (a) no mixis occurred at a salinity of 35 S and above, where G values were lower than 0.30 d^-1, (b) low mictic levels in rotifers cultured at 2 and 30 S, where G values ranged between 0.40 to 0.50 d^-1, and (c) high mictic levels in rotifers cultured at salinities ranging between 4 and 20 S, where G values ranged between 0.50 to 0.85 d^-1. Fluctuations in mictic levels varied with time during the course of the experiments. Results suggest that salinity conditions leading to optimal parthenogenic reproduction also support mixis.     

Elaphoidella grandidieri (Harpacticoida: Copepoda): demographic characteristics and possible use as live prey in aquaculture

In freshwater ecosystems, rotifers and cladocerans are ideal prey for fish larvae whereas copepods, due to their purported low growth rate and predatory tendency, are not. We recently isolated the parthenogenetic Elaphoidella grandidieri (Gueme et Richard, 1893) a benthic freshwater harpacticoid, from a fish farm in the State of Morelos, central Mexico and tested its potential as a live prey organism for larval vertebrates. Population growth and life table demography experiments were conducted, in 100 ml recipients with 50 ml of test medium on a diet of Scenedesmus acutus at a density of 1.0 X 10(6) cell ml(-1); the former on live algae alone while the latter on live algae as well as detritus. We also conducted experiments to document the prey preference for this copepod by the larval Ameca splendens (Pisces: Goodeidae) and Ambystoma mexicanum (Amphibia: Ambystomatidae), fed the rotifer Plationus patulus, the ostracod Heterocypris incongruens, and the cladocerans Moina macrocopa and Daphnia pulex. Elaphoidella grandidieri is relatively easy to maintain under laboratory conditions, reaching densities (copepodites and adults) of more than 10,000 l(-1). The generation time ranged between 30-45 days, depending on the diet. The net reproductive rate was as high as 60 nauplii female(-1) day (1). Population growth rates ranged between 0.03 and 0.11 d(-1), live algae being the superior diet compared to detritus. Both predators showed no preference for E. grandidieri, but in the absence of alternate prey they consumed 80% of the harpacticoids offered. The data have been discussed in relation to the potential of E. grandidierias live food for aquaculture.