Freshwater Rotifer Research Articles

Morphological alterations in the freshwater rotifer Brachionus calyciflorus Pallas 1766 (Rotifera: Monogononta) caused by vinclozolin chronic exposure.

Vinclozolin (VZ) is a dicarboximide fungicide widely used on fruits, vegetables and wines, effective against fungi plagues. In this study we characterized the effects of VZ using a 4-day reproductive chronic assay with the freshwater rotifer Brachionus calyciflorus. The assay included observations of several features of asexual and sexual reproduction. Our results indicate that VZ: (a) increased asexual and sexual reproduction, (b) caused severe abnormality in females and (c) these abnormalities were inherited by sexual and asexual reproduction. At 1.2mg/L three abnormal females were found out of 457 total females (0.66%). This low percentage is consistent and reproducible according to further analysis, where we increased the number of replicates and total females exposed to 1.2mg/L of VZ, and found 18 abnormal females out of 2868 total females (0.63% abnormality). Interestingly, abnormal females found at 5.6mg/L VZ exposure, were able to show mating behavior. Our results suggest that VZ behaves as a strong endocrine disruptor whose effects show the characteristic inverted-U-shape exposure concentration response curve regarding the intrinsic population increase and the percentage of abnormalities as endpoints.

The toxicity of carbofuran to the freshwater rotifer, Philodina roseola.

In this study, the effects of exposing the rotifer Philodina roseola to the pesticide carbofuran were investigated. Its range of sensitivity to potassium dichromate, the acute toxicity of active ingredient carbofuran and of carbofuran dosed as its commercial form, Furadan(®) 350 SC were determined. Chronic toxicity of carbofuran dosed as Furadan(®) 350 SC on P. roseola survival and fecundity were also studied. The sensitivity of P. roseola to K2Cr2O7 ranged from 29.52 to 64.67mgL(-1), averaging 47.10mgL(-1). The 48-h EC50 were 13.36±2.63mgL(-1) for carbofuran and 89.32±6.52mgL(-1) for commercial form. Chronic toxicity tests showed that the survival of this rotifer was not affected by the carbofuran dosed as Furadan(®) 350 SC at the concentrations tested and that at 1.56 and 3.12mgL(-1) their fecundity was higher than in the absence of this commercial product, characterizing the hormesis phenomenon. The sensitivity profile of several species to carbofuran indicated that P. roseola is more susceptible to this pesticide than the fish Clarias batrachus, the bacterium Vibrio fischeri, the protozoan Paramecium caudatum and the rotifer Brachionus calyciflorus, although the acute toxicity of carbofuran dosed as Furadan(®) 350 SC to P. roseola is much lower than that of active ingredient carbofuran. The results also imply that the exacerbated use of pesticides and the constant, accelerated expansion of agricultural activity will make aquatic non-target species even more vulnerable. Furthermore, the relevant role of benthic organisms in aquatic environments justifies the inclusion of P. roseola and other benthic species in toxicity screening for risk assessment, regarding this environmental compartment.

Reduced investment in sex as a cost of inducible defence in Brachionus calyciflorus (Rotifera)

Summary Inducible defences reduce the probability of prey being killed by their predators. However, these defences are often accompanied by costs. Most studies associated with aquatic communities have focused on the effects of inducible defences on the growth and reproduction of prey species, while their effects on sex investment remain unclear. Brachionus calyciflorus is a common freshwater rotifer that develops a defensive morphology in response to the kairomones released by the predatory rotifer Asplanchna. Some studies have reported that no detectable cost, such as decreased reproductive output, is associated with the spines in B. calyciflorus. Thus, we studied the sex investment (i.e. production of mictic offspring and resting eggs) of B. calyciflorus populations at three Asplanchna kairomone concentrations (0, 10, and 100 Asplanchna L−1) and two food levels (1 and 12 mg C L−1) to evaluate the sex cost of inducible defences. We also evaluated the crowding threshold required to trigger sex investment (i.e. lowest population density at which mictic female is produced) in B. calyciflorus under different kairomone and food treatments. Results showed that (i) the B. calyciflorus population exposed to kairomones produced offspring with elongated posterolateral spines; (ii) the production of mictic offspring and resting eggs decreased in the B. calyciflorus population exposed to kairomones, suggesting an investment trade‐off exists between inducible defence and sex investment; (iii) the decrease in sex investment was higher at the high kairomone concentration than at the low kairomone concentration; (iv) the decrease of sex investment was higher at the low food level than at the high food level; and (v) the crowding threshold of the B. calyciflorus population increased upon exposure to kairomones. The results of this study suggest that the decreased sex investment in defended B. calyciflorus is a form of defence cost. Our findings add to our understanding of the effect of predation on the ecology and evolution of phenotypic plasticity in rotifers.

FRESHWATER ROTIFER: (PART I) IMPORTANCE, LARVI FOOD, AND CULTURE

in finfish larval rearing often depends on the production of phytoplankton as well as zooplankton. Phytoplankton serve as feed for the zooplankton which, in turn, nourish the fish larvae. Different size and types of zooplankton may be raised for different larval stages. Feed production at all stages must be consistent in quality and quantity for the duration of the hatchery cycle if larval rearing is to be successful. We investigated native freshwater rorifer Brachionus angularis, B. quadridentatus brevispinus, and. B. durgae where the last one is reported as a rare an uncommon species in the world which have been collected in Tabasco. The report of freshwater rotifer from Tabasco is divided in two parts, part 1 describes freshwater rotifer from Tabasco, Mexico, as live food, and how to culture them. The second part reports on two species which have been succesfully cultivated in laboratory.

Cholinergic neuromuscular junctions in Brachionus calyciflorus and Lecane quadridentata (Rotifera: Monogononta)

Objective: To identify the presence of joint muscular and cholinergic systems in two freshwater rotifer species, Brachionus calyciflorus and Lecane quadridentata. Methods: The muscle actin fibers were stained with phalloidin-linked fluorescent dye, and acetylcholine was detected with Amplex Red Acetylcholine/Acetylcholinesterase Assay Kit, and then confocal scanning laser microscopy was used. Results: The musculature of Brachionus calyciflorus showed a pattern similar to other species of the same genus, while that of Lecane quadridentata was different from other rotifer genera described previously. The cholinergic system was determined by co-localization of both muscles and acetylcholine labels in the whole rotifer, suggesting the presence of neuromuscular junctions. Conclusions: The distribution pattern of muscular and acetylcholine systems showed considerable differences between the two species that might be related to different adaptations to particular ecological niches. The confirmation of a cholinergic system in rotifers contributes to the development of potential neuro-pharmacological and toxicological studies using rotifers as model organism. Peer reviewer

Diapause may promote coexistence of zooplankton competitors

Production of diapausing eggs in many zooplankton species occurs after partial switching from parthenogenesis to sexual reproduction. Storage effect theory predicts the stable long-term coexistence of competitors investing in diapausing stages, but it does not address the effect of such investment on short-term coexistence. The freshwater rotifer Brachionus calyciflorus and the cladoceran Moina micrura were used in this study to test experimentally if diapause could promote coexistence of active individuals under inter-specific competition. Our results show that B. calyciflorus was more affected by inter-specific competition and exhibited a greater and earlier production of resting eggs compared with M. micrura. Costs of diapause investment in Moina were only observed in competition. This was translated into reduced probability of B. calyciflorus of being outcompeted by M. micrura. We show that investment in diapause might promote local and short-term coexistence of competing zooplankton species. Our study strongly suggests that the ecological effects of diapause encompass a wider range of temporal scales, from weekly to decadal, and levels of organization, from individuals to communities, than previously thought.

Chronic effects of PFOA and PFOS on sexual reproduction of freshwater rotifer Brachionus calyciflorus

Rotifers play an important role in the dynamics of freshwater and coastal marine ecosystems, and are also important tools for assessing toxicity in aquatic environments. In this study, the effects of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) on the population growth rate and resting egg production of rotifer Brachionus calyciflorus were investigated. Reproductive bioassays indicated that PFOS increased the rotifer population growth rate at the concentration ⩽2.0mgL−1, and inhibited it at higher concentrations. For PFOA, the inhibition of population growth rate was observed when the concentration was greater than 4.0mgL−1. Exposure to PFOS (0.25mgL−1) or PFOA (2.0mgL−1) increased the mictic ratios of unexposed rotifer offspring. Population variation and increased mictic ratios were likely the two major factors leading to decline of resting egg production. The resting eggs formed under exposure to PFOA/PFOS in the range of 0.125–2.0mgL−1 showed higher hatching percentages in the control medium than that without PFOA/PFOS exposure. When the resting eggs were formed in the control medium and incubated in media with different levels of PFOA/PFOS, higher hatching percentages were induced by PFOS but lower hatching percentages induced by PFOA. The effects on the hatching rate of resting eggs with PFOA/PFOS exposure during the hatching period were greater than those with exposure during resting egg formation period, and the effect of PFOS was greater than that of PFOA. Both PFOA and PFOS exhibited slight effect on the hatching pattern.

The life-table demographic response of freshwater rotifer Brachionus calyciflorus to multi-metal (Cu, Zn, Cd, Cr, and Mn) mixture interaction.

The effects of multi-metal mixtures on the life-table demography of rotifers are not well known. In this study, the freshwater rotifer Brachionus calyciflorus was exposed to mixture of Cu, Zn, Cd, Cr, and Mn, and the life-table demographic parameters including net reproductive rate, generation time, life expectancy at hatching, and intrinsic rate of population increase were calculated. The results showed that interactions between a given element concentration, except Mn, and the other four elements mixture concentration affected the intrinsic rate of population increase (p < 0.01). Interactions between Zn concentration, as well as Mn, and the other four elements mixture concentration affected the net reproductive rate and the life expectancy at hatching, respectively (p < 0.05). The variation of parameters with the rise of the other four elements mixture concentrations from 0 to high was mainly attributed to the difference of interaction among the five metals mixture with different ratio of concentrations.

담수산 로티퍼, Brachionus calyciflorus의 미소 배양 생태계에서 관찰된 혼재생물간의 종간관계

One of freshwater rotifer (Brachionus calyciflorus) is very useful as a live food organism for early larval rearing of freshwater aquaculture industry. However, the knowledge about freshwater rotifer culture is scarce. On the other hand, marine rotifer culture as live food organisms is done, almost perfectly. In this study, I show to be benefit experimental results for successful freshwater larval rearing through the observation with microcosm structure in freshwater rotifer culture tanks.

Toxicity assessment of perfluorinated carboxylic acids (PFCAs) towards the rotifer Brachionus calyciflorus

The effects of acute toxicity, 3-day population growth and morphological effects of perfluorinated carboxylic acids (PFCAs) with carbon chain lengths of 2–6 on the freshwater rotifer Brachionus calyciflorus were investigated. The results indicated that the 24-h median lethal concentration (LC50) values of trifluoroacetic acid (TFA), perfluoropropionic acid (PFPrA), perfluorobutanoic acid (PFBA), perfluopentanoic acid (PFPeA), and perfluorohexanoic acid (PFHxA) towards B. calyciflorus were 70, 80, 110, 130 and 140mgL−1, respectively. The acute effects of PFCAs decreased with the increase of carbon chain length. The parameters used to determine 3-day population growth on these compounds were the rate of population increase (r) and mictic ratio. With the increase of fluorinated carbon-chain length, the r values of TFA, PFPrA, PFBA, PFPeA and PFHxA decreased by 0.99%, 16.8%, 16.5%, 22.4% and 32.0%, respectively. Mictic ratios ranged from 0.707 to 0.953 for PFCAs with carbon chain lengths of 2–6. In addition, the mictic ratio, body size and egg size exposed to some PFCAs were higher than those of the controls. These results offer a useful method for the ecological risk assessment of these short chain PFCAs.

密度信号对两种臂尾轮虫种群增长的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 密度信号对两种臂尾轮虫种群增长的影响 DOI: 10.5846/stxb201303010331 作者: 作者单位: 生物多样性与生态工程教育部重点实验室,生物多样性与生态工程教育部重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目(30970349) Effects of crowding signals on population growth of two Brachionus rotifer species Author: Affiliation: Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering,College of Life Sciences,Beijing Normal University,Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering,College of Life Sciences,Beijing Normal University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为了更好的了解化学干扰对轮虫种间竞争的影响,分别用萼花臂尾轮虫(Brachionus calyciflorus)和角突臂尾轮虫(Brachionus angularis)研究了同种和异种种群密度信号对种群增长的影响。结果表明,密度信号对轮虫种群增长具有一定的影响。萼花臂尾轮虫的密度信号显著降低了本种和角突臂尾轮虫种群的环境容纳量K并提高了它们的种群增长率r(P < 0.05),角突臂尾轮虫的密度信号对本种和萼花臂尾轮虫的种群增长都没有显著影响(P > 0.05)。萼花臂尾轮虫种群增长受同种密度信号抑制十分显著,环境容纳量K降低了50%以上,可能主要受自毒作用的调节,但同种密度信号对高有性生殖的萼花臂尾轮虫种群的混交率影响不明显。角突臂尾轮虫几乎不受自身密度信号的影响。因此,在两种臂尾轮虫的竞争中,由于自身密度信号的抑制作用,萼花臂尾轮虫将更快被角突臂尾轮虫排除。据此可推测密度信号对轮虫的种间竞争具有重要影响。 Abstract:Chemical signal is one of the primary channels of sensory input for zooplankton. Chemicals released by zooplankton individuals can affect their behavior, including migration, feeding, predator defense, growth, reproduction, and so on. Rotifers are adequate model animals for chemical ecology studies in aquatic system, with a rich literature on inducible defense and sexual production. However, studies associated with the effects of chemical signals on population competition have not been reported. Brachionus calyciflorus and Brachionus angularis are both common freshwater rotifer species. B. angularis, who has a lower threshold food concentration because of its smaller body size, would out-compete large body sized B. calyciflorus when the resource is limited. The present work examined the effect of crowding signals on population growth of B. calyciflorus and B. angularis. Culture medium conditioned by rotifers was used as the crowding signals and two crowding levels were set for each rotifer species. Population growth experiments of the two rotifers were carried out at an initial density of 1 ind./mL in 5 ml and 20 ml medium for B. angularis and B. calyciflorus, respectively. Regardless of the treatments, B. angularis reached its maximum population density at 100 ind./mL after 23 days, while it took B. calyciflorus only 3 to 8 days to reach its maximum population density, which was far lower than that of B. angularis. Both B. calyciflorus and B. angularis showed a higher population growth rate (r) and lower maximum population density (K) under the crowding signals of B. calyciflorus. However, neither B. calyciflorus population nor B. angularis population was significantly affected by the crowding signals of B. angularis. The maximum population density of B. calyciflorus was inhibited by its own crowding signal (from 9.124 ind./mL to 4.564 and 3.448 ind./mL under low and high crowding signals, respectively), leading a 50% decreasing of the carrying capacity K of the population. That was probably because of the inhibitory effects of autotoxins. Meanwhile, mixis ratios of B. calyciflorus populations fluctuated between 40% and 80%, and showed no significant differences among groups, because B. calyciflorus was sensitive to population density and mixis ratios were high at all these population densities. Because population growth of B. angularis was obviously affected by its own crowding signals, growing to a higher population density, and its threshold food concentration was lower, as a result, exclusion of B. calyciflorus by B. angularis may become quicker during the competition process. These results indicated that crowding signals may play an important role in the competition outcome between different rotifer species. 参考文献 相似文献 引证文献

Rotifers of southwest Iran: a faunistic and biogeographical study

The fauna of freshwater rotifers from Khuzestan Province (Southwest Iran) was expected to be different from that of the rest of Iran because of its geographical position, past geological events, climatic conditions, and similarities to neighboring zoogeographical areas. To test this hypothesis, we first had to determine the rotifer fauna of Khuzestan and then compare it with the results of surveys from other parts of Iran as well as with those from neighboring regions. Samples were collected from 10 sites throughout the province from May 2009 to April 2010. During the study, 66 species were identified, mostly with distribution in tropical and subtropical areas, from which 21 species are new to Iranian fauna. Surprisingly, one of the species, Colurella sanoamuangae, is not only new to the Iranian fauna, but also to the Palearctic region. Furthermore, another species, Lecane inconspicua , is, for the first time, reported outside the Arabian Plate. Comparisons among the rotifer fauna of Khuzestan, the rest Iran, and the Palearctic, Afrotropical, and Oriental regions, using the Sorenson similarity index, revealed considerable similarities between Khuzestan's fauna and those of the Afrotropical and Oriental regions.

The swimming speed alteration of two freshwater rotifers Brachionus calyciflorus and Asplanchna brightwelli under dimethoate stress

Two common freshwater rotifer species Brachionus calyciflorus and Asplanchna brightwelli were employed as test organisms to investigate the toxic effects of the widely used organophosphate pesticide, dimethoate. The swimming angular speed and linear speed alteration of two rotifers were evaluated under the toxic stress in four concentrations (0.4, 0.8, 1.2, and 1.6mgL−1). For B. calyciflorus, the rotifer swimming angular speed and linear speed were both adversely affected as a function of the toxicant concentrations. After a 2h exposure, the angular speeds at four concentrations were 39.37, 30.74, 26.68 and 23.96°s−1, 65.30%, 50.98%, 44.25% and 39.74% of that of the control, respectively, while the mean linear speed decreased from 194.80 to 91.85×10−3mms−1, which was 70.12%, 48.14%, 34.02% and 33.06% of that of the control (277.82×10−3mms−1), respectively. The pesticide also significantly inhibited the swimming angular speed of A. brightwelli. After a 2h exposure, the angular speeds of this rotifer at four concentrations were 39.37, 30.74, 26.68 and 23.96°s−1, only 22.99%, 17.16%, 16.21% and 13.63% of that of the control (170.80°s−1), respectively. Compared with the results of B. calyciflorus, A. brightwelli was more sensitive on the swimming angular speed when exposed to the toxicant. It implied that A. brightwelli should be an alternative candidate model species about the toxicities of aquatic pollutants. In addition, when the rotifer A. brightwelli was exposed to four pesticide concentrations, the swimming linear speed displayed symptoms of hormesis, characterized by the conversion of low-concentration stimulate to high-concentration inhibition. Our results show that dimethoate had a significant effect on swimming of freshwater rotifers.

베타(Betta splendens)의 부화 후 로티퍼(Brachionus calyciflor)와 물벼룩(Moina macrocopa)의 섭취, 소화속도 및 성장

The purpose of this study was to determine how an ornamental fish, such as the fighting fish, Betta splendens would respond to the use of freshwater live-prey, such as rotifers Brachionus calyciflorus and water fleas Moina macrocopa. Ingested quantity, digestive velocity and somatic growth were compared between larvae fed a freshwater rotifer and those fed boiled yolk. Food efficiency and somatic growth were compared between larvae that were fed freshwater water fleas and those fed a micro-diet developed for flounder (, I-hwa Ltd.). The number of rotifers ingested by larvae reached a maximum of 191 per day. However, based on the number ingested per hour and the digestive velocity of consumed rotifers, the maximum ingestible and digestible number of rotifers was calculated to be 272 per day. A maximum of 67 individuals (mean, 49.8 individuals) could be completely digested within the 1-h period from 90 to 180 min after feeding. Somatic growth was enhanced in larvae that were fed rotifers compared to those fed boiled yolk. Larvae exhibited greater growth at rotifer densities of 30 and 40 per mL than at lower densities. Among the water-flea (M. macrocopa and Bosmina sp.) and micro-particle diets, feeding with M. macrocopa resulted in the greatest somatic growth of larvae during the water-flea feeding stage.

Estimating the toxicity of ambient fine aerosols using freshwater rotifer Brachionus calyciflorus (Rotifera: Monogononta)

The toxicity of atmospheric fine particulate matter (PM2.5) in Atlanta is assessed using freshwater rotifers (Brachionus calyciflorus). The PM-laden quartz filters were extracted in both water and methanol. Aerosol extracts were passed through a C-18 column to separate the PM components into hydrophobic and hydrophilic fractions. Toxicity data reported in the units of LC50 (concentration that kills 50% of the test population in 24 h) shows that ambient particles are toxic to the rotifers with LC50 values ranging from 5 to 400 μg of PM. The methanol extract of the aerosols was substantially more toxic (8 ± 6 times) to the rotifers compared to the water extracts. A sizeable fraction (>70%) of toxicity was found to be associated with the hydrophobic fraction of PM. However, none of the bulk aerosol species was strongly correlated with the LC50 values suggesting a complicated mechanism of toxicity probably involving synergistic interactions of various PM components.

Effects of Microalgae and Alfalfa Meal on Population Growth and Production of a Freshwater Rotifer, Euchlanis dilatata (Rotifera: Mongononta)

AbstractPopulation growth and production of the freshwater rotifer, Euchlanis dilatata, were determined after being fed 1 of 12 diets: Scenedesmus quadricauda (S), Chlorella vulgaris (C), baker's yeast (Saccharomyces cerevisiae) (Y), alfalfa meal (Medicago spp.) (A), and eight combinations of S+C, S+Y, C+Y, S+C+Y, S+A, C+A, S+C+A, and Y+A (mixture in the same ratio by equal nitrogen weight). Results showed that both microalgal and alfalfa meal alone and in combination with Y had a significantly higher (P &lt; 0.05) population growth and production compared with Y alone. The mean maximum E. dilatata population density fed on S, S+Y, C, C+Y, S+C, S+C+Y, Y, A, S+A, C+A, S+C+A, and Y+A diets were 65 ± 7.5 (mean ± SE), 124.6 ± 17.2, 115.8 ± 7.9, 41.5 ± 7.9, 131 ± 14.1, 93.5 ± 8.7, 14.5 ± 7.6, 129.5 ± 18.5, 255.0 ± 20.5, 180 ± 30.5, 124.5 ± 25.4, and 61.5 ± 24.5 individuals/mL, respectively. Correspondingly, the mean population growth rates (K) through the 16‐d culture period were 0.29, 0.40, 0.45, 0.27, 0.34, 0.41, 0.26, 0.51, 0.58, 0.59, 0.39, and 0.45/d, respectively. Results indicated that alfalfa meal in combination with microalgae and yeast could be used as primary diets for E. dilatata culture. This may reduce the costs of rotifer production.

Responses in the population growth and reproduction of freshwater rotiferBrachionus calyciflorusto four organochlorine pesticides

In China, although the production and use of organochlorine pesticides (OCPs) have been banned for decades, relatively high levels of OCP residues have still been found in some water bodies, and can result in adverse acute and chronic effects on zooplankton including rotifers, which have caused public concern for many years. Responses in the population growth and reproduction of freshwater rotifer Brachionus calyciflorus to four OCPs including aldrin, dieldrin, β-hexachlorocyclohexane (β-HCH) and chlordecone were studied by 3-day population growth and 4-day resting eggs (RE) production tests. In comparison with control, aldrin at 10 μg.L−1 , β-HCH at 1000 μg.L−1 and chlordecone at 0.05 μg.L−1 significantly increased the population growth rate (r ); but aldrin at 100 μg.L−1 , dieldrin at 0.001 and 0.1 μg.L−1 , β-HCH at 0.1–100 μg.L−1 and chlordecone at 50 μg.L−1 markedly decreased it. Aldrin at concentrations higher than 1 μg.L−1 , dieldrin at 0.01 and 1000 μg.L−1 , β-HCH at concentrations 0.1 and higher than 1 μg.L−1 , and chlordecone at concentrations 0.005 and higher than 0.5 μg.L−1 significantly decreased the ratio of ovigerous females to non-ovigerous females (OF/NOF), but the reverse was true for aldrin at 0.1 μg.L−1 and β-HCH at 0.001 μg.L−1 . Dieldrin at 0.001, 0.01 and 1000 μg.L−1 significantly decreased the ratio of mictic females to amictic females (MF/AF), but β-HCH at 1 and 10 μg.L−1 highly significantly increased it. Dieldrin at 1000 μg.L−1 and β-HCH at concentrations higher than 10 μg.L−1 markedly decreased the fertilization rate (FR). Both aldrin and chlordecone have no significant effect on the MF/AF and FR of rotifers. Aldrin at concentrations higher than 1 μg.L−1 , dieldrin at lower than 0.1 and higher than 10 μg.L−1 , β-HCH at 1000 μg.L−1 and chlordecone at 0.005, 0.05 and 50.0 μg.L−1 significantly decreased the mictic rate (MR) of rotifers, but the reverse was true for β-HCH at 1 μg.L−1 . Aldrin at 10 μg.L−1 , dieldrin at 0.001, 0.1 and 1000 μg.L−1 , β-HCH at concentrations higher than 1 μg.L−1 and chlordecone at concentrations higher than 0.005 μg.L−1 markedly decreased RE production of rotifers, but β-HCH at 0.01 μg.L−1 significantly increased it. A clear dose–response relationship existed between the RE and the concentration of dieldrin, β-HCH and chlordecone, and the OF/NOF and the aldrin concentration. The RE and OF/NOF in rotifer population might be suitable endpoints for monitoring the low concentration of three OCPs (dieldrin, β-HCH and chlordecone) and aldrin, respectively.

Effects of dimethoate on rotifer Brachionus calyciflorus using multigeneration toxicity tests

As important members of the zooplankton community and sources of food for fish, rotifers are used extensively in ecotoxicological research to assess the health of the environment and safety of compounds. However, most rotifer toxicity tests are only conducted using rotifer neonates derived from unexposed mothers, thus ignoring the potential transfer of contaminants from mother to offspring. To understand better the mother to offspring exposure, a multigenerational study was conducted using three successive generations (F0, F1 and F2) of the common freshwater rotifer Brachionus calyciflorus to investigate the toxic effects of the widely used organophosphate pesticide, dimethoate (O, O-dimethyl S-methylcarbamoylmethyl phosphorodithioate). When the F0 generation was exposed to five pesticide concentrations, the population growth rate (r) displayed symptoms of hormesis, characterized by the conversion of low-concentration stimulation to high-concentration inhibition. Despite this observation, the exposure to any given concentration of dimethoate reduced the population growth rates of the F1 and F2 generation rotifers. Significant differences existed between the F0, F1 and F2 rotifers for the population growth rate under dimethoate stress: F2 individuals were more sensitive than F1, whereas the F1 individuals were more sensitive than F0. The results indicated that the parental exposure to a given toxic stress could result in increased sensitivity and decreased fitness in the offspring. This study illustrates the utility of multigenerational toxicity tests, which may better reflect and more accurately predict the effects of long-term pesticide exposure to aquatic organisms at the population level.

Effects of dieldrin and 17β-estradiol on life history characteristics of freshwater rotifer Brachionus calyciflorus Pallas

The effects of dieldrin and 17β-estradiol (E2) at seven concentrations (0.001, 0.01, 0.1, 1, 10, 100 and 1000 µg/L) on development, survival and reproduction of the freshwater rotifer B. calyciflorus were studied using a life table demographic method. Compared to the control, dieldrin at 0.01, 0.1 and 10 µg/L and E2 at 0.001–0.1 and 10 µg/L shortened the duration of embryonic development (p < 0.05). E2 at 0.01, 0.1 and 10 µg/L prolonged the juvenile period but dieldrin at 1000 µg/L shortened the juvenile period of the rotifers (p < 0.01). Dieldrin at 0.001–100 µg/L, and E2 at 0.001, 0.01, 1, 100 and 1000 µg/L prolonged the reproductive period of the rotifers (p < 0.01), Dieldrin at 0.001 and 10–1000 µg/L and E2 at 100 and 1000 µg/L prolonged the post-reproductive period of the rotifers (p < 0.05). Dieldrin at 100 µg/L decreased the intrinsic rate of population increase of rotifers but the reverse was true for E2 at 1 µg/L. The net reproduction rate was increased by dieldrin at 0.001 µg/L and E2 at 100 and 1000 µg/L. Dieldrin at 0.001–1000 µg/L and E2 at 0.01, 100 and 1000 µg/L prolonged the generation time. Life expectancy at hatching was prolonged by dieldrin at 0.001–1000 µg/L and E2 at 0.01, 1, 100 and 1000 µg/L. Both dieldrin and E2 at low concentrations caused a shortening in the duration of embryonic development, an increase in the reproductive period, post-reproductive period, net reproduction rate, generation time, and life expectancy at hatching of B. calyciflorus.

A new method for analysis of the toxicity of organophosphorus pesticide, dimethoate on rotifer based on response surface methodology

This study analyzed the toxicity of organophosphorus pesticide, dimethoate on freshwater rotifer Brachionus calyciflorus, using swimming angular and linear speed alteration as the sub-lethal endpoints. Response surface methodology (RSM) was applied in experimental design and data analysis to consider two related factors: toxic concentration, exposure time and their interaction. In general, inhibition effect of the pesticide on rotifer swimming was observed clearly at any given toxicant concentration. The highest inhibition rates in angular and linear speed were obtained in the shortest exposure time (11.36min) and the highest dimethoate concentration (1.85mgL−1). The RSM used for the analysis of treatment combinations showed that a cubic polynomial regression model was in good agreement with experimental results, with R2=0.992 and 0.9997, for swimming angular speed inhibition rate and linear speed inhibition rate (p<0.01, F-test, respectively). 3D reference surface plots and contour plots showed that the toxic effect was influenced not only by dimethoate concentration, but also by the exposure time. A time-step effect was observed clearly. Thus, the pesticide dimethoate had toxic stress on the swimming behavior of rotifers.