Rotifer Density Research Articles

Long-term Variation Characteristics of Zooplankton Community Structure in Meiliang Bay, Lake Taihu

Zooplankton, as an important part of the water food chain, plays an important role in lake ecosystems. It is an important monitoring indicator for water bodies. However, due to the lack of long-term monitoring data of zooplankton community structure, there is a lack of understanding about its long-term characteristics. Based on monthly monitoring data from 1997 to 2017 of Meiliang Bay in Lake Taihu, the long-term trends of zooplankton community structure and its relation to the environment were examined. The results showed that the abundance and biomass of zooplankton in Meiliang Bay significantly decreased from 1997 to 2017 (P<0.05). In particular, the abundance and biomass of rotifer and copepod slowly declined, and the abundance of cladocerans fluctuated but its biomass presented a significant decreasing trend (P<0.05). The cladocerous biomass contributed the most to the zooplankton biomass in Meiliang Bay. The dominance of smaller cladocerans and copepods increased with decreasing rotifer density, significantly decreasing the average body size of zooplankton (P<0.05). This study indicated that zooplankton were becoming smaller, potentially weakening the top-down control on phytoplankton. In addition, zooplankton abundance and biomass showed an upward trend in spring and decreased in autumn and winter, and reached maximum values of 1406.70 ind.·L-1 and 25.64 mg·L-1, respectively, in September. In the summer, their changes were the opposite. Pearson correlation analysis showed that zooplankton community structure was significantly related to water physical characteristics (alkalinity, electrical conductivity, water depth, suspended substance, and water temperature), chlorophyll a, and nitrogen (P<0.05). This indicated that the eutrophication of Meiliang Bay in Lake Taihu had a significant impact on the community structure of zooplankton.

Effect of feeding frequency on water quality, growth, and hematological parameters of Nile tilapia Oreochromis niloticus reared using biofloc technology

ABSTRACT The aim of this study was to evaluate the effect of feeding frequency on water quality, growth performance, feed efficiency, and hematological parameters of Nile tilapia reared in biofloc technology (BFT) over a period of 45 days. Fish (n = 6,480; 5.36 ± 1.45 g) were randomly distributed in nine outdoor circular tanks (9,000 L) with individual air-water lift by supplementary aeration and hand-fed with commercial diet (32% crude protein) at 5-3% of biomass, following the respective feeding frequencies: two times per day, four times per day, and six times per day. The experimental design was completely randomized with three treatments and three replicates. Feeding frequency at four times per day decreased rotifer density and improved (P < .05) the weight gain and protein efficiency ratio. No significant differences were observed in hematological parameters. Water quality remained within recommended ranges for tilapia culture. Turbidity and floc volume showed significant differences (P < .05) among treatments, with the greatest concentrations at six times per day. Feeding frequency at four times per day promoted the best growth and feed efficiency responses in Nile tilapia (5 - 20 g)cultured in BFT.

Demographic characteristics of two freshwater cyclopoid copepods in Mexico, fed a plankton diet: the native Mesocyclops longisetus Thiébaud and the invasive Mesocyclops pehpeinsis Hu

ABSTRACTThe introduction of exotic species often results in a loss of biodiversity. Mexico has 4 invasive species of freshwater cyclopoid copepods: Thermocyclops crassus, Mesocyclops aspericornis, M. thermocyclopoides, and M. pehpeiensis. The Asian cyclopoid M. pehpeiensis is now established in several lakes and rivers in Mexico, but how it might compete with native species and potentially change the structure of plankton communities is unknown. Some insights might be obtained from a study of its demography compared to that of a native species. We compared the life cycle parameters of the native Mesocyclops longisetus and the exotic invasive species M. pehpeiensis in separate cultures. Four treatments were set up with 2 densities of Plationus patulus (Rotifera) individuals (1 and 4 mL−1) and 2 concentrations of Scendesmus acutus (Chlorophyte) cells (0.5 × 106 and 1.5 × 106 mL−1). Both species survived and reproduced in the treatment of 4 mL−1 of P. patulus individuals + 0.5 × 106 mL−1 of S. acutus cells. Mesocyclops pehpeiensis had common characteristics in successful invasive species: short generation time, high reproductive capacity, and a wide dietary range. At low rotifer densities, M. pehpeiensis had a higher population growth rate (0.12 d−1) compared to M. longisetus (0.08–0.10 d−1). M. pehpeiensis is likely to outcompete M. longisetus, especially under food-limited conditions, and most likely expand its range in Mexico.

Zooplankton communities in a river downstream from a lake restored with hypolimnetic withdrawal

Restoring lakes with hypolimnetic withdrawal can severely threaten water quality and biocenosis downstream. The objective of this study was to evaluate the effect of lake restoration on riverine zooplankton during a period of intense hypolimnion water inflow. Zooplankton density and biomass were determined in water samples. The water samples were also analyzed to determine the following physicochemical parameters: flow rate, dissolved oxygen, hydrogen sulphide, sulphate, ammonium nitrogen, nitrate nitrogen, total phosphorous, soluble reactive phosphorus, total organic carbon, and temperature. The results of multiple regression indicated that water flow was the most significant variable and was the best predictor of total zooplankton and rotifer density. Soluble reactive phosphorous was the main predictor of copepod biomass and density. Our study showed that hypolimnetic withdrawal disturbed the natural process of planktic community transformation, which was linked to the environmental shift from lacustrine to riverine. During the study, zooplankton density and biomass were low, but not as low as when the pipeline was operating at maximum output. At present, this lake restoration method has become more sustainable, because the adverse effects of hypolimnetic withdrawal on the recipient river have been minimized and limited to several weeks.

鄱阳湖丰水期水位波动对浮游动物群落演替的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 鄱阳湖丰水期水位波动对浮游动物群落演替的影响 DOI: 10.5846/stxb201812142730 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31560133） Impact of water level fluctuations on the succession of zooplankton in Poyang lake Author: Affiliation: 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:为了解鄱阳湖夏季丰水期水位剧烈波动过程中浮游动物的群落演替特征，2012年夏季鄱阳湖水位剧烈波动期间，于6月24日、7月7日和8月27日当水位下降且接近17.6 m时，在江西鄱阳湖国家级自然保护区内的1个浅水碟形湖泊设置4个采样点进行采样调查。共发现浮游动物65种，其中轮虫52种，枝角类7种，桡足类6种，多为营浮游生活的广温性和嗜温性种类。单因子方差分析（one-way ANOVA）显示3个月之间浮游动物的密度和生物量均具有显著差异（P<0.05），7月份浮游动物密度（1030.17±68.18个/L）显著高于6月份（325.16±41.60个/L）和8月份（203.79±24.91个/L）；6月份浮游动物的生物量（0.56±0.04 mg/L）显著低于7月份（1.22±0.11 mg/L）和8月份（0.99±0.11 mg/L）。基于浮游动物多度的聚类分析和自组织映射神经网络图均揭示夏季3个月份的浮游动物可区分为明显的3个群落：6月群落、7月群落和8月群落。蒙特卡罗检验发现水温、电导率、浊度和溶氧与浮游动物群落结构变化显著相关（P<0.05）。典型相关分析显示，6月份浮游动物群落与叶绿素a含量呈显著正相关关系，7月份浮游动物群落与水体温度呈显著正相关关系，8月份浮游动物群落与水深和电导率、浊度和溶氧呈显著正相关关系（P<0.05）。在3个月均为优势物种的盖氏精囊轮虫与叶绿素a含量呈正相关关系（P<0.05），与水温、pH、溶氧呈负相关（P<0.05）。夏季水位波动过程中浮游动物的群落结构在时间上（月份之间）发生明显演替，呈现轮虫密度逐渐降低，枝角类和桡足类密度逐渐增加的变化规律。水位波动引起环境因子的改变，从而对浮游动物的群落演替产生了重要影响。 Abstract:This study aims to understand the succession characteristics of zooplankton communities during dramatic water level fluctuations in Poyang Lake. During the drastic fluctuations in water levels of Poyang Lake in the summer, and on June 24, July 7 and August 27, 2012 when the water level dropped and approached 17.6 meters, four sampling points were established in a shallow dished sub-lake in Poyang Lake National Nature Reserve for the survey of zooplankton. A total of 65 species of zooplankton, including 52 species of rotifers, seven species of cladocerans and six species of copepods, were found during the study period. The zooplanktons were mostly the wide-temperature and mesophilic species of the planktonic type. The one-way analysis of variance revealed significant differences in zooplankton density and biomass within the three-month period (P<0.05). The density of zooplankton in July (1030.17 ±68.18 ind./L) was significantly higher, when compared to that in June (325.16 ±41.60 ind./L) and August (203.79 ±24.91 ind./L). Furthermore, the biomass of zooplankton in June (0.56 ±0.04 mg/L) was significantly lower than that in July (1.22 ±0.11 mg/L) and August (0.99 ±0.11 mg/L). The clustering of zooplankton communities by Bray-Curtis similarity measure and self-organizing maps revealed that the zooplankton was clearly divided into three communities:June community, July community, and August community. The Monte Carlo test revealed that water temperature, conductivity, turbidity and dissolved oxygen were significantly correlated with zooplankton community structure changes (P<0.05). The typical correlation analysis revealed that there was significantly positive correlation between zooplankton community and chlorophyll-a content in June. The water temperature and zooplankton community had a significant positive correlation in July. Furthermore, there were significant positive correlations between the zooplankton community and water depth, conductivity, turbidity and dissolved oxygen in August (P<0.05). Asplanchna girodi, which was the dominant species in the three-month period, was positively correlated with the chlorophyll-a content (P<0.05), but was negatively correlated with water temperature, pH and dissolved oxygen (P<0.05). The present study revealed that the zooplankton community structure exhibited a significant succession between months. Furthermore, the density of rotifers gradually decreased, and the density of cladocerans and copepods gradually increased. Moreover, the water level fluctuations caused changes in environmental factors, which had an important impact on the community succession of zooplankton. 参考文献 相似文献 引证文献

Sessile rotifers (Rotifera) exhibit strong seasonality in a shallow, eutrophic Ramsar site in Mexico

AbstractTo better understand the sessile rotifer community of a shallow, eutrophic lake, we monitored over a 1‐year period the monthly changes in the density and diversity of rotifers on the roots of the common water hyacinth, Eichhornia crassipes, which served as a representative hydrophyte. Selected physical and chemical parameters of the water were also determined. Mean annual density of all sessile species was 630 individuals per ml. Species of Collothecacea (n = 7) were most abundant. Of the 12 species of Flosculariaceae (Flosculariidae), Sinantherina socialis occurred seasonally, while Ptygura beauchampi was most common across all seasons. The Shannon–Wiener diversity index was highest (H′ = 2.8) in April, but decreased in January (H′ = 1.3). Applying the concept of the guild ratio (functional‐based analysis) we found that raptorial species (Collothecacea) were dominant over most of the year (June–February), while microphagous Flosculariidae were dominant during the warm, drier season (March–May). BEST (optimal matching of biota to environment, including stepwise search) analysis and canonical correspondence revealed that temperature, dissolved oxygen, pH, turbidity, and transparency strongly influenced sessile rotifer dynamics. We also found significant correlations between the density of some species and physicochemical variables. These species included Collotheca ambigua, C. coronetta, C. ornata, C. campanulata, C. tenuilobata, and Stephanoceros millsii in the Collothecacea; and Beauchampia crucigere, Limnias melicerta, L. ceratophylli, Ptygura crystallina, P. melicerta, and Sinantherina ariprepes in the Flosculariidae. Our study shows that the communities of sessile rotifers were structured by abiotic factors and that the guild ratio is useful for understanding the relationship between sessile rotifers and their substrata.

Effects of different harvesting and processing methods on Nannochloropsis oculata concentrates and their application on rotifer Brachionus sp. cultures

The effects of the cell separation method and the biomass processing of Nannochloropsis oculata were evaluated with respect to the cultivation performance of rotifers (Brachionus sp.). The algal culture was harvested by centrifugation or flocculation, and the biomass separation efficiency and the concentration factor were determined. The biomass was processed by chilling, freezing, heat-drying, or freeze-drying; and the cell integrity, resuspension percentage, and sedimentation profile of the diets were evaluated. The zootechnical performance (maximum rotifer density, growth rate, maximum egg production, fecundity, and feed ingestion rate) of rotifer cultures that fed the concentrated diets was compared with feeding the fresh culture of N. oculata (control treatment). Centrifugation resulted in 97% separation efficiency and a concentration factor of 578 and flocculation followed by centrifugation showed an efficiency of ~ 100% and concentration factor of 444. The harvesting technique did not have a significant influence on the characteristics of the diets and also on the zootechnical performance of the rotifers. The characteristics of the chilled concentrates (cell integrity, resuspension percentage, and sedimentation profiles) were similar to the control treatment, and the rotifers fed on those diets had the highest growth performances. Rotifers fed on frozen diets presented the worst performances. The heat-dried diets presented the lowest cell viability percentages, lowest resuspension percentages, and higher sedimentation rates. The feed ingestion rates of these diets were the lowest, resulting on inferior growth performance of the rotifers. In summary, both harvesting methods could be used, and chilling is the most recommended method for processing N. oculata biomass.

Growth response of rotifers on a bacterial-based diet made from fishwastes

Fishwastes are potential low-cost diet sources for replacing microalgae, which is the popular diet for rotifers. Growth responses of rotifer were tested under different weights of the diet (i.e. 0.05, 0.1, 0.2 and 0.4 g/L), different culture containers (i.e. using small tall (ST), small-short (SS), medium-tall (MT) and large-short (LS) containers), different initial densities of the rotifer (i.e. 10, 50 and 200 rotifers/mL) and mass cultured trials for 15 and 30 days. Population densities of rotifers increased significantly (ANOVA, p=0.001) when providing 0.1 to 0.4 gr/L than those fed 0.05 gr/L of the diet (Tukey HSD test, p<0.05). The densities also were significantly higher (ANOVA, p=0.001) when cultured using larger containers (LS and MT) than using smaller containers (ST, SS) (Tukey HSD test, p<0.05), but it was not significant when inoculated at different initial densities (ANOVA, p>0.05). The rotifers were successfully mass cultured for 30 days and were successfully harvested for 7 times at densities of about 2500 to 3300 ind./mL.

Comparative population dynamics of six brachionid rotifers (Rotifera) fed seston from a hypertrophic, high altitude shallow waterbody from Mexico

In hypertrophic waterbodies, seston may be an important food for planktonic rotifers. Therefore, we hypothesized that seston in the hypertrophic waterbody (Lake Xochimilco, State of Mexico) supports high diversity and density of rotifers. To test this, we conducted growth experiments using six rotifer species (Brachionus bidentatus, Brachionus budapestinensis, Brachionus calyciflorus, Brachionus caudatus, Brachionus havanaensis and Plationus patulus) cultured on three seston size fractions (< 3, 3–15 and < 15 µm) for 15 days. The three fractions of seston contained 3.15, 6.30, and 9.45 μg C ml−1, respectively. The physical and chemical variables of the waterbody were fairly stable during the study period. Brachionus budapestinensis, B. calyciflorus and B. caudatus showed negative growth rates when cultured on seston size of 3–15 or < 15 µm, while B. bidentatus had negative r on < 3 µm particle size. Brachionus havanaensis and P. patulus were well adapted to feed on different sizes of seston, while B. budapestinensis and B. caudatus had higher growth on < 3 µm particle size. These results explain the high diversity and density of brachionid rotifers in this waterbody where they coexist by partitioning the available seston.

Density and Diversity of Rotifers from Shore of a Flood Plain, Balloki Head Works

The present research work is an investigation of Rotifers from flood plains of Balloki Head Works using diversity indices. Objective: To study the density and diversity of rotifers of flood plain. Methods: collection of rotifers was done from the shore of flood plains from September to July. In total, 15 different species were identified. Rotifers were extracted from soil sample by a customized Baermann Funnel method. A moderate diversity of rotifers was explored by Shannon – Weaver. Simpson index of dominance supported this result. Analysis of variance (ANOVA) showed that there was no significant difference in population density of rotifers among months as the p-value was greater than 5% (α= 0.05). Population density of rotifers was negatively correlated with water temperature and pH whereas a positive correlation was observed with electrical conductivity Results: Overall a moderate diversity was observed. Rotifer density and distribution was under the influence of physico-chemical parameters.

Ecological mechanisms regulating the dynamics of the field rotifer population in a subtropical lake: evidence from the density, reproduction, and morphology of a case rotifer, Brachionus angularis

Understanding the ecological mechanisms driving the dynamics of field rotifer populations remains a challenge in ecology. Brachionus angularis (Rotifera) is preferred in such studies because of their planktonic behavior, high fecundity, and absence of cryptic species. In this study, one-year zooplankton samples were collected twice a month from a subtropical lake and the roles of abiotic and biotic factors regulating the population dynamics of B. angularis were analyzed. The sampled B. angularis were composed of two discontinuous populations: ‘summer and autumn’ and ‘spring and winter’, segmented by high mixis rates. The ‘summer and autumn’ population had high egg ratios, but low egg volumes. Water temperature was the main factor driving temporal dynamics in density, thereby counteracting the negative effect of top-down force. Based on the synchronous dynamics of two fractions of chlorophyll-a, the densities of B. angularis, its potential competitors and predators, together with the reverse correlations between the egg ratio and population density, and Secchi-disk depth, we found that bottom-up and top-down forces were plausible factors regulating variations in population density in spring (March and April). However, the density peak of B. angularis in winter might be primarily ascribed to recruitment from the sediment. We further addressed the necessity for diverse evidence from the speciation of cryptic species, abundance, reproduction, and morphology, in understanding the population dynamics of a field rotifer population.

The Impact of Land Use Transformations on Zooplankton Communities in a Small Mountain River (The Corgo River, Northern Portugal).

Transformation of the river catchment and the river bed cause significant changes in the functioning of river ecosystems. The main effects of anthropogenic transformations are hydrological changes, such as lower current velocity or an increase of nutrient content, and higher temperature. Zooplankton reacts rapidly to the new environmental conditions in rivers, increasing its richness and abundance. We tried to answer two questions: what type of catchment use has a greater influence on the zooplankton communities in a river and how do dam impoundments influence the zooplankton communities downstream? The study was conducted in the Corgo river (drainage of the Douro river, Northern Portugal) at 17 sampling sites in the lotic, free-flowing sections. Crustaceans present in the Corgo can attain relatively high densities in the rural section, which offers them better trophic conditions. The urban catchment use and the presence of dams have a greater impact on the rotifer density and the increase of zooplankton density downstream. The results of this study confirm that zooplankton properties allow for the evaluation of the degree of river-bed transformation.

Effect of two commercial probiotic products on population growth of rotifer Brachionus rotundiformis Tschugunoff

The application of probiotics has varying effects on rotifer culture. These effects can either be directly on their growth and reproduction or indirectly by affecting the culture environment. The role played by specific probiotic candidates is still indistinct and further research is required to ascertain their significance in rotifer culture. In this study, euryhaline rotifer Brachionus rotundiformis (SS-type) was used to evaluate the effect of two commercial probiotic products on rotifer density, reproductive parameters and unionized ammonia concentration for a twelve-day culture period. To estimate these parameters, rotifers were cultured in glass bottles containing dilute sterilized sea water with the following five diet treatments: Nannochloropsis oculata (control), Igsign (PB1), Toaraze Aqua (PB2) or the combination of N. oculata with either PB1 or PB2. The rotifer density was significantly affected by the addition of probiotic. N. oculata + PB2 treatment resulted in higher rotifer density and specific growth rate compared to the control treatment. Mixis induction was unaffected by N. oculata + PB2 while it was repressed by N. oculata + PB1. Ammonia concentration was not significantly affected with the addition of probiotics. These results indicate that probiotics have synergetic effects with microalgae diet that resulted in the highest rotifer densities.

It goes with the flow: Size mediated plankton attenuation through the Niagara River connecting channel

Abstract The Niagara River connecting channel provides a unique system in which to examine the impact of a rapid lentic-lotic-lentic transition on a freshwater ecosystem, particularly on plankton community composition. From June to October 2014, six monitoring sites (three in the upper river and three in the lower river) were sampled monthly for water chemistry, phytoplankton and/or zooplankton composition. Zooplankton biomass decreased exponentially with distance downstream, as expected within a high flow lotic environment. The rapid attenuation of zooplankton occurring within 10 km of the river mouth was likely due to predation by large populations of planktivorous fishes in the river. Densities of phytoplankton, rotifers and bacteria also declined but were less strongly impacted by the lentic-lotic transition. Plankton communities were dominated by species common to Lake Erie, the source waterbody, and also by taxa more resilient to the highly turbulent conditions of the river. These species included siliceous diatoms, filamentous algae, small zooplankters, dreissenid veligers and loricated rotifers. Furthermore, the seasonality of species composition in the Niagara River is the same as its source water body, suggesting no impact from the river on plankton succession. Niagara Falls and the two hydroelectric facilities were not found to be a significant cause of plankton mortality down river. There is some evidence however that entrainment time in the hydroelectric reservoirs may slightly enhance phytoplankton and zooplankton densities, thus contributing to plankton populations downstream of the turbine discharges.

Comprehensive approach to restoring urban recreational reservoirs. Part 2 – Use of zooplankton as indicators for the ecological quality assessment

The presented research is part of the LIFE project (“EH-REK” LIFE08 ENV/PL/000517) on innovative restoration methods for small urban impoundments in the city of Łódź (Poland). The objective was to evaluate the usefulness of zooplankton as a biological quality element, when assessing the effectiveness of restoration efforts in three urban reservoirs and a one pond. The fifth unrestored pond was used as an example of the progressive eutrophication of an urban ecosystem. Studies were conducted during two periods: before (2010−2012) and after (2013–2016) restoration. A selection of zooplankton indices, including the rotifer trophic state index (TSIROT), was used. The influence of the supplying river resulted in the negligible responses of biological parameters to the restoration efforts in the Upper Arturówek (UA) reservoir, which is the first in cascade of reservoirs. However, clear symptoms of water quality improvements were observed in the other two reservoirs (the Middle Arturówek, MA; the Lower Arturówek, LA) and in the Bzura-17 (B17) pond. After restoration, the contribution of species indicative of high trophic levels decreased in these ecosystems. The TSIROT was strongly positively correlated with the trophic state index based on chlorophyll a, and both parameters significantly decreased in the MA, LA and B17. In the unrestored pond (B11), the successive increase in the concentrations of chemical parameters indicated progressing eutrophication. Interestingly, since 2013, the TSIROT values clearly decreased in B11, but the strong negative correlation between ammonium concentration and rotifer density indicated that the reduced TSIROT values didn't result from improvements in water quality; rather, they resulted from the increases in pollution and the associated harmful impacts on Rotifera. In conclusion, the TSIROT can be a useful tool for assessing the ecological quality of small urban ecosystems; however, the use of biological indices must be supported by also monitoring physicochemical parameters.

Fish-processing wastes as an alternative diet for culturing the minute rotiferProales similisde Beauchamp

We evaluated the suitability of fish waste diet (FWD) for culturing the minute rotifer Proales similis through the observation of their population growth and particle size selective feeding. A total of five treatments either with Nannochloropsis oculata or FWD (0.75 and 0.50 g/L) or the combination of N. oculata and FWD were set up in triplicates. P. similis were cultured in diluted natural seawater (8 g/L salinity) and 26 ± 1°C with the diet treatments being applied randomly. We daily monitored the rotifer density, the number of bacteria and the water quality in all the cultures. The population density of P. similis increased exponentially in all treatments, while the mean growth in FWD 0.75 g/L was significantly higher (p < .05) than that in the control. Addition of N. oculata to FWD resulted to lowered P. similis population growth. Bacterial colony count was high in FWD and introduction of P. similis to the diet decreased their density. The estimated bacteria ingestion rates were generally in the range of 6.03 × 102–1.24 × 104 bacteria/rotifer/hr and there was a positive linear relationship between bacterivory and rotifer population growth. We also observed a shift in the particle size distribution with a reduction in the frequency and concentration of small-sized particles (<2.5 μm) at day 6. These results accentuate the potential of fish-processing waste as diet for culturing P. similis which feeds on bacteria and small particles (≤2.5 μm) that are by-products of degradation of this diet.

Temperature-dependent elimination efficiency on Phaeocystis globosa by different initial population sizes of rotifer Brachionus plicatilis

Due to sea water eutrophication and global warming, the harmful Phaeocystis blooms outbreak frequently in coastal waters, which cause a serious threat to marine ecosystem. The application of rotifer to control the harmful alga is a promising way. To investigate the influence of initial rotifer density and temperature on the ability of rotifer Brachionus plicatilis to eliminate Phaeocystis globosa population, we cultured P. globosa with different initial rotifer densities (1, 3, 5 inds mL−1) at 19, 22, 25, 28, and 31 °C for 9–16 d. Results showed that the population of rotifer feeding on Phaeocystis increased rapidly and higher temperatures favored the growth of P. globosa and B. plicatilis. With increased initial rotifer density and temperature, both the clearance rate of rotifer and the reduction rate of P. globosa increased, and thus P. globosa were eliminated earlier. Both temperature and initial rotifer density had significant effects on clearance rate of rotifer and the time to Phaeocystis extinction, and there was a significant interaction between the two factors on the two parameters, i.e., the effect of initial rotifer density on eliminating Phaeocystis decreased with increasing temperature. The rotifer in 5 inds mL−1 at 28 °C eliminated P. globosa in 4 d, whereas the rotifer in 1 ind mL−1 at 19 °C spent about 16 d on eliminating P. globosa. In conclusion, higher temperature and bigger initial rotifer density promote rotifer to eliminate the harmful P. globosa, and the optimal temperature for rotifer to clear P. globosa is 28 °C.

Interaction between simulated dense Scenedesmus dimorphus (Chlorophyta) bloom and freshwater meta-zooplankton community

Algal bloom has been a subject of much research, especially the occurrence of blue-green algae (cyanobacteria) blooms and their effects on aquatic ecosystems. However, the interaction between green algae blooms and zooplankton community was rarely investigated. In the present study, the effects exerted by Scenedesmus dimorphus (green alga) bloom on the community structure of zooplankton and the top-down control of the bloom process mediated by the zooplankton were evaluated using a series of laboratory cultures. The results showed that a dense S. dimorphus bloom could change the zooplankton community structure by decreasing its diversity indices, leading to the enrichment of a particular zooplankton species, Brachionus calyciflorus. In the presence of mixed species of zooplankton, the density of S. dimorphus in the culture was decreased as determined by a change in total chlorophyll a (Chl a) concentration, which was about 200 μg L-1 lower than that of the zooplankton-free culture. Furthermore, the number of species belonging to Cladocera, Copepoda and Rotifera all decreased, with all the cladocerans disappeared in the co-culture within 2 weeks of culturing, while the density of rotifers increased from 818 (±243) ind L-1 at the time of inoculation to 40733 (±2173) ind L-1 on the 14th day post-inoculation. Grazing of S. dimorphus by the rotifer B. calyciflorus neutralized its growth, and the gradual increase in B. calyciflorus density eventually led to the collapse of the bloom. Furthermore, grazing by B. calyciflorus also led to a decrease in the maximal photochemical efficiency (Fv/Fm) of photosystem II (PSII). The combined changes occurring in the zooplankton community structure during the process of S. dimorphus bloom and the negative effects of grazing on algal growth, morphology and photosynthetic activities confirmed the key role of zooplankton in the control of algal bloom. The results of the study therefore indicated that dense algal blooms caused by non-toxic algae could still remain a threat to aquatic ecosystems.

Contested Paradigm in Raising Zebrafish (Danio rerio).

The current body of work on rearing larval/juvenile zebrafish is based on (1) utilization of freshwater and (2) diurnal light/dark cycle, (3) provision of live feed at modest density, and (4) culture in high visibility environment. We challenged these rearing approaches by maintaining zebrafish under constant light for 46-48 days (days postfertilization [dpf]), while securing continuous feeding in high turbidity and saline (1.8-2.1 parts per thousand) environment for the experiment's duration, allowing 24 h feeding/growth of fish from first exogenous feeding to maturation. There was no evidence of negative effects on zebrafish larvae behavior, growth, survival, and life cycle duration at constant illumination when food was continuously available. Zebrafish were stocked at high initial density (100 larvae/L) in a static system and fed high densities of rotifers (Brachionus plicatilis) (200-400/mL) from 6 to 12 dpf. Fish density was then reduced by 50% and two diet treatments, live rotifers or brine shrimp (Artemia) nauplii (10/mL), followed. Fish were reared on these two diets until first maturation. Performance of adult zebrafish fed live rotifer followed by Artemia nauplii diet was the highest recorded in the literature after 42 dpf, 250 ± 29 (males) and 430 ± 5 mg (females). Use of these rearing conditions, during the entire life cycle, until reproduction, resulted in the shortest ever recorded generation time (from egg to egg) of 43-45 dpf and fertilization rate (1 dpf) of 80.3%-94%.

Composting fishwastes as low-cost and stable diet for culturing Brachionus rotundiformis Tschugunoff (Rotifera): Influence on water quality and microbiota

The demand for the rotifers Brachionus spp., which is considered indispensable for larviculture, has increased considerably in the tropical countries. Although freshly cultured microalga is the common rotifer diet, the culture protocols are laborious and costly, thus limit sufficient production of rotifers, and consequently disrupt fish seedling production programs in the microalgae-based hatcheries. This study aimed at developing an alternative low-cost and stable fishwaste diet (FWD), for the rotifers. The diets i.e. FWD1 (fishwastes only), FWD2 (FWD1+carbon source) and control (Chlorella vulgaris only) were used to determine the population density, specific growth rate and dietary value of the rotifer Brachionus rotundiformis (SS-type) in 30l tanks of sea water (22ppt), in which 20rotifersml−1 were stocked and semi-continuously cultured for 18days at 28±1°C without aeration. The coefficient of variation (CV) of the mean specific growth rate was calculated to determine the stability of the cultures. The culture medium and rotifer gut were aseptically screened for bacteria, which were counted and reported as colony-forming units (CFUml−1). The rotifers and microflora were harvested and analyzed for total lipids. FWD2 produced significantly higher rotifer density than FWD1 and control diet (p<0.05), but no significant difference was detected between FWD1 and control cultures (p>0.05). Up to 1188±70rotifersml−1 were obtained on day 13day with FWD2. There was no significant effect of FWD on the CV of the cultures, which were 0.11±0.05, 0.07±0.02 and 0.08±0.04 for FWD1, FWD2 and control cultures, respectively (p>0.05). There was significantly higher DO in the control- than in the FWD-tanks, and higher NH3-N in the FWD- than in the control-tanks (p<0.05). There was no significant effect of FWD on the pH in the diets (p>0.05). However, the water quality values were within the acceptable limits for aquaculture. The FWD-rotifers ingested significantly higher CFUml−1 of bacteria (1.02±0.12×107) than the control-rotifers (8.25±2.19×106CFUml−1). About 0.35 and 0.39mg/g of DHA and EPA, respectively was obtained in the FWD2-fed rotifers, and both were under detectable limit in the control-rotifers. The FWD may have contained essential nutrients and probiotics, which explains the higher rotifer population density in the FWD cultures than in the control cultures. This study offers an opportunity to reduce or eliminate the need for the expensive on-site microalgal production, and rotifer enrichment emulsions, toward a more cost-effective aquaculture, especially in the tropical countries.