Freshwater Rotifer Research Articles

Ontogeny and Growth of Early Life Stages of Barred Spiny Eel Macrognathus pancalus (Hamilton, 1822)

Background: The objective of the study was to examine the growth and development of M. pancalus larvae in captive conditions, including pigmentation patterns, yolk and oil globule utilization, growth rates and metamorphosis, as well as to identify suitable live food for larviculture. Methods: The larvae, produced through induced breeding, were kept unfed until the yolk-sac absorption and then fed with freshwater rotifer, mixed zooplankton and Tubifex worms at different stages of development. The larvae were reared in indoor glass tanks and outdoor reinforced plastic tanks to document their morphological and chronological development. Result: The findings showed that the larvae exhibited typical characteristics of eel. Notably, dentition was observed before yolk resorption, indicating the highly predatory nature of the larvae. The bands of melanophores, which were prominent at the beginning, disappeared between 5-7 days post-hatch. Additionally, the study identified distinct features of spiny eels, such as a trunk-like rostral projection at 14 days post-hatch and erectile dorsal spines at 21 days post-hatch. The growth pattern, morphological changes and adaptation to benthic burrowing habits indicated that the larvae metamorphosed into the fry stage between 28-45 days post-hatch. These results provide valuable insights into the ontogenetic development and rearing of M. pancalus and can be used to support future aquaculture and conservation programs.

Can acclimation of freshwater rotifers to silver nanoparticles or 5-fluorouracil influence their multi- and transgenerational effects?

Emerging chemical contaminants (ECCs) are among the major environmental threats in present century. A variety of ECCs is released into aquatic environments with little knowledge about their long-term impacts to organisms. We examined the role of acclimation of the freshwater rotifer Brachionus calyciflorus to silver nanoparticles (Ag-NPs) and 5-fluorouracil (5-FU) for determining their ability to deal with these ECCs individually and in mixtures along multiple generations. Additionally, transgenerational effects were also assessed during the recovery phase. Rotifers acclimated at EC10 of Ag-NPs along generations showed a higher ability to deal with higher concentrations of these nanoparticles or 5-FU along generations. Rotifers acclimated to EC10 of 5-FU showed varied responses, as their population growth rates were affected at the initial generations once exposed to higher concentration (EC50) of the same or a new contaminant; however, the rotifers acquired resistance in later generations. The exposure of generational Ag-NP-acclimated rotifers to the mixture of Ag-NPs and 5-FU at EC50 led to a shift from no effects to negative effects along successive generations, suggesting a decrease in resistance, which remained even in the post-exposure recovery phase. Similar transgenerational adverse effects were also observed for the generational Ag-NP-acclimated rotifers released from 5-FU. Rotifers acclimated to 5-FU showed a decrease in population growth rate at the first generation of recovery phase, possibly shifting their optimal environmental conditions when released from contaminants. Overall, our results suggest that rotifers had a high level of plasticity to ECC exposure in freshwaters; however, acclimation can be generic or contaminant dependent.

Contrasting toxicity response to a mixture of azithromycin and ivermectin between a freshwater and a euryhaline rotifer.

Organisms are usually exposed to mixtures of emerging pollutants in aquatic environments. Due to their widespread use and environmental relevance, the individual and combined effects of the drugs azithromycin (AZT) and ivermectin (IVM) on the freshwater rotifer Lecane papuana and the euryhaline rotifer Proales similis were investigated. Rotifers showed greater sensitivity to IVM compared to AZT. The LC50 values of IVM and AZT for L. papuana and P. similis were 0.163 and 0.172mg/L, and 13.52 and 20.00mg/L, respectively. Population growth rates, assessed in chronic toxicity assays, responded negatively to increasing concentrations of both toxicants, either individually or in combination. Our results revealed two distinct combined toxicity responses:a strong synergistic effect in the freshwater rotifer and a marked antagonistic impact of the AZT-IVM mixtures in the euryhaline rotifer.

Evaluation of enriched freshwater rotifer, Brachionus calyciflorus as first feed on growth performance, nutrient availability and fatty acid composition of Anabas testudineus (Bloch, 1792) larvae

Climbing perch, A. testudineus (Bloch, 1792), is a widely consumed fish in Asian nations due to its high nutritional value and delicate meat. The main obstacles to the spread of its cultural practises are a scarcity of high-quality seed and larval rearing due to the low survival rates in the initial stages of larval development. The key to improving the seed production of this species may lie in strategies to improve larval survival in the early stages. As a result, the goal of current study was to evaluate the impact of vitamin C, selenium, and highly unsaturated fatty acid (HUFA) enriched Brachionus calyciflorus on the development, nutrient availability, and fatty acid profile of climbing perch larvae. A total of 180 numbers of 3 days post-hatch (dph) larvae (0.021 ± 0.001 mg) were uniformly distributed among five treatments in triplicates. The larvae were fed thrice a day for 15 days with selenium (D1), vitamin-C (D2), HUFA (D3) and combination of selenium-vitamin C- HUFA enriched (D4) and non-enriched rotifer (C). The proximate analysis of various enriched and unenriched B. calyciflorus groups revealed that the vitamin C and HUFA-enriched treatment groups, respectively, had the highest percentages of crude protein (7.50%) and crude lipid (2.51%). Whereas, larvae fed a combination of selenium-vitamin C- HUFA enriched (D4) rotifer showed the highest percentages of crude protein (12.40%) and crude lipid (1.81%). The findings of the fatty acid analysis demonstrate that feeding Se-VC-HUFA enriched B. calyciflorus to larvae resulted in significantly greater concentrations of Eicosapentaenoic acid (9.38%) and Docosahexaenoic acid (11.05%) that are 3.07 and 7.67 times higher, respectively, than feeding unenriched B. calyciflorus to larvae. The highest DHA/EPA ratio (1.18) was also observed with larvae fed Se-VC-HUFA enriched B. calyciflorus. The survivorship analysis revealed that the D4 treatment group fed a combination of Se-VC-HUFA-enriched B. calyciflorus had the highest survival (37.41%) and the lowest (18.70%) observed in the control group. The highest average body weight gain and increased growth (30.79 ± 1.11 mg) were seen in the fishes given the rotifer supplemented with D4 group, which performed substantially better than the other treatment groups (P < 0.05). Weight-specific growth rate (W-SGR) and Length-specific growth rate (L-SGR) of the fish exhibited similar trends across all treatment groups, whereas significantly (P < 0.05) lowest condition factor was observed in D4 (2.63 ± 0.01) and highest in control group (3.21 ± 0.01). The results showed that larvae fed with enriched rotifer had significantly higher (P < 0.05) growth, nutrient availability, and fatty acid profile compared to un-enriched rotifer. The ideal first food for A. testudineus larval growth and survival must be a combination of Se-VC-HUFA enriched B. calyciflorus.

Evaluation of trophic state conditions in the three urban perennial lakes of the Coimbatore district, Tamil Nadu: Based on water quality parameters and rotifer composition

This study aims to examine the trophic state conditions in the three major urban perennial lakes of the Coimbatore district based on the physicochemical properties and rotifer community structure. The study was conducted for a period of three months, from January 2023 to March 2023. The water and plankton samples were collected twice a month. The measured physicochemical properties showed that pH, salinity, total hardness, nitrate, and phosphate were found to be higher in Kumarasamy lake, followed by Ukkadam and Valankulam lake ecosystems. The higher rotifer population density was observed in Valankulam lake (1820 Ind./L), and lower in Kumarasamy lake (1080 Ind./L). In this study, Brachionidae species were abundantly found in the three perennial lake water environments, followed by Asplanchnidae, Lecanidae, Trichocercidae, and Filiniidae. In addition, a total of 28 freshwater rotifer species were reported for the first time from the three perennial lakes of the Coimbatore district, respectively. The determined trophic state index (TSI) (47.57) and rotifer trophic state index (TSIROT) (51.25) values affirm that the three perennial lakes are under meso-eutrophic conditions. The examined diversity indices values revealed that species dominance (D) and species richness (SR) are higher in Valankulam lake, followed by Ukkadam and Kumaraswamy lake ecosystems. This difference may be due to the influence of human activities and the mixing of various points and non-point sources of pollutants. The present study concluded that the three perennial lakes were moderately polluted by various sources of pollutants; therefore, continuous monitoring is needed for the conservation of flora and fauna diversity in the three perennial lakes of the Coimbatore district.

Microplastic fragmentation by rotifers in aquatic ecosystems contributes to global nanoplastic pollution.

The role of aquatic organisms in the biological fragmentation of microplastics and their contribution to global nanoplastic pollution are poorly understood. Here we present a biological fragmentation pathway that generates nanoplastics during the ingestion of microplastics by rotifers, a commonly found and globally distributed surface water zooplankton relevant for nutrient recycling. Both marine and freshwater rotifers could rapidly grind polystyrene, polyethylene and photo-aged microplastics, thus releasing smaller particulates during ingestion. Nanoindentation studies of the trophi of the rotifer chitinous mastax revealed a Young's modulus of 1.46 GPa, which was higher than the 0.79 GPa for polystyrene microparticles, suggesting a fragmentation mechanism through grinding the edges of microplastics. Marine and freshwater rotifers generated over 3.48 × 105 and 3.66 × 105 submicrometre particles per rotifer in a day, respectively, from photo-aged microplastics. Our data suggest the ubiquitous occurrence of microplastic fragmentation by different rotifer species in natural aquatic environments of both primary and secondary microplastics of various polymer compositions and provide previously unidentified insights into the fate of microplastics and the source of nanoplastics in global surface waters.

Removal of weed algal contamination in cultures of Botryococcus braunii with enlarged colonies using rotifers

We proposed a biological contamination control technology that preyed on and removed only invading weed algae by introducing rotifers into the culture ponds of Botryococcus braunii that had enlarged colonies. Botryococcus braunii strains Showa and Sanshiro belonging to race B were used, and the colonies were grown on a high-salt medium containing 3 g L−1 NaCl. Brachionus calyciflorus, a freshwater rotifer with large prey size, was used as the predator, and Westella sp. was used as the model weed algae. In the mixed culture of B. braunii and B. calyciflorus, the growth rate of B. braunii cultured in Chu13, a freshwater medium, was reduced due to predation by B. calyciflorus. However, enlarged B. braunii cultured in a high-salt concentration medium escaped predation and maintained a growth rate equivalent to or higher than that of the control. In the three trials combining B. braunii, B. calyciflorus, and Westella sp., B. calyciflorus was initially applied such that the ratio of the number of rotifers to the algal density of Westella sp. was 2.0 × 10−6. Under these conditions, the initial growth of Westella sp. was suppressed when using the Showa strain, which showed significant growth. The larger colony size of the Sanshiro strain showed greater proliferation of Westella sp. because its optical density was lower than that of the Showa strain. The growth of the Sanshiro strain was suppressed until day 6, when predation reduced Westella sp. density, but the growth rate recovered thereafter. A model for the optimum number of rotifer inputs, considering the optical density and the number of rotifers remaining in the future, and technology for outdoor cultivation must be developed in the future. We demonstrated the potential of an eco-friendly weed-algae-removal technology that uses a predation ecosystem without using special culture environments or pesticides.

Dynamics of Fatty Acids in Pikeperch (Sander lucioperca) Larvae and Juveniles during Early Rearing and Weaning in a Commercial RAS—Implications for Dietary Refinement

The aquaculture production of pikeperch has reached commercial scale in a number of European countries, but the high mortality of early life cycle stages and minor understanding of nutritional requirements are still major bottlenecks. To investigate the fate of fatty acids during early development, weaning and rearing, pikeperch larvae and juveniles from a commercial recirculating aquaculture system (RAS) were sampled over 2 months for morphometric data, as well as fatty acid composition, with a total of 6 sampling days, with four to five replicates per sampling day and between 1 and 25 pikeperch larvae per individual sample, depending on larval biomass. The biomass of sampled pikeperch larvae varied from 0.1 to 420 mg (dry mass DM), depending on the age of the larvae, and the initial length of the pikeperch larvae was about 4.5 mm. Our data confirm that, accompanied by an exponential increase in dry mass, total fatty acids (TFAs) in larval tissues increased with the beginning of exogenous feed uptake and were depleted between days 13 and 25 post hatch, most likely associated with the weaning and metamorphosis of the larvae. We conclude that all fatty acid classes may serve as metabolic fuel during metamorphosis, but the ultimate fatty acid composition is strongly impacted by the available feed. The chosen diet probably caused a lack of alpha-linolenic (18:3n-3; ALA) and docosahexaenoic acid (22:6n-3; DHA) during larval development and a shortage of vaccenic (18:1n-7), alpha-linolenic (18:3n-3; ALA) and arachidonic acid (20:4n-6; ARA) in juvenile pikeperch. This led to low DHA/EPA ratios 13 days post hatch, a high EPA/ARA ratio at days 41 and 56 post hatch and a fluctuating ratio of alpha-linolenic acid to linoleic acid (18:2n-6; LA). A temporary lack of essential fatty acids can cause dysfunctions and eventually mortalities in pikeperch larvae and juveniles. Despite high larval growth rates, the biochemical composition of the first fed Artemia and microdiets was most likely not sufficient and in need of improvement. We suggest that deficiencies must be compensated, e.g., through the substitution of the offered Artemia with more suitable live feed organisms, such as freshwater rotifers, and the enrichment of current microdiets in order to prevent high mortalities during pikeperch rearing and weaning.

Occurrence of Some Freshwater Rotifers from Visapur Dam, Ahmednagar, Maharashtra, India

Rotifers from a reservoir (Vispaur Dam, Ahmednagar, Maharashtra) were studied for a period of seven months. Samples were collected using a 50-micron mesh size plankton net, preserved in 4% formalin and identified under a compound microscope using standard rotifer literature. Nineteen species belonging to 9 families were seen in the studied samples, with family Brachionidae being species rich with 9 species. The genus Brachionus was well represented with 5 species. The results are compared with studies done on rotifers from reservoirs all over Maharashtra state. Detailed studies in the future are required for more exact estimate of rotifer diversity. Detailed studies in future will add to the checklist of rotifers from the studied waterbody.

Suitability of Different Live Feed for First Feeding of Freshwater Fish Larvae

First feeding of many fish larvae depends on live feed. A comparative investigation on the effectiveness of different types of live feed is not available to our knowledge. Hence, we conducted a study to examine the effect of different types and combinations of live feed on the performance (survival rate, total length, body width, body mass, malformation rate) of pikeperch, Sander lucioperca, larvae. From day 0 (onset of exogenous feeding) to day 10, the saltwater rotifer Brachionus plicatilis, the freshwater rotifer Brachionus calyciflorus, the ciliate Paramecium bursaria, copepods (nauplii and copepodites) from a lake population, and Artemia nauplii were tested. Feeding with B. plicatilis, B. calyciflorus, and P. bursaria resulted in high survival rates of 80% and a homogenous and significant growth (increase in total length of 50% and in body width of 20%). As follow-up feed, copepod nauplii and Artemia nauplii were tested from day 11 to day 20. Copepod nauplii were superior to Artemia nauplii, as larvae fed with copepods showed higher survival rates (67–70% versus 38–47%) and a more homogeneous growth. A switch from seawater live feed to freshwater live feed or vice versa resulted in decreased survival rates. Therefore, a feeding regime consisting of B. calyciflorus or P. bursaria followed by copepods is considered optimal as first feed of pikeperch. The malformation rate was not affected by the tested feeding regimes. To investigate the wider applicability and transferability of these findings, complementary investigations were performed on burbot, Lota lota, and the freshwater whitefish Coregonus atterensis. The feeding regimes used for S. lucioperca larvae were also suitable for Lota lota. Moreover, L. lota could be fed with lake copepods from the onset of exogenous feeding. For C. atterensis, initial feeding with B. plicatilis, B. calyciflorus, or P. bursaria had no positive effects. Feeding with copepods from the onset of exogenous feeding was optimal considering survival rate and growth. Therefore, optimal first feeding regimes are very species specific and should be established for each new species.

Fine structure of the retrocerebral organ in the rotifer Trichocerca similis (Monogononta)

AbstractThe retrocerebral organ (RCO) is a complex glandular system that is widely distributed across species of phylum Rotifera (sensu stricto). This system is hypothesized to secrete mucus that aids in benthic locomotion, adhesion, and/or reproduction. Unfortunately, the ultrastructure of the RCO is mostly unknown, having only been partially examined in one species. We used transmission electron microscopy and confocal laser scanning microscopy to describe the RCO in the planktonic freshwater rotifer Trichocerca similis. Results reveal the RCO to be a singular syncytial organ composed of a posterior glandular region, an expansive reservoir, and an anterior duct. The glandular portion has an active synthetic cytoplasm with paired nuclei, abundant rER, ribosomes, Golgi, and mitochondria. Electron‐dense secretion granules accumulate at the anterior end of the gland and undergo homotypic fusion to create larger, more electron‐lucent granules with numerous mesh‐like contents that gradually fuse into tubular secretions that accumulate in the reservoir. Ultrastructure of these secretions suggests they may be hydrated glycoproteins. Cross‐striated longitudinal muscles form a partial sleeve around the reservoir and may function to squeeze the secretions through the single cytoplasmic duct that penetrates the cerebral ganglion. A review of the RCOs from other rotifers suggests that further ultrastructural analyses are required before attempting to discern their functions and homologies.

Recirculation Aquaculture System for Rotifer Brachionus calyciflorus Production: Construction and Operation

AbstractThe aim of the present study was to design and operate a recirculation aquaculture system (RAS) for the production of rotifers Brachionus calyciflorus, with recognition of preferred food type and effective harvest rate. In experiment 1, four food types (Chlorella vulgaris, Spirulina major, Scenedesmus obliquus, and baker's yeast) were used to determine the food type that was preferred by the rotifers. Chlorella vulgaris was the most preferred food type based on the highest rotifer count (365.33 ± 2.18 rotifers/mL). In experiment 2, rotifers were harvested at 10, 30, 50, and 70% of the total volume on a daily basis to determine the sustainable harvest rate. Daily harvesting at 30% maintained the rotifer culture at its stationary phase (381 ± 19.45 rotifers/mL) throughout the experiment. Following use in the RAS, the harvested water was treated using a series of filters (sand, cartridge, and ultraviolet filters) and was reused for algal culture. The results suggested that critical water quality characteristics, including pH (7.4–8.4), dissolved oxygen (3.8–6.8 mg/L), and un‐ionized ammonia (&lt;0.5 mg/L), remained within acceptable limits. We conclude that the freshwater rotifer B. calyciflorus can be produced on a commercial scale by adopting advanced RAS‐based technology with minimum water waste.

The Effect of Brachionus calyciflorus (Rotifera) on Larviculture and Fatty Acid Composition of Pikeperch (Sander lucioperca (L.)) Cultured under Pseudo-Green Water Conditions

A new cultivation system with the chlorophyte Monoraphidium contortum combined with a self-sustaining culture of the freshwater rotifer Brachionus calyciflorus was applied for Sander lucioperca (L.) larviculture. Survival, morphometrics, as well as fatty acid composition of pikeperch larvae were analyzed after a ten-day feeding period. By using the pseudo-green water technique with improved aeration and water movement at the surface, survival rates reached up to 94%, with a total larval length of 8.1 ± 0.3 mm and a specific length growth rate of up to 4.1% day−1 for S. lucioperca. The biochemical composition of B. calyciflorus and especially its contents in C18 PUFAs and suitable n-3/n-6 ratios met the nutritional requirements of pikeperch larvae. The high abundance of highly unsaturated fatty acids (HUFAs) in the diet appeared to be less important in the first feeding due to a possible retention of essential fatty acids, which originate from the yolk sac reserves, at adequate levels. Exponential growth of microalgae and zooplankton under the applied conditions was most effective when stocking M. contortum five days and B. calyciflorus three days before adding the fish larvae. Appropriate timing and sufficient live feed density allowed a successful integration of B. calyciflorus into pikeperch larviculture. We hypothesize that feeding pikeperch larvae with a self-sustaining Brachionus-culture under pseudo-green water conditions with minor disruptions during larviculture will improve survival and growth. This system is a first step towards pikeperch larviculture inside recirculated aquaculture systems (RAS) under continuous feed supply with live feed within the same aquaculture unit.

The genome of the freshwater monogonont rotifer Brachionus rubens: Identification of phase I, II, and III detoxification genes

Monogonont rotifers are common species in aquatic environments and make model species for ecotoxicology studies. Whole genomes of several species of the genus Brachionus have been assembled, but no information on the freshwater rotifer Brachionus rubens has been reported. In this study, the whole-genome sequence of B. rubens was successfully assembled using NextDenovo. The total length of the genome was 132.7 Mb (N50 = 2.51 Mb), including 122 contigs. The GC contents accounted for 29.96% of the genome. Aquatic organisms are always exposed to various external stresses, and a comprehensive genomic analysis is needed to better understand the adverse effects on organisms. This paper focuses on the ecotoxicological aspect and conducted genome analysis of representative gene families involved in detoxification mechanisms against environmental stressors. Specifically, we identified cytochrome P450 genes (CYPs) of phase I, glutathione S-transferase genes (GSTs) of phase II, and ATP-binding cassette transporter genes (ABCs) of phase III in the genome of B. rubens. Gene duplications were found in CYP, GST, and ABC genes, as is the case for other Brachionus rotifers. Our results suggest that these detoxification-related gene families have evolved in a species-specific and/or lineage-specific manner. This paper improves our understanding of how the freshwater Brachionus rotifers respond to environmental stressors in a molecular ecotoxicology context.

Individual and mixed effects of anticancer drugs on freshwater rotifers: A multigenerational approach

Human population growth has led to an increased release of chemical contaminants into aquatic environments. Emerging chemical contaminants (ECCs) are of increasing concern because they can affect non-target organisms in aquatic ecosystems. The application of anticancer drugs is increasing because of enhanced cancer rates and use of chemotherapy. We assessed the impacts of two widely used anticancer drugs known for their distinct modes of action, namely 5-fluorouracil (5-FU) and doxorubicin (DOX), on the freshwater rotifer Brachionus calyciflorus across generations. Rotifer mortality (24 h) and population growth (48 h) were assessed to determine initial lethal and sub-lethal effects. Exposure of rotifers to 5-FU (up to 200 mg L−1) did not cause mortality, while DOX caused mortality at high concentrations (EC50 = 15.6 mg L−1). Effects of 5-FU on population growth rate was higher than DOX (5-FU EC50 =10.49 µg L−1, DOX EC50 = 8.78 mg L−1). The effects of the drugs in binary mixture on population growth rates were dose dependent; significant antagonistic effects were found when 5-FU was present in the mixture at high concentrations. Finally, a transgenerational assay for five generations revealed that rotifers were able to recover their population growth rate after fourth generation when exposed to 5-FU; however, population became non-viable after the second generation of exposure to DOX. At the cellular level, accumulation of reactive oxygen species and plasma membrane damage were observed at EC10 and increased at EC50 for both drugs. After exposure of rotifers to 5-FU across generations, there were signs of oxidative stress recovery, as shown by a decrease in ROS accumulation and plasma membrane damage. Our results showed for the first time that the adverse effects of anticancer drugs on freshwater rotifer populations are drug and dose dependent and can persist or be attenuated along generations.

Lethal effects and ultrastructure of cellular uptake of ingested gold nanoparticles in the freshwater rotifer Brachionus calyciflorus (Monogononta: Brachionidae)

Much of the recent literature concerning the threat posed by anthropogenic microscopic pollution has focussed on marine organisms although freshwater environments face the same degree of pollution and therefore risk. Although several studies have documented the ingestion of nanoparticles (NPs) in species of the pelagic freshwater rotifer genus Brachionus, unambiguous evidence for its cellular uptake in this group remains lacking. We therefore used transmission electron microscopy (TEM) of ultrathin sections through the digestive tract of individuals of Brachionus calyciflorus exposed in vitro to citrate stabilized gold nanoparticles (AuCit NPs) in their culture medium to provide the first concrete evidence for the cellular uptake of NPs in rotifers, a group of organisms that comprise an important part of the zooplankton community. Using this method, AuCit NPs with average diameters of 8.5 ± 1.4 nm and 12.5 ± 1.5 nm could be localized clearly within large vacuoles within the stomach cells. Moreover, the occasional presence of pits containing AuCit NPs in the outer membranes of these cells hints that the particles are taken up by some form of endocytosis. In all cases, the ingestion of AuCit NPs showed lethal effects after only one day with virtually no individuals surviving more than two days of exposure. Combined with the TEM evidence above, we hypothesize that death might derive from some form of lysosomal overload. In total, our results document the potential threat that microscopic pollution also poses for freshwater organisms. Through this, we hope that additional emphasis in this context will be directed toward freshwater environments and the potential for such pollution both to enter as well as to move up the food chain via trophic transfer events.

Life-history responses of a freshwater rotifer to copper pollution.

In organisms with dormant stages, life‐history responses to past pollution can be studied retrospectively. Here, we study such responses in a rotifer (Brachionus calyciflorus) from the once heavily copper‐polluted Lake Orta (Italy). We extracted resting eggs from sediments, established clonal lineages from hatchlings, and exposed newborns of these lineages to one of three copper concentrations that each mimicked a specific period in the lake's pollution history. For each rotifer, we daily collected life‐table data. We then estimated treatment‐specific vital rates and used a stage‐structured population model to project population growth rate λ. We also estimated elasticities of λ to vital rates and contributions of vital rates to observed Δλ between copper treatments. As expected, λ decreased with increasing copper concentration. This decrease resulted mostly from a decline in juvenile survival rate (SJ ) and partly from a decline in the survival rate of asexually reproducing females (SA ). Maturation rate, and with one exception fecundity, also declined but did not contribute consistently to Δλ. λ was most elastic to SJ and SA , indicating that survival rates were under stronger selection than maturation rate and fecundity. Together, our results indicate that variation in juvenile survival is a key component in the rotifers’ copper response. The consistent decrease in SJ with increasing copper stress and the sensitivity of λ to that decrease also suggest that juvenile survival is a useful indicator of population performance under environmental pollution.

Complete mitochondrial genomes of two marine monogonont rotifer Brachionus manjavacas strains

The complete mitochondrial genomes of Brachionus manjavacas German strain were 10,721 bp (mitochondrial DNA I) and 12,274 bp (mitochondrial DNA II) in size, while the complete mitochondrial genomes of B. manjavacas Australian strain were 10,889 bp (mitochondrial DNA I) and 12,443 bp (mitochondrial DNA II) in size. Of 12 protein-coding genes (PCGs), 99.6% of amino acid sequences were identical between the two strains. Of 12 PCGs of both B. manjavacas strains, three genes (ND1, ATP6, and ND5) had incomplete stop codon T. Furthermore, ATA was the start codon for ND4, ND5, and CO3 genes, whereas that for other PCGs was ATG in both strains. The base compositions of 12 PCGs in the B. manjavacas strains were similar, indicating that the mitochondrial genome of the two strains was structurally conserved over evolution. The gene structure and its orientation of 12 PGCs of B. manjavacas strains were identical, as shown in other marine Brachionus rotifers and the freshwater Brachionus rotifers, while the freshwater rotifer B. calyciflorus had an additional cytochrome b gene in the mitochondrial DNA I.

The Species Diversity of Tropical Freshwater Rotifers (Rotifera: Monogononta) in Relation to Environmental Factors

This study aims to evaluate the diversity of rotifers in various freshwater habitats in Da Nang City, Vietnam, and to investigate the relationship between community structure and environmental conditions. A total of 75 rotifer species belonging to 25 genera and 17 families were recorded, out of which seven species are new to Vietnam. Species from the families Brachionidae and Lecanidae are abundant (containing about 50% and 69.44%, respectively) in the total rotifer species in both lacustrine and riverine habitats. The number of rotifers recorded in the lakes (64 taxa) was much higher than those in rivers (36 taxa), and this is possibly due to the conditions in lakes being more favorable for the development of small zooplanktons. The significant influences of environmental factors (temperature, pH, turbidity, and trophic state) on the rotifer community were well-reflected in the distribution of commonly found species in lakes (p-value &lt; 0.05). Our study results enrich the data on the diversity and the ecology of rotifers in Vietnam.

The genome of the freshwater monogonont rotifer Brachionus angularis: Identification of phase I, II, and III detoxification genes and their roles in molecular ecotoxicology

Brachionus spp. rotifers, which are widely distributed in aquatic environments, have been proposed as model organisms for ecotoxicological studies. Although the genomes of several rotifers belonging to the genus Brachionus have been assembled, the genome for the freshwater rotifer Brachionus angularis remains unknown. In this study, we analyzed the whole-genome sequence of B. angularis, which revealed a total length of 56.5 Mb and 21 contigs. The N50 and the GC content were 5.42 Mb and 23.66%, respectively. A total of 13,952 genes were predicted. Of them, we identified the main detoxification-related gene families, including those for cytochrome P450, glutathione S-transferase (GST), and the ATP-binding cassette transporter. In comparison with other Brachionus rotifers, massive species-specific expansion in GST sigma genes was found in B. angularis. This whole-genome analysis of B. angularis provides a basis for molecular ecotoxicological studies and provides useful biological tools for comparative studies of the evolution of detoxification mechanisms in Brachionus spp.