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Predator–prey interactions are crucial components of populations and communities. Their dynamics depend on the covariation of traits of the interacting organisms, and there is increasing evidence that intraspecific trade‐off relationships between defense and competitive traits are important drivers of trophic interactions. However, quantifying the relevant traits forming defense–competitiveness trade‐offs and how these traits determine prey and predator fitness remains a major challenge. Here, we conducted feeding and growth experiments to assess multiple traits related to defense and competitiveness in six different strains of the green alga Chlamydomonas reinhardtii exposed to predation by the rotifer Brachionus calyciflorus. We found large differences in defense and competitive traits among prey strains and negative relationships between these traits for multiple trait combinations. Because we compared trait differences among strains whose ancestors evolved previously in controlled environments where selection favored either defense or competitiveness, these negative correlations suggest the presence of a trade‐off between defense and competitiveness. These differences in traits and trade‐offs translated into differences in prey and predator fitness, demonstrating the importance of intraspecific trade‐offs in predicting the outcome of predator–prey interactions. [ABSTRACT FROM AUTHOR]

The rapid growth of aquaculture over the last century has led to the widespread introduction of aquatic species to freshwater environments. Bighead carp (Cyprinidae: Hypophthalmichthys nobilis) and silver carp (Cyprinidae: Hypophthalmichthys molitrix), collectively referred to as bigheaded carp, are among the top finfishes produced in aquaculture. These filter feeders possess feeding structures that allow them to efficiently remove plankton and other particles from the water. Unfortunately, when introduced into the wild and outside their historical range, their feeding traits generally result in the exploitation and suppression of phytoplankton and zooplankton, reducing food resources for native invertebrates and vertebrates.We conducted a meta‐analysis of published experiments to examine how bigheaded carp directly and indirectly affect organisms in aquatic food webs to better understand their ecological role within ecosystems. Specifically, we addressed the following questions: (1) What is the overall magnitude and direction of bigheaded carp effects on different aquatic organisms? (2) Do bigheaded carp affect organisms in planktonic and benthic habitats? (3) Are effects similar between bighead carp and silver carp? (4) Are effects consistent among experimental arenas (i.e., mesocosm, ponds)?We detected direct and indirect effects of bigheaded carp across multiple trophic levels. Large zooplankton often exhibited the strongest negative effects, with taxa‐specific differences between carp species. The suppression of zooplankton cascaded down to primary producers, resulting in an increase in phytoplankton (i.e., indirect effect). However, we observed no compensatory increases in rotifers when large zooplankton were reduced. Growth rates of planktivorous native fishes were the slowest when stocked with bigheaded carp. Our results further indicated that egested waste from bigheaded carp appeared to subsidise (i.e., direct effect) some benthic invertebrates such as Chironomidae midges. Effects of carp on zooplankton were generally similar between mesocosms and ponds.Invasive bigheaded carp greatly restructure their surrounding food web, both positively and negatively, through a complex suite of direct and indirect effects. These changes manifested across multiple trophic levels and differing habitats. Our analysis provides a more complete understanding of how these invasive carps change their surroundings by exploiting food resources and transferring materials from planktonic to benthic habitats. Taken together, the suite of direct and indirect effects shows how an invasive species can create imbalances within aquatic ecosystems, often to the detriment of native taxa.Bigheaded carp are invasive in many countries across the globe because of their popularity in aquaculture. Our findings reaffirm the threat these planktivores pose to native freshwater organisms. [ABSTRACT FROM AUTHOR]

Superior competitors are known to regulate community structure by influencing competitive outcomes between species of inferior competitors with overlapping ecological niches. However, more research is needed to obtain a detailed understanding of the ecological process.We examined how the superior competitor Daphnia magna influenced competition–exclusion between two coexisting Brachionus rotifer species.Brachionus angularis was no longer the superior competitor when D. magna was introduced into the cultured Brachionus calyciflorus + B. angularis system. Small‐sized D. magna (1.6–1.9 mm in body length) mediated population dynamics and facilitated the persistence of the two Brachionus species, while large‐sized D. magna (2.0–2.3 mm in body length) excluded only B. angularis at the high food level (3 × 106 cells/ml Chlorella) or both rotifer species at the low food level (1 × 106 cells/ml Chlorella).These findings indicate that the different body sizes of a superior competitor species can reverse competitive results between inferior competitor species in relation to food abundance.Our results highlight the dynamic nature of populations in multispecies communities and the need to understand species interactions in relation to their environment. [ABSTRACT FROM AUTHOR]

Coloniality may grant colony members an energetic advantage in the form of lower individual respiration rates as colony size increases. If this occurs it should be apparent as negative allometric scaling of respiration with colony size, and colonial organisms should have scaling factors < 1. However, colonial members from phylum Rotifera have yet to be examined. To test if colonial rotifers possess allometric scaling relationships between respiration rate and colony size, we measured respiration rates for four solitary and three colonial rotifer species; from these respiration rates we estimated scaling factors. We found mixed evidence for allometric scaling of respiration rate in colonial rotifers. Both rotifers with allometric scaling of respiration rate, Conochilus hippocrepis and Lacinularia flosculosa, have extensive mucilaginous coverings. These coverings may represent an investment of colony members into a shared structure, lowering individual metabolic costs and thus respiratory needs. Additionally, we determined which traits are associated with allometric scaling of respiration. We compiled known scaling factors for animal phyla from a wide phylogenetic spectrum with colonial representatives and conducted a hierarchical mixed regression that included attributes of colonies. Traits associated with allometric scaling in colonial animals included colony shape, the presence of shared extrazooidal structures, and planktonic lifestyle. There are many other colonial rotifers and animal taxa for which allometric scaling factors have yet to be estimated, knowing these may enhance our understanding of the benefits of coloniality in animals. [ABSTRACT FROM AUTHOR]

Rotifers are natural initial bait for fish larvae in freshwater. Here, the effects of various concentrations of acidified eggshell powder solutions (0, 20, 40, 80, 160, and 320 mg/L) on the growth and reproduction of the rotifer Brachionus calyciflorus were evaluated in culture experiments (11 days). The population density, catalase (CAT) and superoxide dismutase (SOD) activity, and Na and Mg contents in rotifers were significantly higher in the 20–160 mg/L groups than in the control group. A redundancy analysis showed that the Na, Mg, Cr, K, and Ca contents were positively correlated with the rotifer population density and CAT and SOD activity. Furthermore, the generation time and lifespan of F2 rotifers were significantly higher in the 20–40 mg/L treatment groups (82.0 ± 3.7 hr and 162.0 ± 2.7 hr, respectively) than in the control group (64.0 ± 4.0 hr and 128.0 ± 4.0 hr, respectively). Average egg production in F2 rotifers was significantly higher in the 20–80 mg/L treatment groups (15.2 ± 0.7 individuals) than in the control group (11.7 ± 1.2 individuals). These results indicate that 20 mg/L eggshell powder is optimal for growth and reproduction in B. calyciflorus, providing a theoretical basis for using new mineral sources in high-quality open bait for fish larvae. [ABSTRACT FROM AUTHOR]

Global warming has raised concerns regarding the potential impact on aquatic biosafety and health. To illuminate the adaptive mechanisms of bdelloid rotifers in response to global warming, the ecological and transcriptomic characteristics of two strains (HX and ZJ) of Rotaria rotatoria were investigated at 25°C and 35°C. Our results showed an obvious genetic divergence between the two geographic populations. Thermal stress significantly reduced the average lifespan of R. rotatoria in both strains, but increased the offspring production in the ZJ strain. Furthermore, the expression levels of genes Hsp70 were significantly upregulated in the HX strain, while GSTo1 and Cu/Zn‐SOD were on the contrary. In the ZJ strain, the expression levels of genes Hsp70, CAT2, and GSTo1 were upregulated under thermal stress. Conversely, a significant decrease in the expression level of the Mn‐SOD gene was observed in the ZJ strain under thermal stress. Transcriptomic profiling analysis revealed a total of 105 and 5288 differentially expressed genes (DEGs) in the HX and ZJ strains under thermal stress, respectively. The PCA results showed clear differences in gene expression pattern between HX and ZJ strains under thermal stress. Interestingly, compared to the HX strain, numerous downregulated DEGs in the ZJ strain were enriched into pathways related to metabolism under thermal stress, suggesting that rotifers from the ZJ strain prioritize resource allocation to reproduction by suppressing costly metabolic processes. This finding is consistent with the life table results. This study provides new insights into the adaptive evolution of aquatic animals in the context of global climate change. [ABSTRACT FROM AUTHOR]

Ecological risk assessment (ERA) of metals typically starts from standardized toxicity tests, the data from which are then extrapolated to derive safe concentrations for the envisioned protection goals. Because such extrapolation in conventional ERA lacks ecological realism, ecological modeling is considered as a promising new approach for extrapolation. Many published population models are complex, that is, they include many processes and parameters, and thus require an extensive dataset to calibrate. In the present study, we investigated how individual‐based models based on a reduced version of the Dynamic Energy Budget theory (DEBkiss IBM) could be applied for metal effects on the rotifer Brachionus calyciflorus. Data on survival over time and reproduction at different temperatures and food conditions were used to calibrate and evaluate the model for copper effects. While population growth and decline were well predicted, the underprediction of population density and the mismatch in the onset of copper effects were attributed to the simplicity of the approach. The DEBkiss IBM was applied to toxicity datasets for copper, nickel, and zinc. Predicted effect concentrations for these metals based on the maximum population growth rate were between 0.7 and 3 times higher in all but one case (10 times higher) than effect concentrations based on the toxicity data. The size of the difference depended on certain characteristics of the toxicity data: both the steepness of the concentration–effect curve and the relative sensitivity of lethal and sublethal effects played a role. Overall, the present study is an example of how a population model with reduced complexity can be useful for metal ERA. Environ Toxicol Chem 2024;43:324–337. © 2023 SETAC [ABSTRACT FROM AUTHOR]

Objective: This study aimed to minimize live prey usage and duration in Burbot Lota lota larval culture. Specifically, two trials were conducted to assess the viability of EZ Artemia (liquid Artemia replacement) and Gemma microparticulate diets as alternatives to traditional live feeds, investigating their impact on larval Burbot's growth and survival. Methods: In trial 1, five treatments were evaluated: the control group received rotifers (Brachionus plicatilis) and Artemia spp. from 11 to 50 days posthatch (dph). Treatment (Trt) 1 had live feeds from 11 to 78 dph; Trt 2 received only microparticulate diets; Trt 3 was fed rotifers at 11–22 dph and Gemma microparticulate diets at 21–50 dph; and Trt 4 received rotifers at 11–20 dph, then co‐feeding of Artemia spp. and EZ Artemia at 21–32 dph, followed by EZ Artemia at 33–40 dph. In trial 2, five feeding treatments were assessed: the control group was the same as in trial 1; Trt 1 received rotifers at 11–25 dph and EZ Artemia at 20–50 dph; Trt 2 had Artemia spp. from 11 to 30 dph and EZ Artemia at 25–50 dph; Trt 3 received only EZ Artemia; Trt 4 had Artemia spp. at 11–21 dph, followed by co‐feeding of Artemia spp. and Gemma Wean at 22–32 dph and exclusive feeding of Gemma Wean from 33 to 78 dph. Result: In trial 1, it was found that the utilization of EZ Artemia reduced the live feeding period by 17 days; however, both survival and growth were notably lower compared to the control. In trial 2, survival rates varied from 0% to 30.94%, with Trt 1, Trt 2, and Trt 4 demonstrating a reduction in the live feeding period by 17–24 days. Survival rates for the Trt 1 and Trt 2 groups did not exhibit a significant difference from the control group. Conclusion: These studies collectively show that eliminating rotifers or Artemia spp. during Burbot larval culture can be accomplished with minimal adverse effects on both survival and growth. Impact statementThe production of traditional live feeds (rotifers and Artemia spp.) entails significant expenses and labor. Early weaning of Burbot larvae onto non‐live foods can reduce infrastructure costs, offering flexibility in feeding practices. This study showcases the effectiveness of prepared feeds including (EZ Artemia and Gemma microparticulate diets) in diminishing reliance on live feeds, presenting them as viable alternatives to rotifers or Artemia spp. in Burbot larval production. This approach enhances the economic viability of commercial hatchery operations for producers interested in culturing this new emerging freshwater species. [ABSTRACT FROM AUTHOR]

The rotifer Epiphanes brachionus spinosa occurs in shallow temporary waters with hydroperiods up to several months in the Chihuahuan Desert (U.S.A. and Mexico). Clonal populations from one such habitat were initiated from stem females hatched from fertilised resting eggs in flooded dried sediment, and cultured with the alga Cryptomonas erosa at 19°C in a photoperiod (L:D 16:8). Experiments show that the rotifer has: (1) a morphological response to the predatory rotifer Asplanchna, with which it can co‐occur; and (2) an early and constant propensity for sex and resting‐egg production during population development.Stem females, and females from later generations, have two posterior spines. Measurements of live juveniles and adults indicate that spine length increases isometrically during postnatal growth.Presence of live Asplanchna brightwellii, or its kairomone in Asplanchna‐conditioned medium, significantly increase spine length. In one clone, spine lengths of juvenile Epiphanes from cultures with or without live Asplanchna were, respectively, c. 40 and c. 27 μm. In that clone, spine lengths of adult Epiphanes in cultures with or without Asplanchna kairomone were, respectively, c. 54 and c. 37 μm. In another clone, these spine lengths were, respectively, c. 44 and c. 36 μm. Asplanchna‐induced spine elongation may act as a mechanical defence against capture and ingestion by the predator.Sexual reproduction in E. brachionus spinosa populations is initiated soon after populations develop from stem females and then continues at a rate allowing both population growth by female parthenogenesis and production of resting eggs. Resting eggs hatched after 6–12 days at 19°C. Stem females were amictic (producing daughters parthenogenetically) but produced some daughters that were mictic (producing haploid males parthenogenetically or fertilised resting eggs). In subsequent generations tested 2–7 weeks after hatching of stem females, amictic females from three clonal populations produced similar proportions of mictic daughters (mean c. 0.25) when cultured singly in large volumes (15 and 40 ml) or a small one (1.5 ml).Mictic‐female production is probably automatic and controlled by an endogenous mechanism, rather than specifically induced by crowding or some other environmental factor. Early and continuous sexual reproduction assures production of resting eggs throughout short and unpredictable hydroperiods. [ABSTRACT FROM AUTHOR]

We evaluated the effect of probiotics on the growth and culture condition of rotifer in medium‐sized culture tanks. The influence of probiotics on the changes in swimming patterns, velocity and sinuosity indices of rotifer was also examined. The rotifers (Brachionus rotundiformis) were cultured for 14 days in nine polycarbonate tanks containing seawater which were divided into three groups: a control group (Chlorella product) and two treatment groups: Chlorella + Probiotic I and Chlorella + Probiotic II. The rotifer population and the water quality parameters were monitored daily. To evaluate the locomotory behaviour of the rotifer, a sub‐sample containing rotifers was obtained from each treatment and placed on a glass‐bottomed dish. A high‐speed camera mounted on a stereo microscope was used to record the rotifer movement. The footage was then analysed using motion analysis software to establish the swimming velocity, swimming pattern and sinuosity indices of the rotifers. Co‐feeding rotifer on microalgae and probiotics resulted in a higher rotifer growth rate (0.51 ± 0.03) and decreased concentration of unionized ammonia (0.14 ± 0.02 mg L−1). In addition, the probiotic‐fed rotifers had 1.59 times higher average swimming velocity (0.97 ± 0.11 mm s−1) and more straight swimming pattern compared to rotifers that fed on microalgae alone whose velocity was slow (0.61 ± 0.14 mm s−1) and more sinuous. From these data, we can postulate that probiotics have the potential to attenuate rotifer culture conditions by decreasing ammonia concentration as well as influence rotifer swimming behaviour which could affect rotifer reproduction and the quality of fish larvae in aquaculture systems. [ABSTRACT FROM AUTHOR]

Sedimentary ancient DNA (sedaDNA) has proven to be a useful tool for palaeoenvironmental studies, but only a handful of studies exist so far for tropical regions. In this study we used sedaDNA to study the temporal succession of Brachionus spp. rotifer mitochondrial DNA haplotypes using two sediment cores from two climatically different alkaline‐saline crater lakes from the Kenyan Rift Valley.Data were retrieved from a sediment core (dating back to AD 1800) from Lake Kageinya, located in the remote, hot and hyper‐arid Suguta Valley. sedaDNA was used to study the temporal succession of mitochondrial DNA haplotypes of Brachionus spp. rotifers. The results were compared to previously published data from Lake Sonachi, a well‐studied lake in the humid and colder mountainous region of Kenya near the town of Naivasha, now supported by a 210Pb age chronology.Both records extend back before the onset of substantial anthropogenic impact in these regions. The results revealed that climate—rather than anthropogenic impact—was most strongly correlated with haplotype changes in both lakes. During prolonged dry periods (such as from AD 1910 to the late AD 1960s), certain haplotypes persisted. Sudden changes and the emergence of alter native haplotypes were observed when climate became more humid or during episodes of highly variable climate (before AD 1910 and from AD 1960s onwards).Progressive changes in prevailing haplotypes during periods with variable climate could reflect local adaptation and/or be the result of immigration of new haplotypes after the eradication of previous populations during extreme environmental conditions (high temperatures, UV irradiation, pH and salinity).The results indicate that, despite adverse chemical conditions, sedaDNA in tropical lake sediments is preserved for at least a few hundred years. Therefore, its analysis provides a useful complementary palaeoenvironmental proxy for palaeolimnological reconstructions and novel insights on changes in rotifer populations through time. [ABSTRACT FROM AUTHOR]

The red snapper (Lutjanus campechanus) has one of the most valued fisheries in the southeastern United States and has been largely studied for its aquaculture potential with varied results that revealed production challenges. This study focused on addressing challenges in larval rearing and juvenile production of this species. Broodstock fish were acclimated in a 60 m3 tank equipped with recirculating aquaculture system (RAS) and temperature control. After 1 year in captivity, fish volitionally spawned and larval rearing trials were conducted in replicated flow‐through seawater tanks ranging from 0.4 to 2.4 m3, at a temperature range of 24–26°C. Enriched s‐strain rotifers, Brachionus rotundiformis (lorica length of 100–210 μm), were used for first feeding. Enriched Artemia sp. were gradually introduced after 18 days post hatch (DPH). The survival rate before metamorphosis (12 DPH) averaged 66.09 ± 0.08%. Survival rate from yolk‐sac larvae to post‐metamorphic early juvenile averaged 4.43 ± 0.01%. At 40 DPH, early red snapper juveniles averaged 0.35 ± 0.02 g in weight and 28.83 ± 0.60 mm in standard length. A total of 31,849 fully weaned juveniles were harvested. This study demonstrates that small strain rotifers can be used exclusively as first feeding prey organism for red snapper larvae, representing a significant advancement for red snapper juvenile production. [ABSTRACT FROM AUTHOR]

The effect of live feed diets containing Brachionus plicatilis (B) and Apocyclops panamensis (A) was investigated on pikeperch larval survival, growth, and fatty acid composition in two experiments (E1 and E2). Up to six different diets were provided to the larvae, in which the letters of the diet names represent the live feed organisms as mentioned above and the subsequent number of feed organisms per larva and day. In E1, start cultures with 35 larvae/L were supplied with two diets (B200 and B100 + A100) 7 days until 10 days post hatch (dph). In E2, 50 larvae/L were fed six diets, B280 + A120, B340 + A60, B400, B420 + A180, B510 + A90, and B600. The highest survival and specific growth rates (SGR) occurred in B200 (E1). In E2, B340 + A60 performed best. A trend of increasing survival rates was found in E1 from 68.9% (B100 + A100) to 71.6% B200 and in E2 from 64.0% (B280 + A120) to 93.7% (B340 + A60). Larval SGR tended to increase with higher shares of dietary B. plicatilis in both experiments. The polyunsaturated fatty acid, linoleic acid (LA), followed the same pattern as survival and SGR increasing until a plateau was reached, indirectly indicating a feeding threshold. B. plicatilis provided the LA to pikeperch larvae, which seemed to play an important role in this feeding period. Consequently, a live feed diet should contain at least 340 B. plicatilis ind. larva−1 day−1 and 6.3 B. plicatilis per milliliter until 10 dph to improve pikeperch larviculture. [ABSTRACT FROM AUTHOR]

Many aquatic invertebrates that inhabit temporary ponds produce resting forms to overcome the dry period, building up the egg bank. When the wet phase returns, the resting forms hatch and the community is restored, and then pioneer species may have a major influence on how the pond community will assemble. We aimed to evaluate the diversity of an initial pond metacommunity by comparing the early active metacommunity collected in the field and the egg bank metacommunity (by carrying out a hatching experiment) of 32 Mediterranean temporary ponds. We hypothesised that both metacommunities would be similar but also that species turnover may play an important role, and that γ diversity would be similar with both approaches.After the identification and counting of rotifers and crustaceans in both metacommunities (i.e. the field vs. the experiment) we performed a Partial Triadic Analysis comparing the field metacommunity with those corresponding to each of the eight times the hatching experiment was checked for hatchlings. Furthermore, we compared the field and experimental metacommunities with a PROTEST analysis and identified the taxa responsible for differences between metacommunities with a SIMPER analysis. We assessed γ diversity using a size‐based rarefaction curve and an evenness profile and explored β diversity and its components (turnover and nestedness) for the two metacommunities.Our experimental results showed differences in the temporal pattern of emergence between groups of organisms, with copepods, rotifers, and anostracans appearing first, but ostracods and rotifers reaching the highest diversity at the end of the experiment. The active and experimental pioneer metacommunities were similar according to a Procrustes analysis. Nevertheless, β diversity was high in both metacommunities and the differences among ponds and between both assemblages were mostly explained by species turnover.Both the active and experimental pond metacommunities showed some exclusive species that may be more difficult to uncover with only one type of approach. Furthermore, the high β diversity observed indicates that each temporary pond is an important contributor to γ diversity in the metacommunity.These results show that hatching experiments provide information that is complementary to standard sampling of the active community, and consequently is a useful tool to uncover pond biodiversity. [ABSTRACT FROM AUTHOR]

Human‐induced salinization increasingly threatens inland waters; yet we know little about the multifaceted response of lake communities to salt contamination. By conducting a coordinated mesocosm experiment of lake salinization across 16 sites in North America and Europe, we quantified the response of zooplankton abundance and (taxonomic and functional) community structure to a broad gradient of environmentally relevant chloride concentrations, ranging from 4 to ca. 1400 mg Cl− L−1. We found that crustaceans were distinctly more sensitive to elevated chloride than rotifers; yet, rotifers did not show compensatory abundance increases in response to crustacean declines. For crustaceans, our among‐site comparisons indicate: (1) highly consistent decreases in abundance and taxon richness with salinity; (2) widespread chloride sensitivity across major taxonomic groups (Cladocera, Cyclopoida, and Calanoida); and (3) weaker loss of functional than taxonomic diversity. Overall, our study demonstrates that aggregate properties of zooplankton communities can be adversely affected at chloride concentrations relevant to anthropogenic salinization in lakes. [ABSTRACT FROM AUTHOR]

The growth rate hypothesis (GRH) posits that the relative body phosphorus content of an organism is positively related to somatic growth rate, as protein synthesis, which is necessary for growth, requires P‐rich rRNA. This hypothesis has strong support at the interspecific level. Here, we explore the use of the GRH to predict microevolutionary responses in consumer body stoichiometry. For this, we subjected populations of the rotifer Brachionus calyciflorus to selection for fast population growth rate (PGR) in P‐rich (HPF) and P‐poor (LPF) food environments. With common garden transplant experiments, we demonstrate that in HP populations evolution toward increased PGR was concomitant with an increase in relative phosphorus content. In contrast, LP populations evolved higher PGR without an increase in relative phosphorus content. We conclude that the GRH has the potential to predict microevolutionary change, but that its application is contingent on the environmental context. Our results highlight the potential of cryptic evolution in determining the performance response of populations to elemental limitation of their food resources. [ABSTRACT FROM AUTHOR]

The temperate soft coral Dendronephthya australis has been listed as Endangered in NSW, Australia, owing to its restricted geographic range, rapidly declining populations, and a number of escalating threats. Research to assess practical methods for aquarium cultivation of D. australis for rehabilitation of wild populations is considered a high priority.Previous attempts at restoration by transplanting D. australis fragments have had limited success, but identified key challenges, which included achieving attachment to substrates and identifying appropriate foods to maximize survival.This study presents the results of experiments promoting the attachment of cuttings (nubbins) removed from donor colonies to moveable substrates (small concrete discs). Using a balanced orthogonal experimental design, three feeding regimes were tested: live artemia, live rotifers and dry powdered zooplankton.Donor colony survival and growth were also monitored over a 6 month period in the field.An overall nubbin survival rate of 100% was achieved under all three feeding regimes. Attachment rates were similar across feeding treatments, although nubbin behavioural responses (percentage of open polyps before feeding) suggested some preference for live rotifers.The cutting removal process had no significant effect on donor colonies in the wild, indicating that this is a sustainable approach for restoration.Overall, this study substantially advances the methodology for maintaining an Endangered azooxanthellate soft coral in aquaria and provides valuable input for management programmes aimed at implementing transplantation into the wild to aid species recovery. [ABSTRACT FROM AUTHOR]

To establish the optimal ratios of chicken manure extract (CME) and suspending yeast solution (SYS) for rearing rotifers, the population density, population growth rate, fatty acid compositions of rotifers and the unionized ammonia (NH3‐N) and total phosphorus (TP) concentrations in cultured water under different ratios of CME and SYS (BG, EG1, EG2, EG3, EG4 and EG5) were investigated. The results showed that the population density and population growth rate of rotifers in EG2 (4 ml·L−1 CME: 0.3 ml·L−1 SYS) were the highest and reached 387.33 ± 12.34 and 0.57 ± 0.01 ind.·ml−1, respectively. In addition, Pearson's correlation analysis indicated that the proportions of polyunsaturated fatty acids (PUFAs), n‐3PUFAs, n‐6PUFAs and long‐chain PUFAs in rotifers were positively correlated with the content of CME (p < 0.05). Furthermore, NH3‐N and TP in the cultured water decreased with the SYS contents increasing. Compared with EG5, the concentrations of NH3‐N and TP in EG2 were reduced by 58.83 ± 0.05% and 72.52 ± 0.17%, respectively. These results indicated that both the population growth and fatty acid composition of rotifers, and the concentrations of NH3‐N and TP in the cultured water were significantly affected by the ratios of CME and SYS. And EG2 was optimal for rearing the rotifer. [ABSTRACT FROM AUTHOR]

Improving the lipid composition of feed‐rotifers enhances the survival and growth rates of juvenile fish in aquaculture, but monitoring enrichment profiles using gas chromatography (GC) is slow, labour‐intensive and requires expensive instrumentation. Here, we describe the potential of Raman spectroscopy as an alternative, more rapid tool for quantitation of rotifer fatty acid composition in an aquaculture setting. A compositionally diverse sample set was prepared by periodically subsampling rotifers undergoing enrichment using three different feeding regimens. Sampled rotifers were freeze‐dried and their fatty acid content and composition was measured by GC–MS (mass spectrometry). Raman spectra (1064 nm excitation) were acquired with two instruments: a state‐of‐the‐art Fourier transform (FT)‐Raman spectrometer equipped with a liquid nitrogen‐cooled Germanium detector; and a smaller, portable spectrometer equipped with an InGaAs detector. Fatty acid reference data acquired by GC–MS were related to structured variance in each Raman spectral data set using partial least squares regression. The resultant models could accurately quantitate total fatty acids (TFA) and total polyunsaturated fatty acids (PUFA) using both FT‐Raman spectra (Root Mean Square Error [RMSEV] = 5.0 mg g−1 TFA and 6.1 mg g−1 PUFA) and spectra generated using the portable instrument (RMSEV = 4.2 mg g−1 TFA and 5.3 mg g−1 PUFA). Analysis times with the portable instrument were approximately 3 min, compared to 16 min with the FT‐Raman system. Portable Raman spectroscopy may be a useful tool for high throughput screening of rotifer lipid composition when testing and optimizing enrichment protocols and developing microdiets for aquaculture species. [ABSTRACT FROM AUTHOR]

The effects of feeding rotifers and Artemia enriched with different types of enrichment in the first feeding and later stages of Scylla tranquebarica larvae were investigated. Two different experiments were conducted each with five enrichment treatments including live and digestible Nannochloropsis sp. and Tetraselmis sp. or commercial product. In Experiment I, the zoea 1 (Z1) larvae were fed with enriched or unenriched rotifers as their first feed until they moulted into the zoea 2 (Z2) stage, while in Experiment II, the zoea 3 (Z3) larvae were fed with enriched or unenriched Artemia until they metamorphosed into megalopa stage. In Experiment I, Z1 fed enriched rotifers showed higher survival, larval stage index (LSI) and carapace length than those in unenriched treatment. However, the highest survival was recorded in larvae fed Nannochloropsis sp. treatment. In Experiment II, Z3 fed Artemia enriched with digestible Tetraselmis sp. exhibited the highest survival and LSI, lowest chela‐carapace length ratio and abnormal moulting frequencies. In comparison to live microalgae, digestible treatment resulted in a smaller chela‐carapace length ratio with lower abnormal moulting. In conclusion, enrichments tested in this study can be used to enrich rotifers for the first feeding of Z1, while later stage (Z3 onwards) fed Artemia enriched with digestible Tetraselmis sp. improved survival and decreased the abnormal moulting frequencies of Z5 to megalopa stage. [ABSTRACT FROM AUTHOR]

This study developed an automated filtration system for a selected rotifer, Brachionus ibericus. This system is controlled by a programmable logic controller, and it enables the high‐density cultivation of marine rotifers and the selection of rotifers for palatability. We tested seven mesh sizes (300, 200, 100, 50, 20, 5, and 1 μm) for commercial 10‐inch (25.4‐cm) stainless steel tubular filters in the proposed system, after which we selected the optimal mesh size for filtering impurities, separating rotifers, eliminating wastewater, and minimizing the rotifer loss rate. The results indicated that a combination of the 5‐ and 200‐μm meshes produced optimal filtration efficiency. After every 120 s of filtration followed by a 30‐s flushing process, a rotifer density of 3170 ± 101 individuals/ml, a mesh blocking loss rate of 4.95 ± 3.62%, and impurity‐free rotifer volume of 45.18 ± 1.2 L were obtained. Our study verified that tubular filters can be used in commercial aquaculture. [ABSTRACT FROM AUTHOR]

The 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 (<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. [ABSTRACT FROM AUTHOR]

Primary producer communities are often growth‐limited by essential nutrients such as nitrogen (N) and phosphorus (P). The magnitude of limitation and whether N, P or both elements are limiting autotroph growth depends on the supply and ratios of these essential nutrients. Previous studies identified single, serial or co‐limitation as predominant limitation outcomes in autotroph communities by factorial nutrient additions. Little is known about potential consequences of such scenarios for herbivores and whether their growth is primarily affected by changes in autotroph quantity or nutritional quality. We grew a community of phytoplankton species differing in various food quality aspects in experimental microcosms at varying N and P concentrations resulting in three different N:P ratios. At carrying capacity, N, P, both nutrients or none were added to reveal which nutrients were limiting. The nutrient‐supplied communities were fed to the generalist herbivorous rotifer Brachionus calyciflorus to investigate how changing phytoplankton biomass and community composition affect herbivore abundance. We found phytoplankton being growth‐limited either by N alone (single limitation) or serially, i.e. primarily by N and secondarily by P, altering available food quantity for rotifers. Rotifer growth showed a different response pattern compared to phytoplankton, suggesting that apart from food quantity food quality aspects played a substantial role in the transfer from primary to secondary production. The combined addition of N and P to phytoplankton had generally a positive effect on herbivore growth, whereas adding non‐limiting nutrients had a rather detrimental effect probably due to stoichiometrically imbalanced food in terms of nutrient excess. Our experiment shows that adding various nutrients to primary producer communities will not always lead to increased autotroph and herbivore growth, and that differences between autotroph and herbivore responses under co‐limiting conditions can be partly well explained by concepts of ecological stoichiometry theory. [ABSTRACT FROM AUTHOR]

In this work, we examined the effects of rapid changes in salinity on the availability (mobility and swimming) of the prey rotifer Proales similis. Rotifers were transferred as follows: 5 to 15, 25 and 35 (T1); 15 to 5, 25 and 35 (T2); 25 to 5, 15 and 35 (T3) and 35 to 5, 15 and 25 ppt (T4) during 1–240 min. Results showed that in T2 and T3, the percentage of mobile rotifers in the water column recovered up to 100% after 15 min. At T1 and T4, mobility regained slower at 35 and 5 ppt respectively. All individuals transferred at 15 and 25 ppt maintained their mobility above 93% after 15 min. In general, swimming speed ranged from 0.37 to 0.65 mm s−1 and was higher at 15 ppt and lower at 35 ppt. In all salinities, swimming increased with time and recovered better in T2 and T3. These data suggest that P. similis can acclimate to a wide range of salinity gradients in the short term (1–240 min). According to the literature and our results, P. similis has a greater tolerance to sudden salinity changes than brachionid rotifers used traditionally in fish larviculture. [ABSTRACT FROM AUTHOR]

Experiments were conducted on Guinean Fingerfish Monodactylus sebae to evaluate egg and larval stocking densities, stocking methods, water quality effects on egg hatching success, and the effects of different live food organisms on larval growth and survival. Egg hatching percentage was determined for four egg stocking densities (10, 20, 30, and 40 eggs/L). The lowest stocking density, 10 eggs/L, had a significantly higher mean hatching percentage (65.0 ± 18.54%) than the 30‐ and 40‐eggs/L treatments but did not vary significantly from the 20‐eggs/L treatment. Eggs were incubated in salinities of 0, 5, 10, 15, 20, 30, 40, 45, and 50 g/L to evaluate the effect on hatching success. The hatching success was over 70% for salinities of 0–30 g/L. The highest hatching success (98%) occurred in the 5‐g/L treatment, and the 40‐ and 50‐g/L treatments had significantly lower hatching success than all other treatments. Three live food organisms were fed to larvae to determine effects on growth and survival over a 9‐d period. Diets were enriched rotifers Brachionus plicatilis, nauplii of the copepod Parvocalanus crassirostris, and nauplii of the copepod Pseudodiaptomus pelagicus fed at equal densities of 10 organisms/mL once daily. Larvae were stocked at 20 fish/L. At 9 d posthatch (dph), survival was not significantly different among treatments and larvae fed P. pelagicus had a significantly longer SL (mean ± SD = 4.28 ± 0.42 mm). Larvae were netted and exposed to air as a stressor at 6, 14, 22, 30, 38, and 46 dph for durations of 30, 60, 120, and 240 s. The 30‐dph treatment had the lowest survival among all treatments regardless of experimental duration, followed by the 38‐dph treatment. Results suggest that to avoid high handling mortality, Guinean Fingerfish should not be handled during metamorphosis (30–38 dph). [ABSTRACT FROM AUTHOR]

To develop an effective technique for decreasing rotifer contamination in Spirulina platensis cultivation, the effects of 5-fluoro-2'-deoxyuridine (FUdR; 0, 60, 110, 160, 210, and 260 µg/L) on the development, reproduction and population growth of the rotifer, Brachionus plicatilis and on the growth, photosynthetic properties and nutritional composition of S. platensis were investigated. The results showed that the negative effects of FUdR on the pre-reproductive period, the number of total eggs per female and the egg hatching rate of rotifers were dose-dependent. The egg hatching of rotifers was fully inhibited by exposure to 260 µg/L FUdR. The effects of FUdR on the biomass, maximum quantum yield (Fv/Fm), effective quantum yield (fPSII), amino acid content and fatty acid composition of S. platensis were not significant. Therefore, these results suggest that FUdR has excellent potential for controlling grazing zooplankton contamination in microalgal cultivation. [ABSTRACT FROM AUTHOR]

Decorator crab Camposcia retusa is a popular marine ornamental species; however, it has never been bred previously. To establish a feeding regime for C. retusa larvae, which include two zoeal and a megalopal stage, three experiments were conducted. In all experiments, ≥60% of unfed 1st zoeal (Z1) larvae survived to the next stage, combined with the orange guts observed in larvae fed Artemia, suggesting Z1 larvae are facultative lecithotrophic. Experiment 1 evaluated the suitability of ss‐type rotifer Brachionus rotundiformis as prey. Z1 larvae were fed rotifer at a density from 0 to 90 ind./ml. There was no significant difference in Z1 survival among treatments (56.7–68.3%, p > 0.05); therefore, ss‐type rotifer is considered an unsuitable prey for the larvae. Experiment 2 examined the suitability and optimal density of Artemia nauplii, and co‐feeding copepod Pavocalanus crassirostris with Artemia, for larval rearing. The larvae fed 10 Artemia/ml had the highest survival to megalopae (91.3 ± 3.1%, p < 0.05). However, high mortality occurred in megalopae, resulting in poor survival to the 1st crab stage (1.3%–12.5%) in all treatments (p > 0.05). Meanwhile, co‐feeding copepods with Artemia showed significantly inferior survival and development to megalopae when compared to that of 10 Artemia/ml treatment. Experiment 3 evaluated the effects of Artemia enrichment on larval performance. The results suggested that Artemia enrichment did not improve larval survival or development. Based on our results, Artemia nauplii fed at 10 ind./ml throughout larval development appears to be appropriate for C. retusa. [ABSTRACT FROM AUTHOR]

Challenges associated with first feeding have impeded the intensive culture of larval Yellow Perch Perca flavescens. Live‐food enrichment with polyunsaturated fatty acids (PUFAs) can increase the growth and survival of larval fish, but this method has not been tested with Yellow Perch. This study includes two experiments that were meant to evaluate (1) the relative proportion of docosahexaenoic acid (DHA; 22:6[n‐3]) and arachidonic acid (ARA; 20:4[n‐6]) in enrichment emulsions and (2) the provision of PUFA emulsions in ethyl ester (EE) or triacylglycerol (TG) form on Yellow Perch growth and survival. Fish were provided with live rotifers Brachionus plicatilis and brine shrimp Artemia nauplii for the first 10 d of exogenous feeding within a specialized recirculating system (phase I). Fish were then transferred to flow‐through tanks and were fed Artemia nauplii for 3 d before gradually transitioning to a formulated starter diet (5–7 d; phase II). Fish size, growth, survival, swim bladder inflation rates, and lipid/fatty acid concentrations were evaluated after each phase. Overall, rotifers assimilated ARA in higher concentrations (23.3% of total fatty acids) than Artemia (0.6–0.7% of total fatty acids). Rotifers also tended to assimilate PUFAs better in EE form than in TG form (71.3% versus 66.5% Σn‐3 + n‐6 fatty acids). In the first experiment, fish from the ARA‐ and DHA‐enriched diet groups had greater swim bladder inflation rates (phase I) and growth rates (phase II) than the unenriched control group. In phase I of the second experiment, the EE enrichment group had a significantly faster growth rate than the TG enrichment group (specific growth rate: mean ± SD = 40.5 ± 0.9% and 36.6 ± 1.8%, respectively). Fatty acid composition of zooplankton was heavily influenced by enrichments, and fatty acid composition of larvae/juveniles reflected that of their live prey. The results of this study suggest that PUFA enrichment of live feeds can accelerate Yellow Perch growth and reduce the time spent in the critical period of early development. [ABSTRACT FROM AUTHOR]

One of the major research goals in ecology is to understand predator–prey interactions. However, our understanding of how prey express phenotypic plasticity in response to co‐occurring multiple predators is limited in many systems.Here, we use the rotifer Brachionus calyciflorus as model organism to test how prey responds to co‐occurring predators through a series of related experiments. Firstly, we examined the effects of the density of a fish predator Carassius auratus on morphological traits in B. calyciflorus. Secondly, we examined the effects of larval C. auratus and Asplanchna brightwellii (a rotifer predator) on morphological defensive traits (body length, body width, anterior spine length, and posterolateral spine length) of B. calyciflorus.We show that B. calyciflorus develops smaller body size and shorter spine length when exposed to media conditioned using larval fish, and that high larval fish densities induce more pronounced responses than low densities. We also show that B. calyciflorus is able to discriminate between the two predators by producing opposing morphological adaptations (i.e., larger body size and longer posterolateral spines against A. brightwellii, but smaller body size and shorter spine length when exposed to the visual predator [larval fish]). However, B. calyciflorus develops intermediate, trade‐off responses in all morphological traits when exposed to conflicting threats from a combination of predators with different size and feeding strategies.These results show how prey are not necessarily passive victims, but rather, use countermeasures against predation – they actively develop responses to counteract their vulnerability to different predators by rapidly adjusting their morphology and life‐history traits to the existing predator regimes. [ABSTRACT FROM AUTHOR]

Global change encompasses many co‐occurring anthropogenic stressors. Understanding the interactions between these multiple stressors, whether they be additive, antagonistic or synergistic, is critical for ecosystem managers when prioritizing which stressors to mitigate in the face of global change. While such interactions between stressors appear prevalent, it remains unclear if and how these interactions change over time, as the majority of multiple‐stressor studies rarely span multiple generations of study organisms. Although meta‐analyses have reported some intriguing temporal trends in stressor interactions, for example that synergism may take time to emerge, the mechanistic basis for such observations is unknown. In this study, by analysing data from an evolution experiment with the rotifer Brachionus calyciflorus (~35 generations and 31,320 observations), we show that adaptation to multiple stressors shifts stressor interactions towards synergism. We show that trade‐offs, where populations cannot optimally perform multiple tasks (i.e. adapting to multiple stressors), generate this bias towards synergism. We also show that removal of stressors from evolved populations does not necessarily increase fitness and that there is variation in the evolutionary trajectories of populations that experienced the same stressor regimes. Our results highlight outstanding questions at the interface between evolution and global change biology, and illustrate the importance of considering rapid adaptation when managing or restoring ecosystems subjected to multiple stressors under global change. [ABSTRACT FROM AUTHOR]

Brachionus calyciflorus is a recently described monogonont rotifer species complex that comprises four species. The observation of hybridisation between two of these species challenges this species delimitation. The mechanisms of reproductive isolation essential to the maintenance of species integrity remain unclear.Here, we conducted upscaled hybridisation experiments to obtain large numbers of hybrid and non‐hybrid dormant propagules. Through hatching assays, we compared the zygote viability of hybrid with non‐hybrid dormant propagules. Furthermore, we investigated populations of F1 hybrid clones and assessed their clonal growth rate and the ability to reproduce sexually.Our results demonstrated higher rates of morphological abnormality and associated mortality in dormant propagules of hybrids compared to non‐hybrids yet hatching rates of healthy‐looking propagules proved similar. F1 hybrids exhibited high clonal population growth rates, nevertheless, we also observed strong differences between clones and a strong influence of parental genotype identity. Two‐thirds of the F1 hybrid clones showed a low incidence of sexual reproduction and almost never produced dormant propagules. Clones with high population growth rates seemed to invest less in sexual reproduction.Our results clearly demonstrate the existence of intrinsic postzygotic barriers caused by relatively high mortality of dormant propagules. Furthermore, the low ability of most hybrid clones to engage in sexual reproduction may reduce the long‐term fitness of hybrid clones. These postzygotic barriers probably impede genetic exchange between parental species and contribute to the maintenance of their integrity. [ABSTRACT FROM AUTHOR]

The success of genetically depauperate populations in the face of environmental change is contrary to the expectation that high genetic diversity is required for rapid adaptation. Alternative pathways such as environmentally induced genetic modifications and non‐genetic heritable phenotypes have been proposed mechanisms for heritable adaptation within an ecologically relevant time frame. However, experimental evidence is currently lacking to establish if, and to what extent, these sources of phenotypic variation can produce a response.To test if adaptation can rapidly occur in the absence of initial standing genetic variation and recombination in small populations, we (a) exposed replicate monoclonal populations of the microzooplankton Brachionus calyciflorus to a culturing regime that selected for phenotypic variants with elevated population growth with either high or low phosphorus food for a period of 55 days and (b) examined population level response in two fully factorial common garden experiments at day 15 and 35 of the exposure experiment.Within six generations, we observed heritable local adaptation to nutrient limitation. More specifically, populations with a history of exposure to low P food exhibited higher population growth rates under low P food conditions than populations with a high P exposure history. However, the capacity for such a response was found to vary among clones.Our study finds that although standing genetic variation is considered essential for rapid heritable adaptation, the rapid emergence of de novo genetic variation or alternative sources of phenotypic variation could aid in the establishment and persistence of low‐diversity populations. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Rotifers are widely used as a live prey for finfish larvae, although their content in minerals such as selenium and zinc is lower than in fish. In the present study, mixed microalgae (i.e., Isochrysis aff. galbana and Nannochloropsis oculata) were enriched with different amounts of Se and Zn either alone (45, 90, and 135 mg L−1 of Zn, 60, 120, and 180 mg L−1 of Se) or mixed (22.5, 45, and 90 mg Zn L−1 and 30, 60, and 120 mg Se L−1). The content of minerals in the microalgae was analysed after 1 and 3 h enrichment and their effect on the growth and mineral composition of the rotifer. Based on the results, 1 h enrichment time and 90 and 120 mg L−1 of Zn and Se, respectively, resulted in the highest amount of Se and Zn in enriched microalgae. The maximum Zn content was detected in the rotifers fed 90 mg L−1 Zn and 90 mg L−1 Zn +120 mg L−1 of Se, but the maximum Se was observed in rotifers fed with 120 and 180 mg L−1 Se. Thus, Se‐ and Zn‐enriched rotifers can be used as a mineral delivery method to cover marine fish larvae nutritional requirements. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the effect of the addition of Brachionus plicatilis to Litopenaeus vannamei in a nursery biofloc technology (BFT). Four treatments were used: BFT (without addition of rotifers); BFT‐10 (addition of 10 rotifers mL−1); BFT‐20 (addition of 20 rotifers mL−1) and BFT‐30 (addition of 30 rotifers mL−1), all in triplicate. The shrimp (3.4 ± 0.02 mg) were reared for 42 days at a density of 3000 shrimp m−3. The rotifers were added every 10 days (from day 1 to 30). The final weight (1.26 g) and yield (3.42 kg m−3) were significantly higher at BFT‐30 than those from BFT. The percentage of sucrose‐fermenting gram‐negative bacteria increased and non‐sucrose‐fermenting gram‐negative decreased by the end of the period. The crude protein of bioflocs was significantly higher at BFT‐30 than those from BFT‐10 or BFT treatments, while crude lipid of bioflocs was significantly higher at BFT‐20 and BFT‐30 than the BFT. The best shrimp performance was observed in BFT‐30 and BFT‐20, indicating the benefits of rotifers on enhancing the microbial floc content and growth to L. vannamei in BFT. [ABSTRACT FROM AUTHOR]

Stream biofilms can improve water quality (e.g. excessive nitrogen loads) because their microorganisms such as microphytobenthos and bacteria, are involved in self‐depuration processes in the biofilm. In marine sediments, meiofauna can influence primary productivity of phototrophic biofilms, stimulate bacterial growth, and exert a significant role on nitrogen cycling. We hypothesised that in rivers biofilms, increased meiofauna abundance in combination with nutrient enrichment can lead to improve biofilm nutrient uptake ability.River biofilms (from the Garonne River, France) were incubated in flumes supplied with natural river water. The N - NO3‐ uptake rates of the biofilms as well as the response of microorganisms were studied under different conditions of meiofaunal density and N - NO3‐ concentration over a 10‐day experiment.Rotifers dominated the meiofauna community in all biofilms. Under high nitrate conditions, the N - NO3‐ biofilm uptake rate was significantly higher in meiofauna‐enriched than non‐enriched biofilms over the first 2 days. This suggests that under high nitrate concentration conditions, high densities of rotifers enhanced the nitrogen uptake capacity of phototrophic biofilm despite a lower biomass. Densities of rotifers and bacteria in biofilms were positively correlated under N - NO3‐ enriched conditions suggesting that these two communities interacted over the experimental period. Signature pigment concentrations show that, under low concentrations of N - NO3‐, biomasses of diatoms and green microalgae were higher in meiofaunal‐enriched than non‐enriched biofilms, indicating that rotifer activity favoured biomass accumulation of these algae.This study demonstrates that meiofauna inhabiting biofilms may contribute to the limitation of nitrogen loads in stream water and supports the thesis that the potential interactions between faunal groups and microbial communities of biofilms merits further investigation to improve our understanding of processes which regulate interactions between biofilms and the overlying water in rivers. [ABSTRACT FROM AUTHOR]

Driven by Regulation (EC) No. 1272/2008 and the European Water Framework Directive 2000/60/EC, we have re‐evaluated the available chronic freshwater ecotoxicity data for ionic silver (Ag) using strict data quality criteria. In addition, we generated new chronic ecotoxicity data for species potentially sensitive to Ag (the rotifer Brachionus calyciflorus, the cyanobacteria Anabaena flos‐aquae, and the aquatic plant Lemna minor) using Ag nitrate as the test substance. The 10% effect concentrations for the most sensitive endpoint per test species were 0.31 µg dissolved Ag/L for B. calyciflorus (population size), 0.41 µg dissolved Ag/L for A. flos‐aquae (growth rate), and 1.40 µg dissolved Ag/L for L. minor (root length). We included these values in the set of reliable chronic freshwater data, subsequently covering a total of 12 taxonomic groups and 15 species. Finally, we applied a species sensitivity distribution approach to the data set using various models. The best‐fitting model (Rayleigh distribution) resulted in a threshold value protective for 95% of the species of 0.116 µg dissolved Ag/L. This value is considered reliable and conservative in terms of species protection and can be used as a solid basis for setting thresholds for Ag in freshwater after application of an appropriate assessment factor. Furthermore, this value represents reasonable worst‐case conditions for bioavailability in European Union surface waters (low hardness and low dissolved organic carbon). Environ Toxicol Chem 2021;40:1678–1693. © 2021 European Precious Metals Federation. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

To deal with predation threats, many prey organisms have evolved anti‐predator defences in both morphology and behaviour. Aquatic rotifers were among the first model organisms for studying inducible defences and studies mainly focused on predator‐induced morphological defences. Despite this, we still lack a good understanding of predator‐induced behavioural defences in rotifers.In this study, we conducted three laboratory induction experiments to investigate floating behavioural responses of the prey rotifer Brachionus calyciflorus to the presence of the predator Asplanchna sieboldii and its chemical cues. Two experiments used live A. sieboldii and one used A. sieboldii‐conditioned medium. Subsequently, we examined the protective effects of floating behaviour against predation by Asplanchna by performing predation experiment.We show that B. calyciflorus has a pronounced behavioural response to A. sieboldii and that this response can be induced by both exposure to live A. sieboldii and to Asplanchna‐conditioned medium. We also found that. B. calyciflorus can respond with floating behaviour immediately within 10 min when exposed to Asplanchna‐conditioned medium.We also provide the first experimental evidence that the floating behaviour of B. calyciflorus reduces the predation rate from A. sieboldii by about 50%, and effectively protects them from consumption by this predator. Thus, we concluded that B. calyciflorus can sense chemical cues released during predation by A. sieboldii and use behaviour as a defence, escaping to the water surface as a refuge, thereby reducing predation risk.Our results represent a novel addition to our fundamental knowledge on how prey may not be passive victims, but rather actively use inducible behavioural defences to counteract their vulnerability to predators. [ABSTRACT FROM AUTHOR]

Growth, survival and feeding of early‐stage silver therapon Leiopotherapon plumbeus larvae reared at different stocking densities and feeding levels were examined. Larvae (8 days post hatch (dph); 0.38–0.50 mg body weight (BW); 5.33–6.90 mm in total length (TL)) were stocked at densities of 5, 15, 25 and 35 larvae/L and co‐fed with live food (Brachionus rotundiformis and Artemia nauplii) and formulated microdiet or fed Artemia alone for 28 days. Another batch of 8 dph silver therapon larvae (0.65 mg BW; 9.47 mm TL) were stocked at 15 larvae/L and were fed 1, 2 or 5 Artemia nauplii/mL for 28 days. Survival at lower densities (5 and 15 larvae/L) was significantly improved than in high‐density reared larvae. Furthermore, larvae fed Artemia alone showed higher survival (20.4%–81.4%) than those offered live food and formulated microdiet combined (3.5%–32.9%) in each stocking density, indicating the suitability of Artemia for early‐stage silver therapon larvae. Growth parameters were significantly affected by stocking density in larvae fed Artemia alone but not in the live food and formulated microdiet co‐fed group. No significant differences in growth and survival were observed in silver therapon larvae reared on three feeding levels. However, higher feed intake at 5 nauplii/mL resulted in significantly higher body lipid contents than those fed 1 or 2 nauplii/mL. The results suggest that larvae held at stocking densities of 5 and 15 larvae/L and fed 5 Artemia nauplii/mL promote maximum growth, survival and higher feed intake of early‐stage silver therapon larvae under laboratory conditions. [ABSTRACT FROM AUTHOR]

A study on the use of freshwater rotifers (Brachionus angularis) as initial live feed for pangasius catfish (Pangasianodon hypophthalmus) larvae was undertaken to assess whether this initial feed improved P. hypophthalmus survival during the first 20 days of rearing. This study was comprised of three trials. The first trial contained three treatments and assessed the effectiveness of freshwater rotifers as initial feed compared to homemade feed and water flea (Moina macrocopa). In the second trial, P. hypophthalmus larvae were fed with (a) 100% freshwater rotifers, (b) 100% water fleas and (c) a combination of freshwater rotifers and water fleas (freshwater rotifers fed during first 3 days and then water fleas fed for remainder of experiment). In the third trial, the fish larvae were fed 3 densities of freshwater rotifers and then water fleas (3, 5 and 7 individuals per ml) to determine the most suitable feeding density for P. hypophthalmus larvae. Mouth opening was measured at days 0, 3, 6, 9, 12, 15, 18 and 20, whereas growth and survival were assessed at the end of each trial. These experiments demonstrated that P. hypophthalmus larvae: (a) exhibited a significant increase in survival rate when fed B. angularis rotifers or Moina micrura water fleas compared to homemade feed, (b) exhibited a significant increase in growth and survival rates when fed a combination of freshwater rotifers (first 3 days) and then water fleas (remainder) compared to feeding either freshwater rotifers or water fleas only, and (c) preferred a density of 5 to 7 individual freshwater rotifers and then water fleas per ml. [ABSTRACT FROM AUTHOR]

Many aquarium fish species have diverse morphotypes. Since different morphotypes may have different preferences for various prey items, offering a single prey species is inadequate for successful aquaculture. Poecilia reticulata, a popular aquarium species, occurs in different morphotypes. To test whether the four morphotypes (yellow tail YT, red tail RT, metallic blue tail MBT and black tail BT) of this fish prefer different items, we quantified somatic growth, feeding behaviour, zooplankton selectivity and functional responses. Standard length (4.5 vs. 11.7 mm) and gape size (0.37 vs. 0.91 mm) of four morphotypes increased linearly with larval age; YT and RT had 25% longer body length and larger gape than the others. Prey encounters, attacks, captures and ingestions increased with larval age. Lowest ingestion rates were recorded for the RT morphotype on rotifers. At any given larval age, prey consumption increased with increasing prey availability. During the fourth and fifth weeks, larval YT and RT consumed higher number (37 ± 1 ind./predator/30 min) of cladocerans compared with other two morphotypes (24 ± 1 ind./predator/30 min). Prey selectivity data showed that larvae of MBT and BT continued to prefer rotifers up to 4 weeks, while those of YT and RT preferred cladocerans during the 4th week. [ABSTRACT FROM AUTHOR]

Theory predicts that population genetic structure and metacommunity structure are linked by the common processes of drift and migration, but how population genetic structure and metacommunity structure are related in nature is still unknown. Deeper understanding of the processes influencing both genetic and community diversity is vital for better predicting how environmental change will impact biodiversity patterns. We examined how crustacean zooplankton and rotifer species' metapopulation genetic structure and metacommunities respond to environmental and spatial variation both within and across four regions of boreal Canada. Metapopulation and metacommunity variation partitioning results were compared within and across the four regions. Metapopulations and metacommunities responded differently to environmental variation and spatial structure both within and across regions, as metapopulations were influenced by different environmental variables compared to metacommunities. At larger spatial scales both metapopulations and metacommunities exhibited greater spatial and environmental structuring, again responding to a different subset of environmental variables. Our findings suggest that even though both genetic and species diversity are linked by the same processes, regional variation in environmental characteristics and spatial structure influence resulting biodiversity patterns differently. To date, no other empirical research has explored relationships between entire metapopulation and metacommunity assemblages at large regional spatial scales. [ABSTRACT FROM AUTHOR]

Many urban lakes in Mexico City such as Lake Chapultepec are infested with high densities of cyanobacteria, particularly Microcystis. We tested the effect of cyanotoxins from cyanobacterial crude extracts on the demographic variables of zooplankton. The rotifers Brachionus havanaensis and Brachionus calyciflorus, and the cladocerans Ceriodaphnia dubia and Moina macrocopa were used for the assays. Temperature effects on the response of B. calyciflorus and 2 clones of M.macrocopa were tested. We hypothesized that with an increase in cyanotoxin concentration and temperature there would be an increase in the adverse effect on the test species and that the clone of Moina previously exposed to cyanobacteria from Lake Chapultepec would be more resistant to the cyanotoxins. Demography experiments showed that B. havanaensis was more sensitive than C. dubia. The negative effect of the cyanobacterial crude extract on B. calyciflorus was greater at 30 °C than at 20 °C or 25 °C. The strain of M. macrocopa isolated from Lake Chapultepec was more resistant to the cyanotoxins than the strain that had not been previously exposed to the cyanobacteria. The present study indicated that cyanobacteria in Lake Chapultepec are highly toxic and, considering the recreational use of this lake, should be controlled. Environ Toxicol Chem 2020;39:2409–2419. © 2020 SETAC [ABSTRACT FROM AUTHOR]

In recent decades, an increasing interest in aquaculture for producing good quality and quantity of live food has led to the use of probiotics. Rotifers and cladocerans are important as live prey for fish and invertebrate larval rearing. We carried out an experimental study to evaluate the effect of a commercial probiotic (NanoCrusta®) on improving population growth of Brachionus angularis, Plationus patulus, Moina cf. macrocopa and Simocephalus mixtus. The probiotic was tested by direct supplementation (2.1 × 106, 4.2 × 106, 8.5 × 106 and 1.7 × 107 cells/ml) in addition to C. vulgaris as a source of food (1 × 106 cells/ml). The results indicated that probiotics enhanced maximum population density (Dmax) and the population growth rate (r) in both zooplankton groups. At 4.2 × 106 cells/ml, B. angularis improved their Dmax (62.74%) and r (28%) compared with probiotic‐free control, while P. patulus enhanced their Dmax and r by 51.26% and 20.83% (probiotic at 8.5 × 106 cells/ml). The two lowest probiotic densities resulted in an improvement in the parameters compared with the probiotic‐free control treatments: M. cf. macrocopa enhanced Dmax by 14.82% and r by 18%, and S. mixtus incremented Dmax 10.92% and r by 10%. The addition of probiotic bacteria also resulted in an improvement in the rotifer egg ratio (ER). [ABSTRACT FROM AUTHOR]

This study represents the first phylogenetic reconstruction of Synchaetidae (Rotifera, Monogononta) and combines one morphological and two molecular data sets to derive the most comprehensive database for this taxon to date. Overall, 19 species were examined both morphologically (light‐ and scanning electron microscopy of habitus and trophi) and genetically (COI and 18S rRNA genes), thereby delivering new morphological information as well as the first molecular data for several species. Our results strongly support the monophyly of each of the three genera within Synchaetidae, with Synchaeta being the sister taxon of Polyarthra and Ploesoma. Resolution within each genus, however, was more poorly supported, possibly because of high levels of missing data for the more poorly known species that were also not re‐discovered and revised in the present study. Nevertheless, an evolutionary reconstruction based on the total evidence topology indicates that the common ancestor of Synchaetidae was a rotatorivorous and pelagic freshwater rotifer exhibiting slightly enlarged lamellar trophi that were adapted to an enhanced pumping function. These features together with several, additional key character transformations (e.g., hatching independently from benthic or periphytic habitats) probably account for the success of Synchaetidae in pelagic environments and their being one of the most widely distributed and abundant rotifer taxa. [ABSTRACT FROM AUTHOR]

In the present study, the effects of selenium (Se) enrichment on the rotifer, Brachionus plicatilis, were investigated. Based on the results of six Se treatments obtained from triplicate experiments, we found that the efficiency of bioaccumulation by Se from non‐acid‐soluble sources was 62‐fold greater than that from acid‐soluble sources (Se‐Chlorella 15.6 ± 1.81% vs. selenite 0.25 ± 0.03%). However, supplementation of both acid‐soluble Se at low concentrations (≤40 µg per thousand rotifers) and Se‐Chlorella enhanced rotifer lifespan, increased the rate of spawning, inhibited lipid peroxidation, decreased levels of intracellular oxidization products and maintained the stability of mitochondrial membranes. These positive effects were correlated with the activities of antioxidant enzymes (e.g. catalase‐ and guaiacol‐dependent peroxidase) which increased along with the low Se concentrations (<80 µg per thousand rotifers). In contrast, the opposite effects were found when the rotifers were exposed to high Se concentrations (≥80 µg per thousand rotifers). The antioxidation and toxicity effects appeared to be correlated with the levels of total Se bioaccumulation. Above all, selenite, which is more toxic than Se‐chlorella, is less readily accumulated and biologically active. Se‐enriched rotifers fed by Se‐Chlorella are a fish larvae food supplement in aquaculture. [ABSTRACT FROM AUTHOR]

To evaluate the nutritional quality of the Teleaulax/Plagioselmis/Geminigera (TPG) clade species over the conventional prey species of the Rhodomonas/Rhinomonas/Storeatula (RHO) clade for the enrichment of a rotifer, Brachionus plicatilis, two strains of Teleaulax amphioxeia (TA), CR‐MAL07 and CR‐MAL08‐02, and a Chroomonas sp. strain CR‐MAL10 from Korean coastal waters were mass cultured in 500 L photobioreactors. When harvested from the stationary growth phase, the composition of all three macronutrients and three n‐3 highly unsaturated fatty acids (UFAs) exhibited large deviations among strains and culture media. The composition of essential amino acids and UFAs was higher in CR‐08‐02 by up to 1.1 and 22.2 times, respectively, than that in a commercially available Chlorella sp. strain. For the enrichment of B. plicatilis cultures previously grown with the Chlorella concentrates, high‐density cultures of CR‐08‐02 were offered. After a 3‐hr enrichment, the compositions of eicosapentaenoic acid, n‐3 FA (fatty acids), and n‐6 FA in B. plicatilis increased by 331, 19.5, and 10.48%, respectively, which might reflect the relevant quality compositions in the TA cells. Thus, TA in the TPG clade can be another novel type of prey to enrich rotifer cultures for the marine larviculture. [ABSTRACT FROM AUTHOR]

The effect of a commercial probiotic (NanoCrusta, Altacrusta, Mexico City, Mexico) on the growth performance of Brachionus calyciflorus Pallas, 1766, was evaluated. In a first approach, probiotics were supplied in four densities (2.0 × 103, 1.1 × 105, 2.1 × 105 and 2.1 × 106 cells/ml), alone and in combination with Chlorella vulgaris (1 × 106 cells/ml). The test rotifer did not grow on the probiotic alone. However, when probiotics + C. vulgaris were added, the maximum densities (Dmax; ind/ml) and population growth rates (r) observed were higher. In the second experiment, probiotics were supplied at five higher densities (2.1 × 106, 4.2 × 106, 8.5 × 106, 1.7 × 107 and 3.4 × 107 cells/ml) with C. vulgaris and a control treatment with only C. vulgaris (probiotic‐free). Treatments supplied with probiotics between 2.1 × 106 and 1.7 × 107 cells/ml showed significantly higher Dmax and r than the control treatment. The results showed a positive effect of probiotic bacteria when supplied with C. vulgaris. The best outcome showed a Dmax 2.16 times and an r 1.63 times higher than the density of the control treatment. Growth rates were higher in the treatments with probiotics compared to the control. We conclude that application of NanoCrusta is feasible to improve B. calyciflorus production, but the effects need to be tested in larger scales. [ABSTRACT FROM AUTHOR]

Titanium dioxide nanoparticles (nTiO2) have raised environmental concerns and display potential hazards to aquatic organisms and even humans. However, only a few reports tested the toxicity of nTiO2 to rotifers. In the present study, acute and chronic toxicity of nTiO2 to the freshwater rotifer Brachionus calyciflorus was investigated at different temperatures. At 25°C, the 24 and 48‐hr LC50 was 117.14 and 60.11 mg/L, respectively. At 15°C, 20°C, 25°C, and 30°C, exposure to nTiO2 significantly decreased life expectancy at birth, net reproductive rate, generation time, average lifespan, and/or intrinsic rate of population increase of B. calyciflorus (p <.05). High temperature enhanced the toxicity of nTiO2 to rotifers. The swimming linear speed of rotifers significantly increased (p <.05) in treatments with 200 µg/L nTiO2, compared with the control. In addition, treatments with 8 µg/L to 5 mg/L nTiO2 significantly increased superoxide dismutase activity (p <.05). Glutathione content and catalase activity increased significantly after exposure to 8 µg/L nTiO2 but decreased significantly in treatments with nTiO2 concentrations ranging from 40 µg/L to 5 mg/L (p <.05). There were no significant changes in malondialdehyde contents among nTiO2 treatments and control. Overall, the present study indicated that nTiO2 revealed high toxicity to rotifers, displaying high environmental risks to aquatic ecosystems. HIGHLIGHTS: 1.High temperature enhanced the toxicity of nTiO2 to rotifers.2.The 24 and 48‐hr LC50 of nTiO2 to B. calyciflorus was 117.4 and 60.11 mg/L, respectively.3.nTiO2 displayed high environmental risk to aquatic ecosystems even at the µg/L levels. [ABSTRACT FROM AUTHOR]

SUMMARY: A strain of Pseliodinium pirum was isolated from Jiaozhou Bay, China, identified based on a recently emended classification, and further characterized for its morphology using light, scanning electron, and transmission electron microscopy, and phylogeny based on SSU and partial LSU rDNA sequences. The pigment composition, life history, and potential effects on aquatic animals were also examined. We observed the typical characteristics of Ceratoperidiniaceae, in which its apical structure complex (ASC) formed a circular loop, and the ASC of our isolate comprised four to five rows of vesicles, and connected with sulcal intrusion. Epifluorescence and transmission electron microscopy revealed a bean‐shaped, centrally located nucleus, with at least 76 chromosomes. Numerous rod‐shaped chloroplasts were in connection to the irregularly shaped pyrenoids. Pigment analysis showed that peridinin was the most abundant among all carotenoids and other pigments. Phylogenetic analyses using maximum likelihood and Bayesian inference indicated that our isolate is conspecific with the entity Cochlodinium cf. helix (accession No. KF245459), but different from Ceratoperidinium, Kirithra, and other unidentified species of the family Ceratoperidiniaceae. Pseliodinium pirum could produce sexual, thin‐walled cyst, with subspherical and spherical shape and smooth surface (without spines or rough projections). The cyst could germinate within 3 days. Bioassays did not show adverse effects of P. pirum on the finfish Oryzias melastigma and the rotifer Brachionus plicatilis, indicating it may not be a harmful species. [ABSTRACT FROM AUTHOR]

Brachionus calyciflorus is arguably the most studied freshwater monogonont rotifer. Although it has been recognised as a cryptic species complex for more than a decade, a formal (re‐)description of the four species known so far (B. calyciflorus, Brachionus dorcas, Brachionus elevatus, and Brachionus fernandoi) has only recently been made. Information on the ecology of these species is very scant and fragmented. The aim of this study was to test for ecological divergence between these four species, specifically their life history strategy and population demography.We conducted a life history experiment using 12–16 genotypes per species. For each species, genotypes were extracted from at least three different natural populations. In addition, we performed population‐level culture experiments with the aim to compare population growth rates and demographic structure of experimental populations among species. Finally, we searched the literature for life history studies with molecular data allowing retrospective species identification.We found pronounced differences in life history traits between B. fernandoi and the other three species. B. fernandoi had higher egg and juvenile development times and a lower egg production rate and mictic ratio. We detected no significant life history differences among B. calyciflorus, B. elevatus, and B. dorcas.Population growth rates of B. fernandoi and B. calyciflorus were higher than those of B. elevatus and B. dorcas. Life history divergence resulted in marked differences in the demographic structure of populations. Populations of B. fernandoi contained larger fractions of pre‐reproductive females and lower fractions of adult females with sexual eggs than populations of B. calyciflorus, B. elevatus, and B. dorcas. Mortality was found to be highest in B. elevatus and lowest in B. calyciflorus populations.Our results show that a reverse taxonomy approach is powerful in revealing sources of variation in ecologically relevant traits of cryptic species, such as life history and demographic structure. Explicit consideration of this variation is crucial for future studies of their dynamics in natural communities. [ABSTRACT FROM AUTHOR]