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The aim of the present study was to analyze interannual and seasonal relationshisps between zooplankton communities and their trophic levels along with the physicochemical properties of Lake Eğirdir. Samplings were performed seasonally between January 2016 and October 2018 at five stations. Zooplankton communities comprised Rotifera (88%), Cladocera (3%) and Copepoda (9%). A total of 73 species were recorded. Four species Asplanchna priodonta, Polyarthra dolichoptera, Synchaeta pectinata and Bosmina longirostris were found dominant among the others. During the study, the number of zooplankton species decreased in 2018 compared to 2016 when the average zooplankton density increased in 2018. The variations of zooplankton community were estimated using Shannon–Wiener diversity, Evenness, and Simpson indices. The correlations between the species and environmental variables were analyzed with Canonical Correspondence Analysis (CCA). The variation in the species data was significantly (p < 0.05) related to a set of six environmental variables (electrical conductivity, chloride, ammonium, carbon, depth, temperature) which explains 84.6% of the total variation. CCA indicated that Keratella cochlearis, Lecane bulla, L. clostrocerca, Trichocerca similis and Copepoda spp. were positively correlated with temperature. According to the Brachionus: Trichocerca quotient (QB/T), Lake Eğirdir can be characterized within the mesotrophic-eutrophic trophic status. The lake showed mesotrophic status in terms of total phosphorus, Secchi disc and chl-a in 2016, 2017, 2018 according to the Carlson trophic status index. [ABSTRACT FROM AUTHOR]

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]

For fish oil-free aquafeed development, a photoautotrophic microalga Tisochrysis lutea is believed to be the candidate source of n-3 highly unsaturated fatty acid (n-3 HUFA) because of its docosahexaenoic acid (DHA) biosynthesis. While DHA contents of T. lutea vary during the cultivation periods depending on algal growth phase, little is mentioned about how this dependence should be taken into consideration when evaluating the suitability of microalgae as an alternative to fish oil-formulated diets. Here, we compared nutritionally maximized cells of deceleration growth phase T. lutea and fish oils-formulated product (n-3 HUFA-enriched Chlorella) as a rotifer enrichment diet for enhancement in Japanese flounder Paralichthys olivaceus larviculture. T. lutea had higher concentrations of DHA in the polar lipids than those for enriched Chlorella. Such higher concentrations of T. lutea were estimated only in the deceleration growth phase (not in the logarithmic growth or stationary phase). When deceleration growth phase T. lutea were fed to Brachionus plicatilis rotifers previously cultured on unenriched Chlorella, the DHA of the rotifers was boosted up to the level in those fed with enriched Chlorella. Furthermore, use of T. lutea-fed rotifers for initial feeding of fish larvae enhanced the growth, survival, n-3 HUFA levels, and final juvenile productivity of the larvae as much as feeding the larvae with enriched Chlorella-fed rotifers. We propose that T. lutea in the deceleration growth phase are efficacious, fish oil-free sources of n-3 HUFA for marine fish larviculture. Highlights: Polar lipid DHA % was high in the deceleration growth phase of Tisochrysis lutea. DHA % was high in rotifers fed either T. lutea or fish oil-enriched Chlorella. Rotifers enriched with T. lutea improved marine fish larviculture performance. [ABSTRACT FROM AUTHOR]

Simple Summary: Mystus macropterus, a commercially significant Mystus fish species found in the Yangtze River and Pearl River, is currently experiencing a rapid decline attributed to the construction of hydraulic engineering projects, water pollution, and overfishing. Consequently, extensive artificial breeding efforts are being undertaken for large-scale commercial aquaculture purposes as well as for reintroducing this fish back into its natural habitat. Our aim was the evaluation of the effect of different opening diets on the growth, the structure of the digestive tract, and digestive enzyme activity of larval and juvenile M. macropterus. It is recommended to include Tubifex in the diet of M. macropterus larvae during the standardized farming process. One of the crucial factors influencing the growth and viability of larvae and juveniles is their opening diets. The objective of this study was to identify suitable initial feed options for M. macropterus larvae and juveniles. A total of 1200 newly hatched M. macropterus with an average weight of 18.3 mg and an average length of 11.58 mm were selected and randomly divided into four groups. The fish were fed with different opening diets, including rotifer, Artemia nauplii, Tubifex, and micro-diet from six days after hatching (dahs), respectively. Growth indices and activities of digestive enzymes were assessed at 10, 15, 20, 25, 30, 35, and 40 dahs. Histological examination of the structure of the digestive tract was performed at 40 dahs, while survival rates were also documented. The results demonstrated that different diets had no effect on the survival rate of larvae and juveniles of M. macropterus. The growth performance indices were ranked as follows: Tubifex group > Artemia nauplii group > micro-diet group > rotifer group. Remarkably, the Tubifex group exhibited superior growth performance, which was also reflected in the structure of the digestive tract and digestive enzyme activity. Therefore, it is recommended to include Tubifex in the diet of M. macropterus larvae and juvenile during the standardized farming process. [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]

The species richness is an essential component of biodiversity metrics and an ecological indicator for setting conservation actions. Phylum Rotifera consists of a specious group of conspicuous and minute animals, mainly in freshwater environments. In the Neotropical region, the knowledge of the biodiversity of rotifers is incomplete, with outdated and geographically restricted information. In this regard, we present a comprehensive inventory of rotifers from freshwater ecoregions in Rio de Janeiro. From the literature review and active surveillance, we detected 238 spp.; among these, 39 were previously unknown to the State. We also preliminarily examine the potential use of Rotifera for ecoregions delimitation. The extrapolated number of species shows an increasing richness for the Paraiba do Sul and Fluminense ecoregions, which were also significantly different regarding species composition. Registers from the Ribeira de Iguape and Northern Mata Atlantica ecoregions are still lacking in the State. We believe that future survey efforts will undoubtedly reveal additional records and taxa improving our understanding of biogeographical patterns such as dispersal and biological invasions. Ultimately, support future conservation policies and the potentialities of this group for ecoregion delimitations. [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]

The high intraspecific variability of the morphological characters of Acanthocephala can complicate their taxonomic classification. To solve this problem, molecular markers are used. Here, we present the identification and determination of genetic variability of four species of the Acanthocephala genera Pomphorhynchus, Acanthocephalus and Dentitruncus, obligate endoparasites of freshwater fishes. The DNA sequences of the three markers that evolve at different rates (18S rDNA, COI and ITS) were analysed. To put the genetic position of the Croatian Acanthocephala specimens in a broader context, the COI and ITS sequences of the other European specimens from the NCBI GenBank were used. Genetic structuring at the local level was minor or not visible at all, but in the context of European phylogeographic structuring, the Croatian P. laevis showed a clear grouping to the geographical subcluster Ponto-Caspian Balkans. Only two P. laevis Danubian haplotypes, which were not analysed morphologically, were assigned to the Ponto-Caspian Danube subclade together with the recently identified P. bosniacus from Austria. The haplotypes of P. tereticollis from Croatia were clustered within the two main European clades. In connection with the phylogeographic distribution of Acanthocephala and their hosts, we hypothesised possible phylogeographic patterns. [ABSTRACT FROM AUTHOR]

The Mediterranean area includes a wide variety of shallow water bodies which are recognized as hotspots of biodiversity. Here, we present the results of our study conducted on twenty-two small ponds, divided in two groups, fish free and fish stocked, along the coast and islands of the Adriatic Sea, in the Mediterranean. The main aims covered (1) the assessment of zooplankton structural and functional traits; (2) the impact of top predators (invasive mosquitofish) and macrophyte coverage on zooplankton diversity, abundance, and biomass. Overall, rotifers dominated in zooplankton diversity and abundance; it is likely that due to their small size they were not under direct fish predation. Rotifers prevailed in fish-stocked ponds, where their assemblage was shaped by food availability and macrophyte coverage. Macrophytes had a dual influence on rotifers: dense macrophyte coverage supported a high density of littoral species, while low macrophyte coverage provided a profitable condition for planktonic rotifers. In fish-stocked ponds, cladoceran and copepod density, biomass, and diversity were strongly reduced in relation to fish-free ponds. This study revealed high zooplankton diversity (77 taxa) in a Mediterranean region, structured by habitat heterogeneity and predation. [ABSTRACT FROM AUTHOR]

Aging is a significant internal factor influencing the sexual ability of rotifers. This study examined the effects of maternal aging on a rotifer's reproductive behavior (either sexual or asexual) and how the impacts were transmitted via generations (P − F1 − F2) in two marine species in the Brachionus plicatilis species complex: Brachionus plicatilis (large type) and Brachionus rotundiformis (super-small type). Based on the rotifer reproductive period, we established young and old lineages produced in the first and second halves of the period, respectively. The fecundity and longevity of the progeny in the two species and throughout the generations remained unaffected by maternal age. However, young amictic females in each species (especially in B. plicatilis) produced a larger ratio of mictic offspring. The multigenerational assessment revealed that the amictic offspring from old mothers produced more mictic daughters than those from young rotifers. This implies that aged rotifers may adopt an adaptive strategy (i.e., entering dormancy via sexual reproduction) for survival. [ABSTRACT FROM AUTHOR]

Aquatic organisms are constantly exposed to effluents which often contain microplastics. Microplastics adversely affect aquatic organisms as a result of mechanical damage during ingestion or intoxication by chemicals adsorbed on the microplastics. Sub-optimal temperatures may acerbate the adverse effects of microplastics on aquatic biota. Brachionid rotifers, such as Brachionus havanaensis and Brachionus calyciflorus, are common in tropical freshwaters. They are generalist filter feeders capable of consuming microplastic particles of a wide size range 0.05 to 40 µm, which can eventually affect growth and competitive interactions among species. Here, we evaluated the effect of 30 µm beads of polystyrene microplastics at 10 and 20 mg l−1 on the population growth and competition of B. havanaensis and B. calyciflorus at 20 and 25 °C using 0.5 × 106 cells ml−1Chlorella vulgaris as food. Population growth decreased in treatments with microplastics at both temperatures as compared to the controls. The population growth rates ranged between 0.21 and 0.38 d−1 for B. calyciflorus, and between 0.27 and 0.48 d−1 for B. havanaensis. The presence of the competing species significantly lowered the population growth rate for B. calyciflorus but not for B. havanaensis. On the other hand, while the presence of the microplastics had little impact on the population growth rate of B. calyciflorus in the presence of the competitor, the reverse was true for B. havanaensis, especially at 20 °C. Our results show that the presence of microplastics may affect rotifer community structure in natural water bodies. [ABSTRACT FROM AUTHOR]

To test the hypotheses that multigenerational predation risk favors clones with longer postero-lateral spines and a larger body, and that fitness consequences of selection depend on both tested fitness variables and selection intensity, we expose replicate Brachionus dorcas populations in low (LK) and high (HK) concentrations of Asplanchna kairomones. Over 60 days (23 asexual generations) of selection, LK-selected populations showed the highest equilibrium population densities, and median mictic ratios and postero-lateral spine lengths, and HK-selected populations showed the lowest equilibrium population densities, the highest mictic ratios, and the longest postero-lateral spines, among all the control and treatment populations. In the absence of Asplanchna kairomones, and compared with populations with the control selection history, populations with an LK selection history showed increased growth rates/intrinsic rates of population increase and net reproductive rates, but decreased mictic ratios, indicating three fitness gains and a fitness cost; and those with an HK selection history showed increased life expectancy at hatching and mictic ratios, but decreased growth rates, indicating two fitness gains and a fitness cost. Asplanchna kairomones might increase the heritability of higher equilibrium densities or mictic ratios, and longer postero-lateral spines, and thus enable the prey to survive predation. [ABSTRACT FROM AUTHOR]

A non-genetic transgenerational inhibitory effect on sexual reproduction has been demonstrated in Brachionus plicatilis in relation to environmental predictability. Indeed, clones of this species from more predictable environments do not respond to sex-inducing cues during several generations after leaving diapause. Notwithstanding, the molecular basis of this effect is still unknown. In this work, the expression level of genes related to the synthesis of sex hormones and to a potential epigenetic signalling mechanism were tracked along successive generations from diapausing eggs in clones of B. plicatilis populations inhabiting ponds with different level of environmental predictability. The selected genes were (1) the 17-β-dehydrogenase gene (edh), involved in the synthesis of 17-β-estradiol hormone in rotifers, and (2) the DNMT2 gene (meth), as a candidate epigenetic mechanism of control. According to expectations, results showed an increasing expression of edh across generations in clones from those the more predictable ponds. This finding provides a putative role of estradiol in the transgenerational effect. However, no differences were found in the meth gene neither across generations nor regarding the environmental predictability. Despite this, we point out alternatives for future research on the inherited gene regulation mechanism behind the transgenerational effect. [ABSTRACT FROM AUTHOR]

We quantified the effect of two cyclopoids, an invasive (Mesocyclops pehpeiensis) and a native (Mesocyclops longisetus curvatus) species on the population growth of the rotifers Brachionus havanaensis and Brachionus calyciflorus. We hypothesized that the invasive copepod would have a greater adverse effect on the test rotifers. The population growth of B. havanaensis was tested in the indirect presence of B. calyciflorus (used as prey for the predatory copepods), and the predatory copepods, M. pehpeiensis and M. longisetus curvatus. For B. calyciflorus the experimental design was as above except that we used B. havanaensis as prey. The test rotifers were separated from the competitors and predators by mesh cages placed in the experimental jars. Rotifer density and the egg ratios were quantified, followed by a daily medium change, until the population density declined. The population growth rate of B. havanaensis ranged between 0.26 and 0.30 day−1, while that of B. calyciflorus between 0.19 and 0.21 day−1. The presence of the invasive copepod had an adverse effect on the smaller (< 110 µm) B. havanaensis, but not on the larger (> 180 µm) B. calyciflorus. The results are discussed with emphasis on the differences in the indirect impact invasive and native predatory copepods. [ABSTRACT FROM AUTHOR]

Short-chain chlorinated paraffins (SCCPs) are ubiquitous, persistent chemicals whose toxicity and potential impacts on aquatic ecosystems have been overlooked for many years. This study aims to determine the impact of these chemicals on rotifers. As sexual reproduction is often more sensitive to toxicants than amictic reproduction, this study focuses on endpoints describing sexual reproduction and on the impact on the gene expression of three receptors associated with reproduction: retinoid-x-receptor (rxr), retinoid activated receptor (rar) and membrane-associated progesterone receptor (mapr). Brachionus calyciflorus was exposed to environmental concentrations of SCCPs (10,100 and 1000 ng/L) and the impact on sexual reproduction (mixis rate, fertilization rate, resting egg production and viability, inter-generational effects) was assessed. Variations in the gene expressions of rxr, rar and mapr were also studied through RT-qPCR analysis. Our results show that SCCPs increase the mixis rate but decrease the fertilization rate, leading to unaltered resting egg production. Exposure to SCCPs also affected the mRNA levels of the studied receptors in ways which could be linked to observed changes in mixis and fertilization rates. [ABSTRACT FROM AUTHOR]

We quantified the population growth of the predatory heliozoan Actinosphaerium eichhornii fed separately four rotifer prey (Anuraeopsis fissa, Brachionus calyciflorus, Brachionus havanaensis and Plationus patulus) at three densities (0.5, 1 and 2 ind. ml−1 per day). All the four prey rotifer species were consumed by A. eichhornii. Regardless of the prey species, increasing rotifer prey density resulted in an increased population growth of the heliozoans. Higher cyst production in A. eichhornii occurred at higher prey densities on all prey species. A. fissa offered at the lower densities of 0.5–1.0 ind. ml−1 day−1 did not lead to cyst production by A. eichhornii. The predator did not survive beyond 2 days on Chlorella vulgaris alone. When cultured together with heliozoans, A. fissa, B. calyciflorus and B. havanaensis were eliminated within 4 days. However, the prey rotifer Plationus patulus continued to survive for about 10 days with heliozoans. The highest rate of population increase of heliozoans (0.91 day−1) was recorded when fed B. calyciflorus at a density of 2 ind. ml−1 day−1, while of those of prey varied from 0.30 to 0.41 day−1 when fed Chlorella vulgaris at 1 × 106 cells ml−1 day−1. We have analyzed the impact of heliozoan predation on rotifers. [ABSTRACT FROM AUTHOR]

Most information on rotifers living in lake sands comes from the 1930s, when the first reports on this subject by Jerzy Wiszniewski appeared. After some decline in the interest in lake psammon in the following years, research on lake psammon returned in the last decade of the twentieth century. The last comprehensive review of ecology of psammon Rotifera was included in the excellent 1998 publication by Schmid-Araya on Rotifera in interstitial sediments. More than 20 papers have been published since that time. So far, research conducted almost exclusively in the northern hemisphere have dealt with issues related to distribution of rotifers, their species structure and diversity as well as to their relation to abiotic and biotic factors. The aim of the present study was to collect all available information on psammon rotifers, assess the shortcomings in our knowledge and fill these gaps with the results of some of my recent research. The results of the study show that the species richness of this group in geographical terms is still unknown. It means we also do not know the level of endemism among the psammon rotifers. The role of psammon rotifers in benthic food webs is another issue requiring research. [ABSTRACT FROM AUTHOR]

Freshwater zooplankter Brachionus plicatilis is able to inhabit different habitats and locally adapt to their environmental conditions. It also shows a high degree of population structuring in small geographical regions. Here we try to shed light on the evolution of reproductive isolation in populations of B. plicatilis with presumptive gene flow among locally adapted populations. We have conducted laboratory experiments on admixed pairwise populations that differ in predictability of the water regime. We have assessed the potential for within-population reproductive preferences as a deviation of genotypes from Hardy–Weinberg equilibrium in diapausing eggs, a product of sexual reproduction. We expected heterozygote deficit to increase with environmental distance. We have found signs for incipient reproductive isolation in one third of our admixed populations, however no correlation with environmental distance was found, nor with genetic or geographic predictor variables. The overall inbreeding coefficient showed a tendency for within-population crosses preferences to decrease over time. [ABSTRACT FROM AUTHOR]

Predation is a well-known factor that structures rotifer communities. However, the role of protists as predators is relatively understudied. Here, we investigated predatory behavior of Actinosphaerium sp., a freshwater heliozoan, on seven rotifer species. Predators and prey were collected from a local playa; except for Brachionus calyciflorus that served as a naive prey control. Prey included large species (≥ 175 µm mean length: Asplanchna sieboldii, B. calyciflorus, Platyias quadricornis, and Lacinularia flosculosa) and small species (< 175 µm: Cephalodella gibba, Euchlanis dilatata, and Lepadella patella). Four experiments were conducted. (1) Single prey items of varying size and motility. Larger prey types were ~ 1.7 to 3.0 times more likely to be ingested than small prey. No L. flosculosa were ingested, contrary to field observations. No correlation was found between swimming speed and predation risk. (2) Preference tests. Asplanchna sieboldii and B. calyciflorus were favored prey. (3) Growth rate of Actinosphaerium on mixed diets, with and without Asplanchna. Highest population growth of Actinosphaerium was observed in presence of A. sieboldii. (4) Prey defenses. Susceptibility of spined versus unspined B. calyciflorus resulted in no significant difference in predation risk. Thus, size and being mobile (compared to sessility) are the primary risk factors influencing rotifer predation vulnerability. [ABSTRACT FROM AUTHOR]

Authors have attributed the statement "All science is either physics or stamp collecting" to the Physicist, Ernest Rutherford. Putting this sarcastic quip aside, we know that scientific disciplines come of age when they can generate testable, repeatable, and falsifiable hypotheses; yet disciplines begin, and continue, by simply collecting observational information. It is clear, even with a casual assessment of all 16 International Rotifer Symposia, as well as the extensive literature published since our first congress, that rotifer research has moved beyond describing species, making lists of their occurrences, and describing changes in their population dynamics. In spite of the excellent progress that has been made in rotiferology we believe more remains to be done. In this review we nominate 10 fields in rotifer research that we believe will advance understanding of rotiferan biology; these include the following topics: (1) neurobiological connectomes, (2) genomic architecture and control systems, (3) physiology, (4) life history, including sexuality, development, and aging, (5) ecological responses to stresses, (6) biogeography and distribution of cryptic species, (7) analysis of rotiferan morphospace, (8) rotifer evolution within Gnathifera including Acanthocephala, (9) educational opportunities for beginning students, and (10) fostering international collaboration. [ABSTRACT FROM AUTHOR]

Adaptation to different ecological niches is considered one of the main drivers of species diversification, also in cryptic species complexes, notwithstanding their morphological stasis. We here review all the published information on ecological differentiation within cryptic species complexes within the phylum Rotifera. We found 177 instances of cryptic species identified genetically, published in 101 papers. Only a subset of the papers contained available information on ecological differences and only for two of the 54 known complexes, namely Brachionus calyciflorus s.l. and Brachionus plicatilis s.l., sufficient data were available for analyses of ecological differences. For the B. calyciflorus complex, B. fernandoi consistently occurred at a significantly lower temperature than the other species in the complex; no differences were found for other environmental variables. For the B. plicatilis complex, B. paranguensis occurred in waters with higher pH than the other species; no differences were found for other environmental variables. These results, even if preliminary and based on scattered information, reveal that adaptation to different ecological niches exists also between closely related species. Our aim is to showcase this interesting field of research spurring further detailed studies to focus on the mechanisms of ecological speciation using rotifer cryptic species as a model system. [ABSTRACT FROM AUTHOR]

Zooplankton indicators based on rotifers (TSIROT) and an indicator based on Secchi disk visibility (TSISD) were used to assess trophic state changes in artificial, slow-flowing, and stagnant canal waters. The study was conducted in the summers of 2019, 2021, and 2022 in the Bydgoszcz Canal and the Noteć Canal (Poland). Water samples were taken from five sites once in the month of July and once in August. In terms of the species number and density, rotifers dominated among zooplankton (at almost all sites), which reflected the high trophic state. Our results showed statistically significant correlations between TSIROT and TSISD as well as between the individual indicators TSIROT1 (Rotifer numbers), TSIROT2 (Rotifer biomass), TSIROT3 (bacterivorous numbers of rotifers), TSIROT6 (rotifers indicating high trophic state), and TSISD. According to our study, the presented indices most likely determine the trends between TSIROT cumulative and TSISD in the studied canals. Similarly to previous studies performed on lakes and small reservoirs, zooplankton constituted a useful indicator of trophic state. It seems that, for stagnant and slowly flowing waters of canals such as the Bydgoszcz Canal and the Noteć Canal, the method of zooplankton trophic status indicators based on rotifers may be applied. [ABSTRACT FROM AUTHOR]

The basal splits within Syndermata probably date back hundreds of millions of years, and extant syndermatans greatly differ in reproduction modes (parthenogenesis, metagenesis, heterosexuality) and lifestyles (free-living, epizoic, endoparasitic). Against this background, the present investigation aims to reconstruct genome and transcriptome metrics in the last common ancestor (LCA) of Syndermata. We especially annotated nuclear genome assemblies of one representative, each, of monogononts (Brachionus plicatilis), bdelloids (Adineta vaga), seisonids (Seison nebaliae), and acanthocephalans (Pomphorhynchus laevis), S1 and additionally considered previously published data. Present results suggest that the syndermatan LCA possessed a compact nuclear genome of 50–100 Mb with a coding portion of ≥ 40%. Its ~ 17,000 protein-coding genes probably had about 4–6 exons and 3–5 introns on average. Long interspersed nuclear elements (LINEs) should have occupied 4–5% of the ancestral genome. Based on this, independent evolutionary trajectories involving gene loss, genome duplication, and repeat proliferation resulted in greatly varying genomes within the clade. Nevertheless, we identified 2114 clusters containing proteins of all four syndermatan taxa. About 200 of these clusters lacked sufficiently similar counterparts in the platyhelminths Macrostomum lignano and Schmidtea mediterranea. Gene ontologies assigned to these clusters might reference the muscular pharynx, light perception, and transposition, amongst others. [ABSTRACT FROM AUTHOR]

Microplastic pollution, especially secondary microplastics (MPs), poses a significant threat to marine ecosystems. Despite its prevalence, the impact of natural-aged MPs on marine organisms, hindered by collection challenges, remains poorly understood. This study focused on 1–3 μm natural-aged MPs collected from Japan's coastal sea, investigating their effects on the rotifer Brachionus plicatilis sensu stricto and its reproductive mechanisms. Rotifers exposed to varying MP concentrations (0, 20, and 200 particles/mL) over 14-day batch cultures exhibited reduced population growth and fertilization rates. Down-regulation of reproductive genes and up-regulation of oxidative stress-related genes were observed, indicating MP-induced disruptions. Enhanced activities of superoxide dismutase and acetylcholinesterase and elevated malondialdehyde levels further emphasized oxidative stress. These findings underscore the detrimental impact of MPs on rotifer reproductivity, shedding light on the underlying mechanisms. [ABSTRACT FROM AUTHOR]

Maternal effect plays important role in adaptive evolution and population dynamics. Methylparaben (Mep) is a common organic pollutant exerting diverse impacts on aquatic organisms. However, the impact of maternal Mep exposure on offspring remains poorly understood. This study was designed to explore whether maternal Mep exposure can affect the offspring's population performance, either by amictic mothers in parthenogenesis phase, or by mictic mothers in sexual reproduction phase of the rotifer Brachionus calyciflorus. Here, we exposed either amictic or mictic mothers from one clonal laboratory population to 20 mg/L Mep (T environment) until the offspring or resting eggs were collected. A parallel control group without Mep (C environment) was also set. Thereafter, offspring from amictic mothers or stem female from resting eggs of mictic mothers were treated similarly in T or C environment. Population growth, life history traits and antioxidant indices of the offspring were examined. The results demonstrated that maternal Mep exposure inhibited population performance of offspring in both life history phases, while the negative effects were markedly buffered in sexual reproduction phase. This study clarifies toxicity of Mep on rotifers and highlights the different response patterns of maternal Mep exposure in different life history phase. [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]

Simple Summary: Larviculture is one of the major bottlenecks in current aquaculture, where infectious diseases are responsible for populational collapses and large economic losses. Consequently, the main goal of this study was to evaluate the suitability of rearing tanks of rotifers (Brachionus plicatilis) used as the first live feed in turbot (Scophthalmus maximus, L.) larviculture as a new environmental niche for the isolation of bacterial probiotic candidates in the context of a sustainable aquaculture. Furthermore, the probiotic potential of four lactobacilli (two Lacticaseibacillus paracasei and two Lactiplantibacillus plantarum) isolated from a rotifer-rearing tank was evaluated. Aquaculture is a rapidly expanding agri-food industry that faces substantial economic losses due to infectious disease outbreaks, such as bacterial infections. These outbreaks cause disruptions and high mortalities at various stages of the rearing process, especially in the larval stages. Probiotic bacteria are emerging as promising and sustainable alternative or complementary strategies to vaccination and the use of antibiotics in aquaculture. In this study, potential probiotic candidates for larviculture were isolated from a rotifer-rearing tank used as the first live feed for turbot larvae. Two Lacticaseibacillus paracasei and two Lactiplantibacillus plantarum isolates were selected for further characterization due to their wide and strong antimicrobial activity against several ichthyopathogens, both Gram-positive and Gram-negative. An extensive in vitro safety assessment of these four isolates revealed the absence of harmful traits, such as acquired antimicrobial resistance and other virulence factors (i.e., hemolytic and gelatinase activities, bile salt deconjugation, and mucin degradation, as well as PCR detection of biogenic amine production). Moreover, Enterobacterial Repetitive Intergenic Consensus-PCR (ERIC-PCR) analyses unveiled their genetic relatedness, revealing two divergent clusters within each species. To our knowledge, this work reports for the first time the isolation and characterization of Lactic Acid Bacteria (LAB) with potential use as probiotics in aquaculture from rotifer-rearing tanks, which have the potential to optimize turbot larviculture and to introduce novel microbial management approaches for a sustainable aquaculture. [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]

Water bodies, apart from having aesthetic value, harbor a great diversity of both macro and microorganisms. Rotifers or wheel animalcules are cosmopolitan aquatic invertebrates that play a key role in aquatic food chain. Presently, two species of rotifers (Macrochaetus sericus & Lecane tenuiseta) have been recorded for the first time from Jammu. M. sericus is first record from Union territory of J&K while L. tenuiseta has already been reported from Kashmir. During the one year study period, M. sericus was observed in the plankton sample during the monsoon season while L. tenuiseta was collected from the periphytic zone during the winter season. M. sericus differed from related congeneric species by absence of anal segment and anal spines. L. tenuiseta is distinguished by its long separated claws and long toes. The first report of these two species from Jammu has further expanded their distributional ranges in the Indian subcontinent. [ABSTRACT FROM AUTHOR]

Bromate is receiving increased attention as a typical disinfection by-product in aquatic environments, but bromate toxicity tests on invertebrate such as Brachionus calyciflorus rotifer are inadequate. In the present study, the long-term toxicity tests on B. calyciflorus were performed during 21 days under the exposure of different bromate concentrations and two algal density conditions. Furthermore, we evaluated the feeding behaviors of the rotifers under the impact of bromate. The maximum population density of rotifers was significantly reduced at 100 and 200 mg/L bromate exposure at the two algal density conditions. However, we observed that the maximum population density and population growth rate of rotifers were higher at 3.0 × 106 cells/mL algal density than those at 1.0 × 106 cells/mL under the same conditions of bromate exposure. These results suggest that higher food density may have alleviated the negative effects of bromate on rotifers. Meanwhile, the ingestion rate at an algal density of 3.0 × 106 cells/mL was higher than that at 1.0 × 106 cells/mL. The present study provides a basic reference to comprehensively evaluate the toxic effects of bromate on aquatic organisms. [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]

Simple Summary: In subtropical shallow lakes, large-scale changes in water temperature lead to seasonal succession of some cryptic rotifer species, and the temporal overlap of other cryptic rotifer species is a common phenomenon. However, in tropical shallow lakes, relatively stable water temperatures throughout the year may not lead to a seasonal succession of cryptic rotifer species, but evidence is scarce. Studies on the temporal distribution patterns of the cryptic Brachionus calyciflorus species in three lakes in China revealed that in the warm-temperate Lake Yunlong, B. fernandoi and B. calyciflorus s.s. underwent a seasonal succession, which was largely attributed to their differential adaptation to water temperature. In the subtropical Lake Jinghu, B. fernandoi, B. calyciflorus s.s., and B. dorcas exhibited both seasonal succession and temporal overlap. Seasonal successions were largely attributed to their differential adaptation to temperature, and temporal overlap resulted from their differential responses to algal food concentration. In the tropical Lake Jinniu, B. calyciflorus s.s. persisted throughout the year and overlapped with B. dorcas for 5 months. The temporal overlap resulted from their differential responses to copepod predation. These results indicated that the temporal distribution pattern of the cryptic B. calyciforus species and the mechanism that allows competitor coexistence vary with different climate zones. Sympatric distribution and temporal overlap of cryptic zooplankton species pose a challenge to the framework of the niche differentiation theory and the mechanisms allowing competitor coexistence. We applied the methods of phylogenetic analysis, DNA taxonomy, and statistical analysis to study the temporal distribution patterns of the cryptic B. calyciflorus species, an excellent model, in three lakes, and to explore the putative mechanisms for their seasonal succession and temporal overlap. The results showed that in the warm-temperate Lake Yunlong, B. fernandoi and B. calyciflorus s.s. underwent a seasonal succession, which was largely attributed to their differential adaptation to water temperature. In the subtropical Lake Jinghu, B. fernandoi, B. calyciflorus s.s., and B. dorcas exhibited both seasonal succession and temporal overlap. Seasonal successions were largely attributed to their differential adaptation to temperature, and temporal overlap resulted from their differential responses to algal food concentration. In the tropical Lake Jinniu, B. calyciflorus s.s. persisted throughout the year and overlapped with B. dorcas for 5 months. The temporal overlap resulted from their differential responses to copepod predation. These results indicated that the temporal distribution pattern of the cryptic B. calyciforus species and the mechanism that allows competitor coexistence vary with different climate zones. [ABSTRACT FROM AUTHOR]

Aquaculture plays a crucial role in meeting the increasing global demand for food and protein sources. However, its expansion is followed by increasing challenges, such as infectious disease outbreaks and antibiotic misuse. The present study focuses on the genetic and functional analyses of two Lacticaseibacillus paracasei (BF3 and RT4) and two Lactiplantibacillus plantarum (BF12 and WT12) strains isolated from a rotifer cultivation tank used for turbot larviculture. Whole-genome sequencing (WGS) and bioinformatics analyses confirmed their probiotic potential, the absence of transferable antibiotic resistance genes, and the absence of virulence and pathogenicity factors. Bacteriocin mining identified a gene cluster encoding six plantaricins, suggesting their role in the antimicrobial activity exerted by these strains. In vitro cell-free protein synthesis (IV-CFPS) analyses was used to evaluate the expression of the plantaricin genes. The in vitro-synthesized class IIb (two-peptide bacteriocins) plantaricin E/F (PlnE/F) exerted antimicrobial activity against three indicator microorganisms, including the well-known ichthyopathogen Lactococcus garvieae. Furthermore, MALDI-TOF MS on colonies detected the presence of a major peptide that matches the dimeric form of plantaricins E (PlnE) and F (PlnF). This study emphasizes the importance of genome sequencing and bioinformatic analysis for evaluating aquaculture probiotic candidates. Moreover, it provides valuable insights into their genetic features and antimicrobial mechanisms, paving the way for their application as probiotics in larviculture, which is a major bottleneck in aquaculture. [ABSTRACT FROM AUTHOR]

Background: The present study explored the possibility of using live feed, as vector for supplementing the androgenic hormone in aquaculture seed production. Methods: The study consisted of five treatment doses of 17α-methyl testosterone namely; control (without hormone), T1 (20 mg L-1), T2 (40 mg L-1), T3 (60 mg L-1) and T4 (80 mg L-1) and each were triplicated. The doses were tested in the live feed of Artemia nauplii and rotifer by following completely randomized design. The Artemia nauplii (Artemia salina), collected by hatching the Artemiacyst and 5-8 days old rotifers, collected from mass culture unit of rotifer, were released in their respective treatment doses at 100 and 800 individuals/ml, respectively. Result: The study found significant difference in accumulation of hormone in the tissues of live feed at different time intervals. In Artemia, significantly higher amount of 17α-MT (15.33±0.09 mg L-1) was observed in 80 mg L-1 group at 24 h. In rotifer, significantly higher value of 17α-MT (17.42±0.06 mg L-1) was recorded in 60 mg L-1 group at 6 h. The level of 17α-MT in Artemia nauplii and rotifer started showing a decreasing trend in 24 h and 6 h, respectively. Overall the findings of the present study support that supplementation of hormone through live feed is possible as live feed accumulated 17α-MT in its tissue after enrichment which can be further explored for producing all-male population in a more sustainable way. [ABSTRACT FROM AUTHOR]

Bu çalışmada Türkiye'nin İç Batı Anadolu bölgesinde yer alan Işıklı Gölü'nün zooplankton dağılımı ve kompozisyonu 2003-2005 yılları arasında aylık olarak incelenmiştir. Zooplankton örnekleri yüzeyden Hydro-Bios plankton ağı (55 µm) ile toplanmıştır ve formaldehit (% 4) içerisine sabitlenmiştir. Yüzey suyu sıcaklığı, pH, çözünmüş oksijen ve elektriksel iletkenlik gibi bazı fizikokimyasal parametreler de ölçülmüştür. Ayrıca Işıklı Gölü'nün trofik kompozisyonunu değerlendirmek amacıyla frekans indeksi (% F) ve Brachionus / Trichocerca (QB/T) belirlenmiştir. Toplam 49 tür tespit edilmiştir. Rotifera (%55), Cladocera (%27) ve Copepoda (%18) türleri tarafından temsil edilmiştir. Maksimum tür Mayıs 2004'te (21 tür), minimum tür ise Ekim 2003'te (5 tür) bulunmuştur. Asplanchna priodonta, Keratella cochlearis, Keratella tecta, Polyarthra dolichoptera, Synchaeta pectinata, Bosmina longirostris ve Chydorus sphaericus gölde yaygın olarak görülen türlerdir. Su sıcaklığı 3,9-24,6 °C arasında; pH 8,1 ila 8,8 arasında; elektriksel iletkenlik 341 µS/cm ile 434 µS/cm arasında; çözünmüş oksijen değerleri 5,8 mg/L'den 11,1 mg/L'ye kadar değişmiştir. Sıklık indeksine (% F) göre en baskın türler B.longirostris (%74), K. cochlearis (%62), A. priodonta (%54) ve C. sphaericus (%51)'dur. Bölgeden ilk kez toplam 20 tür rapor edilmiştir. Gölde yeni bildirilen türler: rotifera, A. priodonta, Brachionus angularis, Brachionus calyciflorus, Colurella colurus, Keratella quadrata, Lecane clostrocerca, Lecane ludwigi, Lecane luna, Lecane lunaris, Lecane ohioensis, Lecane quadridentata, Lecane sp., Mytilina mucronata, Notholca acuminata, Notholca squamula, Trichotria tetractis, cladocera Acroperus harpae, Daphnia cucullata ve copepoda Eucyclops macrurus ve Megacyclops gigas. Sládeček (1983) indeksine göre Brachionus / Trichocerca (QB/T) oranı dikkate alındığında; göl mezotrofik özellik göstermiştir [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]

In the deep-water stratified Pleshcheyevo Lake, a cold-water species of rotifer belonging to the "northern invaders," Synchaeta lakowitziana, was discovered for the first time. The rotifer was recorded in the winter–spring (March–May) and late autumn (November) periods at water temperatures of 1.9–12.9°С. The morphology of the trophi of the rotifer is described. [ABSTRACT FROM AUTHOR]

Diapausing embryos of invertebrates represent investments in future populations. Thus, they must be capable of withstanding a variety of environmental assaults. Consequently, their eggshells should be adapted to resist injuries from predators, sediments, or excessive shrinkage if desiccated. To date, there have been no direct nanomechanical measurements of the eggshells of most invertebrates that produce diapausing eggs. Here, we used three approaches to understand how the eggshells of two rotifers, a freshwater species (Brachionus calyciflorus) and a brackish-water species (B. plicatilis), tolerate harsh conditions: (1) atomic force microscopy to measure elasticity and hardness; (2) transmission electron microscopy to study ultrastructure; (3) scanning electron microscopy to examine surface features. We compared these values to measurements of brine shrimp (Artemia salina) cysts and mosquito (Aedes aegypti) overwintering eggs. Our results revealed that rotifer eggshells are structurally similar and have comparable nanomechanical values. While rotifer eggshells had lower Young's moduli (ca 13–16 MPa) and hardness values (1.84–1.85 × 10−2 GPa) than eggshells of Artemia and Aedes, eggshells of all species were relatively elastic and not particularly resistant to deformation. Pliancy of shells that form egg banks (ie Artemia, Brachionus) may be an adaptation to resist cracking under the physical forces associated with burial in sediments. Although there are no obvious relationships among eggshell thickness, ultrastructure, ornamentation, or nanomechanical values in rotifer eggshells, we hypothesise that eggshell composition may play an important role in determining elasticity and hardness. Future studies should consider an integrative approach to understand the importance of eggshell structure, chemistry, and mechanics in protecting diapausing embryos. [ABSTRACT FROM AUTHOR]

In the year 2002, DNA loss model (DNA-LM) postulated that neuropeptide genes to emerged through codons loss via the repair of damaged DNA from ancestral gene namely Neuropeptide Precursor Predictive (NPP), which organization correspond two or more neuropeptides precursors evolutive related. The DNA-LM was elaborated according to amino acids homology among LWamide, APGWamide, red pigment-concentrating hormone (RPCH), adipokinetic hormones (AKHs) and in silico APGW/RPCH NPPAPGW/AKH NPP were proposed. With the above principle, it was proposed the evolution of corazonin (CRZ), gonadotropin-releasing hormone (GnRH), AKH, and AKH/CRZ (ACP), but any NPP never was considered. However, the evolutive relation via DNA-LM among these neuropeptides precursors not has been established yet. Therefore, the transcriptomes from crabs Callinectes toxotes and Callinectes arcuatus were used to characterized ACP and partial CRZ precursors, respectively. BLAST alignment with APGW/RPCH NPP and APGW/AKH NPP allow identified similar NPP in the rotifer Brachionus plicatilis and other invertebrates. Moreover, three bioinformatics algorithms and manual verification were used to purify 13,778 sequences, generating a database with 719 neuropeptide precursors. Phylogenetic trees with the DNA-LM parameters showed that some ACP, CRZ, AKH2 and two NPP share nodes with GnRH from vertebrates and some of this neuropeptide had nodes in invertebrates. Whereas the phylogenetic tree with standard parameters do not showed previous node pattern. Robinson-Foulds metric corroborates the differences among phylogenetic trees. Homology relationship showed four putative orthogroups; AKH4, CRZ, and protostomes GnRH had individual group. This is the first demonstration of NPP in species and would explain the evolution neuropeptide families by the DNA-LM. [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]

Lake Shala, endorheic Soda Lake in the Ethiopian Riftvally Lake, supports an enormous biodiversity, with a large human population and economic development. However soda lakes are under several ecological changes, with unexpected shifts in biodiversity composition and physicochemical changes. This study focuses on assessing the community structure of zooplankton in Lake Shala. Samples were taken at monthly intervals from January to December 2018. A total of 32 zooplankton species were identified, of which 23 species were Rotifers and followed by Copepoda (6) and Cladocera (3). The community was dominated by Brachionus dimidiatus, B. dimidiatus inermis, B. plicatilis and B. calyciflorus. Their abundance exhibit significant seasonal and vertical variations (ANOVA, p < 0.05). Zooplankton community structure of Lake Shala has changed over time, benthic harpacticoids (Nitocra lacustris) have become replaced by small-bodied and generalist-feeder rotifers (genus Brachionus). Such ecological shifts may be driven mainly by partial atelomixis in this deep tropical lake. Overall, zooplankton species distribution and abundance are influenced by various environmental factors such as conductivity, salinity, Chl-a and nutrients. This study concludes that the composition and community structure of zooplankton in Lake Shala has changed over time with the change in physicochemical and internal limnological dynamics (atelomix). [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]

The present work aimed to study the distribution of Cladocera and Rotifera populations in two reservoirs in western Algeria (Sidi Mhamed Benali Lake and Sarno Dam), taking into account two physical parameters: water temperature and pH in the Mediterranean climate. The abundance of zooplankton groups, specifically Cladocerans and Rotifers, exhibited an evolution closely paralleling the environmental characteristics of the ecosystem. Both populations were monthly sampled from January to July 2017 using a plankton net of 64µm mesh size. In total, 35 taxa were recorded, of which 18 species belong to the Cladocera and 17 others are members of the Rotifera. The results of this comparative study showed, on the one hand, heterogeneity in the specific richness of Cladocera and Rotifera on a spatiotemporal scale and a relationship with the physical quality of the water in the two environments on the other hand. Furthermore, Sidi Mhamed Benali Lake appeared to be more diverse and the richest in Cladocera. Overall, the highest taxon richness and abundance were recorded during the rainy season from January to April (35 species) compared with 22 taxa in the dry season. These results were confirmed and clearly demonstrated by the results of the principal component analysis (PCA). [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]

In the Anthropocene, scientists have an imperative to prioritize the sharing of scientific knowledge as a fundamental responsibility in fostering collective action. Scientific names are essential in communicating biodiversity, and to maximize their impact, they need to be consistently labeled across all organisms and made accessible to diverse audiences. In our study, we examined the etymological and temporal patterns in naming practices of rotifers and microcrustaceans (cladocerans and copepods). By analyzing a dataset comprising 992 species present in Brazil, but described worldwide since the eighteenth century, we identified various factors influencing specific epithets, including morphology, ecology, behavior, geography, and cultural references, as well as names honoring notable individuals. Our findings revealed that while morphology was the primary basis for etymology (62.1%) in naming rotifers, cladocerans, and copepods, its relative importance has decreased over time. We observed a significant increase in etymologies related to geography and the recognition of influential scientists in the field. Furthermore, our study unveiled a gender bias, with male scientists being more frequently honored with species names (86.4%). In addition to acknowledging the contributions made by taxonomists studying these groups, our study offers valuable insights intended to stimulate reflections on the significance of naming practices in biodiversity research and communication, in line with current social-ecological needs. [ABSTRACT FROM AUTHOR]

To test the hypothesis that non-consumptive predation pressures favor genotypes that have higher equilibrium densities or mictic ratios, we expose replicate populations of the rotifer Brachionus angularis to low (LK) and high (HK) concentrations of predator Asplanchna kairomones. Over 75 days (25 asexual generations) of selection, LK-treated populations have higher equilibrium densities and lower mictic ratios than the control populations. The opposite occurs for HK-treated populations. These results suggest that compared with the control, LK and HK select for genotypes with higher equilibrium densities and mictic ratios, respectively. Common garden bioassays reveal that in the absence of Asplanchna kairomones, populations with an LK selection history have a higher average intrinsic rate of population increase, and those with an HK selection history have a higher average mictic ratio than those with the control selection history, which suggest that adaptations to LK and HK increase average intrinsic rate of population increase and mictic ratio of prey populations, respectively. Increased intrinsic rate of population increase and mictic ratio can serve as strategies of offsetting mortality from predation and escaping the predator, and thus enable prey to survive low and high predation pressures, respectively. [ABSTRACT FROM AUTHOR]

Rotifer species are widely used as biomonitoring agents of water quality parameters. Therefore, assessment of rotifer diversity is very important to get current information about the status of the aquatic environment. Hence, during the study period seven new rotifer species were identified for the first time in Kumaraswamy Lake, Coimbatore district, Tamil Nadu, India, and they were described based on their morphological features by referring to standard manuals and textbooks. In addition, some hydrographical characteristics like water temperature, pH, dissolved oxygen, total dissolved solids, and electrical conductivity were analysed during the study period. [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]