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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.

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.

Under natural conditions, organisms can experience a variety of abiotic (e.g., temperature, pH) and biotic (e.g., species interactions) factors, which can interact with toxicant effects. By ignoring species interactions conventional ecotoxicological studies (i.e., single-species tests) oversimplify the actual field situation. We investigated whether temperature and interspecific competition affected the effects of zinc (Zn) on a Daphnia longispina population. The D. longispina populations were exposed in a full factorial design to 3 different Zn treatments (background, 29, and 110 μg Zn/L), 2 different temperature regimes (cold, 17-18 °C; warm, 21-22 °C), and 2 interspecific competition levels (no interspecific Brachionus competition = no Brachionus calyciflorus added; interspecific Brachionus competition = B. calyciflorus added). Interspecific Brachionus competition and temperature by itself had a limited effect on the Daphnia abundance but significantly interacted with the highest Zn concentration. Without Brachionus competition the D. longispina juvenile and adult abundances under warm conditions were up to 5.5 and 21 times lower, respectively, in the high Zn treatment in comparison with the Zn control, whereas under cold conditions no significant Zn effect was observed. However, with Brachionus competition the highest Zn treatment was on average 2.2 times less toxic to the D. longispina juvenile abundance at higher temperatures. Under cold conditions the highest Zn treatment affected the juvenile abundance sooner and up to 9 times more negatively when simultaneously faced with Brachionus competition. It is possible that the competition for food reduced the amount of energy that could be used by D. longispina for reproduction, and the metabolic costs increased as a result of Zn stress. The present study clearly illustrated the influence of temperature and competition on the effects of a chemical stressor. Thus, not considering such factors in ecological risk assessment may underestimate or overestimate risks in aquatic ecosystems when extrapolating data from standard single-species tests to the field. Environ Toxicol Chem 2018;37:1668-1678. © 2018 SETAC.

Development, ontogeny of the digestive system and the fatty-acid (FA) profile, were analysed during development of Epinephelus marginatus. Larvae were analysed 7 and 17 days post fertilization (dpf) to evaluate fatty-acid profile and morphological variables, respectively. Epinephelus marginatus larvae have relatively slow development of digestive structures, but were able to capture, ingest and digest prey by 5 dpf. Eggs were composed of high percentages of polyunsaturated fatty acids (PUFA) in phospholipids. The percentage of n3 PUFAs was higher than n6, especially docosahexaenoic acid (DHA), which exhibited higher levels compared with other marine species during the first 3 days of development, both in terms of phospholipids and triglycerides. The larvae present a high content of docosahexaenoic acid-eicosapentaenoic acid (DHA-EPA) and, during this phase, live food of small size was required (copepods or SS-strain Brachionus rotundiformes), enriched with DHA-EPA. These results may guide future studies on the contribution of FAs required during this stage of the life cycle of E. marginatus, to advance knowledge of the use of these FAs throughout ontogeny and contribute to the culture of this species commercial production or restocking.

Although DNA barcoding is a promising tool for the identification of organisms, it requires the development of a specific reference sequence library for sample application. In the present study we developed a Lake Kasumigaura, Japan, zooplankton DNA barcode library to increase the sensitivity of future zooplankton monitoring for detecting lake ecosystem condition changes. Specifically, the mitochondrial cytochrome c oxidase subunit I (mtCOI) haplotype, i.e., the primary DNA barcode, was examined for each zooplankton taxon. In crustaceans, 37 mtCOI haplotypes were obtained from 99 individuals, representing four and 15 morpho-species of Copepoda and Cladocera, respectively. Comparing these sequences with those in GenBank shows that the lake harbors putative non-indigenous species, such as Daphnia ambigua. In rotifers, 132 mtCOI haplotypes were obtained from 302 individuals, representing 11 genera and one unclassified taxon. The automatic barcode gap discovery (ABGD) algorithm separated these haplotypes into 43 species. Brachionus cf. calyciflorus was divided into five ABGD species, and different ABGD species tended to occur in different seasons. Seasonal ABGD-species succession was also observed within Polyarthra spp. and Synchaeta spp. These seasonal successions were not detected by inspections of external morphology alone. Accepting up to 7% sequence divergence within the same species, mtCOI reference sequences were available in GenBank for three, 13, and 17 species in Copepoda, Cladocera, and Rotifera, respectively. The present results, therefore, reveal the serious shortage of mtCOI reference sequences for rotifers, and underscore the urgency of developing rotifer mtCOI barcode libraries on a global scale.

The adaptive response of organisms to unpredictable environments is increasingly recognized as a central topic in fundamental and applied evolutionary ecology. Selection due to environmental unpredictability can act on multiple traits of an organism's life cycle to reduce the impact of high environmental variance. The aim of this research was to study how unpredictability selects for diapause traits: 1) the timing of sex (a proxy of the timing of diapausing egg production), and 2) the diapausing egg hatching fraction (a proxy of diapause duration). We used an experimental evolution approach with the facultative sexual rotifer Brachionus plicatilis. Laboratory populations experiencing two contrasting regimes of environmental fluctuation (predictable versus unpredictable) evolved divergently over a short time span (< 77 days). The populations under the unpredictable regime showed an earlier initiation of sexual reproduction and a lower hatching fraction of diapausing eggs than populations under the predictable regime. These findings demonstrate empirically the existence of bet-hedging strategies in B. plicatilis regarding both traits, consistent with theoretical predictions of bet-hedging evolution under conditions of unpredictable environmental variance. Given that scenarios of increased environmental variability are expected to occur in the near future, a comprehensive understanding of the role of bet-hedging strategies is necessary for predicting population responses to environmental change.

The univariate effects of Ca, pH, and dissolved organic carbon (DOC) on chronic (48-h) Pb toxicity to the freshwater rotifer Brachionus calyciflorus were investigated. High pH (8.2) and higher concentrations of DOC were protective against filtered Pb toxicity, whereas Ca was not. However, expressed as the free Pb2+ ion, Pb2+ toxicity increased with increasing DOC concentration, indicating that Pb-fulvic acid (FA) complexes may be bioavailable and may contribute to toxicity. Two different bioavailability models were developed. The pH effect was modeled as a single-site competition effect by H+ (log KHBL = 7.14). In the first model, only this H+ effect was considered; in a second model, a log-linear fulvic acid bioavailability effect (SFA = 0.602) was also incorporated. Both models predicted chronic Pb toxicity for most waters used for model development within a 2-fold error. To validate the predictive capacities of the models, chronic Pb toxicity to B. calyciflorus was tested in 5 natural waters and a reference water. Both models consistently underestimated Pb toxicity in the natural waters, as a result of a shift in rotifer sensitivity to Pb between the development and the validation test series. However, optimizing the intrinsic sensitivity in the models specific for the validation test series resulted in reasonable predictions of Pb toxicity in the natural waters. The second, more complex model predicted chronic Pb toxicity most accurately. The protective effects of water chemistry on Pb toxicity to Brachionus are comparable to those observed for Ceriodaphnia. However, the developed Brachionus models were not able to accurately predict chronic Pb toxicity to the rotifer Philodina rapida. It remains unclear why the influence of water chemistry on chronic Pb toxicity appears to be different between 2 rotifer species. Environ Toxicol Chem 2016;35:2977-2986. © 2016 SETAC.

Seahorses are ambush predators that swallow the prey through their tubular snout. In order to better understand mouth growth and its effect on prey preference by juveniles of the seahorse Hippocampus guttulatus, experimental assays were carried out by feeding juveniles (0–30 – d after male's pouch release [dar]) on a mixture of rotifers, Brachionus plicatilis; Artemia nauplii; and copepods; Acartia tonsa. Mouth development in juveniles was accomplished by growth of upper and lower jaws, which were linearly correlated with juvenile length, whereas mouth width (MW) and height (MH) grew exponentially with juvenile size. Additionally, MW and MH were exponentially correlated, so that the transversal section of the mouth increased linearly with juvenile age and length. Gut content and Ivlev' selectivity index demonstrated a permanent rejection of rotifers for the whole experimental period and a clear preference of juveniles for copepods from 0 to 15 dar and for Artemia nauplii afterwards. Results also suggest that juveniles are able to ingest larger prey than those provided as the limiting factor in prey ingestion was not MW, as for many marine fish larvae, but mouth area. A tentative feeding schedule to successfully feed H. guttulatus juveniles from 0 to 30 dar is proposed.

Zooplankton inhabiting deep, oligotrophic, tropical lakes must cope with scenarios where the combination of resource limitation, high visual-predation risk, UV-induced damage and seasonal development of anoxic waters, entail particular challenges for organisms, uncommon in temperate environments. We assessed the diel vertical migration—DVM—(UV/predation-avoidance strategy), numerical response, and starvation resistance (physiological strategies to cope with food scarcity) of the copepod Leptodiaptomus garciai and the rotifers Hexarthra jenkinae and Brachionus sp. “Mexico,” which constitute the zooplankton assemblage of Alchichica, a high-altitude, deep, oligotrophic, hyposaline, warm-monomictic lake located in Mexico. L. garciai followed the normal pattern of DVM in all seasons; with organisms concentrated ≈ 20 m deeper than the depth of 1% photosynthetically active radiation at mid-day, with evasion from the planktivore Poblana alchichica as the most probable driver. However, copepods could not evade the euphotic zone owing to the anoxic conditions of the hypolimnion during the well-established stratification period. Rotifers did not migrate vertically. The dominance of copepods throughout the year can be explained by their low food threshold, high proportion of usable reserves and the lowest rate of mass loss at food deprivation. Contrastingly, rotifers are scarce and intermittent due to frequent resource limitation and because they lose mass at higher rates. However, they are able to suddenly increase due to their high growth rates. We demonstrated that the interaction between environmental constraints and the specific combinations of traits can explain zooplankton structure in the lake. This study enlightens the necessity to improve current limnological models with data from tropical lakes.

In this study, we explain the environmental variables that mainly influence the seasonal pattern of rotifer communities in shallow wetlands (Upo Wetlands, South Korea). Long-term data (n = 197, 2006–2013) were used to analyze the patterns by means of a self-organizing map (SOM), which extracts information through competitive and adaptive properties. A total of 32 variables (24 groups of rotifers and 8 environmental variables) were patterned onto the SOM, and then each variable was compared in accordance with four seasonal patterns. Three clusters were categorized according to the Euclidian distance between the clusters on the SOM, and these were interpreted in relation to seasonal features. Using the SOM, the rotifer groups were clearly distinguished by water temperature and rainfall. In particular, pelagic rotifer groups (Brachionus, Keratella, and Polyarthra) were less abundant when high rainfall occurred, but epiphytic rotifers (Lepadella, Leacne, and Monostyla) were strongly associated with high rainfall. Moreover, strong rainfall occurring on several consecutive days increased the rotifer abundance on macrophytes. The SOM results depicted a clear pattern of rotifer density clusters partitioned by rainfall, which determined the seasonal distribution of rotifer groups in a shallow wetland.

Although triphenyltin (TPT) compounds are ubiquitous pollutants in urbanised coastal environments in Asian regions, their toxicities to marine organisms are still poorly known. This study was designed to investigate the toxicity of triphenyltin chloride (TPTCl) on the rotifer Brachionus koreanus across different levels of biological organisation. Firstly, we concurrently performed a 24 h static-acute toxicity test and a 6-day semi-static multigenerational life-cycle test using the rotifer. Our results demonstrated that the 24-h median lethal concentration of TPTCl for the rotifer was 29.6 μg/L and the 6-day median effect concentration, based on the population growth inhibition, was 3.31 μg/L. Secondly, we examined the expression of 12 heat shock protein (hsp) genes, four glutathione S-transferase (GST) genes, one retinoid X receptor (RXR) gene and 13 cytochrome P450 (CYP) genes in the rotifers after exposure to 20 µg/L TPTCl for 24 h. Among these studied genes, hsp90α2, GST-O and CYP3045C1 were the most significantly up-regulated genes with a relative expression level up to 32.9, 4.4 and 62.6 folds, respectively. The expression of these three genes in the rotifers showed an increasing trend in the first few hours of TPTCl exposure, peaked at 3 h (hsp90α2 and GST-O) and 12 h (CYP3045C1) respectively, and then gradually returned to a lower level at 24 h. Such up-regulations of hsp and GST genes probably offer cellular protection against the TPT-mediated oxidative stress while the accelerated induction of CYP genes possibly facilitates the detoxification of this toxicant in the rotifer.

Rotifers, in nature, are consumed by several vertebrates and invertebrates. In response to predation, they show a certain degree of plasticity in their life history traits. In this regard, there is an ample database of information on the effect of Asplanchna on brachionids; much less is known on the effect of other common freshwater predators. We studied the chemical effects of four invertebrate predators, Stenostomum leucops (Turbellaria), Asplanchna girodi (Rotifera), Eosphora najas (Rotifera) and Mesocyclops pehpeiensis (Copepoda) on the demography of Brachionus havanaensis. Population growth and life table demography experiments were conducted in 50 mL vessels with 25 mL of moderately hard water and 0.5 × 106 cells mL−1 of Chlorella vulgaris as food. Two predators of each phylum were introduced into small meshes with 50 µm mesh and fed 15 individuals of another rotifer species Plationus patulus. Each experiment was set up with two controls, with and without the prey (P. patulus) in meshes, as in all the other treatments. We started the experiments with 15 individuals of B. havanaensis in the population growth experiments and 15 neonates (

We investigated the influence of light on phototactic behavior and reproduction in two species of rotifer from the Brachionus plicatilis species complex (B. plicatilis sensu stricto (s. s.) and Brachionus manjavacas). This was done to understand how light effects these species so that we might use this knowledge to establish a more efficient aquaculture protocol. We used four different light wavelengths (white, with peaks at 460 and 570 nm; blue at 470 nm; green at 525 nm; and red at 660 nm) and four intensities (i.e., 0.5–30.0 W/m2). Using micro-spectrophotometry we determined that eyespots of these two Brachionus species absorbed blue and green light 5.5 times more than red light. B. plicatilis s. s. showed positive phototaxis under white, blue, and green light at lower light intensities, but no phototaxis under red light at all intensities (0.5, 6.2, 15.0, and 30.0 W/m2). Similar patterns of phototaxis were observed in B. manjavacas and did not differ among mictic, amictic females, and male rotifers. Population growth rate of B. plicatilis s. s. under dark condition was 1.1–1.2 times higher than that under white light condition. No significant differences were observed in population growth rate at 3.8 and 6.2 W/m2 at all light wavelengths. On the other hand, population growth rates at 0.5 and 1.6 W/m2 were the lowest under blue light. According to these results, both wavelength and intensity of light affect the population growth of rotifers, which in turn may be influenced by the rotifers' wavelength-dependent phototaxis.

We investigated the effects of fortifying a diet of Chlorella vulgaris with Selenium (Se) on sexual and asexual reproduction of rotifers in the Brachionus plicatilis species complex: i.e. two strains of B. plicatilis sensu stricto and one of Brachionus rotundiformis. These rotifers were cultured for 8–10 days on one of three different diets that were adjusted to provide the same dry weight of food: non-fortified Chlorella, Se-fortified Chlorella, and Nannochloropsis oculata. B. plicatilis (Makishima strain), which is obligatorily asexual, showed no difference in population growth rate among the three different diets (r = 0.55–0.61). On the other hand, B. plicatilis (NH17L strain), which reproduces by cyclical parthenogenesis, showed higher population growth (r = 0.25) and also higher rates of fertilization (35.9%) and absolute resting egg production (2803.9 eggs/g food) with the Se-fortified Chlorella diet than with other foods. Although B. rotundiformis (Kochi strain), which also exhibits cyclical parthenogenesis, showed no differences in population growth among the three different diets (r = 0.42–0.48), sexual reproduction parameters were different depending on the feeding regime. The highest mixis (26.2%), fertilization (72.6%), and resting egg production (3489.9 eggs/g food) were observed with the Se-fortified Chlorella diet. We posit that the effect of Se-fortified diet was greater on the resting egg production by enhancing male fertility than on population growth.

Here we report one of the first investigations of evolvability of lifespan and reproduction in metazoans, examining both extrinsic and intrinsic factors. We tested effects on senescence of an environmental variable (simulated lake hydroperiod, the length of time an aquatic habitat is inundated), female reproductive physiology (asexual females that reproduce by ameiosis, versus sexual females reproducing by meiosis), and time in a benign culture environment (minimal, if any, external mortality factors). To do this we established chemostat cultures of the rotifer Brachionus plicatilis s.s., and maintained the cultures for 385 d. Hydroperiod alone or in interaction with the effects of time in the benign environment (season) or reproductive physiology had no significant effect on the net reproductive rate, generation time, or rate of aging. Yet combining animals from both ephemeral and permanent hydroperiods revealed a 26% increase in asexual female lifespan across seasons (23% decrease in the rate of aging) and a 56% increase in asexual fecundity, suggesting that maintenance in benign laboratory conditions leads to slower aging. The relative stasis of traits for sexual females implies an impact of reproductive physiology on evolvability. In addition we found a positive correlation between fecundity and lifespan, suggesting an absence of trade-offs in life history traits in the benign laboratory environment.

Summary 1. Toxic compounds produced by many phytoplankton taxa are known to have negative effects on competitors (allelopathy), anti-predatory effects on grazers (mortality or impaired reproduction) or both. Although mixotrophs of the genus Ochromonas are known to be toxic to zooplankton, it has often been assumed in studies of plankton community processes that all flagellates in the size range of this taxon are edible to typical zooplankton grazers (i.e. cells ≤30 μm for Daphnia, ≤6 μm for rotifers). 2. We explored the toxicity of a species of Ochromonas to other planktonic taxa, including its competitors (two species of phytoplankton and protists) and consumers (two species of zooplankton). To test if mode of nutrition by this mixotroph influences its toxicity to other taxa, we exposed each test species to Ochromonas cultured in chemostats under four different nutritional regimes: osmotrophy (labile dissolved organic carbon) and phagotrophy (bacterial prey) in both light and dark conditions (i.e. with or without photosynthesis). 3. Filtrate from osmotrophically fed Ochromonas had a significant negative effect on the population growth rate of two obligate phototrophic phytoplankton, Cryptomonasozolini and Chlamydomonas reinhardtii. The protists Tetrahymena tetrahymena and Paramecium aurelia were also negatively affected by Ochromonas filtrate. Ochromonas cells were toxic to both the rotifer Brachionus calicyflorus and the cladoceran Daphnia pulicaria, with the toxic effects significantly more severe when fed at high cell densities (75 000 cells mL−1) than at low densities (7500 cells mL−1). Ochromonas cultured osmotrophically in the light was more toxic to the Daphnia than cells cultured under other conditions. In contrast, Ochromonas from all nutritional conditions was equally highly toxic to Brachionus. 4. Our findings support the view that Ochromonas can be toxic to other components of the food web with which it interacts. It is especially toxic to zooplankton that directly consume it, although the effect depends upon Ochromonas cell density and whether or not a good food source is simultaneously present. Our results call into question the common practice of pooling flagellates into a single ‘functional group’ included in an ‘edible phytoplankton’ category of cells

Classical models of prey-predator interactions assume that per capita prey consumption is dependent on prey density alone and that prey consumption (functional response) and consumer proliferation (numerical response) operate on the same timescales and without time lags. Several modifications have been proposed for resolving this timescale discrepancy, including variants where the functional response depends on both prey and predator densities. A microcosm system with the rotifer Brachionus 'Nevada' feeding on the prasinophyte Tetraselmis sp. showed significant (P0.0005) increases in steady-state biomasses of both prey and predators with increasing carrying capacity (represented by total phosphorus of the growth medium), which is inconsistent with predictions based on the traditional prey-only-dependent functional response. We provide data indicating that surfaces where the predator can attach provide a high-quality habitat for rotifers, which can result in a predator-dependent functional response. We also show that partitioning between the attached and free-swimming habitats was fast compared to the timescale of the numerical response. When attached to surfaces, rotifers maximized net energy gain by avoiding the high cost of swimming and by increased food capture due to reduced viscous drag. A mathematical model with prey-dependent functional response and wall-attached and free-swimming fractions of the population describes our data adequately. We discuss the implications of this finding for extrapolating microcosm experiments to systems with other surface-to-volume ratios, and to what extent our findings may apply to other popular model organisms for prey-predator interaction.

Nannochloropsis oculata and Chlorella sp. were cultivated in industrial scale bioreactors 300 L, under full sunlight and artificial light during night-time at various temperatures. The most abundant fatty acids were C18:3n-3 and C16:0 in Chlorella sp., whereas in N. oculata C16:0, eicosapentaenoic acid (EPA) and C16:1n-9 were predominant. Brachionus plicatilis cultivated in 2,500-L tanks on N. oculata, Chlorella sp. and Saccharomyces cerevisiae, was able to de novo synthesize as well as to elongate and desaturate pre-existing fatty acids in the feed. When fed with S. cerevisiae, B. plicatilis synthesized lipids containing EPA and docosahexaenoic acid (DHA), despite the fact that these fatty acids were absent in yeast lipids. Brachionus fed with Nannochloropsis synthesized DHA in non-negligible quantities. Brachionus enriched with various commercial preparations incorporated into its lipids substrate fatty acids but also synthesized new fatty acids such as C16:1n-9, C18:1n-9, C18:2n-6, EPA and DHA. Neutral lipid was the main lipid fraction while phospholipids predominated over glycolipids plus sphingolipids. The major amounts of EPA and DHA were observed in neutral lipids, noteworthy quantities of these fatty acids were also incorporated into body phospholipids. Interestingly, the high n-3 fatty acids content of rotifer lipids was retained even after the rotifers were grown in low n-3 fatty acid media.

Two trials were conducted to evaluate two gram-negative bacterial control strategies in batch cultures of the rotifer Brachionus plicatilis. In the first trial, rotifers at an initial density of 47/mL were cultured for 5 d and dosed with a 10-mg/L solution of either oxytetracycline or a commercial probiotic consisting principally of Bacillus and Lactobacillus. In the second trial, rotifers at an initial density of 140/mL were cultured for 4 d and dosed with 20-mg/L solutions of oxytetracycline or the probiotic. Rotifer density, egg counts, and egg : female ratios were determined daily. At the termination of trial 1 and on days 0, 2, and 4 of trial 2, counts of bacterial colonies were conducted to estimate bacterial loads in the rotifer culture water. Oxytetracycline was an effective antimicrobial and enhanced rotifer production in the higher-density culture but had only a marginal effect on production in the lower-density culture. Conversely, inoculation of the low-density culture with the probio...

Spatio-temporal patterns and processes of genetic differentiation in passively dispersingzooplankton are drawing much attention from both ecologists and evolutionarybiologists. Two opposite phylogeographical scenarios have already been demonstratedin rotifers, which consist of high levels of genetic differentiation among populationseven on small geographical scales on the one hand and the traditionally knowncosmopolitanism that is associated with high levels of gene flow and long-distancedispersal via diapausing stages on the other hand. Here, we analysed the populationgenetic structure and the phylogeography of the Brachionus calyciflorus species complexin eastern China. By screening a total of 318 individuals from ten locations along a 2320-km gradient and analysing samples from two growing seasons, we aimed at focusing onboth small- and large-scale patterns. We identified eight cryptic species and verifiedspecies status of two of these by sexual reproduction tests. Samples in summer andwinter yielded different cryptic species. The distribution patterns of these geneticallydistinct cryptic species were diverse across eastern China, from full cosmopolitanism tolocal endemism. The two most abundant cryptic species BcWIII and BcSW showed apattern of strong genetic differentiation among populations and no significant isolationby distance. Long-distance colonization, secondary contact and recent range expansionare probably responsible for the indistinct pattern of isolation by distance. Our resultssuggest that geographical distance is more important than temporal segregation acrossseasons in explaining population differentiation and the occurrence of cryptic species.We explain the current phylogeographical structure in the B. calyciflorus speciescomplex by a combination of recent population expansion, restricted gene flow, priorityeffects and long-distance colonization.Keywords: Brachionus calyciflorus, cryptic species, phylogeography, rotifer, spatio-temporal pat-tern, species complexReceived 9 February 2010; revision received 2 May 2011; accepted 3 May 2011

Eggs of a single spawning batch from wild-caught Norwegian Atlantic cod Gadus morhua were hatched and first fed on either natural zooplankton or enriched rotifers Brachionus plicatilis during the larval period. Juvenile G. morhua (initial mass 14·2 g) from the two first-feeding groups were then reared for 3 months under a variety of temperature (10 and 14° C) and salinity (15 and 32) combinations. All fish were individually tagged and microsatellite markers were used in a multiplex to trace the pedigree of all fish and body mass variation analysed according to different environmental and genetic sources. After the termination of the laboratory trial, the fish were transferred to land-based tanks and later to sea pens and reared at ambient conditions for 26 months until they were harvested in March 2009. Growth gain from the larval and juvenile periods was persistent during the 26 months of sea pen ongrowing. The final mass of the zooplankton group was 12% higher compared to the B. plicatilis group. Similarly, rearing under a temperature of 14° C and salinity of 15 during the initial 3 month period during the early juvenile stage resulted in 7-13% larger size at harvesting compared to the other three temperature and salinity combinations. The study indicates that the first-feeding method and temperature and salinity manipulation explain nearly 90% of the body mass variation explained by the model. The genetic effect (measured as body mass variation within the families studied) only accounted for c. 2% during the initial rearing period, whereas it has a large effect on growth variation (30%) during the long-term rearing at ambient conditions. Sex proportion and final maturation did not differ between family groups, and no interaction between sex and family group was seen.

Intrinsic rates of population increase (r) were evaluated as a measure of population dynamics of four strains of Brachionusplicatilis and two strains of B. urceolaris from Iran in response to different salinities and feeding algae. Each rotifer strain was cultured at four salinities: 5, 20, 25 and 30‰ and fed with two microalgal species: Chlorella vulgaris and Nannochloropsis oculata. Salinity of 5‰ was critical for all the examined strains, at which r was at minimum and was different from the other salinities (P < 0.05). For B. plicatilis strains, the maximum r was observed in those fed on Chlorella at salinities of 10 and 30‰ (64 ± 0.01 day−1). While, in B. urceolaris, maximum r was for Nannochloropsis fed rotifers at salinity of 20‰ (0.69 ± 0.01 day−1). Maximum final population density (FD) was obtained for a strain of B. urceolaris fed on Nannochloropsis at 20‰ (329.3 ± 10.9 ind.mL−1). FD was relatively lower in B. plicatilis strains among all examined salinities. ANOVA showed the significant effect of salinity and rotifer strain, and algae × rotifer strain on both r and FD, and salinity × rotifer × algae on FD (P < 0.05). (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Nutritional enrichment for rotifer is necessary for the stable production in larviculture. Although manufacturers recommend feeding amount for enrichment diets, the effects of these recommended amounts on nutritional enrichment of rotifer are unknown. We assessed the effects of normal and overdose amount of enrichment diets on nutritional enrichment of rotifer using batch and continuous culture methods. Rotifer populations in two culture systems were enriched using four enrichment conditions, matched two diet levels, and two enrichment durations: 0.25 g/L for 8 h (normal enrichment) 0.25 g/L for 24 h (longer enrichment), 0.75 g/L for 8 h (overdose enrichment), and 0.75 g/L for 24 h (overdose + longer enrichment). When the batch-cultured rotifer populations were enriched, longer and overdose enrichments could not make the fatty acid contents differ from the normal one. Overdose enrichment was most effective of all enrichment conditions when continuous-cultured rotifer populations were used. In both culture methods, the docosahexaenoic acid (DHA) content under overdose + longer enrichment conditions was two to three times as high as normal enrichment conditions and it resulted in two- to threefold increase in DHA/eicosapentaenoic acid ratio by overdose + longer enrichment. Accordingly, it is possible to alter the fatty acid composition of rotifer by changing the enrichment method.

Summary 1. Life-table experiments with Brachionus calyciflorus test several hypotheses related to the idea that sexual reproduction in monogonont rotifers should occur when food resources are favourable. 2. The food concentration necessary for a fertilised mictic female to produce one phenotypically normal resting egg was higher than that for an amictic female to produce one daughter. At the lowest concentration of Cryptomonas erosa (1.25 × 103 cells mL−1), the lifetime fecundity of these two types of females was 0.9 and 1.4, respectively. 3. The lifetime fecundity of both fertilised mictic females and amictic females increased with food concentration to 3.4 resting eggs and 15.2 daughters female−1, respectively. The approach to maximal fecundity with increasing food concentration was more rapid for fertilised mictic females, such that their lifetime fecundity relative to that of amictic females gradually decreased from 0.64 (at 1.25 × 103 C. erosa mL−1) to 0.22 (at 2.5 × 104 C. erosa mL−1). 4. The probability of a fertilised mictic female producing one or more abnormal resting eggs during her lifetime was high (approximately 75%). The mean proportion of abnormal eggs produced per female varied among the different food-concentration treatments (26–38%) but was not higher at the low food concentrations. 5. The proportion of normal resting eggs that hatched was high (51–71%); those produced at low food concentrations were no less likely to hatch than those produced at high food concentrations. No abnormal resting eggs hatched. 6. The probability of a fertilised mictic female producing an abnormal resting egg increased rapidly with her age at all food concentrations. The probability of a normal resting egg hatching declined with maternal age at the low food concentration in one of two experiments. 7. The results support the idea that induction of mictic females should occur when food resources are good. Coincidence of sexual reproduction with low food availability risks low production of resting eggs for several reasons. Population size may be small, with a low probability of encounters between young mictic females and males, and fertilised mictic females may be unable to mature and produce resting eggs.

Summary 1 Extension of life span by food shortage, often mimicked by calorie restriction (CR) in the laboratory, is one of the most common life-history alterations in eukaryotes. Although the life-history of offspring often changes in response to the parental environment, it has remained ambiguous whether or not CR-induced longevity is transmitted to the next generation. 2 Here, we investigated the effects of CR on life span, oxidative stress resistance and the expression levels of two antioxidant enzymes, catalase and manganese superoxide dismutase (Mn SOD), in the parthenogenetic rotifer Brachionus plicatilis during two consecutive generations. 3 Rotifers under CR lived 50% longer than those fed ad libitum (AL) in association with enhancement of oxidative stress resistance and increased mRNA levels of catalase and Mn SOD. 4 The daughters from the CR-treated mothers lived 20% longer than those from the mothers fed AL regardless of food-rich and CR conditions for the daughter. Furthermore, the daughters from the CR-treated mothers were endowed at birth with a higher ability to resist oxidative stress and the increased mRNA levels for catalase, but not for Mn SOD. In agreement with the mRNA expression patterns, CR increased the protein levels of catalase and Mn SOD in eggs and the whole body of mothers, respectively. 5 Our results for these asexually reproducing rotifers provide the first evidence that the longevity and oxidative stress resistance resulting from CR can be passed on to subsequent generations.

The seasonal variations in biomass, abundance, and species composition of plankton in relation to hydrography were studied in saline lake Namuka Co, northern Tibet, China. The sampling was carried out at approximately monthly intervals from June 2001 to July 2002. The salinity ranged from 5.5 to 26 g/L. The mean annual air and water temperature showed a clear seasonal pattern, which was approximately 4.4 and 7.4°C, respectively, with the lowest water temperature in winter (from December to March, -1°C) and the highest in June and July (18°C). The results showed that 36 taxa of phytoplankton and 16 taxa of zooplankton were identified. Both the biomass and abundance of total phytoplankton were lower in the winter and peaked once or twice during the summer and spring in the early August (8.23 mg/L and 158.2 x 10 6 ind./L). The seasonal variation in total zooplankton biomass and abundance was characterized by lower values in both winter and early spring, and one maximum (90.5 mg/L and 935 ind. L -1 ) occurred in the late summer. Major phytoplankton species were Gloeothece linearis, Oscillatoria tenuis, Gloeocapsa punctata, Ctenocladus circinnatus, Ulothrix sp., and Spirogyra sp. And major zooplankton species included Vorticella campanula, Brachionus plicatilis, Daphniopsis tibetana, Cletocamptus dertersi, Arctodiaptomus stewartianus. The production of D. tibetana was 420.3 g m 3 a -1 . The total number of plankton species has a significant negative correlation with the salinity.

Kreitzer JD, Belk MC, Gonzalez DB, Tuckfield RC, Shiozawa DK, Rasmussen JE. Ontogenetic diet shift in the June sucker Chasmistes liorus (Cypriniformes, Catostomidae) in the early juvenile stage. Ecology of Freshwater Fish 2010: 19: 433–438. © 2010 John Wiley & Sons A/S Abstract – Ontogenetic diet shifts are common in fishes and often occur during early life stages. The larval and early juvenile period is critical in the life cycle of the endangered June sucker, Chasmistes liorus (Teleostei: Catostomidae). High larval and juvenile mortality leads to low recruitment to the breeding population and hence a declining natural population. To understand diet composition and dynamics in June sucker at early life stages, diet was quantified and compared to available food items in the natural environment during the early juvenile stage. Rotifers (Brachionus sp.) were the primary diet item at week 10, but by week 12 a small cyclopoid copepod (Microcyclops rubellus) became predominant. Availability of diet items varied little across the experimental period. The increase in size of young suckers may explain this rapid dietary shift, but there are some inconsistencies with the size selection argument. This diet shift represents an important nutritional change that should be considered in development of diets for young June sucker and in assessing suitability of nursery habitats.

The zooplankton in the littoral and open water zones of Bahir Dar Gulf, Lake Tana, collected in June and July 2007, were investigated using basic statistical measurement of diversity indices and one way analysis of variance to characterize the zooplankton fauna, with respect to its composition, abundance and spatial distribution patterns. The zooplankton composition was typical of a tropical freshwater lake, with a total of 44 species made up of sixteen rotifers, sixteen c1adocerans and twelve copepods and their developing stages in the following order of dominance; Rotifera > Cladocera > Cylopoida > Calanoida. Variation in spatial distribution was noticeable, the abundance of zooplankton was significantly higher (P < 0.05) at the littoral zone (Stations 2 and 3) than the open water (Station 1) as a result of the preponderance of the small-bodied nauplii stages, small rotifers and c1adocerans particularly Bosmina longirostris. Species richness, evenness, and diversity also increased as abundance increased in the littoral zones of the lake. The rotifers, particularly the brachionids Keratella and Brachionus spp., which are considered good indicators of lake trophic status constituted the dominant zooplankton group in terms of abundance and diversity, thus indicating that the lake has a high fisheries potential.

We investigated the nutritional effects of both food quantity and quality on Brachionus plicatilis. Decomposition of particulate and dissolved organic matter by rotifer digestive enzymes play a crucial role in rotifer nutrition. Among other enzymes, rotifers produce phosphatases, non-specific enzymes that allow for the release of orthophosphate from a variety of organic phosphorus compounds. Phosphatase saturation was measured in B. plicatilis homogenates using the spectrofluorimetric method. We examined population growth rate, reproduction and phosphatase activity in the homogenate of rotifers (PARH) fed by nutrient-replete algal food supplied at different quantities. Population growth rate, number of eggs per individual and PARH were affected by food quantity. Growth rate and number of eggs per individual significantly increased in rotifers fed by food supplied at the highest quantity. The highest population growth rate was reached by rotifers fed by nutrient-replete food, while it did not significantly differ between rotifers fed on nitrogen (N)-depleted and phosphorus (P)-depleted food. The number of eggs per individual was more affected by N than P supply. PARH and rotifer RNA content were not influenced by different food quality. The results indicate that B. plicatilis is not able to regulate its digestive apparatus in terms of efficiently getting access to essential nutrients when scarce, but do this when nutrient-replete food is available in different quantity. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Cyclical parthenogens, which combine asexual and sexual reproduction, are good models for research into the ecological and population processes affecting the evolutionary maintenance of sex. Sex in cyclically parthenogenetic rotifers is necessary for diapausing egg production, which is essential to survive adverse conditions between planktonic growing seasons. However, within a planktonic season sexual reproduction prevents clonal proliferation. Hence, clones with a low propensity for sex should be selected, becoming dominant in the population as the growing season progresses. In this context, we studied the dynamics of the heritable variation in propensity for sexual reproduction among clones of a Brachionus plicatilis rotifer population in a temporary Mediterranean pond during the period the species occurred in plankton. Clonal isolates displayed high heritable variation in their propensity for sex. Moreover, the frequency of clones with low propensity for sex increased during the growing season, which supports the hypothesized short-term selection for low investment in sex within a growing season. These results demonstrate (1) the inherent instability of the cyclical parthenogenetic life cycle, (2) the cost of sexual reproduction in cyclical parthenogens where sex produces diapausing eggs and (3) the role of the association between sexual reproduction and diapause in maintaining sex in these cyclical parthenogens.

Water and quantitative zooplankton samples were collected at approximately monthly intervals from June 2000 to June 2002 in the middle section of the Po River (Northern Italy). Highly variable hydrological conditions were observed in the 2 years, with river flow varying approximately between 400 and 9300 m3 s−1. Dissolved inorganic nitrogen (DIN) usually decreased at higher river discharges. Autotrophic production was limited by phosphorus availability during the growing period (May–October); no significant adverse effect of zooplankton grazing upon algal biomass was detected. A total of 161 zooplankton taxa were found. The records of the rotifers Lecane incospicua, L. cornuta, Proales sigmoidea, Cephalodella limosa, and of the cladoceran Phrixura leei were new for Italy. Rotifers strikingly were the most abundant group over the entire sampling period. Zooplankton abundance was positively correlated to water temperature and chlorophyll-a concentration, and only in warmer months inversely correlated to river flow. Species of the genus Brachionus were responsible for the two density peaks (>1000 ind L−1) of the rotifer taxocoenosis observed in July 2000 and August 2001, coinciding with chlorophyll-a peaks higher than 50 µg L−1 and minima of Shannon equitability index. Water temperature, chlorophyll-a, and soluble reactive phosphorus (SRP) were found to be the most important variables in explaining the observed rotifer assemblages by Canonical Correspondence Analysis. A simple descriptive model is proposed to represent the combined influence of abiotic constraints and biotic interactions on the zooplankton abundance and diversity in the middle reach of the Po River. Copyright © 2008 John Wiley & Sons, Ltd.

The transition from asexual to sexual reproduction in rotifers of the genus Brachionus (Monogononta) is triggered by a chemical signal produced and released by the rotifers themselves; the signal accumulates in the environment as population density increases. The response to this signal has been hypothesized to be speciesspecific. If not, the timing of sex and final diapausing egg production of a species might not be optimized. In this study, a set of experiments—based on individual and mass culture approaches—was carried out to investigate the differentiation in sex induction signals between sympatric and allopatric congeneric Brachionus populations by analyzing the capability of the medium conditioned by the growth of a population (i.e., medium containing the inducing signal) to induce sex in a different one. We found that populations induce sex in response to medium conditioned by congeneric populations. Results suggest differences among species in their production and responsiveness to sex-inducing signals, as well as slight differentiation in these signals. The observed lack of strong differentiation between sympatric populations is proposed to have implications in avoidance of competition.

A previously reported protocol for culture of larval sunshine bass (female white bass Morone chrysops × male striped bass M. saxatilis) to fingerling size in tanks involved an initial feeding of rotifers for several days before the larvae were weaned to nauplii of brine shrimp Artemia spp. and prepared feed. Maintaining rotifer cultures requires space, time, equipment, supplies, and trained culturists. The rotifer cultures are often unstable, which increases risk of poor sunshine bass fingerling production in tanks. Elimination of the use of rotifers would greatly enhance the feasibility of reliable tank culture of fingerlings and should reduce production cost. This experiment compared three treatments with three replicates per treatment. In one treatment, larvae were initially fed rotifers Brachionus plicatilis and then were weaned to brine shrimp nauplii (0.48 × 0.19 mm). In a second treatment, larvae were fed brine shrimp nauplii throughout the experiment. In a third treatment, larvae were fed...

Chemical defenses have been hypothesized to be widespread among aquatic bacteria, but few studies have assessed the susceptibility of pelagic consumers to bacterial secondary metabolites. In this study, we determined the effect of bacteria containing the indole alkaloid violacein on a range of freshwater plankton organisms that ingest bacteria. Growth and survival of two nanoflagellates (Bodo saltans, Ochromonas sp.), two ciliates (Colpidium campylum, Tetrahymena pyriformis), two rotifers (Keratella cochlearis, Brachionus calcyfloris), and adults and juveniles of the cladoceran Daphnia magna were examined in laboratory experiments in which these organisms were fed bacterial diets supplemented with violacein-producing bacteria such as Janthinobacterium lividum and Chromobacterium violaceum. Unselective uptake of violacein-producing bacteria resulted in significantly lower survivorships, indicating acute toxicity to all zooplankton taxa tested. The presence of 10% C. violaceum in an otherwise nontoxic bacterial diet, equivalent to 9 ng violacein mL21, reduced growth rates and peak abundances of flagellates, ciliates, and rotifers by 18–100%. For D. magna, wild-type C. violaceum was poisonous starting at concentrations ,1 3 106 cells mL21, whereas a violacein-deficient mutant did not have any lethal effect on the animals. Species-specific variability in predator susceptibility was explained by the negative correlation between toxin sensitivity and biomass-specific clearance rates. The susceptibility of a broad spectrum of planktonic bacterial consumers to violacein-producing bacteria illustrates the potential effect of bacterial bioactives on the structure of aquatic food webs, biodiversity, and ecosystem functioning.

The rotifer Brachionus plicatilis is widely used in aquaculture, but problems remain with its utilization. It is often difficult to synchronize rotifer production with larval demand, year-round culture maintenance is a technical nuisance, and cross-strain contamination is a persistent problem. Rotifers produce resting eggs that are thick-walled encysted stages which can remain dormant for extended periods. These resting eggs are analogous to Artemia cysts and could be used in a similar fashion in aquaculture. The mass production of rotifer resting eggs depends upon our ability to manipulate the rotifer life cycle in mass cultures. This paper examines several factors regulating the rotifer life cycle and identifies environments that promote resting egg production. Depending on the rotifer strain used, the strongest mictic response occurs at moderate temperatures and salinities. A mixed diet of Chlorella and baker's yeast promoted the greatest resting egg production. The RUS B. plicatilis strain exhibited the strongest mictic response in all environments tested and was 5 times that of any other strain. Success in manipulating the rotifer life cycle for resting egg production will depend upon a thorough understanding of sexual reproduction and how it is integrated into the life cycle. The major problem currently limiting resting egg production in laboratory populations is fertilization rate. The prospects for the controlled mass production of rotifer resting eggs are nonetheless good, but they are not imminent.

Japanese aquaculturists have contributed greatly to the culture technology of Pacific puffer fish of the genera Fugu, which presently rank second only to the yellow tail (Seriola quinqueradiata) in total annual tons cultured in Japan. Culture of the Atlantic puffer fish of the genera Sphoeroides, however, has received little attention despite its high commercial value. Adult northern puffers (Sphoeroides maculatus) were collected from local waters in the spring and summer and maintained in both open and closed sea water systems. Eggs were stripped onto glass plates and fertilization was achieved using the wet method. One hundred percent fertilization and approximately 90% hatching were obtained when specially designed incubation chambers were used. The time from fertilization to hatching was 72 hours at 24 C and the newly hatched larvae were between 1.9 and 2.4 mm in length. Yolk sac absorption required 2–3 days at 24 C, during which time feeding was not observed. The larvae were maintained in 160–liter algal bloom systems using a Chlorella sp. and were fed marine rotifers, Brachionus plicatilis, as a first food. Newly hatched Artemia salina were provided 10 days post-hatching. Thirty days posthatching the fish were given a prepared fish diet which they readily accepted and are presently being maintained. Cannibalism was observed to occur when the fish were approximately 20 days old and did not appear to be correlated to stocking densities or size. This behavior ceased when the fish were eating the prepared fish flesh diet.

A closed system was designed for mass culture of marine finfish larvae. Southern sea bass (Centropristis melana) brood stock were collected in the Gulf of Mexico during January-March, 1975, their natural spawning season. Brood stock were maintained in a simulated spawning environment of 17–19 C temperature and 10 hr L:14 hr D photo-period. Vitellogenesis of ovarian oocytes remained in the tertiary yolk globule stage in females held under these conditions and males would release milt freely upon manual stimulation. Final oocyte maturation and spawning were induced with Human Chorionic Gonadotropin and manual spawning techniques. Approximately 2,500 larvae were reared in three trials using 2,000–liter silo tanks with biological filtration. Laboratory reared rotifers (Brachionus plicatilis) were solely used as food the first 4 days after feeding began. Wild plankton, rotifers, Artemia nauplii, and prepared flake were also used as larvae developed. Greatest larval survival from hatching was 10.0%. Larvae grew from 2.78 mm to 9.0 mm in 24 days; the greatest growth rate occurred after day 14. Physiological edema was observed in two trials affecting 30–50% of the larvae. Physiological edema appears to be the principal constraint to successful rearing of sea bass larvae.

Twenty-five spawning attempts on the most reproductively developed fish were conducted on conditioned and unconditioned Florida pompano (Trachinotus carolinus). Human chorionic gonadotropin (HCG) was used to stimulate ovarian development. Dosage levels of .55 IU/g and .275 IU/g were usually administered 24 to 48 hours apart. Strip spawning and semi-natural spawning were used, Spawning occurred 7 to 208 hours after initial injection depending on initial oocyte size. Optimum oocyte size (580–718 μ) produced spawning in 30–40 hours. A close correlation exists between rate of fertilization and oocyte growth during the first 16–25 hours. Fertilized eggs may shrink as much as 16% within one hour after fertilization. Two successive batches of pompano were reared to juvenile stage in 23 days. Larvae were fed a mixed diet of natural plankton (66 μ mesh net), protozoans, rotifers (Brachionus plicatilus) and copepod nauplii (Oithona sp.). Water was initially conditioned with 40 liters of dense algae (Dunaliella sp. and Tetraselmis sp.). Water quality was controlled by partial exchanges from a 40,000-liter biologically filtered system. Eighteen-hour lighting was used. Larvae developed edema at 8–10 days and, combined with low aeration, reduced survival to only 300 juveniles.

We investigated the effect of temperature (20, 25 and 30 °C) on fecundity, life span and morphology of the rotifer Brachionus caudatus f. apsteini. For each temperature, short posterior-spined and long posterior-spined clones of B. caudatus f. apsteini were individually cultured for up to six generations. The rotifers were fed Chlorella sp. at a density of 1 × 106 cells ml–1. Morphometric data (body size and spine length) were collected. Total number of offspring producing by a single female per life cycle at high temperature was higher than at low temperature. The duration of juvenile period, reproductive period, post-reproductive period and life span of both clones of B. caudatus f. apsteini decreased with increasing temperature. All offspring of short posterior-spined clone produce posterior spines at 20 and 25 °C, with an average length of 19.8 ± 6.6 and 11.9 ± 2.6 μm, respectively. In contrast, they cannot develop posterior spines at 30 °C, at which the average length of the posterior spine remnant was 6.4 ± 1.3 μm. On the other hand, all offspring of long posterior-spined clone have long posterior spines with average lengths of 36.8 ± 6.1, 36.3 ± 5.2 and 36.6 ± 6.2 μm at 20, 25 and 30 °C, respectively. This study indicated that the production of posterior spines can be induced by low temperature and that short posterior-spined and long posterior-spined clones are genetically different. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Summary 1. With increases in river discharge over time and space, zooplankton generally encounter increased turbulence, turbidity, hydraulic forces, downstream advection and food limitations, all of which should affect species diversity and densities. Of these factors, the role of turbulence on the distribution of zooplankton is least known along longitudinal and lateral dimensions in river networks. 2. We tested the factorial effects of turbulence and grazing level on Ohio River potamoplankton in spring and summer using twelve 1600-L, outdoor mesocosms. Turbulence was calculated using the Froude number for equal depths but with current velocities of 0.064 and 0.32 m s−1. Grazing levels corresponded to a high density treatment (=ambient river densities of rotifers, copepods and cladocerans) and a low density treatment (initially no zooplankton >64 μm). All tanks had the same water residence time, and hydraulic stress was minimized by circular flow patterns. 3. Zooplankton densities and population growth rates were significantly affected by turbulence level and season. In general, rotifer populations grew faster in high turbulence tanks (though Keratella and Brachionus populations flourished in both treatments in summer) and microcrustaceans thrived better in low turbulence environments. The larger, calanoid copepods handled more turbulent conditions much better than cyclopoids or nauplii. Zooplankton had no detectable effects on particulate organic carbon concentrations in either month (values were higher in spring), but rotifers reduced chlorophyll concentrations in both months. 4. The relative importance of turbulence in controlling potamoplankton is probably to vary not only on a longitudinal basis in river networks but also with both the hydrogeomorphic complexity of river reaches and the type and amount of river regulation. Plans for river rehabilitation and management should incorporate non-turbulent habitats in large rivers as a means of enhancing zooplankton populations and providing an important food web component for planktivores.

Aspects of the life cycle of the peritrich ciliate Zoothamnium intermedium, an epibiont on calanoid copepods in the Chesapeake Bay, were investigated using host and epibiont cultures. Experiments were designed to characterize the formation, survival, and attachment of free-swimming stages (telotrochs) and to assess whether telotrochs preferentially attach to primary (Acartia tonsa and Eurytemora affinis) or alternate hosts from the zooplankton community (the rotifer Brachionus plicatilis, barnacle nauplii, polychaete larvae, and a harpacticoid copepod). The results showed that telotroch formation started 2 h after the death of the host, with >90% of the zooids leaving the host carapace within 7 h. Formation of telotrochs was triggered only by the death of the host, failing to occur when the host was injured or unable to swim. Telotrochs failed to attach to non-living substrates and survived for only 14 h in the absence of host organisms, suggesting that members of Z. intermedium are obligate epibionts. Attachment success decreased with telotroch age, indicating that colonization success in nature may strongly depend on the ability to find a suitable host in a short period of time. Individuals exhibited no preferences in colonizing juvenile or adult stages of A. tonsa or E. affinis. While telotrochs were able to colonize barnacle nauplii and the harpacticoid copepod in the absence of individuals of A. tonsa or E. affinis, they did not attach to the rotifers or polychaete larvae. Telotrochs preferentially colonized individuals of A. tonsa when in the presence of other non-calanoid host species.

Eighteen species of monogonont rotifers (Rotifera: Eurotatoria), belonging to eight genera and seven families, are documented presently from North-Eastern India. Among these, seven species namely Brachionus kostei, Lepadella biloba, L. quinquecostata, Lecane thailandensis, L. superaculeata, Macrochaetus danneeli and Filinia brachiata are new to the Indian subcontinent, Filinia saltator and Lepadella costatoides are new records from N.E. India and Trichocerca abilioi represents second record from the Oriental region. The occurrence of four Australasian elements i.e., Brachionus kostei, B. dichotomus reductus, Macrochaetus danneeli and Lecane batillifer illustrates an interesting link between the rotifer faunas of the North-Eastern India, southeast Asia and Australia. In addition, Keratella edmondsoni, Lecane thailandensis, L. superaculeata and L. blachei are the Oriental species. Other reported species include the palaeotropical Testudinella greeni; the pantropical Lepadella lindaui and L. minoruoides; the cosmotropical Filinia camasecla, and the cosmopolitan F. saltator and Lepadella biloba. A majority of the documented species are rare in the examined material.

Incubation methods and larval feeding regimes were investigated for North American burbot Lota lota maculosa over 2 years. Three upwelling incubators were tested: 6.0-L McDonald-type jars, 2.0-L pelagic egg jars, and 1.2-L Imhoff cones. Larvae were allocated to five feeding regimes in year 1 (trial 1) and three feeding regimes in year 2 (trial 2). In trial 1, a live diet (marine rotifers Brachionus plicatilis and brine shrimp Artemia spp.) was administered from 11 d posthatch (dph) until introduction of a commercial diet at 21, 31, or 41 dph; the fourth treatment applied the commercial diet exclusively starting at 11 dph, and the fifth treatment used only the live diet. Trial 2 examined (1) exclusive use of live feed beginning at 16 dph; (2) use of live feed at 16–50 dph, which was combined with commercial feed at 31–50 dph, and use of only the commercial diet at 51–76 dph; and (3) use of the live diet at 16–50 dph, the addition of frozen brine shrimp at 31–50 dph, and use of the commercial diet ...

Summary 1In this study we address how growth rate in consumers may be regulated by nitrogen (N)- and phosphorus (P)- limitation of ribonucleic acid (RNA), using the rotifer Brachionus calyciflorus as the model organism. 2Growth rate, RNA and weight-specific concentrations of carbon (C), N and P were analyzed in B. calyciflorus fed algae with different C : N, C : P and N : P ratios. 3Growth rate correlated negatively with food C : N, but not with C : P or N : P, strongly suggesting N-limited growth. Growth rate also strongly correlated with tissue concentrations of RNA and P, in support of the growth rate hypothesis which states that specific P-content of organisms reflects their RNA-content and thus capacity for protein synthesis. 4Food C : N rather than C : P regulated the growth, RNA and P in this consumer under the food conditions applied. This suggests that availability of N can also be an important regulator of cellular acquisition of P and build-up of ribosomes in that animals released from N-limitation have an increased demand for the P-rich cellular machinery for protein synthesis. 5The data suggest a strong reciprocal regulation of consumer demands and their C : N : P stoichiometry via the intimate connections between ribosome allocation and protein synthesis and also lend support to the view that reduced protein synthesis efficiency under high growth rates may affect stoichiometry of the consumer.

Determining optimum parameters for tank culture of sunshine bass (white bass Morone chrysops × striped bass M. saxatilis) fingerlings will facilitate a year-round supply of seed for the production cycle of this increasingly popular food fish. This experiment determined the relationship between the stocking density of sunshine bass larvae in tanks and their survival rate and size at the time they were trained to accept commercial feeds. Four-day posthatch (dph) larvae were stocked at 10 densities from 30 to 120 larvae/L in 10-larvae/L increments. Larvae were initially fed rotifers Brachionus plicatilis cultured with Nannochloropsis spp. algae paste and commercial rotifer feed at 60 rotifers·mL−1·d−1 until 10 dph. Conversion to brine shrimp Artemia spp. began at 7 dph. The daily ration of brine shrimp started at 4/mL and increased by 4/mL every 4 d up to 20/mL. Training to dry starter feed began at 20 dph when 6 g/d of a commercial larval starter meal was offered; 2 d later, salmon starter meal was...

Summary 1. One at a time during the reproductive period of amictic females, oocytes fill with yolk and undergo a mitotic maturation division (oogenesis), are oviposited as single cells, and then develop parthenogenetically into females. Sexual reproduction in Brachionus and several other genera is initiated when amictic females are crowded and oviposit some eggs induced to differentiate into mictic females. Mictic females produce haploid eggs that can develop parthenogentically into males or be fertilised and develop into diapausing embryos called resting eggs. 2. This study examines the time when oocytes in amictic females respond to maternal population density. Is the fate of all oocytes in the germarium irreversibly determined during the early postnatal life of the mother, or is each oocyte labile until just before oviposition? In the former case, the probability of an amictic female producing a mictic daughter at any time throughout her reproductive period would reflect the population density she experienced while young and not that at the time she oviposited an egg. 3. Amictic females of two clones of a Florida strain of B. calyciflorus were cultured singly from birth at a low or high density (in a large or small volume) until about halfway through their reproductive period and then switched (experimental treatment), or not (control treatment), to the other density condition. The results indicate that the female fate of an oocyte is determined by maternal population density during oogenesis. Eggs oviposited soon after transfer from low to high density had the same, or a higher, probability of becoming mictic females compared with those produced by control females kept at the high density; eggs oviposited after transfer from the high to the low density had the same low probability of becoming mictic females as those produced by control females kept at the low density. 4. Control females kept at the high density were less likely to produce mictic daughters as they aged. This decline is not because of a decreased propensity of older females to respond to crowding, as older females responded maximally when transferred from a low to a high population density. 5. As oocytes in amictic females respond to maternal population density only during oogenesis, there is a negligible lag between the population-density signal in the environment and the commitment to sexual reproduction. This minimises the obligatory two-generation lag between this signal and production of resting eggs, and thus reduces the possibility that crowding will lead to food limitation before production of these eggs.

Recent phylogeographical assessments have consistently shown that continental zooplankton display high levels of population subdivision, despite the high dispersal capacity of their diapausing propagules. As such, there is an apparent paradox between observed cosmopolitanism in the zooplankton that is associated with long-distance dispersal, and strong phylogeographical structures at a regional scale. Such population dynamics, far from migration-drift equilibrium, have been shown in the rotifer species complex Brachionus plicatilis, a group of over a dozen species inhabiting salt lakes and coastal lagoons worldwide. Here we present the mitochondrial DNA phylogeography of one of these species, Brachionus manjavacas, in the Iberian Peninsula, where it often co-occurs with the morphologically similar species B. plicatilis sensu stricto. We obtained sequences from 233 individuals from diapausing eggs and clonal cultures from 16 lakes in the Iberian Peninsula, and a Tunisian lake. Two strongly supported deep mitochondrial DNA clades were found (A and B). Phylogenetic and nested clade analysis showed that clade A has a strong phylogeographical structure, with a strong similarity of phylogeographical patterns between B. manjavacas clade A and B. plicatilis s.s. These include (i) signatures of allopatric fragmentation between central and southern populations, and (ii) range expansions in the Iberian Peninsula, both likely to have occurred during the Pleistocene. We find evidence for a glacial refugium in the Guadiana basin. Clades A and B co-occurred in several of these lakes because of range expansion and secondary contact between both clades. The co-occurrence between B. plicatilis s.s. and B. manjavacas is not recent, and both species might have experienced similar environmental challenges during the Pleistocene. The strong correlation of genetic and geographical distance found suggests that historical events can lead to such correlation, mirroring the effects of 'isolation by distance' in equilibrium populations.

Rotifers are a dominant zooplankton that are a preferred prey for some larval fish and are used by culturists during larval fish culture. The rotifer Brachionus plicatilis is a brackish-water species suited for mass culture because it is prolific and can tolerate a wide variety of environmental conditions. Although the culture of this rotifer has been well documented, little information is available regarding the use of concentrated algal paste for the production of B. plicatilis. Thus, we investigated algal paste for rotifer production. Rotifers were cultured in four translucent, low-density polyethylene tanks with a culture volume of 45 L of artificial seawater. The feed solution was a mixture of commercially available Nannochloropsis algal paste and artificial seawater. During a 21-d culture period, the rotifer population in each of four tanks was maintained between 500 and 1,500 rotifers/mL. A volume of 15 L was harvested when the rotifer count was 1,500 rotifers/mL or more. The results indic...

In order to test whether phytoplankton such as the red tide dinoflagellate Karenia brevis negatively affect rotifer grazers and what mechanisms are involved in these interactions, we conducted laboratory feeding experiments using K. brevis cultured from Gulf of Mexico coastal waters and two species of rotifers, one co-occurring and the other from an inland sea in Russia. The co-occurring rotifer Brachionus ibericus did not ingest K. brevis as a sole diet but tolerated K. brevis in a diet mixed with Rhodomonas lens, whereas the allopatric rotifer, Brachionus plicatilis, rejected K. brevis in either diet, although B. plicatilis started feeding on the mixed diet after a delay of 4 days. The deterrence of K. brevis was mediated by its cellular organic extracts and not by exudates, with compounds other than brevetoxins PbTx-2, PbTx-3, and PbTx-9 implicated in deterrence. The finding that closely related rotifers respond differently to K. brevis and to its chemical defense suggests that a shared evolutionary history may have led B. ibericus to tolerate K. brevis in a mixed diet.

The effects of culture parameters of tank color and feeding regimes were examined on larval white bass Morone chrysops during 1994–1995. Under high surface illumination (998 lux), dark tank walls were essential for effective prey capture. Larvae reared in clear glass aquaria did not grow and had died by day 6 of the study. In contrast, 48.7% of the larvae reared in black-walled tanks were alive on day 24 and had grown to 17.2 mm total length (TL). In another study, larvae were fed rotifers Brachionus plicatilis and Artemia nauplii in different feeding protocols. In one treatment only rotifers (10/mL) were fed day 1 (4 d post-hatch), rotifers and Artemia (3/mL) were fed days 2–4, and Artemia fed days 5–15. This protocol produced similar growth (mean size 11.7 mm TL) and survival (mean 30.3%) as slower weaning times from rotifers to Artemia. Juveniles (27-day-old, 17.2 mm TL) were converted to a dry crumble diet over a 14-d period by slow transfer from a combination diet consisting of live Artemia nauplii, frozen adult Artemia, plankton flakes and dry crumbles. Survival offish weaned to the dry diet was 64.5%. Most of the mortalities during the weaning period were fish with uninflated swim bladders which were cannibalized by larger fish. Using the above tank culture techniques, white bass were reared to a mean size of 73.2 mm TL (mean weight 5.8 g) over a 73-d period. This essentially closes the life cycle of white bass.