Brachionus Plicatilis Research Articles

The genome of the marine monogonont rotifer Brachionus plicatilis: Genome-wide expression profiles of 28 cytochrome P450 genes in response to chlorpyrifos and 2-ethyl-phenanthrene

Brachionus spp. (Rotifera: Monogononta) are globally distributed in aquatic environments and play important roles in the aquatic ecosystem. The marine monogonont rotifer Brachionus plicatilis is considered a suitable model organism for ecology, evolution, and ecotoxicology. In this study, we assembled and characterized the B. plicatilis genome. The total length of the assembled genome was 106.9 Mb and the number of final scaffolds was 716 with an N50 value of 1.15 Mb and a GC content of 26.75%. A total of 20,154 genes were annotated after manual curation. To demonstrate the use of whole genome data, we targeted one of the main detoxifying enzyme of phase I detoxification system and identified in a total of 28 cytochrome P450 s (CYPs). Based on the phylogenetic analysis using the maximum likelihood, 28 B. plicatilis-CYPs were apparently separated into five different clans, namely, 2, 3, 4, mitochondrial (MT), and 46 clans. To better understand the CYPs-mediated xenobiotic detoxification, we measured the mRNA expression levels of 28 B. plicatilis CYPs in response to chlorpyrifos and 2-ethyl-phenanthrene. Most B. plicatilis CYPs were significantly modulated (P < 0.05) in response to chlorpyrifos and 2-ethyl-phenanthrene. In addition, xenobiotic-sensing nuclear receptor (XNR) response element sequences were identified in the 5 kb upstream of promoter regions of 28 CYPs from the genome of B. plicatilis, indicating that these XNR can be associated with detoxification of xenobiotics. Overall, the assembled B. plicatilis genome presented here will be a useful resource for a better understanding the molecular ecotoxicology in the view of molecular mechanisms underlying toxicological responses, particularly on xenobiotic detoxification in this species.

Early ontogenetic development, digestive enzymatic activity and gene expression in red sea bream (Pagrus major)

Red sea bream (Pagrus major) is an important aquaculture species in Japan. This study aimed to determine the ontogenetic development of the digestive system, enzyme activity and related gene expressions of red sea bream larvae from hatching to post-metamorphosis (40 days after hatching, DAH). The larvae were fed with the euryhaline rotifer Brachionus plicatilis species complex L-type enriched with Chlorella vulgaris containing DHA from 3 to 15 DAH followed by Artemia nauplii from 16 to 40 DAH. Post culture analysis included, histological analysis of the larval gut, enzyme assays (trypsin, chymotrypsin, lipase, pepsin) and real time PCR with larvae sampled from 1 to 40 DAH. At hatching, the larval digestive tract was undifferentiated and resembled a straight tube. There was low detection of enzyme activity and gene expression of trypsin, chymotrypsin, lipase, and amylase during yolk-sac stage, before mouth opened. At 3 DAH, the mouth opened and the larvae began to exogenous feeding followed by the differentiation of the digestive tract into buccopharyngeal capacity and intestine at 5 DAH. The pancreas, liver, and gallbladder were functional indicating the transition from endogenous to exogenous feeding. The enzyme activity and gene expression of trypsin, chymotrypsin, lipase, and amylase increased and fluctuated throughout the larval development, a pattern that is common among marine fish species. Pepsin activity and gene expression were not detected until 15 DAH and strongly increased from 20 DAH. Metamorphosis was complete by 40 DAH following the regular arranging of microvilli and the abundance of vacuoles in intestine.

Optimized application of rotifers Brachionus plicatilis for rearing pikeperch Sander lucioperca L. larvae

This study aimed to optimize the use of euryhaline rotifer Brachionus plicatilis for rearing larval pikeperch Sander lucioperca L. We assessed motility of rotifers under salinities of 0‰, 2‰, 4‰, 8‰, and 16‰ over a 6-h period. Rotifers stocked into freshwater were completely immotile within 2 h. The motility of rotifers after 6 h was 10 ± 2.27% at 2‰, 35 ± 5.58% at 4‰, 79 ± 30.35% at 8‰, and 92 ± 1.98% at 16‰. A second trial quantified the effect of the target salinity levels on pikeperch gut fullness over the course of 11 h. The gut fullness of larvae fed with rotifers was significantly lower at 8‰ salinity than in other tested groups. Salinity of 16‰ resulted in 100% mortality. Survival and growth of pikeperch larvae from 4 to 11 days post-hatching (DPH) was analyzed at low (2‰ and 4‰) and medium (8‰) salinity. Differences in larval performance under tested salinities were found in survival (S), total length, SGR, eye diameter, myotome height, and gut fullness. The highest mean survival (S) and specific growth rate (SGR) were obtained at 2‰ (S = 64%; SGR = 10 ± 5.4% day−1) and 4‰ (S = 65%; SGR = 8.23 ± 3.4% day−1) salinity and significantly differed from 8‰ (S = 36%; SGR = 5 ± 2.3% day−1) and control (S = 34%; SGR = 7 ± 3% day−1) at 11 DPH. At the conclusion of the trial (11 DPH), larvae of all exposures and control presented normal histology with no signs of pathology. Morphometric analyses revealed significant differences in brush border and fold height of anterior intestine among treatment groups. Larvae at 2‰ salinity showed significantly higher intestinal fold height (31.2 ± 5.40 μm) compared to those at 4‰ (26.5 ± 6.11 μm), 8‰ (26.3 ± 4.52 μm), and control (22.8 ± 5.13 μm) (p ˂ 0.05). Larvae at 4‰ salinity had significantly higher brush border height (2.50 ± 0.73 μm) compared to those at 2‰ (2.27 ± 0.63 μm) and 8‰ (1.87 ± 0.44 μm) salinity and control (1.66 ± 0.56 μm) (p < 0.05). The results showed 2‰ and 4‰ salinity supported higher numbers of motile B. plicatilis and higher larval survival and growth rate to 11 DPH.

Small-Sized Microplastics Negatively Affect Rotifers: Changes in the Key Life-History Traits and Rotifer-Phaeocystis Population Dynamics.

Most coastal waters are at risk from microplastics, which vary in concentration and size. Rotifers, as important primary consumers linking primary producers and higher trophic consumers, usually coexist with the harmful alga Phaeocystis and microplastics in coastal waters; this coexistence may interfere with rotifer life-history traits and ingestion of Phaeocystis. To evaluate the effects of microplastics on rotifers, we designed a series of experiments concerning rotifer Brachionus plicatilis life-history traits and rotifer-Phaeocystis (predator-prey) population dynamics under different concentrations and sizes of microplastics. The results showed that small-sized microplastics (0.07 μm) at high levels (≥5 μg mL-1) decreased rotifer survival and reproduction, prolonged the time to maturation, and reduced the body size at maturation, whereas large-sized microplastics (0.7 and 7 μm) had no effect on rotifer life-history traits. For rotifer-Phaeocystis population levels, small-sized microplastics (0.07 μm) significantly delayed the elimination of Phaeocystis by rotifers; this is the first study to test the effects of microplastics on predator-prey dynamics. The results of rotifer-Phaeocystis population dynamics are consistent with the changes in the life-history traits of rotifers and further confirm the negative effects of small-sized microplastics (0.07 μm) on rotifers. These findings help to reveal the effect of pollutants on predator-prey population dynamics.

Treatment of Real Textile Wastewater by Using Potassium Ferrate(VI) and Fe(III)/H2O2. Application of Aliivibrio Fischeri and Brachionus plicatilis Tests for Toxicity Assessment

The paper presents the possibility of applying combined chemical oxidation processes using potassium ferrate(VI) (K2FeO4) and Fe(III)/H2O2 for the treatment of real wastewater from the textile industry characterised by an increased content of organic substances (COD = 1920 mg O2/L). The use of both processes under optimal conditions included the use of the RSM method (Response Surface Methodology) in order to make it possible to decrease the COD of the wastewater by 75.4% (final COD = 472 mg O2/L). The toxicity of wastewater treated under the most favourable conditions, determined using two test organisms (Aliivibrio fischeri and Brachionus plicatilis), decreased by 33 and 45%, respectively. In some cases the method described can be used on a larger scale.

Metabolomics reveals novel insight on dormancy of aquatic invertebrate encysted embryos

Numerous aquatic invertebrates survive harsh environments by displaying dormancy as encysted embryos. This study aimed at determining whether metabolomics could provide molecular insight to explain the “dormancy syndrome” by highlighting functional pathways and metabolites, hence offering a novel comprehensive molecular view of dormancy. We compared the metabolome of morphologically distinct dormant encysted embryos (resting eggs) and non-dormant embryos (amictic eggs) of a rotifer (Brachionus plicatilis). Metabolome profiling revealed ~5,000 features, 1,079 of which were annotated. Most of the features were represented at significantly higher levels in non-dormant than dormant embryos. A large number of features was assigned to putative functional pathways indicating novel differences between dormant and non-dormant states. These include features associated with glycolysis, the TCA and urea cycles, amino acid, purine and pyrimidine metabolism. Interestingly, ATP, nucleobases, cyclic nucleotides, thymidine and uracil, were not detected in dormant resting eggs, suggesting an impairment of response to environmental and internal cues, cessation of DNA synthesis, transcription and plausibly translation in the dormant embryos. The levels of trehalose or its analogues, with a role in survival under desiccation conditions, were higher in resting eggs. In conclusion, the current study highlights metabolomics as a major analytical tool to functionally compare dormancy across species.

Utilization of &lt;i&gt; Schizochytrium mangrovei &lt;/i&gt; PQ6 as feed for rotifer &lt;i&gt; Brachionus plicatilis &lt;/i&gt; in rearing black sleeper’s larvae (&lt;i&gt;Bostrichthys sinensis&lt;/i&gt;, Lacepede, 1881)

Schizochytrium mangrovei PQ6 contains many important polyunsaturated fatty acids, such as docosahexaenoic acid (DHA, C22: 6w-3), eicosahexaenoic acid (EPA, C20: 5w-3) and docosapentaenoic acid (DPA, C22: 5w-6). These fatty acids are essential for survival and growth of many marine fish larvae. In this paper, fresh biomass of S. mangrovei PQ6 was used for culturing rotifer Brachionus plicatilis. In the first formula (L1), rotifers were fed on baker’s yeast; in second formula (L2), rotifers were fed on mixed two microalgae, Nannochloropsis oculata and Chaetoceros gracilis; in the third formula (L3), rotifers were fed on S. mangrovei PQ6 biomass. The results indicated that S. mangrovei PQ6 biomass can replace baker’s yeast and autotrophic microalgae in feeding rotifers. Total lipid, total fatty acid and polyunsaturated fatty acid contents of rotifers fed on formula 3 (S. mangrovei PQ6) were higher than those within others. High polyunsaturated fatty acid (C ≥ 20) in omega-3 and 6 groups; DHA and DPA contents of rotifers fed on S. mangrovei PQ6 were the highest, accounting for 39.81% of total fatty acid; 41.95% and 8.24% polyunsaturated fatty acids, corresponding to 20.52; 12.15 and 2.4 mg/g of dried weight, respectively.The survival rate of black sleeper’s larvae was highest when they were fed on rotifers grown on L3 formula (51.20 ± 0.89%), followed by L2 formula (48.70 ± 2.67%) and the lowest with L1 formula (43.44 ± 1.54%) (P &lt; 0.05). However, among three formulas, no significant difference was found in the growth of black sleeper’s larvae (P &gt; 0.05). These results suggest that biomass of S. mangrovei PQ6 can replace traditional feed like autotrophic microalgae or baker’s yeast for biomass culture of the Brachionus plicatilis rotifer for rearing black sleeper’s larvae to enhance seed quality to meet demands of market.

Small, but surprisingly repetitive genomes: transposon expansion and not polyploidy has driven a doubling in genome size in a metazoan species complex

BackgroundThe causes and consequences of genome size variation across Eukaryotes, which spans five orders of magnitude, have been hotly debated since before the advent of genome sequencing. Previous studies have mostly examined variation among larger taxonomic units (e.g., orders, or genera), while comparisons among closely related species are rare. Rotifers of the Brachionus plicatilis species complex exhibit a seven-fold variation in genome size and thus represent a unique opportunity to study such changes on a relatively short evolutionary timescale. Here, we sequenced and analysed the genomes of four species of this complex with nuclear DNA contents spanning 110–422 Mbp. To establish the likely mechanisms of genome size change, we analysed both sequencing read libraries and assemblies for signatures of polyploidy and repetitive element content. We also compared these genomes to that of B. calyciflorus, the closest relative with a sequenced genome (293 Mbp nuclear DNA content).ResultsDespite the very large differences in genome size, we saw no evidence of ploidy level changes across the B. plicatilis complex. However, repetitive element content explained a large portion of genome size variation (at least 54%). The species with the largest genome, B. asplanchnoidis, has a strikingly high 44% repetitive element content, while the smaller B. plicatilis genomes contain between 14 and 25% repetitive elements. According to our analyses, the B. calyciflorus genome contains 39% repetitive elements, which is substantially higher than previously reported (21%), and suggests that high repetitive element load could be widespread in monogonont rotifers.ConclusionsEven though the genome sizes of these species are at the low end of the metazoan spectrum, their genomes contain substantial amounts of repetitive elements. Polyploidy does not appear to play a role in genome size variations in these species, and these variations can be mostly explained by changes in repetitive element content. This contradicts the naïve expectation that small genomes are streamlined, or less complex, and that large variations in nuclear DNA content between closely related species are due to polyploidy.

Impact of Copper and Cadmium on the Nutritional Value of the Rotifer Brachionus plicatilis and their Effect on Dicentrarchus labrax Fish Larvae.

Impact of Copper and Cadmium on the Nutritional Value of the Rotifer Brachionus plicatilis and their Effect on Dicentrarchus labrax Fish Larvae.

Characterization of the unarmored dinoflagellate Pseliodinium pirum (Ceratoperidiniaceae) from Jiaozhou Bay, China

SUMMARYA 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.

Effect of oil enrichment on Brachionus plicatilis rotifer and first feeding red sea bream (Pagrus major) and Japanese flounder (Paralichthys olivaceus)

Euryhaline rotifer belonging to the genera Brachionus are often used as live feed for first feeding marine finfish larviculture. Two common rotifer enrichments, a single usage of docosahexaenoic acid (DHA)-enriched Chlorella vulgaris and a combination of DHA-enriched C. vulgaris and salmon roe emulsion oil were used to assess: (i) nutritional status of rotifers and, (ii) performance when rotifers were fed to Pagrus major and Paralichthys olivaceus larvae from 2 to 15 days after hatching (DAH). Both rotifer enrichment treatments were found to be nutritionally effective with high unsaturated fatty acid (HUFA) content, especially in the combined treatment with significantly higher eicosapentaenoic acid (EPA). Despite deficient levels of EPA, DHA-enriched C. vulgaris was found to be a suitable enrichment for rotifer and also had positive response in survival, growth and trypsin activity in both P. major and P. olivaceus. DHA-enriched C. vulgaris only treatment had higher rotifer population growth (13% higher), egg bearing capacity (7% higher), almost double the soluble protein content and generally higher free amino acid content. Oxidation of lipids in the combined diet due to its high-saturated fatty acid content could be a possible cause to the inferior performance of the combined treatment. Both P. major (20.1 ± 10.1%) and P. olivaceus (12.3 ± 3.87%) suffered low survival and lower gut content in the combined treatment especially during periods of significant growth in both species (7–11 DAH). Despite high HUFA content in the combined treatment, this study revealed that consideration of free amino acids and soluble protein content as parameters of nutritional indicators for first feeding P. major and P. olivaceus should not be discounted.

Bacterial communities protect the alga Microchloropsis salina from grazing by the rotifer Brachionus plicatilis

Open algal ponds are likely to succumb to unpredictable, devastating crashes by one or several deleterious species. Developing methodology to mitigate or prevent pond crashes will increase algal biomass production, drive down costs for algae farmers, and reduce the risk involved with algae cultivation, making it more favorable for investment by entrepreneurs and biotechnology companies. Here, we show that specific algal-bacterial co-cultures grown with the green alga Microchloropsis salina prevented grazing by the marine rotifer, Brachionus plicatilis. We obtained seven algal-bacterial co-cultures from crashed rotifer cultures, maintained them in co-culture with Microchloropsis salina, and used a microalgal survival assay to determine that algae present in each co-culture were protected from rotifer grazing and culture crash. After months of routinely diluting and maintaining these seven algal-bacterial co-cultures, we repeated the assay and found the opposite result: none of the seven bacterial communities protected the microalgae from rotifer grazing. We performed 16S rRNA gene amplicon sequencing on the protective and nonprotective co-culture samples and identified substantial differences in the makeup of the bacterial communities. Protective bacterial communities consisted primarily of Alphaproteobacteria (Rhodobacteraceae) and Gammaproteobacteria (Marinobacter, Pseudomonas, Methylophaga) while nonprotective bacterial communities were less diverse and missing many putatively crucial members. We compared the seven protective communities with the seven nonprotective communities and we correlated specific bacterial amplicon sequence variants with algal protection. With these data, our future work will aim to define and develop an engineered-microbiome that can stabilize industrial Microchloropsis salina cultures by protecting against grazer-induced pond crashes.

Nutritional value and production performance of the rotifer Brachionus plicatilis Müller, 1786 cultured with different feeds at commercial scale

The rotifer Brachionus plicatilis is the first live feed in larviculture of marine fish species. Rotifer diets differ in their biochemical composition, physical properties, and production technology while feeding protocols largely vary among facilities. The objective of the present study was to determine the effects of two different forms of Nannochloropsis oculata and commonly used commercial diets on growth performance and biochemical composition of rotifers produced under commercial conditions. Rotifers were fed one of five different types of feed: Algome® (dried Schizochytrium sp.), Protein Plus® (PP), Inactive Baker’s Yeast® (INBY), spray-dried Nannochloropsis oculata (SDN), or freshly cultured Nannochloropsis oculata (FN). Rotifers fed SDN diet resulted in significantly higher rotifer biomass during 16 days of semi-continuous culture, with an increasing biomass trend that lasted 11 days, high egg production, and egg-carrying female numbers, whereas rotifers fed PP showed highest ∑n-3, arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid contents. Amino acid profiles of rotifers were enhanced by utilization of both INBY and SDN diets. Overall, the results indicated that SDN is optimal for long-term biomass production of rotifers. However, their nutritional profile needs to be enriched by feeding PP (EFA source) and INBY (EAA source) once desired biomass production is obtained.

Toxicity and haemolytic activity of a newly described dinoflagellate, Heterocapsa bohainensis to the rotifer Brachionus plicatilis

The algae Heterocapsa bohaiensis is a newly described species of dinoflagellate associated with Penaeus japonicus and larvae of Eriocheir sinensis in a coastal pond of Liaodong Bay China. The rotifer Brachionus plicatilis is used as live feed for aquaculture organisms including prawns and crabs larvae. To evaluate the potential toxicity of H. bohaiensis, the effects on Brachionus plicatilis and haemolytic activity were investigated in this study. The results showed that H. bohaiensis had significant toxic effect on B. plicatilis, and this effect was dependent on the cell concentration. Significant rotifer growth suppression was observed in the ruptured cells of H. bohaiensis with ultrasonic. Relatively similar rotifer mortalities were induced both in the light and in the dark. Interestingly, haemolysis to erythrocytes was also caused in a cell density-dependent and time-dependent manner, which meant the results of haemolytic activity were consistent with the toxicity. Therefore, haemolytic toxins were considered to be involved in the toxic mechanism of H. bohaiensis against rotifers. Then, the concentrations of calcium were measured in the mastax, stomach and ovary of B. plicatilis. Obviously increased fluorescence intensity was found in the stomach, which indicated the alteration of calcium homeostasis and membrane permeability after ingesting H. bohaiensis. These results implicated haemolytic activity as a causative factor linked to the toxicity of H. bohaiensis against B. plicatilis. The results contributed to research the production and control of H. bohaiensis toxins.

Effect of probiotic Pediococcus acidilactici on growth, reproductive and bacterial count of marine rotifer Brachionus plicatilis

This study investigated the effects of different concentrations of probiotic Pediococcus acidilactici on the total number, specific growth rate, attached egg number and microbial count (lactic acid and total aerobic bacteria) in culture water and body of marine rotifer Brachionus plicatilis . The experiment was conducted as a completely randomized design in four groups: first group fed probiotic at 0.5×10 6 CFU ml -1 (P1), the second group fed probiotic at 1×10 6 CFU ml -1 (P2), the third group fed probiotic at 1.5×10 6 CFU ml -1 (P3), and the last group fed without probiotic (NP, control) . Rotifers were cultured in standard conditions at an initial density of 30 ind.ml -1 using a 2.5×10 6 cell mL -1 of Nanochloropsis oculta . Based on the results, the maximum number (215±4.91 ind.ml -1 ) of rotifers were significantly obtained after ten days in the third group in comparison to other treatments ( P 0.05). Moreover, it was revealed that the total aerobic bacteria was significantly related to the 3rd group that found be 1.80×10 3 CFU rotifer -1 and 34.0×10 4 CFU ml -1 in rotifer body and culture water,respectively ( P <0.05). Nonetheless, lactic acid bacteria of rotifer body and culture water was not concentration-dependent and the highest number of lactic acid bacteria in rotifer body (50.58±6.08 CFU rotifer -1 ) and rotifer culture water (4.43±3.28×10 3 CFU ml -1 ) was obtained in the treatments of P1 and P2, respectively. In conclusion, the present study showed that the bacteria P. acidilactici with N. oculta algae provide a higher growth rate and total aerobic bacteria in rotifer B. plicatilis.

Using Proales similis (Rotifera) for toxicity assessment in marine waters.

There is a need to develop more animal species for assessing toxicity in marine environments. Cyst‐based toxicity tests using invertebrates are especially fast, technically simple, cost‐effective, and sensitive to a variety of toxicants. Over the past 30 years, a variety of toxicity endpoints have been measured using the marine rotifer Brachionus plicatilis hatched from cysts, including mortality, reproduction, ingestion, swimming, enzyme activity, and gene expression. A consensus has developed that the most ecologically relevant toxicity measurements should be made using more than one species. Furthermore, it has been noted that the rotifer species toxicant sensitivity distribution is much broader than which endpoint is measured. This implies that toxicity should be measured with the simplest, fastest, least expensive test available on as many species as feasible. If a battery of test species is to be used to estimate toxicity, diapause egg‐based toxicity tests that do not require culturing of test animals will be key. In this paper, we describe how diapause eggs of a new marine rotifer, Proales similis, can be produced, stored and hatched under controlled conditions to produce animals for toxicity tests. Methods are described for quantifying the toxicity of copper, mercury and cadmium based on mortality, ingestion, reproduction, and diapause egg hatching endpoints. We found that reproduction and ingestion endpoints were generally more sensitive to the metals than mortality or diapause egg hatching. When the copper sensitivity of P. similis was compared to Brachionus manjavacas and B. plicatilis using an ingestion test, similar EC50s were observed. In contrast, the B. rotundiformis ingestion EC50 for copper was about 4× more sensitive. Although diapause egg hatching was not the most sensitive endpoint, it is the most ecologically relevant for assessing sediment toxicity. Our discovery of diapausing eggs in the P. similis life cycle has created a conundrum. We have not observed males or sex in P. similis populations, which is a direct contradiction to the orthodox view of the monogonont rotifer life cycle. Work is needed to clarify how diapause egg production is accomplished by P. similis and whether sexual reproduction is involved.

Aspects of the feeding biology of the copepodPseudodiaptomus hessei(Copepoda: Calanoida) under culture conditions

This study aimed to investigate the feeding behaviour (particularly gut fullness and evacuation, preying on rotifers and feeding preference in the water column) of the calanoid copepod, Pseudodiaptomus hessei, as a potential live feed species for aquaculture. Fed and starved, male and female P. hessei were fed rotifers (Brachionus plicatilis) in the presence and absence of microalgae for 24 hr. Starved copepods consumed more rotifers (11.31 ± 1.01, individual rotifers) than fed (8.06 ± 1.01, individual rotifers) while the number of rotifers consumed in the presence of microalgae was similar when fed or starved. Gut fullness and evacuation was determined by feeding copepods two different cell size microalgae species (Tetraselmis suecica and Isochrysis galbana). Gut fullness and evacuation percentage were observed under the dissecting microscope (as 0, 25, 50, 75 and 100%). Copepods fed on T. suecica (large cell) filled their guts more rapidly, while those fed on I. galbana (small cell) evacuated their guts faster. Feeding preference was determined using a multifactorial experiment where copepods were fed two microalgae species, T. suecica and I. galbana, each presented as benthic and planktonic food sources. P. hessei preferred to feed on planktonic microalgae first regardless of microalgae choice species for ±80 min, before shifting to benthic food source. This information can be used as baseline information for aquaculturists to rear the species as live feed for marine fish larvae.

Effects of defatted Haematococcus pluvialis meal (DHPM) supplementation on the growth performance, and the carotenoid content and composition in the rotifer (Brachionus plicatilis)

A feeding study was conducted to determine the effects of defatted Haematococcus pluvialis meal (DHPM) on the growth performance of rotifers (Brachionus plicatilis). To assess the efficiency of DHPM as a new additive for rotifer enrichment, the effects of DHPM supplementation on carotenoid and astaxanthin concentrations of the rotifers were investigated. The results showed that the addition of DHPM (125 mg l−1) increased the total number of rotifers (TR), the number of egg-bearing rotifers (EBR), and the number of rotifer eggs (RE). The large proportion of total egg-bearing rotifers indicated that DHPM was good for rotifer growth and reproduction. After feeding on DHPM, rotifers had significant increases (P < .05) in carotenoids including astaxanthin. Total carotenoid and astaxanthin concentrations in the treated rotifers increased 4.8 times and 9.0 times respectively as compared with the control group (no DHPM). In addition, the ratios of β-carotene, each astaxanthin isomer (all-trans, 9-cis, 13-cis and 15-cis astaxanthin) and the degradation product astacin, to the total carotenoid content, were calculated for rotifers of the control and treatment groups. The results suggested that the addition of DHPM led to a decrease in the proportions of β-carotene (from 9.34% to 2.51%) and astacin (from 41.83% to 12.44%) of the total carotenoids, but to an increase in the proportion of all-trans astaxanthin (from 40.46% to 77.73%) to the total carotenoid. We propose that the different compositions of carotenoids had effects on the growth performance of rotifers. As a result, it was concluded that the addition of DHPM is beneficial for rotifer growth and enhanced the nutritional quality of the rotifers as first feed for aquaculture.

Rotifer adaptation to the unpredictability of the growing season

Sexual reproduction in cyclically parthenogenetic rotifers results in the production of diapausing eggs that tolerate harsh conditions. Theory predicts that the adaptation to environmental unpredictability can occur by the evolution of bet-hedging strategies. When facing unpredictability in the length of rotifer growing season, patterns of diapausing egg production and hatching can disperse risks and act as bet-hedging strategies. Here, we identified the methodologies to test bet-hedging theory and summarized predictions on rotifer diapause traits. We assessed these predictions by reviewing and reanalyzing results from other studies on field and experimentally evolving populations of Brachionus plicatilis from Spanish ponds. These studies include (1) a quantification of the unpredictability in field populations, (2) the measurement of diapause-related traits in laboratory conditions, and (3) genomic data. The view arising is that these rotifers adaptively respond to the unpredictability in their localities. As expected, propensity for sex increased with unpredictability. Hatching fractions of diapausing eggs were intermediate and decreased with unpredictability only in experimentally evolving populations. In field populations, genetic variance in the focal traits did not increase with unpredictability. Finally, environmental features and diapause-related traits are associated to suites of specific genes, although the molecular mechanisms linking these genes with life history are still unknown.

A comparative study on the allelopathy and toxicity of four strains ofKarlodinium veneficumwith different culturing histories

The dinoflagellate Karlodinium veneficum blooms kill fish by the production of karlotoxins. We investigated the allelopathy (Akashiwo sanguinea as the target species) and toxicity (Oryzias melastigma, Artemia salina and Brachionus plicatilis as test animals) of four strains of K. veneficum isolated from coastal waters of China and the USA to explore the ecological implications of allelopathy and toxicity. In general, all four strains of K. veneficum at high cell densities (>100 000 cellsmL(-1)) significantly inhibited the growth of A. sanguinea to different extents, but they exhibited either positive or negative allelopathy at lower densities. The toxicity of the four strains showed a decreasing order coinciding with their culture histories in the laboratory, suggesting K. veneficum may have gradually lost toxicity during laboratory culturing. The allelopathic and toxic potencies among K. veneficum strains were not perfectly parallel, indicating that either the allelochemicals and toxins of K. veneficum may be different chemicals, or the same chemicals functioned in different modes. Moreover, we found A. salina avoided feeding on more toxic strains. These results together suggest that toxins provide an advantage for K. veneficum via avoiding predation, but allelopathy may not play an important role in initiating blooms of K. veneficum.