Rotifer Growth Rate Research Articles

Adequate nutrient intake mitigate the toxic effects of bromate on the rotifer Brachionus calyciflorus.

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

Locomotory behaviour of euryhaline rotifer Brachionus rotundiformis: The potential influence of probiotics on swimming pattern and speed

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

Dinoflagellate Karenia mikimotoi on the growth performance, antioxidative responses, and physiological activities of the rotifer Brachionus plicatilis.

The harmful dinoflagellate Karenia mikimotoi is responsible for the mortality of aquatic animals. However, the mechanism behind these toxic effects has not been fully determined. Herein, the toxic effects of K. mikimotoi on the growth performance, antioxidative responses, physiological activities, and energetic substance contents of rotifer Brachionus plicatilis were assessed. Rotifers were exposed to Nannochloropsis salina (Eustigmatophyceae), K. mikimotoi, and a mixture of N. salina and K. mikimotoi with biomass ratio proportions of 3:1, 1:1, and 1:3, respectively. Results indicated that K. mikimotoi negatively affected the population growth, survival, and specific growth rates of rotifers within 24 h. The level of reactive oxygen species (ROS), the content of malondialdehyde, and the activity of amylase increased. However, the total antioxidant capacity level, pepsase, cellulase, alkaline phosphatase, xanthine oxidase, and lactate dehydrogenase activities, and glycogen and protein contents decreased with increasing proportions of K. mikimotoi. The mixture of 50% N. salina and 50% K. mikimotoi promoted the increase in glutamic-pyruvic transaminase activity and triglyceride content. These findings underscore ROS-mediated antioxidative responses, physiological responses, and energetic substance content changes in B. plicatilis work together to affect population dynamics inhibition of rotifers by K. mikimotoi.

Bioaccumulation and biomagnification effects of nano-TiO2 in the aquatic food chain.

The increasing production of nano-TiO2 has attracted extensive concerns about the ecological consequence and health risk of these compounds in natural ecosystem. However, little is known about its toxicity on zooplankton, especially its possibility to access to the food chain via dietary exposure. To address this concern, the toxic and cumulative effects of nano-TiO2 on an aquatic food chain were explored through two trophic levels independently or jointly including producer and consumer. The results revealed that exposure to suspensions of nanomaterials had negative effects on both producers and consumers. Specifically, nanoparticles reduced the density of algal cells in a concentration-dependent way, and hatching life expectancy, average lifespan, net reproductive rate, and population intrinsic growth rate of rotifers decreased significantly with the concentration of nanomaterials increased (P < 0.05). Notably, nanoparticles accumulated in algal cells and were transferred to consumers through dietary exposure. Biomagnification of nano-TiO2 was observed in this simplified food chain, as many of the biomagnification factor (BMF) values in this study were >1. Exposure concentration, exposure time and their interactions play a strong part in the accumulation of nanoparticles in algae and rotifers. Overall, the present findings confirmed that nano-TiO2 was deleterious to plankton, posing a significant environmental threat to aquatic ecosystems. Graphical abstract.

Variations in the life-cycle parameters and population growth of rotifer Brachionus plicatilis under the stress of microplastics and 17β-estradiol

The toxic effects of microplastics (MPs) on biota are related to their particle size. In addition, MPs could adsorb ambient pollutants in water, which increase the threat of MPs to organisms. In this study, the effects of different particle sizes and concentrations of MPs on the life-cycle parameters and population growth of rotifer Brachionus plicatilis were investigated, and the combined effects of MPs and 17β-estradiol (E2) on rotifers were studied. Results showed small particle size (50 nm) MPs had negative effects on the lifespan, time to first batch of eggs, fecundity, and population growth rate of rotifers, which were dose-dependent, but large (100 nm and 500 nm) MPs were not. In addition, both life-cycle parameters and the population growth of rotifers were not affected by E2. However, the combination effects of different particle sizes of MPs and E2 on the lifespan, reproductive period, offspring per female, and population growth of rotifers were significant. Therefore, rotifers were more vulnerable to smaller particle MPs, and the coexistence of MPs and other environmental pollutants posed a serious threat to rotifers.

Suitability of Tisochrysis lutea at different growth phases as an enrichment diet for Brachionus plicatilis sp. complex rotifers

In larviculture of marine finfish, Tisochrysis lutea cultured cells have a potential to be a sustainable enrichment diet for rotifers due to its de novo synthesis of docosahexaenoic acid (DHA). To improve its effectiveness in rotifer enrichment for later larviculture, we determined which growth phase of T. lutea can enhance DHA in polar lipids (PLs) in Brachionus plicatilis sp. complex rotifers without reducing their vigor. Tisochrysis lutea was harvested at logarithmic growth phase, deceleration growth phase, and stationary phase. The ambient concentrations of phosphorus (P) and nitrogen (N), and fatty acid composition of microalgae were measured. P was limited between logarithmic and deceleration growth phases, followed by N starvation in stationary phase. Total lipid DHA was lowest in logarithmic growth phase, whereas DHA levels increased in deceleration growth phase and maintained at high levels even in stationary phase. PL-DHA also increased during deceleration growth phase, although its abundance dropped during stationary phase. In a rotifer enrichment trial, T. lutea harvested in each phase were fed to B. plicatilis sp. complex rotifers for 12 h. The highest PL-DHA value for cells in deceleration growth phase reflected the concentrations of the rotifers. No significant differences were found in rotifer growth rate and egg ratio. Rotifers fed cells in deceleration growth phase exhibited higher swimming speeds than those fed the other cells, potentially linking to increased larval capture success. Therefore, we recommend the deceleration growth phase as an optimal timing for T. lutea harvest for the effective enrichment of B. plicatilis sp. complex rotifers.

Lecane tenuiseta (Rotifera, Monogononta) as the best biological tool candidate selected for preventing activated sludge bulking in a cold season

Rotifers in activated sludge reduce the quantity of dispersed bacteria, ingest filamentous bacteria, enhance flocculation and limit biomass production. Growth rates of rotifers are inversely correlated with temperature; thus, their density declines drastically in wastewater treatment plants (WWTPs) during the winter. The only species already demonstrated to be able to control bulking is Lecane inermis. However, they cease proliferation at 8°C. The goal of our research was to select other rotifers species whose growth rates at lower temperatures are sufficiently high to maintain a favourable density during cold seasons. We conducted selection experiments in the laboratory at temperatures reflecting the temperature distribution in the majority of municipal WWTPs in the temperate zone. In the first experiment, the general selection stage, we tested the influence of the temperatures 8, 15 and 20°C on competition among different rotifer taxa in sludge samples originating from different WWTPs. The rotifers best adapted to lower temperatures were found among the genera Lecane and Cephalodella. The second stage, focused on Lecane selection, showed that the genus Lecane was represented most abundantly by L. inermis and Lecane tenuiseta. At 8°C, only clones of L. tenuiseta exhibited positive growth rates. At 15°C, more selected clones were identified as L. tenuiseta than as L. inermis, but the r-value for L. inermis was higher. Our results suggested that L. tenuiseta is the best candidate for bulking control in cold seasons.

A comparison among different Pavlova sp. products for cultivation of Brachionus plicatilis

In the present study the potential of different products of the marine microalga Pavlova sp. for the cultivation of rotifers (Brachionus plicatilis) was tested. Two growth performance trials were conducted: In a first laboratory scale experiment rotifers were cultivated for 14 days with Pavlova viridis concentrate, P. viridis fresh culture, Pavlova sp. fresh culture, baker's yeast and Nannochloropsis sp. concentrate. The P. viridis fresh culture fed groups resulted in significantly the highest rotifer density (109.2 rotifers mL(-1)) and instantaneous growth rate (G = 0.14 +/- 0.02 d(-1)). There were no significant differences found of the G between the P. viridis concentrate group and the Pavlova sp. fresh culture group. The baker's yeast fed group showed significantly the lowest rotifer numbers and growth rate. Based on the high growth rate of the P. viridis fresh culture group in the first experiment, different P. viridis products (concentrate, fresh culture, frozen concentrate, and freeze- dried powder) were examined in the second (larger scale) experiment and compared to Nannochloropsis sp. concentrate. The highest rotifer growth rate G in experiment 2 was determined for the frozen P. viridis group (G = 0.09 +/- 0.03 d(-1)), although it was not significantly different in comparison to the G of the rotifers fed with Nannochloropsis sp. and the Pavlova concentrate and fresh culture. The frozen Pavlova product seems the most suitable Pavlova product for the cultivation of live feed and it provides advantages of storability and application. (C) 2014 Elsevier B.V. All rights reserved.

Indirect bottom‐up control of consumer‐resource dynamics: Resource‐driven algal quality alters grazer numerical response

The nature of the growth‐rate response of grazing zooplankton to algal concentration depends critically upon food quality, which is often a plastic function of environmental conditions. Phytoplankton quality depends upon nutrient and light availability, which together affect cell C : P and C : N, so that the links from external environment to phytoplankton and then to zooplankton can vary in ways that influence consumer‐resource interaction strengths, and ultimately, food web structure. We measured the effects of resource‐limitation on the population growth rate of rotifers, Brachionus calyciflorus, feeding on the alga Chlamydomonas reinhardtii, and grown in nitrogen‐limiting, phosphorus‐limiting, or nutrient‐sufficient conditions. Consumption of nutrient‐sufficient algae produced a Type II numerical response with a low half saturation constant (Ks) and high asymptotic growth rate (λmax) consistent with high food quality; P‐limited algae also yielded a Type II response but with high Ks and low λmax, meaning poor food quality. In contrast, N‐limited Chlamydomonas resulted in a novel Type IV numerical response in which rotifer growth rate rose to an intermediate λmax and then declined at the highest algal densities, suggesting the production of toxic compounds whose negative effect on growth increases as a function of cell density. Experiments with mixed diets confirmed that N‐limited food was indeed toxic, whereas P‐limited food was simply nutritionally deficient compared with light‐limited algae. Additional experiments showed that even the filtrate of N‐limited algae can be detrimental to rotifer growth.

Biochemical nutrient requirements of the rotifer Brachionus calyciflorus: co‐limitation by sterols and amino acids

Summary It has been proposed that growth and reproduction of animals is frequently limited by multiple nutrients simultaneously. To improve our understanding of the consequences of multiple nutrient limitations (i.e. co‐limitation) for the performance of animals, we conducted standardized population growth experiments using an important aquatic consumer, the rotifer Brachionus calyciflorus. We compared nutrient profiles (sterols, fatty acids and amino acids) of rotifers and their diets to reveal consumer–diet imbalances and thus potentially limiting nutrients. In concomitant growth experiments, we directly supplemented potentially limiting substances (sterols, fatty acids, amino acids) to a nutrient‐deficient diet, the cyanobacterium Synechococcus elongatus, and recorded population growth rates. The results from the supplementation experiments corroborated the nutrient limitations predicted by assessing consumer–diet imbalances, but provided more detailed information on co‐limiting nutrients. While the fatty acid deficiency of the cyanobacterium appeared to be of minor importance, the addition of both cholesterol and certain amino acids (leucine and isoleucine) improved population growth rates of rotifers, indicating a simultaneous limitation by sterols and amino acids. Our results add to growing evidence that consumers frequently face multiple nutrient limitations and suggest that the concept of co‐limitation has to be considered in studies assessing nutrient‐limited growth responses of consumers.

Selection of Suitable Species of Chlorella, Nannochloris, and Nannochloropsis in High- and Low-Temperature Seasons for Mass Culture of the Rotifer Brachionus plicatilis

To find seasonally optimal microalgae for mass culture of the rotifer Brachionus plicatilis, the growth rates of 12 microalgal species (two marine Chlorella spp., five marine Nannochloris spp., two marine Nannochloropsis spp., one estuarine Nannochloropsis sp., and two estuarine Chlorella spp.) were compared at 25°C at 15 psu and 30 psu. Among these, six species showing high growth rates were chosen and examined again at high (30°C and 32°C) and low (10°C) temperatures. Their amino and fatty acids and the dietary value of the rotifers that fed on each microalgal species were examined. Nannochloris sp. (KMMCC-119) and Chlorella vulgaris (KMMCC-120) showed the highest growth rates at temperatures over 30 o C and at 10°C, respectively. The growth rate of Nannochloris was higher than those of Chlorella and Nannochloropsis at high temperatures, but lower than those of the latter at low temperatures. The growth rate of rotifers fed on Nannochloropsis was highest and that of those fed on Chlorella was lowest. Levels of eicosapentaenoic acid and docosahexaenoic acid were highest in Nannochloropsis and lowest in Nannochloris. However, total amino acid content was highest in Nannochloris and lowest in Chlorella. In conclusion, Nannochloropsis sp. (KMMCC-33) was the best microalgal species for the mass culture of the rotifer. However, during high- or low-temperature seasons in which Nannochloropsis does not grow well, Nannochloris spp. (KMMCC-119, 395) and C. vulgaris (KMMCC-120) would adequately replace Nannochloropsis sp. (KMMCC-33).

Effect of temperature and dietary elemental composition on RNA/protein ratio in a rotifer

Summary 1 Temperature and the elemental composition of food are key regulators of consumer growth rate, yet the knowledge on how these factors interact is scarce. In this study, we addressed this issue by using the rotifer Brachionus calyciflorus as a model organism. 2 Rotifers were raised at four different temperatures under a range of C/P and C/N ratios in their food and assessed the responses by analysing somatic RNA/protein ratios as a marker of growth rate. 3 Both N- and P-limited algae restricted the growth rates of rotifers. The interaction between C/P ratio of a given algae and temperature demonstrated that P limitation became intensified with increasing temperature. 4 Animals that were relieved from N limitation increased their RNA/protein ratio, as did animals fed on constant C/N ratio but with P-enriched food. This illustrates a mutual dependency and interaction between N and P in the protein synthesis by up-regulating the biosynthetic machinery, and that even while the effect of N limitation was more pronounced, P limitation was also potentially important in this species. 5 Our results provide evidence that over the tested range of temperature and food qualities, nutrient limitation in these animals was more important than the temperature effect. We also found, however, that increasing temperature can shift from P to N limitation in the consumer.

Effect of the Nutritional Status of Semi-continuous Microalgal Cultures on the Productivity and Biochemical Composition of Brachionus plicatilis

The rotifer Brachionus plicatilis was cultured using the microalga Isochrysis aff. galbana clone T-ISO as feed. T-ISO was cultured semi-continuously with daily renewal rates of 10%, 20%, 30%, 40%, and 50% of the volume of cultures. The increase of renewal rate led to increasing nutrient and light availability in microalgal cultures, which caused differences in the biochemical composition of microalgal biomass. Growth rate, individual dry weight, organic content, and biomass productivity of rotifer cultures increased in response to higher growth rate in T-ISO cultures. Rotifer growth rate showed a strong negative correlation (R² = 0.90) with the C/N ratio of microalgal biomass. Rotifer dry weight was also affected by nutrient availability of T-ISO cultures, increasing up to 50% from nutrient-limited to nutrient-sufficient conditions. Consequently, biomass productivity of rotifer cultures increased more than twofold with the increase of renewal rate of T-ISO cultures. Rotifer organic content underwent the same trend of total dry weight. Maximum content of polyunsaturated fatty acids was reached in rotifers fed T-ISO from the renewal rate of 40%, with percentages of docosahexaenoic acid (22:6ω-3, DHA) and eicosapentaenoic acid (20:5ω-3, EPA) of 11% and 5% of total fatty acids, respectively. Selecting the most appropriate conditions for microalgal culture can therefore enhance the nutritive quality of microalgal biomass, resulting in a better performance of filter feeders and their nutrient content, and may constitute a useful tool to improve the rearing of fish larvae and other aquaculture organisms that require live feed in some or all the stages of their life cycle.

Analysis of the evolution of microbial communities associated with different cultures of rotifer strains belonging to different cryptic species of the Brachionus plicatilis species complex

The evolution of the composition of microbial communities associated with cultures of 3 different strains belonging to different cryptic species of the rotifer Brachionus plicatilis was monitored during four subsequent cycles of batch cultivation using denaturing gradient gel electrophoresis, cluster analysis, multidimensional scaling and principal component analysis. The data suggest that the evolving microbial communities are different with different B. plicatilis strain cultures. Moreover, large changes in rotifer growth rate were found to be associated with large changes in the microbial community composition, suggesting that there might be a causal link. Finally, Lorenz curves and Gini-coefficient analysis revealed that good performing B. plicatilis cultures showed a more even microbial community structure.

Diet quality impact on growth, reproduction and digestive activity in Brachionus calyciflorus

We examined population growth rate, reproduction and phosphatase activity in digestive tracts of individual Brachionus calyciflorus fed by P-replete (molar C:P = 107) or P-depleted (C:P = 920) algal food supplied at three carbon (C) concentrations (1, 2, and 4 mg C L −1 ). Rotifer growth rate was significantly influenced by P content, whereas the effect of algal C concentration was not significant. Both algal P content and C concentration had a significant effect on the egg ratio. The individual amount of chlorophyll a (chl-a) was considered as a proxy for the ingested algal food occurring in the rotifer's gut and phosphatase activity in the gut likely reflected variable individual assimilation of P under different food treatments. The amount of both chl-a and phosphatase activity in the rotifers fed by P-replete algae significantly increased with an increase in C concentration in the food suspension. In contrast, the amount of chl-a significantly decreased with an increase in food concentration, and phosphatase activity did not change significantly over different food quantity in the rotifers fed by P-depleted algae. Thus, the hypothesis that P-deficient rotifers use preabsorptive regulation by changing activity of the digestive enzymes is not supported by the data.

Tasa de crecimiento poblacional del rotífero Brachionus rotundiformis (Rotifera: Brachionidae) en un quimiostato de dos cámaras

The population growth rate of the rotifer Brachionus rotundiformis (Rotifera: Brachionidae) in two-stage chemostat. The population growth rates of Brachionus rotundiformis were estimated in two-stage chemostat cultures. Chlorella sorokiniana was supplied continuously from a steady state culture growing with constant illumination on limiting nitrate. Rotifer growth in the second stage was limited by the rate of algal supply. The algal supply rate and rotifer population growth rate were determined by the second-stage dilution rate. The maximum population growth rate in the transient state of B. rotundiformis (1.96 day(-1)) was observed at 2.5 x 10(6) cel/ml of the algae whereas in the steady state the maximum population growth rate (1.09 day(-1)) was similar to the point Hopf's bifurcation predicted by Fussmann and was observed at 1 x 10(6) cel/ml of the algae. In the transient state, the rotifer's growth rate increased and the duplication time decreased at higher algal concentrations, until reaching a peak where the population growth rate begins to decrease. In the steady state, the opposite was true. The growth rates observed in this work are among the highest recorded for this rotifer in continuous cultures.

Gnotobiotically grown rotifer Brachionus plicatilis sensu strictu as a tool for evaluation of microbial functions and nutritional value of different food types

Axenic rotifers ( Brachionus plicatilis sensu strictu, clone 10) were obtained by treating amictic eggs with glutaraldehyde. Depending of the batch of rotifers, total disinfection could be obtained by exposure to 50–100 ppm from 1 to 2 h at 28 °C. The hatched axenic neonates were used to test the effect of microbial communities (MCs) which were isolated from either normal-performing or crashed rotifer cultures. These MCs were either used directly or were first regrown on Marine Agar. MCs were introduced to gnotobiotic Brachionus cultures in combination with three different food types, i.e. Chlorella, wild-type yeast and the mnn9 yeast mutant, which is deficient in cell wall-bound mannoprotein. In the absence of MCs or when heat-killed MCs were added, Chlorella was always the best food, while lower growth rates were observed with wild-type yeast and the mnn9 mutant as food. In the presence of live MCs and when rotifers were fed with Chlorella, the added MCs had no effect on rotifer performance. When yeasts were used as major food, all the tested MCs were able to increase the rotifer growth rate. The experiments with heat-killed MCs yielded no increase in rotifer growth rate, suggesting that the observed enhancement in rotifer growth rate was truly a probiotic effect rather than a nutritional effect. The results of this study demonstrate that gnotobiotic rotifer cultures obtained from axenic amictic eggs can be used as a test system for studying microbial-attributed as well as nutritional functions in the aquatic food chain. In addition, since the MCs originating from the crashed rotifer cultures did not decrease the growth rate in the tested rotifer cultures, it is likely that the observed crashes were not due to the presence of a standing deleterious MC.

고밀도 배양에 있어 먹이종류와 공급량 및 vitamin B12첨가에 따른 담수산 rotifer (Brachionus calyciflorus)의 성장

This study investigated the effects of food type (condensed freshwater Chlorella, dried Chlorella, dried Spirulina, dried Schizochytrium, baker's yeast and <TEX>$\omega-yeast$</TEX>) and amount, and supplementation of vitamin <TEX>$B_{12}$</TEX> on the growth of freshwater rotifer (Brachionus calyciflorus) in high density culture. Growth of rotifers fed condensed freshwater Chlorella was the highest and its density ranged <TEX>$7.65-8.14{\times}10^3\;inds./mL.$</TEX> The primary lipid acids of rotifers fed condensed freshwater Chloyella were linoleic and linolenic, and their amount (<TEX>$\%$</TEX> of total fatty acids) were <TEX>$48.8\%\;and\;26.8\%,$</TEX> respectively. This suggests that condensed freshwater Chlorella would be an effective diet for high quality and quantity rotifers, which in turn serve as live food for freshwater fish larvae. Growth rate of rotifers with Chlorella supplementation increased as amount of supplementation increased up to 1.5 and 2.5 mg at 28 and <TEX>$32^{\circ}C$</TEX>, respectively. However, undissolved ammonia toxicity and packing volume of Chlorella in culture medium, reached the optimal conditions for the stable and effective cultivation of rotifers when amount of condensed freshwater Chlorella was 1.5 mg in dry weight per 1,000 rotifers at <TEX>$28^{\circ}C\;and\;32^{\circ}C$</TEX> Growth of rotifers in condensed freshwater Chlorella with vitamin <TEX>$B_{12}$</TEX> supplementation was significantly higher than that of rotifers without supplementation. However, no significant difference was found among the different concentrations of vitamin <TEX>$B_{12}.$</TEX> Therefore, vitamin <TEX>$B_{12}$</TEX> could improve the growth of rotifers (B. calyciflorus).

Elimination of the associated microbial community and bioencapsulation of bacteria in the rotifer Brachionus plicatilis

The bioencapsulation of live bacteria in the rotifer Brachionus plicatilis was determined under monoxenic conditions. The first objective was to evaluate the microbiota of the rotifer during intensive production and to obtain sterile rotifer cultures starting from adult females or amictic eggs using PVP-Iodine, Hydrogen peroxide or antibiotic mixtures. In the rotifers, the proportion of vibrios increased significantly during the mass production, displacing other unidentified marine bacteria. Rotifers, in the absence of culturable bacteria were obtained starting from amictic eggs and using Trimetroprim-sulfametoxasole (Bactrim Roche®) at 10 ml l−1. The effect of members of Vibrionaceae on the survival and growth rate of rotifers was determined under monoxenic conditions. The survival of rotifers was not affected in the presence of different isolates, while amictic egg formation occurred and the populations increased when the strains Vibrio proteolyticus C279 and Aeromonas media C226 were tested. All isolates were successfully incorporated in the rotifers, since there was no significant difference between the numbers of bioencapsulated cells of different strains of isolates. The results show that it is possible to replace the microbial community in rotifer cultures, started from disinfected amictic eggs, with selected bacterial strains. This could be used as a tool for future studies to reveal the role of specific bacteria on first larval stages of marine fish species.

Bacterial additives that consistently enhance rotifer growth under synxenic culture conditions: 2. Use of single and multiple bacterial probiotics

Axenic rotifers were cultured under synxenic conditions on a bacteria-free artificial diet. The cultures were inoculated either with one of four strains of cultured marine bacteria, or with mixtures of bacteria made up with the same four strains and differing only in the proportions of cells from each strain within the blends. Control cultures were inoculated with bacteria present in freshly collected samples of seawater (SW). The lowest rotifer growth rates were observed in these control cultures. The highest growth rates were determined in cultures inoculated with either an Alteromonas strain or a mixture of strains (M2) composed of a larger proportion of the Alteromonas cells than any of the other microbial constituents. The largest variations in rotifer growth rate between replicate cultures were determined in cultures seeded with SW bacteria, while the lowest were determined in cultures inoculated with either Alteromonas or two blends including mixture M2. Similar results were obtained with both species of rotifers tested, Brachionus plicatilis Müller and B. rotundiformis Tschugunoff.