Particle size dependent feeding by the rotifer Brachionus plicatilis

Size selective feeding by Brachionus plicatilis was investigated with algae and bacteria (0.3–3.5 µm) and mono-disperse latex beads (0.3–3.0 µm) in short term feeding experiments. B. plicatilis demonstrated maximum clearance rate of particles with diameter 2µm, but particles with diameter down to 0.3 µm were also ingested. The clearance rate of bacteria was 15–55% of that obtained for optimal sized particles (2 µm), and was related to particle size. The relative reduction in retention of particles with diameter < 2 µm was more pronounced for latex beads than for natural food particles, suggesting other mechanisms than size to be important for the particle retention by the rotifer. This is emphasized by the fact that the clearance rates were much lower for latex beads than for natural food particles of comparable size. Efficient retention of bacteria was observed for rotifers in poor physiological condition, i.e. rotifers with low maximum clearance rate. This may reflect a strategy to optimize energy utilization by reducing locomotion costs and increasing energy intake.The results indicate that B. plicatilis has a low to medium ability to feed on bacteria. In natural ecosystems, its importance as a bacterial grazer is of limited importance. At high population densities, such as in live feed cultures, the rotifer may, however, efficiently remove bacteria from the culture.     

Production of the rotifer Brachionus plicatilis for aquaculture in Kuwait

Macrophytes, plankton samples, salinity and depth data were collected from wetlands in October 1981. Species diversity and distributions are recorded and relationships drawn between macrophytes and plankton occurrence. An examination of the data of Geddes et al. (1981) enables comparisons of species composition in a similar range of Western Australian lakes in 1978 at a different stage in the seasonal cycle. Comparison with the biota of salt lakes in Australia's eastern states and elsewhere lead to biogeographical speculations for the macrophytes and for some of the planktonic species.     

褶皱臂尾轮虫同胞物种复合类群分类的研究进展

褶皱臂尾轮虫包含复杂的同胞物种,对其分类研究经过了一个长期发展的过程。综述了轮虫分类手段的发展进程,介绍和分析了轮虫特别是褶皱臂尾轮虫同胞物种复合类群分类的研究进展。褶皱臂尾轮虫的L-型和S-型属于B.plicatilis和B.rotundiformis两个物种。这个复合类群中还包括更多的种类,如B.plicatilis sensu stricto、B.ibericus和B.rotundiformis,其中B.plicatilis sensu stricto属于L型,B.ibericus属于SM-型,B.rotundiformis属于SS-型。此类研究丰富了轮虫系统分类学,提高了水域生态调查的准确性。     

Factors influencing the biomass of the rotifer Brachionus plicatilis in culture

The contribution of the egg weight and the population size structure to the body mass have been studied in two strains of Brachionus plicatilis of different size. A mathematical model was developed in order to obtain a reliable estimate of the dry mass from two single easily determined parameters; the egg/female ratio and the mean lorica length.     

Continuous culture of the rotifer Brachionus plicatilis fed recycled algal diets

A culture system for the rotifer Brachionus plicatilis was designed to maintain higher food conversion rates and stable population densities. Two 2001 plastic tanks were employed in the culture experiments, tank A for feedback culture and tank B for a control culture. The experiments were carried out for 70 days at 24 °C, light intensity, 1500 lux, and a photoperiod of L:D 15:9. B. plicatilis were fed once a day on baker's yeast and Chlorella.Food conversion rates in tanks A and B were 24.7% and 10.1%, respectively. Population density of B. plicatilis in tank A was consistently stable at 100–150 ind. ml^–1 throughout the culture period. Density in tank B, however, showed large fluctuations after 40 or 50 days and by the end of the experiment, declined to zero.     

Effect of feeding on the respiration rate of the rotifer Brachionus plicatilis

The effect of feeding on the respiration rate of Brachionus plicatilis was studied. Oxygen consumption was determined under two feeding regimes, duplicate feeding and constant feeding. Oxygen consumption rate increased during feeding. The oxygen consumption profile is discussed in relation to the following processes:

1. filtration, mastication, and locomotion during feeding
2. specific dynamic action (SDA)
3. egg formation and routine metabolism.

     

Infectious diseases affecting mass production of the marine rotifer Brachionus plicatilis

During recent years, investigations on decrease ofrotifer density in culture tanks from severalhatcheries have shown that infectious diseases mightbe associated with abnormal mortality. The firstreported infection was caused by an unusual birnavirusreferred as rotifer birnavirus (RBV). Viral lesionsappeared in cells of gastric glands and spread toother epithelia. Virus particles were also foundwithin ovarian cells. Highly infected rotifersexhibited abnormal behavior and died. The secondimportant pathogen found in Brachionusplicatilis has been provisionally related to theLagenidiaceae. The fungus developed in up to 85% ofrotifers and caused sudden, precipitous decrease inanimal density. The occurrence of these diseases showsthat in the future infectious agents will have to beconsidered as important factors capable of reducingthe productivity of rotifer mass cultures.     

Specific toxic effect of dinoflagellate Heterocapsa circularisquama on the rotifer Brachionus plicatilis

Heterocapsa circularisquama (Dinophyceae), a noxious red tide dinoflagellate, is known to have a specifically lethal effect on shellfish, especially bivalves such as pearl oyster (Pinctada fucata), but no detrimental effects of this alga on fishes have not been observed so far. In this study, we found that H. circularisquama was toxic to a microzooplankton, a rotifer (Brachionus plicatilis) in a cell concentration-dependent manner, while the cultured supernatant or ultrasonic ruptured H. circularisquama had no significant toxic effect on the rotifer. Since no such toxic effects on the rotifer were observed in Chattonella marina, Heterosigma akashiwo, or Cochlodinium polykrikoides, other species of harmful red tide plankton, H. circularisquama may have a strictly specific toxic mechanism against the rotifer as well as bivalves.     

Nutritional effect of freshwater Chlorella on growth of the rotifer Brachionus plicatilis

Mass production of Brachionus plicatilis is usually accomplished by feeding so-called marine Chlorella (Nannochloropsis oculata) to the rotifers in marine fish hatcheries. If the marine Chlorella are in short supply, baker's yeast is usually used as a supplementary food. Recently, a condensed suspension of freshwater Chlorella (Chlorella vulgaris, k-22) was commercially developed as another supplementary food. We have evaluated the dietary value of this freshwater Chlorella for growth of the rotifer by means of individual and batch cultures. Rotifers cultured with the freshwater Chlorella suspension under almost bacteria-free conditions, showed very suppressed growth. However if the Chlorella was supplemented with vitamin B₁₂ by adding the vitamin solution into the suspension or by culturing the Chlorella in a medium containing vitamin B₁₂, the nutritional value of freshwater Chlorella was greatly improved and almost at the same level as that of marine Chlorella. Condensed Chlorella may therefore be effective as a supplementary food if vitamin B₁₂ is supplied.     

Population growth dynamics of the rotifer Brachionus plicatilis cultured in non-limiting food condition

Population growth parameters in batch culture of Brachionus plicatilis under a continuous supply of freeze-dried microalgae powder have been determined. Two B. plicatilis strains (L- and S-types) and four microalgae species (Nannochloropsis oculata, Nannochloropsis gaditana, Nannochloris oculata and Tetraselmis suecica) have been tested, establishing the dynamics of growth at different daily food rations. Cultures showed a short lag phase, an exponential growth phase, a long post-exponential growth phase and long decline with episodic increases. In both rotifer strains, the best growth was obtained with Nannochloropsis oculata and the poorest with Nannochloris oculata.     

Asexual and sexual reproduction in the rotifer Brachionus plicatilis cultured at different salinities

Two strains of the rotifer Brachionus plicatilis (L-type) differing in the levels of mictic female and male production, were grown in batch cultures with the alga Nannochloropsis gaditana as food, at two low (2.5 and 10), and two high (40 and 50) salinities. While both the low (strain S-1) and the high (strain S-3) sexual reproducing strains developed similar growth cycles at 2.5 and 10, the population growth response at 40 and 50 showed that; 1) in strain S-1, mixis can be suppressed in conditions that still allow asexual reproduction, and 2) in strain S-3 mictic female and male production are possible at nearly zero asexual population growth rates. In strain S-3, a double log linear relationship between the densities of males and females was found. These results show that mixis can occur over a wide ranges of female population density, and support the hypothesis that sexual reproduction is a strain dependent component of the general reproductive response.     

Coexistence of rotifer (Brachionus plicatilis) clones in Soda Lake,Nevada

Patterns of genetic variation among Brachionus plicatilis clones collected at different times from Soda Lake, Nevada (U.S.A.) were determined using polyacrylamide gel electrophoresis of isozymes. Six of the eleven enzymes assayed were variable. Three of these — malic dehydrogenase (MDH), cholinesterase (CHO), and phosphoglucomutase (PMG) - were selected to screen the 138 clones established from the field collections. Each enzyme revealed variation both within and between field samples. Thirty-eight of the 100 potential composite electromorphs formed by combining isozyme variants were found in the 138 clones. A substantial amount of genetic variation is therefore present. Patterns of electromorph frequency change resembled those reported for cladocerans. No evidence was found for a seasonal succession of distinct electromorphs. We suggest that the B. plicatilis in Soda Lake constitute a single population.     

Ecological genetics of the rotifer Brachionus plicatilis in Soda Lake,Nevada, USA

In an earlier study we found that the rotifer Brachionus plicatilis in Soda Lake, Nevada (USA) maintains extensive genetic variation for three isozymes. This variation was present both within and between different collections. No evidence was found that there was a seasonal succession of distinct electromorphs. In this paper we ask: is the genetic variation maintained by selective neutrality among electromorphs? Parthenogenetic females from ten clones representing seven different composite electromorphs were selected for life table analysis. Substantial main effects of genotype or interactions of genotype with experimental food quantities and temperatures, were found for the intrinsic rates of increase, net reproductive rates, and mean life spans of these clones. We conclude that these fitness differences permit us to reject the hypothesis that genetic variation is maintained because of selective neutrality among clones. Instead, it seems likely that directional selectional may be either too weak or of too brief a duration in Soda Lake for clonal exclusion to occur.     

Atkinsiella parasitica sp. nov. isolated from a rotifer,Brachionus plicatilis

A new species ofAtkinsiella (Lagenidiales, Oomycetes),Atkinsiella parasitica is described and illustrated. It was isolated from the eggs and bodies of a rotifer,Brachionus plicatilis, with fungal infection in 1992. The rotifer was reared in a hatchery as the first food supply for seed production of crustaceans and fishes. The fungus is characterized by producing monoplanetic, lateral biflagellate zoospores, and infrequently branched discharge tubes. Optimum temperature for the fungus was 25°C. The fungus was considered an obligate marine fungus, because its growth was observed only on PYGS medium including seawater.     

Coexistence of cryptic rotifer species: ecological and genetic characterisation of Brachionus plicatilis

1. The coexistence of five cryptic species of the rotifer species complex Brachionus plicatilis was investigated in four coastal Mediterranean ponds. Monthly sampling was undertaken for 15 months and species were characterised using allozyme electrophoresis. 2. We describe species‐diagnostic allozyme loci that can be used for rapid identification of these species. 3. The five species overlapped to some extent in their temporal use of the ponds, although some seasonal segregation was observed. 4. The match between temporal and spatial distribution and limnological conditions suggested ecological specialisation in some cases, although we found striking examples of extensive seasonal overlap. 5. Our results indicate that sympatry of cryptic rotifer species is largely because of seasonal ecological specialisation, which allows seasonal succession and partitioning of resources. The processes that might be involved in the long periods of overlapping seasonal distributions of species which are potentially competitors are discussed. This example illustrates that the ‘paradox of the plankton’ is more the rule than the exception.     

Protein and lipid content of the rotifer Brachionus plicatilis during variable growth and feeding condition

Rotifers (Brachionus plicatilis) grown atdifferent growth rate ( = 0.05–0.39 d^–1)were analyzed for protein, lipid, fatty acids, aminoacids and free amino acids, and values are expressedin terms of individuals and dry weight. Increase ingrowth rate is equivalent with increased food rationof the individual rotifer, which responded by higheregg ratio. The protein content per individualrotifer increased by 60–80% when the growth rate increased, whereas the protein content per dryweight showed a slight, although insignificant,increase (p > 0.05). The lipid content perindividual was constant, whereas lipid per dryweight decreased when the growth rate increased. Theratio DHA/EPA decreased when the growth ratesincreased. The amino acids profile in percent oftotal amino acids showed low variation betweencultures maintained at different growth rates,whereas the values expressed in terms of amino acidper individual showed higher variation. The range ofvariation for free amino acids was more pronouncedthan for total amino acids.Short-term food enrichment of poorly fed rotifers( = 0.05 d^–1) with balanced protein richdiet resulted in increased protein and lipid contentper rotifer. The protein content per dry weightshowed only minor changes whereas lipid per dryweight increased. Contrary, short term enrichmentwith a lipid rich diet resulted in increased lipidcontent per individual rotifer and per dry weight,whereas the protein content per individual remainedconstant and the protein content per dry weightshowed a slight decrease.Our experiments show that the amount of protein, wasquite variable in rotifers, and that feeding andgrowth condition were decisive factors affecting it.The range of variation was large enough to be animportant factor during first feeding of marinelarvae, and should therefore be considered infeeding larvae.     

Effect of diazinon on life stages and resting egg hatchability of rotifer Brachionus plicatilis

The effects of organophosphate pesticide, diazinon, on life history parameters and hatchability of resting eggs of rotifer Brachionus plicalitis were assessed. Newly hatched (<1 h-old) neonates were individually cultured in six varying concentrations (0/control, 0.1, 1.0, 2.5, 5.0 and 10.0 mg/l) of diazinon. The life history parameters such as time (h) the rotifers bear first egg and release first neonate, reproductive period, net reproductive rate, mixis, intrinsic rate of population increase, and life span were evaluated. Results showed that among the life history parameters, the time the rotifers took to release neonates is the most sensitive, giving the lowest EC₅₀ value of 1.24 mg/l. The fecundity of maternal females, amictic and mictic daughters was also investigated. Rotifers exposed to 10.0 mg/l produced significantly fewer amictic daughters, and at this concentration, rotifers did not produce any mictic daughter. At 5.0 mg/l, the number of male offspring was significantly lower than the control. Furthermore, the hatchability of resting eggs produced by the rotifers was evaluated when exposed to diazinon: from birth until they produced resting eggs (early development); during late developmental stage of resting eggs (before diapause); and during diapausing stage. The hatchability of the resting eggs was not affected when exposure was timed at late developmental and diapausing stages. Overall results showed that even though amictic females reproduced normally in the presence of low-concentration of diazinon, sexual reproduction is severely affected, especially the hatchability of resting eggs when the exposure was timed on its early developmental stages. Guest editors: S. S. S. Sarma, R. D. Gulati, R. L. Wallace, S. Nandini, H. J. Dumont & R. Rico-Martínez Advances in Rotifer Research