Suspended clay reduces Daphnia feeding rate

SUMMARY. 1. Suspended sediments often reduce cladoceran abundance in the field, and reduce the algal feeding rates of cladocerans in the laboratory. This paper explores the behavioural mechanisms by which suspended clay reduces Daphnia feeding rates. Feeding experiments using radiolabelled Cryptomonas cells showed that 50–200 mg 1-^?1 coarse suspended clay (particle size<2 μm) reduced the algal ingestion rate of Daphnia ambigua by 29–87%, but fine suspended clay (<1 μm) had no effect. Suspended clay decreased feeding rate by 60–70% at low algal concentrations (≤5×10³ cells ml^?1), but by only 27% at high algal concentrations (20×10³ cells ml^?1). Thus, the inhibitory effects of suspended clay are greater at low algal concentrations. The sudden addition (or removal) of suspended clay caused immediate reductions (or increases) in algal ingestion rate. 2. Observations of the feeding behaviour of tethered D.pulex showed that the frequency of postabdominal rejections increased greatly in the presence of suspended clay. The rejected boluses contained both algae and clay. Thoracic feeding appendage beat frequency decreased in the presence of suspended clay, decreasing the volume of water searched for food particles. 3. These behavioural responses indicate that clay reduces cladoceran feeding rate by mechanically interfering with both the collection and ingestion of algal cells. Both inhibitory effects are caused because cladocerans collect and ingest suspended clay particles. The behavioural mechanisms by which cladocerans regulate their feeding rate in very high concentrations of algal cells (rejection of excess food and reduction in thoracic limb pumping movements) are the same mechanisms responsible for the inhibition of algal ingestion rate in the presence of high concentrations of suspended clay particles.     

Feeding in the rotifer Brachionus calyciflorus

Summary The laboratory feeding behavior of Brachionus calyciflorus varies depending upon the type of food cell available in suspension. When feeding on the yeast Rhodotorula glutinis, rotifers show a continuous increase in ingestion with increased cell density between 0.01 and 1000 g dry weight ml^-1. Effective clearance rates drop from ca. 50 l animal^-1 h^-1 to less than 0.5 l animal^-1 h^-1 over this food density range. When feeding on Englena gracilis, B. calyciflorus ingestion rates are constant between 1.0 and 100 g ml^-1 of available food, averaging close to 25 ng animal^-1 h^-1. The decrease in clearance rate is more striking than with R. glutinis, dropping from 45 l animal^-1 h^-1 at 0.1 g ml^-1 to 0.13 l animal^-1 h^-1 at 100 g ml^-1. Differences between the patterns obtained with the two food types indicate fundamental dissimilarities in the feeding behavior of this rotifer species when presented with these different foods.     

Bacterial feeding by the rotifer Brachionus calyciflorus: Clearance and ingestion rates,behavior and population dynamics

Summary The rotifer Brachionus calyciflorus is capable of collecting and ingesting cells or short chains of a laboratory-grown bacterium Aerobacter aerogenes. Clearance rate, the volume of water effectively processed animal ^-1h^-1, does not vary systematically with bacterial density between 0.01 and 100 g dry weight ml^-1. Consequently, ingestion rates are strongly density-dependent, reaching maximal values at the highest food densities tested. Bacterial feeding rates are consistently lower than those determined with larger food types, except in very dense cell suspensions. A. aerogenes in high concentration (100 g ml^-1) induces Brachionus to orient their pseudotrochal cirri to form screens over the buccal funnel; this behavior is at least four times less frequently observed at low (10 g ml^-1) food density. Despite its occurrence, pseudotrochal screening appears ineffective in regulating bacterial ingestion rate. B. calyciflorus can be cultured xenically for greater than 40 generations fed A. aerogenes alone, with no diminution in net reproductive rate or intrinsic rate of natural increase, and no lengthening in cohort generation time.     

Swimming behaviour of <Emphasis Type="Italic">Brachionus plicatilis</Emphasis> in relation to food concentration and feeding rates

We examined feeding rates and swimming speed in amictic females of Brachionus plicatilis over algal cell concentrations ranging from 15 × 10³ to 30 × 10⁶ cell ml⁻¹, to determine to what extent filtration rate is a consequence of a real modulation of swimming speed in response to food availability. Swimming rates were measured using an automated motion analysis system via video recording. The results showed that swimming speed changed as a function of food density. Swimming speed increased from the lowest tested concentration of algae to reach a maximum at 6 × 10⁶ cell ml⁻¹. Above this density, swimming speed declined slightly and then remained constant at a mean speed of 0.45 mm s⁻¹. Filtration and ingestion rates changed as cell concentration increased, following patterns consistent with those generally described for suspension feeders. However, the observed swimming pattern did not explain the recorded changes in clearance rate. These results suggest that filtration, and therefore ingestion, is mainly regulated by modifying particle retention efficiency. Guest editors: S. S. S. Sarma, R. D. Gulati, R. L. Wallace, S. Nandini, H. J. Dumont & R. Rico-Martínez Advances in Rotifer Research     

Utilization of cyanobacteria by Brachionus calyciflorus: Anabaena flos-aquae (NRC-44-1) as a sole or complementary food source

The rotifer Brachionus calyciflorus can utilize the cyanobacterium Anabaena flos-aquae as either a sole or supplementary food source in laboratory culture. Positive population growth rates accompany food densities of 10 or 100 µg dry weight ml^–1, but slightly negative rates are found at a lower density (1.0 µg ml^–1). These results are consistent for rotifers feeding on two strains of A. flos-aquae, UTEX-1444 and NRC-44-1, with slightly enhanced survivorship and reproduction with the latter food. A 1:1 mixture (by dry weight) of Euglena gracilis and A. flos-aquae (NRC-44-1) produces survivorship comparable to that of control rotifer cohorts fed E. gracilis alone, but elicits significantly greater fecundity and population growth rates than found with the control food suspension at the same biomass density.     

Influence of bacterial density and water temperature on the grazing activity of two freshwater ciliates

1. The influences of bacterial density and water temperature on the grazing activity of the ciliates Uronema sp. and Colpoda inflata were studied. The conditions assayed were two prey densities (10⁶ and 4 × 10⁷ bacteria ml^?1) and three water temperatures (10, 15 and 22 °C). 2. The response of the ciliates was measured from changes in protistan biovolumes and specific clearance rates. At high prey density, both ciliates showed lower biovolumes as water temperature increased, while at low prey density this tendency was minimized. 3. At the intermediate temperature of 15 °C both ciliates filtered ten times more body volume when bacteria were scarce; however, the ingested bacteria were fewer than at high prey density. At low prey density, a decrease from 15 to 10 °C evidenced different strategies of the two ciliates, which led to a similar ingestion of bacteria: C. inflata reduced its specific clearance rates and increased its biovolume, while Uronema sp. did not show changes. At high prey density, an increase from 15 to 22 °C caused lower biovolumes and a noticeable increase in specific clearance rates in both ciliates, indicating opportunist behaviour.     

Growth,reproduction and longevity in nematodes from sewage treatment plants

The growth, reproduction and longevity of Diplogasteritus nudicapitatus, Paroigolaimella bernensis and Rhabditis curvicaudata were investigated under conditions of excess food within the temperature range 5°C–20°C. In all three species growth rate increased with temperature, and in D. nudicapitatus and R. curvicaudata the adult size attained varied significantly with temperature. P. bernensis did not reproduce at 5°C, but showed a progressive increase in reproductive output at higher temperatures. D. nudicaitatus showed increased egg production as temperature increased while R. curvicaudata had maximum egg output at 10°C. Longevity is temperature dependent, decreasing with higher temperatures. Virgin females survived for longer than reproducing females. The data indicate that while D. nudicapitatus and P. bernensis are thermophilic species, R. curvicaudata is adapted to lower temperatures.     

Combined Effects of Food Concentration and Temperature on Competition Among Four Species of <Emphasis Type="Italic">Brachionus </Emphasis>(Rotifera)

We evaluated the effect of algal food density (1.5 × 10⁶, 3.0 × 10⁶ and 4.5 × 10⁶ cells ml⁻¹ of Chlorella) and temperature (22° and 28 °C) on competition among the rotifers Brachionus calyciflorus, Brachionus havanaensis, Brachionus patulus and Brachionus rubens, based on population growth experiments for 24 days. The growth experiments were conducted seperately for each individual rotifer species (i.e., controls), and in mixtures of all four species in equal initial proportions (i.e., under competition). The population growth of B. calyciflorus, B. havanaensis, B. patulus and B. rubens grown separately at two temperatures and at three algal food densities showed typical patterns of lag, exponential and retardation phases in the controls. This pattern differed considerably under competition. In general, we observed that in all of the test species, the highest growth rates were observed at higher food levels and in the absence of congenerics. At 22 °C, under the lowest food level, the differences in the population abundances of B. havanaensis, B. patulus and B. rubens grown alone and in the presence of competition were large. However, these differences reduced as food density was increased from 0.5 × 10⁶ to 4.5 × 10⁶ cells ml⁻¹. At 28 °C and at the lowest food level, all of the other rotifer species eliminated B. havanaensis in mixed cultures. Each brachionid species had a higher rate when grown alone than when cultured with other species. The highest r (mean ± standard error: 0.54 ± 0.01 day⁻¹) was recorded for B. havanaensis at 28 °C under 4.5 × 10⁶ cells ml⁻¹ of algal food density. At 28 °C at low algal food density, the presence of competitors resulted in negative population growth rates for three of the four rotifer species tested.     

Effects of temperature on food ingestion rate and absorption,retention, and equilibrium burden of phosphorus in an aquatic snail,Goniobasis clavaeformis Lea *

The effects of sublethal temperatures on feeding rates and phosphorus dynamics of a freshwater snail, Goniobasis clavaeformis Lea, were determined and feeding rates were measured at four temperatures. The food source was aufwuchs labelled with radioactive phosphorus. A model was developed to elucidate the results of this type of study. Food ingestion rate increased with increasing temperature up to 14°C and then decreased at temperatures above 14°C. The elimination rate of absorbed phosphorus increased with increasing temperature throughout the entire range of experimental temperatures, 10-19.3°C. Mean retention times of absorbed phosphorus i n Goniobasis were estimated to be 34, 24, 10, and 6 days at 10, 13.8, 15, and 193°C, respectively. Mean retention time of unabsorbed ³²P in the gut of this species as a function of temperature followed the same temperature relationship as that of ingestion rate. The absorption efficiency of phosphorus was estimated to be constant at about 39% for ail experimental temperatures, although the data suggest that the absorption ePRciency may have been related inversely to the rate of gut clearance or directly to the residence time of food in the gut. The equilibrium body load of phosphorus at each experimental temperature was estimated based on concentrations of stable phosphorus in the food source and the kinetics of ³²P in Goniobasis. The equilibrium body burden of phosphorus in Goniobasis increased with increasing temperatures up to a maximum at 11–12°C and then decreased at temperatures above 12°C.     

Influence of ethanol and ethylene on the seed germination of three nymphaeid water plants

1. We offered Scenedesmus obliquus in five densities, from 0.5 to 8 ± 10⁶ cells ml^?1, to the rotifer Anuraeopsis fissa. Growth rates (r) during the exponential phase (first 7 days) were significantly and positively related to food density. The r values (mean ± SD) varied between 0.454 ± 0.067 and 0,856 ± 0.090, from the lowest to the highest food concentration, respectively. Population growth went through a phase of exponential increase which lasted from 7 to 10 days before a plateau and, in some cases, a decrease occurred. 2. There was a linear relation between food density and rotifer plateau density. At the highest food density, a peak abundance (mean ± SD) of 2312 ± 226 individuals ml^?1 was reached, while at the lowest food density there was no identifiable single peak but a plateau, at a density of 361 ± 62 ind. ml^?1. 3. The egg ratio decreased with increasing population density. The ratio of loose eggs to eggs attached to females indicated that more eggs became detached at higher food densities. 4. As in many other rotifer species studied so far, population density of A. fissa was less stable at higher algal food concentrations. Numerically, A. fissa could be grown at twice the density achieved in Brachionus.     

Suspension feeding in Bithynia tentaculata (Prosobranchia,Bithyniidae), as affected by body size,food and temperature

The suspension feeding of Bithynia tentaculata was tested in laboratory experiments. The animals were fed in 1-1 aerated glass beakers, and filtration rates were calculated from changes in cell concentrations during the 6-h experiment. Temperature influenced the filtering rate, with minimum values of 5ml · ind^–1 · h^–1 at 5° C and maxima of 17.2 ml · ind^–1 · h^–1 at 18° C. Three food species of different size, motility and cell surface characteristics (Chlamydomonas reinhardii, Chlorella vulgaris and Chlorogonium elongatum) did not affect filtration rates. Suspension feeding increased with increasing food concentrations up to 12 nl · ml^–1, above which feeding rate was kept constant by lowering the filtering rates. Even the smallest animals tested (<4 mm body length) were found to be feeding on suspended food at a rate of 2.7 ml · ind^–1 · h^–1, and increasing rates up to 8.4 ml were found in the 6–7 mm size class. All size classes of Bithynia showed a circannual fluctuation of their filtration rates. The ecological consequences of Bithynia's ability to switch between two feeding modes, grazing and suspension feeding, are discussed.     

Acute and chronic toxicity of the pesticide methyl parathion to the rotifer Brachionus angularis (Rotifera) at different algal (Chlorella vulgaris) food densities

Methyl parathion is a commonly used insecticide in Mexico to eradicate insect pests. We evaluated the effects of this insecticide on rotifer B. angularis using both acute and chronic toxicity tests. Median lethal concentration (LC₅₀) of methyl parathion for B. angularis for a 24-h bioassay in the presence and absence of an algal diet was derived. Elevated LC₅₀ due to the survival of a greater number of test individuals in the presence of food was observed. Regardless of the toxicant concentration, population growth curves of the animals maintained at the low food level (0.75×10⁶ cells ml^-1) had a longer lag phase than those at the high food level (1.5×10⁶ cells ml^-1). Regardless of food level, an increase in the toxicant concentration in the medium resulted in decreased population growth. The lowest peak population density (50 ind. ml^-1) was observed at the highest toxicant concentration and the lower food level. The highest population density (200 ind. ml^-1) was observed in the controls at high food level. The rates of population increase per day (r) in the controls were higher (from 0.14 to 0.37 depending on the food level). Irrespective of food level, there was a decrease in the r values with increasing pesticide concentration in the medium. In order to detect the effect of population density on the growth rates in relation to the toxicant stress, we plotted the daily growth rate against initial density for the entire duration of the experiment. We observed the existence of a significantly inverse relation at all treatments except at the low food level and high toxicant concentrations (0.625 and 1.25 mg l^-1). We discuss the role of algae in the toxicity of methyl parathion to zooplankton.     

The significance of some methodological effects on filtration and ingestion rates of the rotiferBrachionus plicatilis

Filtration rate(F) and ingestion rate(I) were measured in the rotiferBrachionus plicatilis feeding on the flagellateDunaliella spec. and on yeast cells(Saccharomyces cerevisiae). 60-min experiments in rotating bottles served as a standard for testing methodological effects on levels ofF andI. A lack of rotation reducedF values by 40 %, and a rise in temperature from 18° to 23.5 °C increased them by 42 %. Ingestion rates increased significantly up to a particle (yeast) concentration of ca. 600–800 cells · l^–1; then they remained constant, whereas filtration rates decreased beyond this threshold. Rotifer density (up to 1000 ind · ml^–1) and previous starvation (up to 40 h) did not significantly influence food uptake rates. The duration of the experiment proved to have the most significant effect onF andI values: in 240-min experiments, these values were on the average more than 90 % lower than in 15-min experiments. From this finding it is concluded that ingestion rates obtained from short-term experiments (60 min or less) cannot be used in energy budgets, because they severely overestimate the actual long-term feeding capacity of the rotifers. At the lower end of the particle size spectrum (2 to 3 µm) there are not only food cells, but apparently also contaminating faecal particles. Their number increased with increasing duration of experiments and lead to an underestimation ofF andI. Elemental analyses of rotifers and their food suggest thatB. plicatilis can ingest up to 0.6 mJ or ca. 14 % of its own body carbon within 15 min. The long term average was estimated as 3.4 mJ · ind^–1 · d^–1 or ca. 75 % of body carbon · d^–1.Contribution to research project "Experimentelle Marine Ökosystemanalyse" sponsored by the Bundesministerium für Forschung und Technologie, Bonn (Grant No. MFU - 0328/1)     

The relationship between food density and short term assimilation rates in Potamopyrgus antipodarum and Deleatidiumsp.

Much of the variation in individual growth rates can be attributed to differences in individual feeding rates. Therefore, in order to build predictive models of individual, or population growth, the factors influencing an individual's feeding rate must be described. An important determinant of the feeding rate is the relationship between the local abundance of food and the individual's ingestion rate – otherwise known as the functional response. We determined functional responses for two species of invertebrate grazers: the snail Potamopyrgus antipodarum and the mayfly Deleatidium sp., by measuring their assimilation rate with increasing densities of radiolabelled periphyton. The assimilation rates were consistent with the Holling Type II or Michelis Menten functional response curve. The parameters of the functional response yielded estimates of the search area and handling time for the stream invertebrates. Our functional response data indicate that the half-saturation food density for P. antipodarum and Deleatidium sp. were 980 mg and 3200 mg AFDM m^–2, respectively, suggesting that Deleatidium growth may be subject to food limitation more often than is P. antipodarum – despite the lower assimilation efficiency of the latter species.     

Feeding Rate of Brachionus plicatilis O. F. Müller on Two Types of Food Depending on Ambient Temperature and Salinity

Feeding rates of Brachionus plicatilis were studied for two types of food — algae Monochrysis lutheri and baker's yeast Saccharomyces cerevisae. The main regularities of changes in filtration rate and ration were studied in small culture volumes (1 ml) for adult amictic females depending on food concentration (1, 2, 4, 8 and 16 · 10⁶ cells · ml⁻¹), ambient temperature (16 and 26 °C), and salinity (5, 10, 15, 20, 25 and 30 ppt). B. plicatilis ration did not depend on the salinity, but was largely determined by temperature and food concentration. It was found that at 16 and 26 °C the dependence of the ingestion rate (ration) on food concentration differed greatly. A hypothesis was suggested to explain this phenomenon. A critical concentration of both types of food at which the increase in the rotifer ration ceased is 4 · 10⁶ cells · ml^−1. This is the minimum “background” food concentration for B. plicatilis mass cultivation. The average rations measured at the concentration of M. lutheri and S. cerevisae of 4 · 10⁶ cells · ml⁻¹ where 1.3 ± 0.1 and 4.8 ± 1.3 μg dry weight. · ind⁻¹ · day⁻¹ at 26 °C and 0.54 ± 0.1 and 1.9 μg d. w. · ind⁻¹ · day⁻¹ at 16 °C, respectively. The rations obtained in the laboratory were corrected for the conditions of rotifer commercial production in the open field in summer time. The correct values were 0.86 and 0.72 μg d. w. · ind⁻¹ · day⁻¹ for algae and yeast, respectively.     

Ecological problems of Lake Ladoga: causes and solutions

We studied the outcome of competition between a large (Brachionus calyciflorus) and a small (Anuraeopsis fissa) rotifer species at five algal (Scenedesmus acutus) concentrations (0.5 × 10⁶ to 40.5 × 10⁶ cells ml^–1) and with varying initial densities in mixed populations (100 to 0% of B. calcyciflorus or A. fissa), the combined initial biomass being 0.2 µg ml^–1 in all test jars. Experiments were conducted at 28 ± 1 °C.Regardless of food concentration, B. calcyciflorus showed a greater increase in biomass than A. fissa, peak densities (mean ± standard error) at the lowest food concentration in the controls being 1.34 ± 0.31 µg dry weight ml^–1 and 0.82 ± 0.08 dry weight ml^–1, respectively. At the lower food concentrations, A. fissa displaced B. calyciflorus and vice versa at the higher food concentrations. At the intermediate food concentrations of 4.5 × 10⁶ cells ml^–1, B. calyciflorus outcompeted A. fissa only if its initial population density was three times higher. The rates of population growth in controls varied from 0.792 ± 0.06 d^–1 to 1.492 ± 0.13 d^–1 for B. calyciflorus and 0.445 ± 0.04 to 0.885 ± 0.01 for A. fissa depending on food level. When both species were introduced together, low food levels favoured higher abundance of A. fissa than B. calyciflorus, suggesting, in nature, it is likely that small Anuraeopsis colonize oligotrophic water bodies more successfully than larger Brachionus. The results also suggest that the outcome of competition depends not only on the size of the competing species and food availability but also on their colonizing density.     

Effects of UV-B irradiated algae on zooplankton grazing

We tested the effects of UV-B stressed algae on grazing rates of zooplankton. Four algal species (Chlamydomonas reinhardtii, Cryptomonas sp., Scenedesmus obliquus and Microcystis aeruginosa) were used as food and fed to three zooplankton species (Daphnia galeata, Bosmina longirostris and Brachionus calyciflorus), representing different taxonomic groups. The phytoplankton species were cultured under PAR conditions, and under PAR supplemented with UV-B radiation at two intensities (0.3 W m^–2 and 0.7 W m^–2, 6 hours per day). Ingestion and incorporation experiments were performed at two food levels (0.1 and 1.0 mg C l^–1) using radiotracer techniques. The effect of food concentration on ingestion and incorporation rate was significant for all three zooplankton species, but the effect of UV-B radiation was more complex. The reactions of the zooplankton species to UV-B stressed algae were different. UV-B stressed algae did not affect Daphnia grazing rates. For Bosmina the rates increased when feeding on UV-B stressed Microcystis and decreased when feeding on UV-B stressed Chlamydomonas, compared with non-stressed algae. Brachionus grazing rates were increased when feeding on UV-B stressed Cryptomonas and UV-B stressed Scenedesmus, and decreased when feeding on UV-B stressed Microcystis, compared with non-stressed algae. These results suggest that on a short time scale UV-B radiation may result in increased grazing rates of zooplankton, but also in decreased grazing rates. Long term effects of UV-B radiation on phytoplankton and zooplankton communities are therefore difficult to predict.     

An energy budget for Simocephalus vetulus (O. F. Muller) (Crustacea : Cladocera)

We discuss the energetics of a cladoceran, Simocephalus vetulus at different temperatures (8.0 ± 1.0, 15.0 ± 1.0, 21.0 ± 1.0 and 28.0 ± 1.0 °C) and food (Chlamydomonas sp.) concentrations (25 × 10³, 50 × 10³, 75 × 10³ and 100 × 10³ cells ml⁻¹). Increase in temperature accelerated ingestion and, to some extent, oxygen consumption. The study revealed a high reproduction efficiency in S. vetulus. Net growth efficiency (ECI) was higher (13.17–41.18%) in pre-adults than in adults (2.71–8.40%). The assimilated energy (A) increased with increasing food concentration at all temperatures. Assimilation efficiency (AD) decreased with increasing food concentrations. The energy used for growth (P) was nearly constant at all food levels because the egested energy increased and assimilation efficiency decreased as food concentration increased.     

A model for growth of Artemia franciscana cultures based on food ration-dependent gross growth efficiencies

Laboratory cultures of Artemia franciscana grown under batch regimes at constant temperatures (28 °C) and salinity (35 g l^–1), three initial food concentrations (0.1, 0.4 and 1 M cells ml^–1), various daily food rations (0.1–9M Dunaliella tertiolecta cells Artemia ^–1), and different population densities (1–16 ind ml^–1) were used to develop a model of population growth. Growth rates and gross growth efficiencies (K ₁) were largely independent of population densities and initial food concentrations but determined by age and daily amount of food ingested. While maximum growth rates were found with the highest rations, K _{1 max} peaked at rations of 0.5 million cells d^–1 and decreased at feeding levels above this. A contour plot showing the trend relating K ₁ to Artemia size and ingestion rate in combination and was used to model growth in analogous controlled feeding conditions. Computer simulations using this model paralleled published results of final 15-day average individual sizes of Artemia. Optimal results for near constant food utilization are predicted for high initial population densities (100 Artemia nauplii ml ^–1) and daily culls of enough animals to equilibrate food demand with food availability. This strategy could permit a range of Artemia sizes harvested, maximize final individual sizes and retain high total yields (> 1.2 kg dry wt 1^–1). Effects of different culture strategies are discussed.     

A laboratory investigation of the filtration and ingestion rates of the tilapia,Oreochromis niloticus,feeding on two species of blue-green algae

Synopsis Quantitative aspects of the filter-feeding of the tilapia,Oreochromis niloticus, on two species of the blue-green algae —Anabaena cylindrica andMicrocystis aeruginosa — were investigated in the laboratory. The ingestion rate of 85 mm SLO. niloticus was best fitted using a linear regression over the range of biovolume concentrations studied (3 × 10⁶ – 3 × 10⁸ m³ ml^–1). The ingestion rate of 40 mm SL fish gave a curvilinear relationship and was best fitted using a logarithmic regression. For each size class of fish, ingestion rates were higher when fed the largerAnabaena thanMicrocystis. The results of ingestion and filtration rates are comparable to work on other aquatic suspension feeders and tend to substantiate a universality in the fundamental regulatory mechanism of filter feeding.