Rotifers as predators on small ciliates

Clearance rates of Synchaeta pectinata, Brachionus calyciflorus and Asplanchna girodi on Tetrahymena pyriformis (46 µm in length) at a density of 10 cells ml^–1, in the presence of algal food, were 2.5 to 6.1 ml rot.^–1 day^–1. Clearance rates of these rotifers were, respectively, about 2, 3, and 13 times lower on Strobilidium gyrans (58 µm in length) than on T. pyriformis, indicating that the saltations of S. gyrans are an effective escape response. Clearance rates of S. pectinata were considerably lower on Colpidium striatum (81 µm) than on S. gyrans, suggesting that S. pectinata may not be able to ingest ciliates of this size. S. pectinata had a clearance rate of 19 ml rot.^–1 day^–1 on S. gyrans at a density of 1.2 cells ml^–1, in the absence of edible algal food. Rotifers may prey extensively on ciliates in natural plankton communities, ingesting 25 to 50 individuals in the 45–60 µm size range day^–1.     

Characterization of the bacterial flora of mass cultivated Brachionus plicatilis

Bacterial density and composition in association of mass cultivated rotifers (Brachionus plicatilis, SINTEF-strain) was investigated, during experimental conditions identical to the procedures used for preparing rotifers as live food for marine cold water fish larvae. These procedures include cultivation, enrichment with squid meal and acclimation to low temperature by storage of the rotifer culture at 6 °C. Large variations were observed in the number of rotifer associated (1.8–7.6 · 10³ colony forming units per rotifer^–1) and free-living (0.6–25 10⁷ cells·ml^–1) bacteria. An increase of 50–150% in the bacterial number was normally observed after feeding the rotifer with squid meal, but after three days of acclimation at 6 °C, the bacterial numbers decreased to the initial level.After enrichment of the cultures with squid meal, the similarity in the composition of the bacterial flora between the rotifers and water was reduced. However, acclimation of the culture at 6 °C resulted in better agreement of the rotifer associated flora and that in water. Enrichment of the cultures induced a shift in the bacterial composition from Cytophaga/Flavobacterium dominance to Pseudomonas/Alcaligenes dominance. The bacterial flora of the rotifer cultures are dominated by presumably opportunistic species after enrichment, which may have detrimental effects when rotifers are fed as live food to marine fish larvae.     

High density culture of the freshwater rotifer,Brachionus calyciflorus

The freshwater rotifer, Brachionus calyciflorus is one of the live food organisms used for the mass production of larval fish. In this study possibility of obtaining high density cultures of the freshwater rotifer B. calyciflorus were investigated. The two culture systems used differed in their air and dissolved oxygen supplies using three temperatures in each case: 24, 28 and 32 °C. Rotifers were batch-cultured using 5 l-vessels and fed with the freshwater Chlorella. The growth rate of rotifers significantly increased with an increase in temperature. The maximum density of the rotifers with air-supply at 24 °C, 6500 ind. ml^–1, was significantly lower than those cultured at 28 and 32 °C, i.e. 8600 and 8100 ind. ml^–1, respectively. Dissolved oxygen levels decreased with time and ranged from 0.8 to 1.4 mg l^–1 when the density of freshwater rotifer was the highest at each temperature. The highest density (19200 ind. ml^–1) of freshwater rotifer was obtained in cultures with a supply of oxygen at 28 °C. Densities of 13500 and 17200 ind. ml^–1 were found at 24 and 32 °C, respectively. Levels of NH₃-N increased with time and a dramatic increase of NH₃-N was observed at high temperatures. Levels of NH₃-N at 24, 28 and 32 °C were 13.2, 18.5 and 24.5 mg l^–1, respectively. These levels coincided with the highest rotifer density at each of the three temperatures. When rotifers were cultured with an oxygen-supply and pH was adjusted to 7, the maximum density of rotifer reached 33500 ind. ml^–1 at 32 °C . These results suggested that high density culture of freshwater rotifer, B. calyciflorus could be achieved under optimal conditions with DO value of exceeding 5 mg l^–1 and NH₃-N values of lower than 12.0 mg l^–1.     

Combined Effects of Algal (<Emphasis Type="Italic">Chlorella vulgaris</Emphasis>) Food Level and Temperature on the Demography of <Emphasis Type="Italic">Brachionus havanaensis</Emphasis> (Rotifera): a Life Table Study

We evaluated the combined effects of food (0.5 × 10⁶, 1.0 × 10⁶ and 2.0 × 10⁶ cells ml⁻¹ of Chlorella vulgaris) and temperature (15, 20 and 25 °C) on life history variables of B. havanaensis. Regardless of Chlorella density there was a steep fall in the survivorship of B. havanaensis at 25 °C. Both food level and temperature affected the fecundity of B. havanaensis. At any given food level, rotifers cultured at 15 °C showed extended but low offspring production. At 25 °C, offspring production was elevated, the duration of egg laying reduced and the fecundity was higher during the latter part of the reproductive period. The effect of food level was generally additive, at any given temperature, and higher densities of Chlorella resulted in higher offspring production. Average lifespan, life expectancy at birth and generation time were 2–3 times longer at 15 °C than at 25 °C. At 20 °C, these remained at intermediate levels. The shortest generation time (about 4 days) was observed at 25 °C. Gross and net reproductive rates and the rate of population increase (r) increased with increasing temperature and generally, at any given temperature, higher algal food levels contributed to higher values in these variables. The r varied from 0.11 to 0.66. The survival patterns and lower rates of reproduction at 15 °C suggest that the winter temperatures (10–15 °C) prevailing in many waterbodies in Mexico City allow this species to sustain throughout the year under natural conditions.     

Biology of Moina mongolica (Moinidae,Cladocera) and perspective as live food for marine fish larvae: review

Moina mongolica, 1.0-1.4 mm long and 0.8 mm wide, is an Old World euryhaline species. This paper reviewed the recent advances on its autecology, reproductive biology, feeding ecology and perspective as live food for marine fish larviculture. Salinity tolerance of this species ranges from 0.4–1.4 to 65.2–75.4. Within 2–50 salinity, Moina mongolica can complete its life cycle through parthenogenesis. The optimum temperature is between 25 °C and 28 °C, while it tolerates high temperature between 34.4 °C and 36.0 °C and lower temperature between 3.2 °C and 5.4 °C. The non-toxic level of unionised ammonia (24 h LC₅₀) for M. mongolica is <2.6 mg NH₃–N l^–1. Juvenile individuals filter 2.37 ml d^–1 and feed 9.45×10⁶ algal cells d^–1, while mature individuals filter 9.45 ml d^–1 and consume 4.94×10⁶ algal cells d^–1. At 28 °C, M. mongolica reaches sex maturity in 4 d and gives birth once a day afterward; females carry 7.3 eggs brood^–1 and spawn 2.8 times during their lifetime. A variety of food can be used for M. mongolica culture including unicellular algae, yeast and manure, but the best feeding regime is the combination of Nannochloropsis oculata and horse manure. Moina mongolica reproduces parthenogenetically during most lifetime, but resting eggs can be induced at temperature (16 °C) combined with food density at 2000–5000 N. oculata ml^–1. The tolerance to low dissolved oxygen (0.14–0.93 mg l^–1) and high ammonia makes it suitable for mass production. Biochemical analyses showed that the content of eicospantanoic acid (20:53) in M. mongolica accounts for 12.7% of total fatty acids, which is higher than other live food such as Artemia nauplii and rotifers. This cladoceran has the characteristics of wide salinity adaptation, rapid reproduction and ease of mass culture. The review highlights its potential as live food for marine fish larvae.     

Structure, development and induction of a new diapause stage in rotifers

1. This study shows that females of Synchaeta pectinata Ehrenberg can produce two morphologically and physiologically distinct kinds of amictic eggs that develop parthenogenetically into females. One kind, until now the only one known in monogonont rotifers, is a thin-shelled (about 1.4 μm) subitaneous egg that develops without arrest. The other kind is a thick-shelled (about 9 μm) egg that enters obligatory diapause after 1–3 cleavage divisions before resuming development. The thicker shell of the diapausing egg is due to an expansion of the outer sublayer of the single-layered shell. 2. The mean duration of the diapause at 19 °C (L : D 16 : 8) is about 14 days. This diapause is not broken by low temperature (5 °C), and it is not greatly extended by storage at low temperature (5 °C). 3. Diapausing eggs are induced immediately after a brief starvation period, and seem to be produced at no additional energetic cost. However, a population producing a high proportion of diapausing eggs has a much reduced reproductive potential. 4. Production of diapausing amictic eggs may be a strategy to increase the ability of clones to survive food limitation. 5. Diapausing amictic eggs differ markedly from fertilized resting eggs produced following bisexual reproduction during favourable conditions.     

Life history characteristics of three types of females in Brachionus calyciflorus Pallas (Rotifera) fed different algae

This study describes the life history characteristics of amictic, unfertilized mictic and fertilized mictic females of the rotifer Brachionus calyciflorus cultured individually on two different algae at 0.1 mg ml^–1 food concentration and 27 °C. The duration of the juvenile period of amictic females was significantly shorter on Chlorella pyrenoidosa Chick than on Scenedesmus obliquus Kütz or both algae together. The duration of the juvenile period of unfertilized mictic females was significantly longer, and the number of eggs produced by amictic females was significantly larger on Chlorella pyrenoidosa than on S. obliquus. When fed the same type of alga, the duration of the juvenile period of the fertilized mictic females was the longest among the three types of females, and the durations of the reproductive period of the amictic females and the post-reproductive period of the fertilized mictic females were longer than, or equal to those of the other two types of females, respectively. The number of eggs produced by an unfertilized mictic female was the largest among the three types of females, and that of amictic females was larger than or equal to that of fertilized mictic females, depending on the type of diet.     

Factors Affecting Swimming Speed in the Rotifer <Emphasis Type="Italic">Brachionus plicatilis</Emphasis>

This study examines the swimming speed in amictic females of Brachionus plicatilis in laboratory cultures. Five different stages were examined: recently hatched females, juveniles, adult non-ovigerous females, ovigerous females with 1 attached egg and ovigerous females with 2 attached eggs. We tested the speed at two temperatures, 15 °C and 25 °C, and two feeding conditions, presence and absence of microalgal cells. An automated motion analysis system was used to measure speed which was then video recorded. Swimming speed (μm s⁻¹) increased with increasing body size. There was a slight decrease in the speed of adult females as the number of attached eggs increased. Swimming activity was higher at 25 °C than at 15 °C and in the absence of food than if microalgae were present. Average values under the different experimental conditions ranged between 500 μm s⁻¹ for the recently hatched and fed females and 1500 μm s⁻¹ for the adult non-ovigerous females in the absence of microalgae. Mass-specific swimming speed decreased with body mass increase.     

Life cycle of Macrothrix flabelligera Smirnov, 1992 (Cladocera, Macrothricidae), recently reported in the Neotropical region

Information on the life cycle of individual species is vital to an understanding of their ecology, particularly their distribution. In this investigation, aspects of the Macrothrix flabelligera (Cladocera, Macrothricidae) life cycle were studied in laboratory cultures under controlled conditions. Neonates from parthenogenetic females previously acclimatized were isolated and grown at constant temperature, in a 12-h/12-h light/dark cycle. Organisms were fed with a suspension of Scenedesmus bijugus at a concentration of 10⁵ cells ml^–1. Daily measurements of body length and age were made, to obtain the growth rate, size and age of primipara. M. flabelligera had high fecundity rates, producing broods of 13.6 eggs female^–1. At 23.0°C, the duration of embryonic and post-embryonic development was 35.9 h and 4.9 days, respectively. The mean longevity was 12.7 days. A length–weight relationship was established and used to convert measured length into weight, in order to plot weight growth curves, as subsidiary information for future secondary production calculations.     

A study of the freshwater rotifer Brachionus calyciflorus in Pekanbaru, Riau, Indonesia

Brachionus calyciflorus is one of freshwaterrotifers found in fish ponds in Pekanbaru, Riau,Indonesia. Its density varied depending on that ofphytoplankton. Maximum of 2.5 ×10³ ind. l^–1 was found in ponds fertilised with animal wastes.The fecundity and population growth of B.calyciflorus was studied. Results indicated that the fecundity of amictic females was higher thanthat of unfertilized mictic females. During their life span, amictic and mictic females produced29.7 and 12.5 eggs per female, respectively. In the mass culture of 500 ml media, the highestdensity of female and male rotifers was 975.8 and 9.6 ind. ml^–1, respectively. During 8 days cultureperiod, they also produced eggs as many as 124.2 ml^–1.Human and animal wastespromoted the growth of phytoplankton as food forrotifers in the pond. A laboratory study confirms this. The best growth of B. calyciflorus at a density of 109 ind. ml^–1 was found at 0.5 g l^–1 of humanexcreta. A high density of B. calyciflorus (542ind. ml^–1) was also found in semi-continuous culturewith chicken excreta.     

Reproduction of the calanoid copepod Calanus propinquus in the southern Weddell Sea,Antarctica: observations in laboratory

Reproduction of the dominant Antarctic copepod Calanus propinquus was studied in February–April, 1989 aboard the R.V Dmitry Mendeleev during cruise N° 43 to the Weddell Sea. Single females were kept at 0 °C in the laboratory for 56 days with abundant food concentration (above 300 µg C l^–1 of Platymonas viridis). Females released clutches at night at 2–3 day intervals. Most clutches contained from 10 to 40 eggs, mean 37.3 eggs female^–1. Average carbon content of an egg was 0.37 ± 0.05 µg C. The maximum daily egg production rate of 30–50 eggs female^–1 d^–1 was observed for the first 3 days of the laboratory incubation, corresponding to 3.7–6.2% body C. The state of gonadal development of females showed the decline of the reproductive season in late February. The data suggest that egg laying in the region under study starts in December and lasts until March. The state of ovarian maturation, changes in vertical distribution and biochemical body composition of females suggest the possibility of two-year life cycle in C. propinquus in the southern Weddell Sea.     

Extracellular laccase activity in Tetraploa aristata

Tetraploa aristata CLPS 419 produced maximum extracellular laccase activity at over 9 mU ml^–1 in shaking cultures supplemented with glucose and 3.5 mU ml^–1 in sucrose-grown ones. Laccase activity did not exceed 0.7 mU ml^–1 in stationary cultures with glucose and was not detected in similar cultures with sucrose or in ones grown on lignin.     

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.     

Effect of food concentration on the production and viability of resting eggs of the rotifer Brachionus: implications for the timing of sexual reproduction

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

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.     

Temperature conditions enhancing resting egg production of the euryhaline rotifer Brachionus plicatilis O. F. Müller (Kamiura strain)

We examined the effect of low temperature treatment(12°C), followed by transfer to highertemperature (25°C), on resting egg formation ofthe rotifer Brachionus plicatilis, Kamiurastrain. This strain has been mass cultured as livefeed at Kamiura Station (Japan Sea FarmingAssociation) for 9 years at 20°C without theappearance of sexual reproductive stages.After preculture in 20 l of 27 seawater at 12°C for 0, 10, 20, and 30 days,rotifers were inoculated into 0.5 l mass cultures andcultured at 25°C for 7–9 days. The inoculationdensities were changed from 20 to 400 ind. ml^–1,depending on mixis rate. Condensed and frozen Nannochloropsis oculata was fed to rotifers at thefeeding rate of 0.14 µg (dry weight)rotifer^–1day^–1. The control was cultured at12°C for the entire 36 day experiment. No mixisappeared and no resting eggs were produced when thelow temperature treatment was 0 or 10 days. However,mixis rates reached 50-60% after 20 or 30 days ofexposure to 12°C. The number of resting eggsproduced in these treatments reached 25,500 about 13 times higher than the control. Our resultssuggest that low temperature stimulated mictic femaleproduction and the transfer to the high temperatureaccelerated resting egg formation. This method may beuseful for producing resting eggs of rotifer strainsthat lack sexual reproduction in the common culturecondition at larval rearing facilities.     

Coexistence of Tetranychus urticae (Acarina: Tetranychidae) with different capacities for diapause: comparative life-history traits

Summary Individuals of the two-spotted spider mite, Tetranychus urticae Koch (Acarina: Tetranychidae), with and without a capacity for diapause, coexist in central Japan. Diapause appears to be adaptive because females in diapause suffered less mortality than non-diapausing individuals when frozen at –24°C for more than 4 h. However non-diapausing females showed good survival up to 4 h of freezing. Active non-diapausing mites survived on rose leaves in Kyoto (35°N) throughout the winters of 1988–1989 and 1989–1990. Cultures of mites with low (LD) and high (HD) diapause capacities at 18°C and 9L-15D photoperiod were successfully selected from the rose population and from a population on chrysanthemum in Nara (34.4°N). Their life-history traits at 15, 20, 25 and 30°C were characterized. HD and LD mites from both populations were of similar ages at first reproduction at 15–30° C. However, at temperatures 20° C, HD individuals produced more eggs than LD individuals, resulting in higher fecundity and intrinsic rate of natural increase. These traits allow HD individuals, which stop breeding between October and April, to increase faster in summer than LD individuals. This provides a mechanism, together with climatic fluctuations, in maintaining the coexistence of diapausing and non-diapausing T. urticae in Kyoto where winter conditions are rarely lethal to the non-diapausing individuals.     

Life table demography and population growth of Brachionus variabilis Hempel, 1896 in relation to Chlorella vulgaris densities

We studied the life history variables and population growth characteristics of Brachionus variabilis, which was recorded for the first time from Mexico. The animals were fed Chlorella, using five concentrations (0.25, 0.5, 1, 2 and 4 × 10⁶ cells ml^–1) at 25 °C. Food density was observed to have significant effect on life expectancy, average lifespan, gross reproductive rate, net reproductive rate, generation time and population growth rate. The average lifespan ranged from 3 to 6 days depending on the food density. The net reproductive rate ranged from 2 to 7 neonates female^–1 d^–1. The rate of population increase per day varied from 0.14 to 0.35. The highest net reproductive rate and average lifespan and life expectancy were recorded at Chlorella concentrations of 1 × 10⁶ and 2 × 10⁶ cells ml^–1.     

Successful oviposition and reproductive biology of Aprostocetus vaquitarum (Hymenoptera: Eulophidae): A predator of Diaprepes abbreviatus (Coleoptera: Curculionidae)

Aprostocetus vaquitarum (Wolcott) causes 78–91 percent mortality to eggs of Diaprepes abbreviatus (L.), under field conditions in southern Florida. In the laboratory, A. vaquitarum was reared on D. abbreviatus eggs at 25 °C, a photoperiod of 12:12 (L:D) and with abundant hosts, A. vaquitarum adult females lived around 15 days. Oviposition was significantly affected by the age of the host egg mass. Egg masses aged 0- to 3-day-old were accepted significantly better than those aged 4–6 days. The mean number of eggs deposited per female was around 53, with extreme values of 124 and 19 eggs per female. Using these data in combination with the sex ratio observed in the field (0.16) and the duration of the preimaginal stages, r_m (0.168–0142 day⁻¹), T (22.39–22.89 days), and R₀ (43.03–25.81 females per female) were calculated.     

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.