Hydrobiologia 457: 25–37, 2001.© 2001 Kluwer Academic Publishers. Printed in the Netherlands.

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

Z.H. He1, J.G. Qin2∗, Y. Wang1, H. Jiang1 & Z. Wen1

1Department of Aquaculture, Dalian Fisheries University, Dalian, 116024, China2School of Biological Sciences, Flinders University, P.O. Box 2100, Adelaide 5001 SA AustraliaTel: +61-8-8201-3045; Fax: +61-8-8201-3015; E-mail: jian.qin@flinders.edu.au (∗Author for correspondence)

Key words: Moina mongolica, morphology, salinity, temperature, growth, reproduction, fish larviculture

Abstract

Moina mongolica, 1.0-1.4 mm long and 0.8 mm wide, is an Old World euryhaline species. This paper reviewed therecent advances on its autecology, reproductive biology, feeding ecology and perspective as live food for marinefish 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 ◦Cand 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 mld−1 and consume 4.94×106 algal cells d−1. At 28 ◦C, M. mongolica reaches sex maturity in 4 d and gives birthonce a day afterward; females carry 7.3 eggs brood−1 and spawn 2.8 times during their lifetime. A variety of foodcan be used for M. mongolica culture including unicellular algae, yeast and manure, but the best feeding regime isthe combination of Nannochloropsis oculata and horse manure. Moina mongolica reproduces parthenogeneticallyduring 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 itsuitable for mass production. Biochemical analyses showed that the content of eicospantanoic acid (20:5ω3) in M.mongolica accounts for 12.7% of total fatty acids, which is higher than other live food such as Artemia nauplii androtifers. This cladoceran has the characteristics of wide salinity adaptation, rapid reproduction and ease of massculture. The review highlights its potential as live food for marine fish larvae.

Introduction

Cladocera, as a general rule, appear to be restrictedto freshwater environments of salinity <1000 mg l−1

(Hart et al., 1991). There is a need for considerablymore information on the salinity tolerance of Clado-cera, and especially, we need to know more about thechange of biological activities such as feeding, repro-duction within the range of salinity tolerance. Moinamongolica is a halophilic species in the Old World.Its distribution covers from North Africa, across theMiddle East and the Central Russia and to Mongolia(Goulden, 1968). This species is particularly commonin Caucasus Region of Central Russia and Aral Sea(Behning, 1941; Zenkevitch, 1963). Moina mongolicawas first collected in Northwest China in 1984 from

an ephemeral pond of 5‰ salinity in Shanxi Provincewhere the climate is hot and dry (He et al., 1989).Since then, Dalian Fisheries University has initiateda saline water research program specifically studyingthe biology of M. mongolica aiming to use this spe-cies for marine fish larviculture. Although much workhas been done on this species, most information waspublished in Chinese literature which is not generallyavailable to other readers. The aim of this paper is toprovide a brief review based on recent advances onM. mongolica research, including its distribution, tol-erance to environmental stress (temperature, salinityand ammonia), feeding biology, reproduction, nutri-tional composition, methods of mass production andfeeding trials on larval fish. The primary focus is toprovide a comprehensive outline of the information

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existing in Chinese literature. We believe that such areview is necessary because (1) there is a general lackof scientific knowledge of saline cladoceran speciescompared with other freshwater and marine species,(2) Moina mongolica extremely tolerates salinity fluc-tuation, (3) more importantly, this species may beintroduced to aquaculture industry as live food formarine finfish. This review, although it concentrateson Chinese scientific information, should be of wideinterest to other countries and regions where there is aneed to explore saline water resources for aquacultureor fisheries.

The reason to explore brackish resources is obvi-ous. For example, In China alone, over 2300 lakeshave area >1 km2 and half of the total lake areaof China is contributed by saline lakes (Williams,1991). The development of finfish culture industryrequires mass production of fingerlings. As a neces-sary consequence, it in turn has promoted the searchof suitable food organisms for larvae and juvenile.The genus Moina is widely distributed in the world(Goulden, 1968), and with the increasing demand forfood of larvae and juvenile fin fish, Moina has attrac-ted researchers’ interest because of its rapid growthpotential (Pennak, 1989; Benider et al., 1998). Threespecies of Moina (M. hutchinsoni, M. mongolica andM. salina) have been found in salt lakes (He et al.,1989; Garcia et al., 1995; Vasilyeva & Smirnov, 1995;Martinezjeronimo et al., 1997), but none of them havebeen used as food for marine fish larvae.

In most marine fish hatcheries, the rotifer (Bra-chionus plicatilis) has been widely accepted as astarter food for larval fish (Fulks & Main, 1991).As larval fish grow, the size of rotifers becomes toosmall for fish to ingest, and subsequently, rotifershave been replaced by brine shrimp (Artemia spp.)Although brine shrimp has been used for many years,the resource crisis of brine shrimp in Great Salt Lakealarmed researchers to seek alternative food to sub-stitute Artemia in larval fish rearing (Anonymous,1998). Development of the culture technology in mar-ine copepods for larval fish has been making progressbut because the long generation time in most copepodspecies makes it difficult to produce mass copepods inintensive culture systems (Stottrup & Norsker, 1997;Schipp et al., 1999). Between cladoceran and cope-pods, most fish larvae prefer the former because thejerky movement of cladocerans makes them more vis-ible to fish while copepods swim too fast for fish larvaeto catch (Mayer & Wahl, 1997). In freshwater aquacul-ture, cladocerans such as Daphnia and Moina have

been successfully used as larval fish food in pond cul-ture (Qin & Culver, 1996). Rapid population growth ofmost cladoceran species make them suitable for massproduction because cladocerans reproduce partheno-genetically when the amount of food is adequate andthe environmental conditions are favourable (Innes,1997). In marine aquaculture, however, the use clado-cerans as food for fish larvae has rarely been exploredpartially because only few species of Cladocera areavailable in the world ocean (Nybakken, 1993). Therapid reproduction of M. mongolica and its adaptab-ility to marine environment shed light for the futureof using alternative living resources in marine finfishlarviculture.

Distribution and morphology

Moina mongolica has been found in brackish watersin north Africa, Middle East, mid Russia, Mongolia,Spain and northwest China (Goulden, 1968; Comin,1983; He et al., 1989). This species is frequentlyfound in ephemeral and permanent water of salinity10–23‰. In natural habitats, its density could reach275 ind l−1.

The female body is oval and laterally compressed.Juveniles are 0.6–0.7 mm long and 0.5 mm wide,while the adults are 1.0–1.4 mm long and 0.8 mmwide. The head of the female is broadly rounded buthas an indication of a supraocular depression (Fig.1A). The eye is rather small and lies close to the an-terior margin of the head. The first antennae are shortand thick (Fig. 1B). There is a row of long hairs onthe posterior margin of the first antenna, and the sens-ory seta is on the dorsal side. There are also rings ofshort setae on the first antenna. The shell is broadlyrounded especially when the broad pouch is filled withembryos. There are no hairs on the surface of the shell,and the shell is only faintly reticulated. The postabdo-men lacks long hairs on the dorsal margin but hasseveral horizontal rows of short setae (Fig. 1C). Thedistal conical part has 7–10 lateral feathered teeth.There is also a bident tooth that is placed dorsallyto the plane of the feathered teeth. The postabdomenclaw has only a small pecten of fine hairs at its base.The ephippium of the sexual female contains one eggand is reticulated over its entire surface (Fig. 1D). Thecolour is usually brown.

The males of M. mongolica vary from 0.8 to 1.0mm. The head is rounded in front but has a distinctsupraocular depression above the eye (Fig. 2A). The

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Figure 1. Illustration of a female M. mongolica. (A) A whole body.(B) First antenna. (C) Postabdomen. (D) Ephippium.

eye is rather large and fills the anterior end of the head.The first antennae originate below the eye. There isa bend in the first antenna at a point about 1/3 thedistance from the head (Fig. 2B). The short, thick-based sensory seta originates near the knee of thebend. The shell is oblong in shape and lacks hairs onthe surface. The first leg is very well developed andhas a large, recurved hook on the third segment (Fig.2C). The postabdomen is similar to that of the femaleindividuals.

Tolerance to environmental stress

The presence and success of an organism dependsupon a complex of conditions. Any condition whichapproaches or exceeds the limits of tolerance is saidto be a limiting factor. Distribution and abundance ofan organism is controlled by any one of several factorswhich may approach the limits of tolerance for that

Figure 2. Illustration of a male M. monglica. (A) A whole body. (B)Last segment of the first leg. (C) First antenna.

organism. The major environmental factors that havebeen considered important for the survival and growthfor M. mongolica include temperature, salinity andammonia nitrogen.

Temperature

Temperature is a very commonly studied environ-mental factor as it is extremely important ecologic-ally. Any organism has a limit of thermal tolerancethough this limit may change with other environmentalfactors. He et al. (1994) studied the upper and lowertemperature limits that M. mongolica can tolerate inthe salinity of 32.0‰ when all animals are fed withN. oculata at 20–30 mg l−1. The lower or upper tem-perature limit (LD50) is defined as the temperature atwhich 50% experimental animals are killed in 24 h.In their study, the experimental animals were accli-matised at 15, 20, 25, 27, 29.5 and 32 ◦C for 5–10d, then 100 animals acclimatised at each temperature

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Table 1. Growth and age structure of M. mongolica at differenttemperatures

Temperature rm Birth rate Death rate Age structure(◦C) Juvenile (%) Adult (%)

20 0.14 0.26 0.12 70.8 29.225 0.32 0.57 0.25 67.1 32.928 0.28 0.54 0.26 76.6 23.230 0.30 0.58 0.28 82.6 17.435 −0.14 0.15 0.29 47.6 52.4

were transferred to six temperatures: 32, 33, 34, 35, 36and 37 ◦C, respectively. The upper LD50 for animalsacclimatised at 15, 20, 25, 27, 29.5 and 32 ◦C was34.4, 34.5, 35.0, 35.7 and 36.0 ◦C, respectively. Priorto testing the lower temperature limit, experimentalanimals were acclimatised at 20, 24, 28, 30 and 32◦C for 5–10 d, then 100 animals acclimatised at eachtemperature were transferred to six temperatures: 2, 4,6, 8, 10 and 12 ◦C, respectively. After 24 h, the lowerLD50 for animals acclimatised at 20, 24, 28, 30 and32 ◦C was 3.2, 3.6, 3.9, 4.4 and 5.4 ◦C, respectively.

He et al. (1994) used intrinsic population growthrate (rm) as an indicator to identify the optimal tem-perature for M. mongolica. During their experiment,10 newborn females were transferred from 28 ◦C into20, 25, 28, 30 and 35 ◦C and algae were added to theculture twice a day at 20–30 mg l−1. When the tem-perature increased from 20 ◦C to 25 ◦C, the intrinsicgrowth rate increased from 0.14 to 0.32 (Table 1). Thefurther increase of temperature beyond 25 ◦C resultedin reduced rm values. At 35 ◦C, the rm became negat-ive, i.e. the death rate exceeds the birth rate. Below 30◦C, juveniles dominated the population, but at 35 ◦C,the number of adults exceeded the number of juveniles(Table 1).

Salinity

Marine and freshwater organisms may be affected intheir distribution by the salinity of the waters wherethey live. Salinity in the open ocean water is notvariable and consequently does not limit marine plank-tonic organisms, but in brackish waters where annualevaporation is high, salinity is a critical factor fororganism distribution. Many aquatic ecologists havestudied salinity in the hope of explaining distributionalproblems (Macan, 1974). Based on the analysis of 116samples in Chinese saline lakes with salinity from 0.98to 175.2‰, Zhao & He (1999) showed that the speciesdiversity and richness decline as salinity increases.

Based on the survey of 79 Australian salt lakes, Wil-liams et al. (1990) suggested that salinity per se doesnot determine what species occurs in a particular lake,but species richness is strongly correlated with salin-ity. This implies that the impact of salinity on speciesdistribution may depend on other factors. Edmondson(1944) studied the distribution of sessile rotifers in 194localities of the northeastern United States and foundthat eight species were limited by pH, not bicarbonate;six species were limited by reference to bicarbonate,but not pH; and three species limited with referenceto both pH and bicarbonate. In a laboratory study, Leiet al. (1985) confirmed the interactive effect betweenalkalinity and pH on fish.

He & Jiang (1990) found that the salinity toler-ance of M. mongolica is temperature dependent. Theytested the salinity tolerance of M. mongolica at 20, 24,28 and 30 ◦C. At each temperature, four salinities (52,54, 56 and 58‰) were used to test the upper salin-ity limit and six salinities (0.2, 0.4, 0.8, 1.0, 1.3 and1.5‰) were used to test the lower salinity limit. Foreach temperature and salinity combination, 20 animalswere used for the test. The upper LD50 for 24 h at 20,24, 28 and 30 ◦C was 53.6, 55.5, 54.2 and 53.6‰,respectively. The lower LD50 at 20, 24, 28 and 30◦C was 0.4, 0.6, 1.1, and 1.4‰, respectively. Theseresults again show that M. mongolica is a euryhalinespecies which can survive from freshwater to salinewater up to 53.6–55.5‰ salinity. When animals wereacclimatised from 40 to 55‰ over a 3-day period, thisspecies could survive in 65.2–75.4‰ salinity.

Unionised ammonia

Ammonia is present in most waters as a normal bio-logical degradation product of protein. The unionisedform of ammonia (NH3) is considered toxic to aquaticanimals. An & He (1996) tested the tolerance of M.mongolica to unionised ammonia under the followingcondition: temperature 25 ◦C, salinity 31.7‰, pH 8.48and alkalinity 2.4 mmol CaCO3. The 24 h LC50 and48 h LC50 of unionised ammonia for M. mongolicawere 9.89 mg l−1 and 7.52 mg l−1, respectively. An& He (1996) recommended the safe concentration ofunionised ammonia for M. mongolica culture is lessthan 2.63mg NH3–N l−1. This ammonia level is lowerthan that for aquatic insect larva, Chironomus thunmmi(4.3 mg l−1), but higher than that for Daphnia magna(0.66 mg l−1, Alabaster & Lloyd, 1980).

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Food and feeding

Most cladocerans remove particulate organic matterfrom water by filtration. The size of particles that canbe cleared from the water is a function of the mor-phology of the setae on the moving appendages. Themaximum rate at which energy is gained from food is,however, the function of the combined rate of filteringand feeding as well as food density (Leham, 1976).Filtering rate refers to the volume of water cleared ofsuspended particles per unit time while feeding rateis a measure of the quantity of food ingested by ananimal in a given time (Wetzel & Likens, 1990).

Wang & He (1997a) studied the effect of temperat-ure on filtering rate, feeding rate, and food consump-tion rate of M. mongolica. They found that the indi-vidual filtering and feeding rates of M. mongolica onN. oculata are 1.52–2.37 ml d−1 and 6.09–9.45×106

cells d−1 for juveniles, and 2.75–7.72 ml d−1 and10.88–14.94×106cells d−1 for adults, respectively(Table 2). The maximum filtering rate of a juveniles(2.37 ml d−1) occurred at 25 ◦C while that of an adults(7.72 ml d−1) occurred at 33 ◦C. The maximum feed-ing rate for both juveniles (9.45×106 cells d−1) andadults (14.94×106 cells d−1) occurred at 25 ◦C. Thedaily food consumption rate increased with temperat-ure and accounted for 67.7–103.0% body weight forjuveniles and 60.0–109.9% body weight for adults.The maximum daily consumption occurred at 33 ◦Cfor both juveniles and adults (Table 2).

Wang & He (1997b) also studied the effect of salin-ity on filtering rate, feeding rate and food consumptionrate of M. mongolica. There is no clear pattern ob-served for the effect of salinity on the filtering rate,feeding rate and food consumption for both juven-iles and adults (Table 3). At the juvenile stage, themaximum individual filtering rate (2.44 ml d−1) andfeeding rate (9.75×106 d−1) occurred in 40‰ salin-ity, while at the adult stage, the maximum individualfiltering rate (3.54 ml d−1) and the maximum feedingrate (14.15×106 d−1) occurred in 10‰ salinity. Themaximum daily consumption rate for juveniles (84.4%body weight) and for adults (80.8% body weight) oc-curred in 20‰ salinity. In 5–40‰ salinity, the dailyconsumption rate was 70.6–84.3% body weight for ju-veniles and 69.5–80.8% body weight for adults, againindicating this species can adapt to a wide range ofsalinity change.

Growth and reproduction

Effect of temperature and salinity

Temperature has long been known to influence thegrowth and reproduction for zooplankton species. Thegeneral positive effect of temperature on reproductivebiology of zooplankton is that growth rates increase(Vijverberg, 1980), egg development times decrease(Bottrell, 1975) and rates of population growth in-crease (Armitage et al., 1973) with increased temper-ature. These factors tend to increase production at hightemperature. On the other hand, O’Brien et al. (1973)suggests that average clutch size of eggs decreaseswith temperature. Clearly, temperature variations canhave either positive or negative effect on zooplanktonproduction, depending on the range of temperature andzooplankton species.

He et al. (1988a) studied the effect of temperatureon the growth rate, reproduction and life span on M.mongolica at five temperatures: 20, 25, 28, 30 and 35◦C. In their experiment, 30 female animals were usedat each temperature and N. oculata was used as food.Each animal was fed with N. oculata twice a day andthe algal density was maintained above 2.5×106 cellsml−1. All offspring were removed soon after they wereborn and the experiment lasted until all the initial 30animals died.

Moina mongolica required 5.8 d to reach maturityat 20 ◦C, but the age at maturity reduced to 3.4 d at30 ◦C (Table 4). The animals reproduced once a day at28 ◦C, but the reproduction intervals increased to 4.1days at 20 ◦C. The maximum fecundity averaged 9.1eggs♀−1 at 20 ◦C, while the fecundity reduced to 5.4eggs ♀−1 at 35 ◦C. The animals reproduced 2.8 timesat 28 ◦C, but only gave one birth during lifetime at35 ◦C. The longest life span was 10.8 d at 25 ◦C, butreduced to 4.2 d at 35 ◦C.

Most marine invertebrates have an internal saltcontent isotonic with the environment, hence osmore-gulation poses no problem except where salinity issubject to change. Species in inland brackish watersneed the ability to adapt the changing salinity. He etal. (1988a) also studied the effect of salinity on thegrowth rate, reproduction and life span of M. mon-golica with eight salinity gradients: 2, 5, 10, 15, 20,32, 40 and 50‰ at 25 ◦C (Table 5). Across all salin-ities, the animal reached maturity in 4.7–6.8 d. Theyoungest mature age was 4.7 d in 40‰ salinity andthe oldest mature age was 6.8 d in 10‰ salinity. Theshortest spawning interval was 1.4 d in the salinities

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Table 2. Individual filtering rate, feeding rate and daily consumption of juvenile and adult M. mongolica at different temperatures

Developmental Temperature Filtering rate Feeding rate Daily consumption

stage (◦C) (ml d−1) (106 cells d−1) (% body weight)

Juvenile 20 1.91 7.65 67.7

25 2.37 9.45 89.5

30 1.57 6.29 100.0

33 1.52 6.09 103.0

Adult 20 2.75 11.01 60.0

25 3.74 14.94 85.3

30 2.90 11.60 98.9

33 7.72 10.88 109.9

Table 3. Individual filtering rate, feeding rate and daily consumption of juvenile and adult M. mongolica at different salinities

Developmental Salinity Filtering rate Feeding rate Daily ration

stage (‰) (ml d−1) (106 cells d−1) (% body weight)

Juvenile 5 2.20 8.81 70.6

10 2.33 8.93 84.0

20 2.28 9.11 84.3

30 2.08 8.33 75.6

40 2.44 9.75 76.9

Adult 5 3.16 11.65 70.8

10 3.54 14.15 73.0

20 3.07 12.27 80.8

30 2.78 11.10 69.5

40 3.08 12.36 76.5

Table 4. Reproduction and life span of M. mongolica at different temperatures

Temperature Mature age Spawning Fecundity Lifetime spawning Life fecundity Life span

(◦C) (d) interval (d) (eggs ♀−1) (no life−1) (eggs) (d)

20 5.8 4.1 9.1 1.5 13.7 9.8

25 4.8 2.4 5.7 2.8 16.0 10.8

28 4.0 1.0 7.3 2.8 20.4 8.0

30 3.4 1.2 5.6 1.8 10.1 4.4

35 4.0 n/a 5.4 1.0 5.4 4.2

of 10‰ and 40‰, while the longest spawning intervalwas 2.6 d in 15‰ salinity. The minimum fecunditywas 4.2 eggs ♀−1 in 50‰ salinity and the maximumfecundity was 11.9 eggs ♀−1 in 5‰ salinity. The max-imum number of spawning during the life span was4 times in the salinity of 20‰ or 50‰, and the min-imum number of reproduction in the lifetime was 1.6

times in 5‰ salinity. The maximum fecundity duringthe lifetime averaged 42.1 eggs at 10‰ salinity andthe lowest fecundity averaged 9.8 eggs at 2‰ salinity.The longest life span averaged 14.2 d in 50‰ salin-ity, while the shortest life span averaged 6.9 d in 40‰salinity. Overall, the pattern of salinity impact on the

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Table 5. Reproduction and life span of M. mongolica at different salinities

Salinity Mature age Spawning Fecundity Spawning Life fecundity Life span

(‰) (d) interval (d) (eggs ♀−1) (No life−1) (eggs) (d)

2 5.5 1.6 6.1 1.6 9.8 10.3

5 4.9 2.0 11.9 2.4 28.6 11.4

10 6.8 1.4 11.7 3.6 42.1 10.2

15 5.0 2.6 11.5 2.4 27.6 11.6

20 5.1 1.5 9.6 4.0 38.4 13.8

32 4.8 2.4 5.7 2.4 13.7 10.9

40 4.7 1.4 9.6 2.0 19.2 6.9

50 5.0 2.0 4.2 4.0 16.8 14.2

Table 6. Reproduction and life span of M. mongolica fed different foods

Food type Mature age Spawning Fecundity Spawning Life fecundity Life span

(d) interval (d) (eggs ♀−1) (no life−1) (eggs) (d)

Nannchloropsis oculata 4.8 4.1 5.7 3.0 17.1 11.4

Platymonas sp. 4.9 3.6 5.1 4.8 24.5 15.4

Dunaliella salina 5.5 6.2 5.3 2.2 11.7 10.8

Diorteria zhanjiangensis 6.6 n/a 3.7 1.0 3.7 6.6

Yeast 5.4 n/a 3.1 1.0 3.1 10.3

Yeast + N. oculata 5.1 2.9 6.3 4.1 25.8 14.1

Horse manure 5.2 4.3 5.6 2.6 14.6 12.0

Horse manure + N. oculata 5.4 2.3 7.5 4.6 34.5 13.8

Bean powder 5.5 n/a 4.8 1.0 4.8 7.2

animal reproduction is not clear, further indicating theadaptability of this species to a wide salinity change.

Effect of food types

The quality and quantity of food are the most im-portant factors controlling biological production. Heet al. (1988b) tested the reproduction performanceof M. mongolica feeding on various food types, in-cluding five species of algae (N. oculata, Platymonassp. Dunaliella salina and Diorateria zhanjiangensis)yeast, horse manure and bean powder (Table 6). Thedensity of each alga was adjusted to 45–70 mg l−1

(equivalent to 2.5–4.0×106 cells ml−1 of N. oculata).In the culture with yeast only, the density of yeastcells was adjusted to 2.5–3.5×106 ml−1. The culturemedium of horse manure was prepared by soakingdry manure for 1–2 d to allow time for bacterial de-velopment, then only the liquid was used by filteringthrough a fine screen (0.5 mm mesh size). The mixtureof horse manure and N. oculata contained 0.5 g dry

manure l−1 and 1×106 algal cells ml−1. The mixtureof yeast and N. oculata contained 0.2×106 yeast cellsand 1×106 algal cells ml−1. The bean powder culturemedium contained 50 mg dry powder l−1.

The maximum age at maturity was 6.6 d when M.mongolica fed on D. zhangiangensis, while the min-imum age at maturity was 4.8 d with N. oculata asfood (Table 6). The spawning intervals averaged 6.2 dwhen D. salina was used as food, while the spawningintervals reduced to 2.3 d when the combination ofhorse manure and N. oculata was used as food. Themaximum fecundity (6.3 eggs ♀−1) occurred whenthe animals fed on the combination of yeast and N.oculata, but the minimum fecundity (3.1 eggs ♀−1) oc-curred when only yeast was used as food. The animalsreproduced 4.5 times during their lifetime when eitherPlatymonas or the combination of horse manure andN. oculata was used as food, but reproduced only onceduring the lifetime when D. zhanjianensis or yeast,or bean powder was used. The lifetime fecundity was34.5 egg ♀−1 when animals fed on the combination

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of horse manure and N. oculata. The total fecundityduring the lifetime was less than 5 eggs ♀−1 whenD. zhanjianensis or yeast or bean powder was used asfood. The life span averaged 15.4 d when Plantymonaswas used as food, while the animal survived only 6–7d when D. zhanjiangensis or bean powder was used asfood.

Resting eggs

Parthenogenesis is common in M. mongolica, andparthenogenetic diploid eggs hatch into females forseveral generations without producing males in thepopulation (Lu & He, 1999). At some point of thelife history, certain factors such as (1) crowding ofthe females and the subsequent of accumulation ofexcretory products, (2) a decrease in available food,(3) a decrease in water temperature, and (4) reducedphotoperiod, can affect the chromosome mechanismin such a way that parthenogenetic male eggs ratherthan parthenogenetic female eggs are released intothe brood chamber (Pennak, 1989). The same con-ditions responsible for male production, if continuedfor a longer time, will induce sexual eggs. Femalesproducing such eggs are morphologically similar toparthenogenetic females, but they produce mictic eggs(i.e. sexual eggs) which require fertilisation to de-velop. Unlike parthenogenetic females, mictic femalesare capable of copulation with males (Barnes, 1987).Lu & He (1999) reported that the fertilised egg of M.mongolica is larger and only one egg is produced ina single clutch. When the resting egg is produced, thewalls of the brood chamber are transformed into a pro-tective, saddle-like ephippium. This will be cast off atthe next moult, either separating from or remainingwith the rest of the detached exoskeleton. The ephip-pium sinks to the bottom, or adheres to walls of theculture vessel.

Reduced food density can trigger the productionof resting eggs in M. mongolica. At 25 ◦C M. mon-golica reproduced parthenogenetically as long as food(N. oculata or yeast) density was above 5000 cellsml−1. When food density was between 1000 and2000 cells ml−1, males were produced in the firstbrood and the number of males accounted for 83.3%and 33.3% of newborns, respectively, but no micticfemales were produced. The threshold food densitythat triggers male production in M. mongolica is con-sidered between 2000 and 5000 cells ml−1 (Lu & He,1999).

Although population crowding could induce rest-ing eggs, no resting eggs were found when thedensity of M. mongolica was less than 300 l−1.When the animal densities increased to 400, 800 and1600 l−1, mictic females increased to 4%, 13% and17%, respectively. In Cladocera, sexual reproduc-tion is density-dependent (Stross & Hill, 1965) andthis can be explained by the accumulation of meta-bolic products (Hobaek & Larsson, 1990). Lu & He(1999) found that water extracted from an old mediumcrowded with M. mongolica (>1000 l−1) stimulatedmale production. Males accounted for 14.7% of new-borns in the second brood and 33.3% in third broodwhen M. mongolica was cultured in an old medium,while no males were produced in the fresh medium(Lu & He, 1999).

Lu & He (1999) showed that reduced temperaturestimulated the production of males and mictic females.At 16 ◦C, males accounted for 50% and mictic femalesfor 8% of the population, while no males or micticfemales were produced at 17, 19, 21, 23 or 25 ◦C.When M. mongolica were directly transferred from25 ◦C to 16 ◦C, 38% of broods produced males, and8% broods produced mictic females. When animalswere directly transferred from 25 ◦C to 21 ◦C, 29% ofbroods produced males. At 16 ◦C, when the N. ocu-lata density was at 300 000 cells ml−1, although 50%of broods produced males, only 8% broods producedmictic females; when the N. oculata density reduced to1000 cells ml−1, 50% broods produced males and 33%broods produced mictic females. The combination oflow temperature (16 ◦C) and low food level (1000 cellsml−1) is considered a way to induce both males andmictic females.

Reduced photoperiod can induce sexual reproduc-tion in D. magna (Stross & Hill, 1968), but at 19 ◦C,sexual reproduction in D. magna is not light depend-ent (Garvalho & Hughes, 1983). The work by Lu &He (1999) shows that sexual reproduction of M. mon-golica is, however, light and temperature dependent.At 25 ◦C, the change of photoperiod (8 h light:16 hdark versus continuous light) did not induce any maleproduction. At 16 ◦C, 50% of broods produced malesand 8% of broods produced mictic females under re-duced photoperiod (i.e. 8 h light:16 h dark), while only38% of broods produced males and no brood producedmictic females when continuous light was provided.No males or mictic females were produced when sa-linity increased from 31.2‰ to 50‰. This is probablybecause M. mongolica is a euryhaline species and

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Table 7. Comparison of highly unsaturated fatty acids in M.mongolica with Artemia and B. plicatilis

Amino acids M. mongolica Artemia Rotifer

(%) (%) (%)

16:4ω3 0 0 3.9

18:3ω3 0.6 27.6 10.2

18:4ω3 0.5 3.1 0.3

20:3ω3 0 1.2 0.8

20:4ω3 2.4 0.3 1.1

20:5ω3 12.7 2.3 1.9

22:5ω3 0 0 0.3

18:2ω6 7.3 6.6 15.9

Table 8. Comparison of essential amino acids in M. mongolicawith Artemia and rotifers

Amino acids M. mongolica Artemia Rotifer

(%) (%) (%)

Arginine 3.4 5.0 4.6

Histidine 1.2 1.3 1.5

Isoleucine 3.4 2.6 3.4

Leucine 5.3 6.1 6.1

Lysine 3.4 6.1 6.1

Methionine 1.5 0.9 0.8

Phenylalanine 3.4 3.2 3.9

Threonine 3.2 1.7 3.2

Tryptophan 1.2 1.0 1.2

Valine 3.9 3.3 4.2

the change of salinity does not alter its reproductivestrategy (He & Jiang, 1990).

Nutritional composition

An important perspective is that M. mongolica canbe used as a live food for marine fish culture. Al-though the essential fatty acid requirement of fishdiffer markedly from species to species, it seems thathighly unsaturated fatty acids (HUFA) are required bymany marine fish (Watanabe et al., 1983). Tong et al.(1988) compared the contents of highly unsaturatedfatty acids (ω3, ω6 and ω 9) in M. mongolica withother live food zooplankton such as Artemia naupliiand B. plicatilis. The content of 20:5ω3 (eicosapentae-noic acid) in M. mongolica was 12.7% of the total fattyacid while this fatty acid in Artemia and B. plicatiliswas only 2.1% and 1.9% of the total fatty acid, re-

spectively (Table 7). The concentration of 20:5ω3 inArtemia nauplii has been used to determine the nu-tritional value for larvae of various marine fishes andcrustaceans (Leger et al., 1986). Because the 20:5ω3fatty acid is always low in Artemia, it is a commonpractice to enrich Artemia in a fatty acid rich emulsionfor 2–6 h (Watanabe et al., 1983). Considering thehigh content of 20:5ω3 fatty acid, M. mongolica is avaluable food for fish larvae.

Tong et al. (1988) also compared the essentialamino acids in M. mongolica with other commonlyused live food organisms (Artemia napulii and B.plicatilis). They found that the content of most essen-tial amino acids in M. mongolica was lower than thatin Artemia or in B. plicatilis, but the content of me-thionine in M. mongolica was 1.5% of the total aminoacids, which was higher than that in Artemia (0.9%) orB. plicatilis (0.8%, Table 8). Methionine is an essentialamino acid for fish and its content in most inverteb-rates is only 62% of that in fish tissues (Dabrowski &Marian, 1983). Moina mongolica, therefore, can be agood source of methionine for fish larvae.

Methods of mass production

Four methods (static batch method, static continu-ous method, aerated static method and flow-throughmethod) have been used for the mass production of M.mongolica (He et al., 1998). In each culture method,salinity ranges from 30‰ to 32‰ and temperaturevaries from 19.2 ◦C to 26.0 ◦C in the culture.

Static batch method

In this method, animals are harvested at the end ofthe culture. Nannochloropsis oculata was used aslive food for M. mongolica and inoculated into 500 lfibreglass tanks up to 1/5–1/4 of the tank volume at2–5×106cells ml−1. Moina mongolica was then in-troduced into each tank at 250 ind l−1. During theculture, the density of N. oculata was maintained at>2×106ml−1. The density of M. mongolica in eachtank reached 540–3 500 ind 1−1 during the cultureperiod. The biomass yielded 9.8–47.4 g m−3d−1 after28 days. He et al. (1998) found that food supply canbe a limiting factor in this type of culture due to thehigh filtering rate of M. mongolica (3.0 ml d−1ind−1

at 25 ◦C, Wang & He, 1997a). It is difficult to maintainthe M. mongolica density >1000 l−1 by using algae asa sole food supply. Harvesting is recommended whenthe animal density reaches 500–1000 l−1.

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Static continuous method

In this culture method, animals are harvested period-ically after the biomass reaches a target level. Nan-nochloropsis oculata was used as live food for M.mongolica and inoculated into 500 l tanks in a waysimilar to the static batch method, but beer yeast wasadded as supplemental feed together with N. oculata.The dry yeast power was soaked in water for 1–2 h,and 25 mg yeast cells l−1 were added to the culturetwice a day. Moina mongolica was harvested when thepopulation number reached 500 l−1. At each time ofharvest, 10–50% of the tank volume was drained andcollected with a fine mesh filter. The tank was toppedup with N. oculata (2–5×106 cells ml−1) after eachharvest and the remaining M. mongolica populationin the tank was used as seed for further production.When the density of M. mongolica was in the range of1225–5400 l−1, the wet weight production could reacha yield 14.3–45.8 g m−3d−1. Due to high food con-sumption by M. mongolica, He et al. (1998) suggestedthat the addition of supplemental food such as yeast isa practical method to increase the unit production, butdissolved oxygen can be a limiting factor for furtherincrease of production.

The oxygen consumption rate of M. mongolica is0.008 mg ind−1d−1 and the lowest oxygen that the an-imal can tolerate is 0.14–0.93 mg l−1 (Wang, 1993). Instatic culture, the minimum level of dissolved oxygenin the culture vessels should be >0.5 mg l−1. Whenthe animal density reaches 1000 l−1, the daily oxygenconsumption can reach 8 mg l−1. Therefore, when thedensity of M. mongolica is more than 1000 l−1, aer-ation should be supplied. The recommended level ofdissolved oxygen for M. mongolica culture is 6–8 mgl−1.

Aerated static method

This method is similar to the static continuous culture,but aeration is provided when dissolved oxygen dropsto a threshold level. Nannochloropsis oculata and M.mongolica were inoculated into 500 l tanks in the waysimilar to the static continuous culture, but the culturewas daily aerated 2–4 times when dissolved oxygendropped <6 mg l−1. Each aeration period lasted 1–3 h. The yeast cells were added 2 times a day and40 mg l−1 was added each time. The density of M.mongolica reached 4735–10 520 l−1 in the tanks anddaily biomass production reached 43.3–103.3 g m−3.The animals in tanks were harvested between 5 and 24

d. Dissolved oxygen was maintained 5–8 mg l−1 in allculture tanks.

Flow-through method

This method is an innovation of the static continu-ous culture, but algae are continuously supplied to M.mongolica. At the beginning, Nannochloropsis ocu-lata and M. mongolica were inoculated into 100 ltanks. The food was supplied through a 30 l algal tankin which N. oculata (2–5×106 cells ml−1) was cul-tured. The algal tank was placed at an elevated positionso that algae could be supplied to the Moina tank bygravity. In the Moina tank, the water exchange ratewas 0.9–1.5 times d−1. In this method, the density ofM. mongolica reached 6723–7890 l−1 in the tank anddaily biomass production reached 33.5–88.6 g m−3.The production level in the flow-thought system ishigher than that in both static batch culture and staticcontinuous culture, but is lower than that in the aeratedstatic culture.

Using M. mongolica as live food for fish larvae

He et al. (1997) studied the feasibility of using M.mongolica as a live food for two species of marine fishlarvae: red seabream Pagrosomus major and sea perchLateolabrax japonicus. Red seabream (21–27 mm TL)were fed with M. mongolica or Artemia nauplii. Fishlarvae were stocked into four, 1000 L fibreglass tanksat 30 fish m−3. Fish were daily fed under two feedingregimes: M. mongolica versus Artemia nauplii at 500–1000 ind l−1. Water temperature was maintained at25–27 ◦C and dissolved oxygen was above 8 mg l−1

by aeration. After 10 d, fish survival rate is 100% inboth feeding regimes and weight gain averages 101.5mg d−1 when fed with Moina, and 92.5 mg d−1 whenfed with Artemia (Table 9).

Sea perch larvae were also fed with M. mongolicaor Artemia nauplii for 16 d. Fish larvae (29.8 mg) werestocked into four 34 1 fibreglass tanks at 1470 fishm−3. Two feeding regimes were compared: M. mon-golica vs. Artemia nauplii. Moina and Artemia werefed with yeast but enriched by N. oculata 24 h beforebeing fed to fish. The amount of Artemia or Moinaadded to the fish tank was 500–1000 l−1d−1. The tankswere aerated and dissolved oxygen was maintained at7–8 mg l−1. During the experiment water temperat-ure was maintained at 13–14 ◦C. At the end of theexperiment, fish survival averaged 89% when the fish

35

Table 9. Comparison of growth and survival rates of red seabream fed on M. mongolica and Artemia nauplii

Food type Fish density Initial length Final length Initial weight Final weight Weight gain Survival

(No m−3) (mm) (mm) (mg) (mg) (mg) (%)

M. mongolica 30 25.2 42.0 150 1064 914 100

M. mongolica 30 25.2 41.9 150 1085 935 100

Artemia 30 25.2 42.5 150 1280 1130 100

Artemia 30 25.2 40.3 150 1050 900 100

Table 10. Comparison of growth and survival rates of sea perch fed on M. mongolica and Artemia nauplii

Food type Fish density Initial weight Final weight Weight gain Survival

(No m−3) (mg) (mg) (mg) (%)

M. mongolica 1470 29.8 99.7 69.9 84

M. mongolica 1470 29.8 101.0 71.2 94

Artemia 1470 29.8 109.6 79.8 92

Artemia 1470 29.8 114.9 85.1 80

fed on Moina and 86% when fish fed on Artemia. Theweight gain was 82.5 mg d−1 and 70.6 mg d−1 whenfed Artemia and Moina, respectively (Table 10). Thereason why fish grew slower when fed with Moina wasprobably that Moina size was too big for fish larvae<29.8 mg in the beginning (He et al., 1997).

Summary and perspective

This review has highlighted the general dearth of in-formation on the biology of this halophilic species.Moina mongolica is 0.6–0.7 mm long and 0.5 mmwide, and the adult is 1.0–1.4 mm long and 0.8 mmwide. Its size is about 5–10 times larger than B. plicat-ilis and 1.2–3.5 times larger than Artemia nauplii (Heet al., 1989). The size dimension of M. mongolica fitsthe mouth opening of most fish postlarvae (He et al.,1997). If the rotifer is a suitable starter food for mar-ine fish larvae, then juvenile M. mongolica may serveas live food for fish postlarvae after rotifer, and adultM. mongolica can be a transitional food for fish fin-gerlings between live food and formulated feed. Thepotential of M. mongolica for finfish larviculture hasbeen demonstrated in terms of its adaptability to en-vironmental change, rapid reproduction, wide choiceof food, applicability to mass culture, nutritionalcomposition and suitable size for fish ingestion.

Moina mongolica is a euryhaline species whichcan survive a sudden salinity change from 32‰ to

55.45‰, or from 32‰ to 0.4‰. When acclimatisa-tion is involved it can tolerate the salinity change from32‰ to 74.5‰, or from 32‰ to 0.15‰. The max-imum salinity (74.5‰) that M. mongolica can survivein the laboratory is closed to the upper limit (73‰)found in nature (Hammer, 1986), but the minimum sa-linity (0.15‰) it can tolerate in the laboratory is lowerthan the lower limit (4‰) found in nature (He et al.,1989). When the daily salinity change is by 2‰, M.mongolica can reproduce parthenogenetically in 0.3–58.7‰ salinity (He & Jiang, 1990). The adaptability ofM. mongolica to a wide range of salinity change makesit a suitable live food for finfish larvae in brackish andseawater aquaculture.

Moina mongolica is an eurythermal species, whichcan survive in 2–35 ◦C (He et al., 1994). The max-imum intrinsic rate (rm=0.32) and longest life span(10.8 d) occur at 25 ◦C while the shortest spawninginterval (1.0 d), and maximum lifetime fecundity (20.4♀−1) occur at 28 ◦C. Between 25 and 28 ◦C, M. mon-golica reaches maturity in 4–4.8 d and spawns every1–2.4 d; in the lifetime, M. mongolica reproduces1.5–2.8 times and produces 16–20.4 offspring (He etal., 1988b). At 25 ◦C, for example, if daily popula-tion intrinsic grate rate (rm) is 0.32, the populationabundance after 10 d will increase 25 times based onthe calculation of population growth (i.e. Nt=Noert,where, No is the initial population number; Nt is thepopulation number after a given time, e.g. t=10 d; and

36

r is the daily intrinsic growth rate; and e is the naturallog). According to this calculation, if parthenogeneticfemales are inoculated at 10 l−1, the population willreach 2500 l−1 in 10 d. The fast population growth rateis an ideal characteristic for selecting M. mongolica aslive food in marine fish larviculture.

Moina mongolica feeds on a variety of food (1–20 µm) including microalgae, yeast and bacteria (Heet al., 1988b). Although M. mongolica can surviveon N. oculata at 2.5–4.0×106 cells ml−1, the highestfecundity in the lifetime (34.5 eggs) occurs when thecombination of N. oculata and horse manure is usedas food. The second highest fecundity in the lifetime(25.8 eggs) occurs with the combination of yeast andN. oculata as food. The ease of food choice makesit possible either culture in indoor facility with al-gae and yeast or culture in outdoor facility (tanks orponds) with algae and manure. Moina mongolica tol-erates low dissolved oxygen (0.14–0.93 mg l−1, Wang,1993) and high nonionised ammonia (<2.63 mg l−1,An & He, 1996). Therefore, it can be cultured at a highdensity in static batch culture or continuous culture.In static batch culture, the density of M. mongolicareaches 3500 l−1 and productivity is 47.4 g m−3d−1.In the aerated static culture, its density reaches 10 520l−1 and productivity reaches 103.3 g m−3 d−1.

Its body size is suitable as a food for finfish lar-viculture when the size of rotifer becomes too small.In the feeding trials, both red seabream and sea perchdemonstrate a high survival and fast growth fed withM. mongolica. It is possible that M. mongolica cansubstitute Artemia cysts as a new food source in mar-ine larviculture. Similar to Artemia cysts, the restingeggs of M. mongolica can be induced by low temper-ature and low food supply, and the resting eggs canhatch after drying for 7–10 days (Lu & He, 1999). Theformation of resting eggs makes it easier to transportto a new location. Future research on M. mongolicashould focus on its commercial use for other aquacul-ture species including shrimp, crab larvae in variousgeographic locations.

Acknowledgements

The research on saline water organisms was suppor-ted by Chinese National Science Foundation (grantNo. 38970589). The preparation of this manuscriptwas partially funded by Flinders University ResearchBoard (grant No. 3304651091). We thank MichaelSierp for editing the English text.

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