daphnia

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Version 3.2

written & compiled byJohn Clare, B.A., Ph.D.

Table of Contents

Background

Introduction and Version InformationWhat are Daphnia?Anatomy of DaphniaWhat kinds are there?Where can they be found/obtained?

Culturing

Where can I culture them?Physical RequirementsWhat do I feed them?How do I maximise the yield?HarvestingMaintenance

Dos and Don'ts

Further Information

ContactsDaphnia Related LinksReferences/Bibliography/Credits

Introduction and Version Information

This document is aimed primarily at aquarists and anyone wishing to culture

Daphnia http://www.caudata.org/daphnia/#cult2

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Daphnia as a food for fish or other animals (such as young newts and salamanders).It is also aimed at anyone interested in learning more about Daphnids, and inparticular, the genus Daphnia. Many of the culturing aspects of this documentborrow from Kai Schumann's Daphnia FAQ. Interspersed throughout are useful tipsfrom the live_foods mailing list ([email protected]). A full list of credits canbe found in the References/Credits section. I wrote and compiled this documentbecause despite the culturing aspect being well covered by Kai and a number ofothers, correct detailed information on Daphnia is hard to obtain from almost allsources except scientific journals/post-graduate theses, and the internet (though youhave to really dig for it). There is also a lot of conflicting advice out there, most ofwhich I have tested and have used this experience to "filter" out what I think isgood advice from the bad before putting it in here. I have explained much of thescientific phraseology and terminology used below, but if you are having problems,or if you see some incorrect information, please contact me using this form.

A note on volume: I use Imperial Gallons to measure volume. An Imperial gallon is4.545 litres. A US gallon is 3.8 litres.

- The first version of this document was written in August 1998.- Version 2.0 is dated December 1999.- Version 2.5 features fixed links and many new ones for suppliers and information(January 2000).- Version 3.0 features additions to the feeding section based on advice I've given onthe Axolotl Mailing List, as well as new links and some dead links removed. If youspot any dead ones or you have one I should add, please let me know.- Version 3.1: Removed the photos and made some minor corrections. I'll put someup of my own ASAP.- Version 3.2: Added my own photo of Daphnia magna.

What are Daphnia?

Daphnia (or Daphnids) are members of a collection of animals that are broadlytermed as "water fleas". These are predominantly small crustaceans, and Daphniabelong to a group known as the Daphniidae (which in turn is part of the Cladocera,relatives of the freshwater shrimp, Gammarus et al, and the brine shrimp, Artemiaspp). They get their common name from their jerky movement through the water.Apart from the jerky movements, the resemblance to real fleas (Pulex iritans, etc),ends: real fleas are insects and share only an extremely distant common ancestrywith Daphnia, since both crustaceans and insects are arthropods. In this document,the terms Daphnia, Daphnids/Daphniidae are used interchangeably and though nottechnically the same, they should be read as such in all cases except that of speciesnames which are absolute. These terms will be used to describe species of the genusDaphnia, especially D. pulex and D. magna. All species of Daphnia occur indifferent strains - sometimes the same species can look completely different, both interms of size and shape, depending on its origin, and environmental factors at thatlocation. As many of their traits will apply to other related genera, we will alsotouch on Moina, a group of close relatives.

It is important to distinguish between Daphnia and other "water fleas" such as thevarious species of copepod (like Cyclops spp) and ostracod (Cypridopsis et al)


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which do not directly come under the scope of this document, but share many of thefeeding habits of Daphnids. The jerky movement, general shape (and, to a lesserextent, colour) of daphnia are the best way to distinguish them withoutmagnification. The morphology and anatomy of Daphnids are discussed in detail inthe Anatomy Section below.

There are approximately 150 known species in North America, and a similarnumber in Europe (many of these species are found on both continents, eitherthrough accidental introduction by man, or nature). Many foreign species have beenintroduced to America and Europe from Asia and Africa (the most notorious ofwhich is Daphnia lumholtzi, which is native to Africa). It is not uncommon to collect20 or more species in one small area of lake bottom. A few species of Cladocera arepredacious but most are herbivores or detritivores. An important link in food chainsof virtually every inland body of water, cladocerans convert phytoplankton/benthicplants, bacteria, fungi and decaying organic matter into animal tissue that can beused by larger animals. In large lakes they are a major food source for many kindsof fish such as sticklebacks, minnows, the fry of larger fish and also larvalamphibians. Many aquatic insect larvae and other invertebrates also feed oncladocerans.

The daphnia covered in this document feed on particles found floating in the water(phytoplankton, but also attached vegetation or decaying organic material), but thepredominant foods are free-living algae (eg Chlamydomanas spp, Volvox spp, etc),bacteria and fungi. In the summer months, they can often be seen "blooming" inponds and lakes as the concentration of algae builds up. Their prolificity is due to agreat extent to their ability to replicate by parthenogenicity.

Parthenogenicity is the ability to self-replicate without fertilisation of any form (atype of asexual reproduction) - the offspring are exact genetic replicas of the parent(clones), and any differences in the physical state of the clones is due toenvironmental conditions. Parthenogenesis seems to have evolved to allow daphniato take advantage of good conditions (food, temperature, etc) as soon as they arise.In the wild, during the late spring, summer and early autumn (depending ontemperature, food availability and presence of waste products of their metabolism),daphnia reproduce by parthenogenicity, bearing, on average, ten live young perindividual (the entire race is made up of females during this period). Developingembryos are often visible in the mother's body without the aid of a microscope.Generation after generation of females can be born in this way, with new femalesreproducing as early as four days old at intervals as often as every three days, for upto twenty five times in their lifetime (though this number is usually far smaller, andfemales tend to produce a lot less than one hundred offspring). You don't need to bea mathematician to imagine the magnitude of a healthy daphnia population.

When food is scarce some eggs develop into males and the females produce eggsthat must be fertilised (the sexes reproduce via haploid means, i.e. half the numberof chromosomes to procreate from each sex, as opposed to parthenogenicreproduction which is diploid). These eggs develop into small embryos which thengo into suspended animation, and are shed with the carapace as dark brown/blacksaddle-shaped cases known as ephippia (ephippium is Latin for saddle). These can


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survive harsh conditions and are quite capable of withstanding a dry spell if theirpond dries up for a while, and they can sometimes even survive freezing. Theephippial females of most Daphnids are easy to tell from their live-bearingcounterparts because the developing ephippium is visible as a black spot towardsthe rear end of the animal. When conditions improve again, the egg producinggenerations begin producing live young once again (all females), and the male sexdies out completely until it is needed when conditions worsen once again.

There are often pulses of population growth, when numbers increase almostlogarithmically by parthenogensis, using up a lot of food and causing overcrowding,and then the numbers fall sharply and ephippia are produced. There are usually twoof these pulses every year, though in a good year there can be many pulses. Even inan aquarist's culture, pulses will be noticeable. See the Maintenance section forways to counter population fall-off.

Daphnia are represented worldwide as a number of different species. This documentuses D. pulex and its variants as its model (found throughout the northernhemisphere), but its characteristics can be applied equally well to most otherspecies, be they from the same genus or related genera. Once thought of as ananimal of polluted waters, Daphnia have been proven to be very sensitive to poorwater conditions and a number of research and industrial groups use Daphnia to testwater quality. For example, they are very sensitive to halide concentration, like thechloride or fluoride in tap water, which are extremely toxic to daphnia, even moreso than to fish. They are also sensitive to metal ion concentration, like sodium,potassium, magnesium and calcium, which in increased concentrations can causeimmobility and death, and daphnia are extremely sensitive to copper, zinc and mostdissolved toxins (e.g. dichromate ions). They are often used to monitor water qualityso that only safe water is released into the environment by industry and watertreatment plants.

In terms of nutritional information, Daphnia have a protein content of around 50%dry weight and a fat content of 20-27% for adults (4-6% for juveniles). Somespecies have been reported to have a higher protein content, and Moina are quiteoften found to be 70% protein. As with most live foods, "they are what they eat",and so vitamin and other formulas are available as food for filter feeders likeDaphnia and Artemia which will give them certain food values or an increase in agiven fatty acid, for example (H.U.F.A. or Highly Unsaturated Fatty Acids are oftensold for this purpose).

Anatomy of Daphnia


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Figure 1 Figure 2

Figure 1: Anatomy of female Daphnia pulex (De Geer) (greatly magnified); diagrammatic; (muscles not shown in fig 1). B,brain; BC, brood chamber; C, digestive caecum; CE, compound eye; F, fornix; FA, first antenna (antennule); H, heart; INT,intestine; O, ocellus; OV, ovary; R, rostrum or beak; SG, shell gland. (Fig 1 was greatly modified from Storch, 1925.)

Figure 2: Photograph of a female Daphnia magna (by John P. Clare).

Daphnia tend to be almost kidney shaped, possessing only a single compound eye(though they have an ocellus, a simple eye), two doubly-branched antennae(frequently half the length of the body or more), and leaf-like limbs inside thecarapace that produce a current of water which carries food and oxygen to themouth and gills. Their bodies are almost transparent and with a microscope you cansee the heart beating, and sometimes even their last meal (the gut may appear greenif the individual has been feeding on algae).

A carapace covers the body, including the 4 to 6 pairs of thoracic appendages, andis used as a brood chamber. The abdomen and post-abdomen (distal to the anus) isgenerally bent forward under the thorax. The post-abdomen bears two large clawsused primarily for cleaning debris out of the carapace. Swimming is accomplishedby downward strokes of the large second antennae.

In most species complex movements of the thoracic appendages produce a constantcurrent of water between the valves. Small particles (less than 50 microns indiameter) in the water are filtered out by fine setae on the thoracic legs and movedalong a groove at the base of legs to the mouth. Although there is some evidencethat certain types of food, such as particular types of algae, Protozoa, or bacteriamay be selected by some species, it is generally believed that all organic particles ofsuitable size are ingested without any selective mechanism. When undesirablematerial or large tangled masses are introduced between the mandibles, they may beremoved by spines on the first legs and then kicked out of the carapace by the


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post-abdomen.

Males are distinguished from females by their smaller size, larger antennules,modified post-abdomen, and first legs, which are armed with a hook used inclasping.

Adult daphnia range in size from half a millimetre to almost a centimetre, dependingon the species, though within a given species, size can vary greatly (female Daphniamagna can be between 3 mm and 5 mm).

Colour is sometimes quoted in literature as a means of identifying species, but thiscan be a very vague indicator of species because within a species (and even astrain), the colour of genetically-identical individuals can be quite different due tothe adaptive physiology of Daphnids - in water which has low oxygen levels,Daphnia tend to develop more hemoglobin to increase their oxygen uptake from thewater. Oxy-hemoglobin, i.e. that which has coordinatively bound oxygen, is red incolour and this gives the see-through body of daphnia a red pigmentation.Individuals of the same strain in oxygen-rich environments tend to be yellow oralmost unpigmented. An example of a species that seems to exist with very littlehemoglobin in comparison to other members of its genus, is Daphnia hyalina. It isusually found in the open water of lakes where dissolved oxygen is plentiful. Thecolour is also moderated by what food is predominating in the diet. Daphnia fed ongreen algae will be transparent-green in colour, while those feeding on bacteria willbe salmon-pink.

The life span of Daphnia, from the release of the egg into the brood chamber untilthe death of the adult, is highly variable depending on the species andenvironmental conditions (Pennak, 1978). Generally the life span increases astemperature decreases, due to lowered metabolic activity. The average life span ofD. magna is about 40 days at 25 oC and about 56 days at 20oC. The average lifespan of Daphnia pulex at 20oC is approximately 50 days. Four distinct periods maybe recognized in the life history of Daphnia: (1) egg, (2) juvenile, (3) adolescent and(4) adult (Pennak, 1978). Typically, a clutch of 6 or 10 eggs is released into thebrood chamber. The eggs hatch in the brood chamber and the juveniles, which arealready similar in form to the adults, are released in approximately two days whenthe female molts (casts off her exoskeleton). The time required to reach maturityvaries from 6 to 10 days. Daphnia typically invest most of their energy inreproduction (D. magna 69%, D. pulex 67%), while they invest comparatively littlein growth (23%). This serves to highlight the heavy emphasis on fast reproduction totake advantage of good conditions.

What kinds are there?

There are many different species of Daphnia and closely-related genera. However,those of main concern to the aquarist will probably be Daphnia pulex, Daphnia magna,and the various Moina species. Moina are very tiny Daphnids and are often used as aneasier-to-culture substitute for Artemia (brine shrimp) as fry food, because youngMoina are only slightly larger than newly-hatched brine shrimp, and first stagedaphnia are not much bigger. Identifying Daphnia species accurately is best achievedusing their size, the shape of the ephippium, the shape of the rostrum and whether the


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post-abdominal extension is long/short and/or whether smaller appendages close to itare setose (covered with small hair-like structures). It should be noted that within eachspecies there are usually different strains, some of which may have different traits tothe "norm".

Daphnia pulex - Although a species in its own right, D. pulex is very hard todistinguish from a number of closely related forms (some consider them seperatespecies, others sub-species, since hybridisation is common. One example of this is D.galeata). Generally, it is like a smaller replica of D. magna, and is usually fed to thesame size of fish. The strain which I culture and know as D. pulex (from the F.B.A.'s1966 Key to British Cladocera), tends to be larger than that described by many texts(such as that by the British Columbian Resources Inventory Committee), but it is thislatter variety which I have found in the wild and identified as D. pulex. I obtained myDaphnia pulex strain from a local aquarist shop only because it happened to come inon some plants. The males are usually 1.5 mm and females 2.5 - 3.5 mm, but thegeneric D. pulex is taken to have males of about 1.3 mm, and females up to 2.2 mm.Other than the size difference, the two species are almost exactly the same inappearance. D. pulex's colour ranges from yellow to almost red, and in this respect canbe very similar to D. magna. The are a number of ways to distinguish D. pulex from D.magna. These include D. pulex's smaller size, one of the appendages of the carapacenear the post-abdominal is setose, the ephippium is more triangular than D. magna'sand the embyos in it are not parrallel, and there is only one extension from the topedge of the ephippium. D. pulex produces ephippia quite readily in bad conditions.

Daphnia magna is the species normally associated with the name Daphnia by mostaquarists. It has been a favourite live food source since the hobby began. D. magnamales are 2 mm in length and females are 3-5 mm. They range in colour from a paleyellow to salmon-pink, often this is affected by their food source. D. magna has a widetemperature tolerance, but its optimum temperature is between 18 and 22 oC(64-72F). In the wild, Daphnia magna is quite rare, but where it does occur, it isusually very abundant. Like all Daphnia spp ephippia, the ephippium of D. magna isshaped like a saddle. However, the embryos inside the ephippium (of which there areusually two in Daphnia species) are parallel, and it is like a curve-edged rectangle,with the top long side having two extensions beyond the rectangle at either end.Although magna does produce ephippia, it is less inclined to do so than D. pulex. D.magna is usually considered more "delicate" than D. pulex and as a result it is not astolerant of culture fouling as D. pulex.

Moina spp are, although similar to daphnia and other members of the Daphniidae, isquite distinct from the genus Daphnia. They are very small in comparison to mostDaphniidae (less than 0.5mm in length), and their young are only about the size ofnewly-hatched brine shrimp. However, their culture is almost identical to that ofDaphnia, and although they are harder to acquire, their use as a cheap alternative tobrine shrimp as a first fry food has made them popular with many fish breeders.

Related speciesThere are many other species of Daphnia/Cladoceran to be found throughout theworld. Some of the less well-known are described below, but it should be noted thatthese are much harder to come by unless you happen to live in a country which hasthe species in the wild.


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D. hyalina is more often found in the open water of lakes. In comparison to D. magna,D. hyalina is very transparent and as a result it is sometimes hard to see individuals inthe water. D. hyalina is generally 3 mm in length, the body shape slightly less rotundthan that of D. magna, and the "head" is less distinct as it doesn't extend as far fromthe body as it does in D. magna. At this time the I'm not aware of any large-scaleculturing of this species, despite the fact that is quite common in Europe.

Bosmina coregoni is a rather small species (about 1 mm in length) and is found inweedy ponds and canals. Due to its small size it is more suitable for use as a fry foodthan other Daphnia. It is a very active species and can often be confused with othersmall daphnids without the aid of a microscope or high power magnifying glass. Itsbody shape is shaped rather like a pea which has started to sprout. It is commonlyfound in Northern Europe. Interestingly, many "Moina" cultures are actually Bosminacultures.

Simocephalus vetulus is a large daphnid which seems prone to being trapped in thesurface film of water. It tends to be more tolerant of acidic water than other Daphnids,and often exceeds 6 mm in length. The author has encountered this species on anumber of occasions in the wild, and it is almost comical to watch an individualwheeling about in the surface film attempting to break free. Again this species iscommonly found in Northern Europe.

Where can they be found or obtained?

The answer to this question really depends on your location and which species youwish to culture. "Daphnia magna" is probably the most known. I use the invertedcommas because most so-called D. magna cultures turn out to be D. pulex becauseD. pulex is far more readily available, and to most people, one species looks thesame as the other. I have obtained most of the species mentioned above in nature inmy own country, Ireland (particularly the smaller variant of Daphnia pulex and D.hyalina). I have found that lakes/ponds located in limestone-based areas are goodsources of Daphnia, but have never found D. hyalina in small lakes/ponds. But nomatter where you are in the world, the chances are there is a locally occuringspecies of daphnid which is as good as any for fish food purposes.

Starter cultures can be obtained via mail order in the US and Europe. Contactinformation for some of these sources can be found in the Contacts section.

If you intend to obtain species from the wild, it is advisable that you use a finemeshed-net or sieve (or a home-made one made of muslin/net-curtain and a bentcoat-hanger on a broom handle). This is swept through the water at an even pace ina figure of eight pattern, or dragged slowly behind a boat. Try to ensure the meshisn't too small and that the net isn't swept too fast, otherwise the pressure of thewater on the creatures caught in it may well kill them. The best time of day to obtaindaphnia is when they bloom in large clouds where there is a high concentration ofalgae, or alternatively, in the evening before dusk in shallow water. It is importantthat you screen any daphnids you obtain in this manner to ensure you don'tintroduce parasites and/or predators (almost anything can eat fish fry, even hydra).It is recommended that you obtain your daphnids from a fish-free lake/pond for tworeasons: a fish-free lake/pond will mean there is more chance of obtaining daphniabecause there will be less predators to eat them, and also if you're planning on using


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daphnia as live food for fish, daphnia from a fish-free lake/pond will almost beguaranteed disease free.

Where can I culture them?

Daphnia are undemanding in terms of what you culture them in. I personally culturethem in 4 (3.4 US) gallon plastic crates because I don't have the space for multipleaquaria. Many people like to use children's blow-up paddling pools (I've used thesein the past with great success), but what you keep them in is really up to you. Thereare some things to bear in mind though when selecting containers:

Is the container made of a material that won't dissolve in water, and/or leechchemicals into the water (some plastics, particularly polypropylene do this)?

If you use a metal container, stainless steel is the safest because many metalswill react slowly with water over time (e.g. Aluminium oxidises to form a skinof aluminium oxide, but small amounts of aluminium are released into thewater).

Just like ordinary aquaria, it is desireable to have as high a surface area tovolume ratio as possible to ensure that there is good gaseous exchange(though not very demanding, Daphnia appreciate a good oxygen supply).

If you're keeping the "tank" outside in strong sunlight or with heavyillumination around, it is a good idea to use a container larger than 10 gallonsas the water temperature will fluctuate less markedly, thus providing greaterstability for the culture. It is also important when putting a container in stronglight that it isn't a dark colour (especially black), because as you probablyknow, dark colours produce more heat in the light than white or yellowcontainers.

For someone who only wants a modest amount of Daphnia per week, cultures canbe maintained in two litre bottles. For an aquarium, a light bulb in the lid which is ona timer makes it easy to keep indoors (you can get timers from electrical shops orfrom good aquaria outlets). I have found that Daphnia magna likes gentle aeration.In theory this would seem to be a good idea for all daphnia as it not only helpsincrease gaseous exchange at the surface of the water, and it also helps stabilise thewater conditions and acts against culture-fouling. However, I have found thatalthough Daphnia pulex does better with aeration, very gentle aeration seems to bethe key. Airstones should be avoided, since fine bubbles can lodge inside thecarapaces of daphnia, floating them to the surface and also preventing them fromfeeding, and eventually resulting in death (Artemia also suffer from this problem).

Physical Requirements

In places, this section borrows heavily from Kai Schumann's FAQ and FrancGorenc's article, with additions and changes by myself.


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Salinity - Daphnia are typically freshwater organisms and there are no marinespecies of the Daphnia genus. 99% of Cladocerans are found in freshwater, and theremaining few species are mostly found in brackish, not sea water. Some specieshave been observed in salinities up to 4 ppt, and salinities of 1.5 to 3.0 ppt arecommon in pond cultures in the Orient.

Oxygen - Daphnia are generally tolerant of poor water quality, and dissolvedoxygen varies from almost zero to supersaturation. Like the Brine Shrimp, theirability to survive in an oxygen poor environment is in their ability to synthesizehemoglobin. The production of hemoglobin may be promoted by high temperatures,and a high population. Also, like brine shrimp, Daphnia are not tolerant of fine airbubbles. A slow aeration is needed with Daphnia as a large bubble column will stripthe Daphnia out and kill them. I (and a number of others), have found that Bio-foamfilters (designed for fry-tanks) are ideal for aerating Daphnia culture, and theremoval of larger particles from the water is an added bonus. However care shouldbe taken to use them at minimal air flow to avoid over-agitating the water.

pH and ammonia - A pH between 6.5 and 9.5 is acceptable, with the optimum beingbetween 7.2 and 8.5. Ammonia is generally highly toxic to all organisms, even insmall amounts, but in alkaline conditions, the toxicity is radically increased, and thiswill drastically impair Daphnia reproduction, but will not affect the actual health ofthe animals themselves. So it seems that on the small scale that we require,monitoring of pH and ammonia is not critical to success. NOTE: in general, themore extreme the pH, the higher the toxicity of dissolved minerals and gases. Also,remember that pH is a logarithmic scale - a pH of 5 is ten times more acidic than apH of 6, and likewise, a pH of 9 is ten times more alkaline than a pH of 8.

Dissolved minerals - In contrast to their tolerance of low oxygen, Daphnia are verysensitive to disturbances of the ionic composition of their environment. Theybecome immobile and eventually die with the addition of salts like sodium,potassium, magnesium, and calcium. Low concentrations of phosphorus (less than0.5 ppm) will stimulate reproduction, but concentrations higher than 1.0 are lethal tothe young. Daphnia magna are quite resistant to phosphorus and can withstandconcentrations as high as 5-7 ppm. Daphnia are not affected by the addition ofnitrogen in fertilizers for the promotion of algae growth. As with any aquariumventure, the water used should be treated with aeration or de-chlorinator to removechlorine before the culture is started. Concentrations of only 0.01 ppm copper willresult in reduced movement in Daphnia. They are extremely sensitive to metal ionslike copper and zinc, pesticides, detergents, bleaches and other dissolved toxins. Forthis reason, they are often used to test waste-water from industry. Municipal andwell water may be contaminated enough to kill the culture. The best source of wateris from your aquarium water changes, but you could also use filtered stream or lakewater (fish-free water bodies are recommended due to possible disease introductionto your fish aquarium by way of the daphnia), or rain water collected from areas oflow/no air pollution (and rain water collected in cities or industrial areas is usuallysafe if left to stand for a week and only the top-most 3/4 used). Never use distilledor deionised water, as it does not have the minerals needed for growth.

A small degree of temporary and permanent hardness in the water usuallyencourages growth and reproduction because Daphnia make use of calcium andother minerals in their chitinous carapaces. D. magna tends to prefer harder water


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(170 mg carbonate hardness) and D. pulex a little less hard (90 mg carbonatehardness). I usually add a very tiny pinch of powdered Tufa rock (often used inMarine aquaria) to my water because there is very little temporary hardness in thewater I use and no permanent hardness whatsoever.

Temperature - Daphnia have a wide tolerance to temperature. The optimumtemperature for Daphnia magna is 18-22 oC (64-72F). D. pulex seems to do well atwell at almost any temperature above 10oC. Moina withstand extremes even more,resisting daily variations of 5-31oC (41-88 F); their optimum being 24-31oC (75-88F). The higher temperature tolerance of Moina make this species a better choicewhere temperatures may rise above the comfort levels for D. magna at certain timesof the year.

What do I feed them?

This is a general section on feeding Daphnia. I have summarised my ownexperiences at the end of this section. Daphnia have similar feeding habits to othertiny crustaceans (especially to the likes of Artemia). The best foods for culturing arealgae (typically free-living green algae species which tend to turn water to "peasoup"), yeasts (Sacromyces spp, and similar fungi), and bacteria. Combinations ofthe above seem to have the most success (i.e. yeast and algae seem to complimentone another). Each food type will be discussed in turn, together with its advantagesand disadvantages, and means of attaining/growing it.

AlgaeMicro algae is consumed in great quantities by Daphnia, and the abundance ofdaphnia is usually proportional to the density of algal blooms. There are a number ofways to grow algae, all of which are very basic and require little effort.

Placing a container of water outside in good sunlight will usually guarantee agood growth of algae within two weeks, usually a lot less. Algal spores arecarried on the wind and will colonise the water, but it usually speeds up theprocess if you "seed" the water with some algae from a container that hasalready has a bloom.

1.

Miracle grow, an organic plant fertiliser, can be used to grow algae (after allthey're just plants). One method is to use 1 gallon containers, 1 for each dayof the week. These sit on a window sill which gets good sunlight for as muchof the day as possible. By bubbling air through the containers (an airpumpwith 7 side lines will do, because there really only needs to be a smallmovement in the water), algae won't grow on the sides of the containerswhere it can block the sunlight. Add 1 tea spoon of Miracle grow per gallon.This system is then seeded with green water in tank #1 - two days later tank#2 - two days later tank #3, etc. When this has turned bright green (within 2weeks), pour it into a Daphnia tank. Refill the container with water mixtureand seed with tank #2 which should be about to turn bright green. This isrepeated with each container as they turn bright green. As you might be ableto tell, this will provide about 1 gallon of fresh green water every two days.

2.


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The advantages of algae as a food are that it is very easy to culture and it isexcellent for growing daphnia. There are no disadvantages really, other than the factthat it requires bi-daily maintenance / renewal.

YeastsThere are two general kinds of yeast that we need be concerned about - activatedand inactive. Activated yeast is generally a better food to feed because it will notfoul the water as quickly/as much as the inactive kind. Bakers, brewers, and almostany kind of yeast are suitable for daphnia cultures, but it is recommended that nomore than half an ounce of yeast per five gallons of water be fed every five days. Ifyou're using yeast, especially inactive yeast, consider adding some algae to thewater as this will counter any fouling which may result from adding the inactiveyeast (this isn't so important with activated yeasts). Do take care not to overfeedinactive yeast as it will foul the culture and therefore kill your daphnia.

Some bakers yeasts come with added ingredients like Calcium Sulphate andAscorbic acid (vitamin C) to aid fast activation of the yeast. These are harmless todaphnia cultures, but care should be taken when adding this kind of yeast becauseAscorbic acid can give pHs less than 6, which are far from ideal with Daphnia.However, I have never had any pH changes when using such "mixes" inmoderation, and the calcium sulphate gives vital calcium for the daphnia'scarapaces.

The advantages of yeast as a food are that it's easy to acquire, and there is aminimum of fuss when preparing it for the culture. The only slight disadvantage isthat it's not quite as good a food as algae (the daphnia need to consume more weightof yeast than algae to get the same food value). However, yeast is far better thanany other food except some bacteria, which have almost as high a food value.

BacteriaBacteria have a similar food value to fungi, but they generally reproduce faster thanfungi and algae, although the food value doesn't tend to be as high. Bacteria are"cultured" by taking 5-6 ounces of dried horse, cow or sheep dung (dried for tworeasons: it's easier to deal with, and most antibiotics or growth promoters whichwere fed to the animal will break down if the dung is left to dry for a while) andtying it in a nylon bag (such as tights/pantyhose), and hanging this in the water withthe daphnia. Animal dung (including human dung, though don't use human faecesunless you want typhoid or worse...) contains copious quantities of bacteria from thedigestive system, and these will leech out of the dung into the water and reproduce.Typically, the water will go cloudy after a time, indicating that the bacteria arestarting to multiply. This should be changed once a week for maximum effect.Another method is to soak the dung for weeks until it decomposes into a nutrientslurry, then drip the liquid into the tank at a rate of 16 fluid ounces per five to eightdays.

Another way to culture bacteria in a hurry is to throw a handful of salmon (or troutpellets), dog biscuits or other meat-based food into a few gallons of water with someadded aquarium water. Within a few days it is usually cloudy with bacteria.

Bacteria are a good food source, and easily acquired/cultivated. The only downsideis the smell of the decaying matter (which can be pretty bad at times). An important


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thing to remember is that horse dung usually contains tetanus (also a bacterium), socare should be taken when handling it (make sure you have no open cuts/sores onyour hands or arms).

Other FoodsThese include bran, wheat flour, and dried blood. These should be consideredsimilar to inactive yeast, and the same amounts and care should be taken whenadministering them. The only real difference is that the food value isn't as high asthe corresponding weight of yeast. Some of My Own ExperienceUnless you have a very large container, like an outdoor pond, I don't think "greenwater" is worth the effort. I fertilise the water with salmon pellets (the IndianaUniversity Axolotl Colony's at the moment - May 2000). The amount depends onyour container size and current daphnia population. Too much and you foul thewater and everything dies. As a guide, I would say for a 4 foot long aquarium one oreven two handfuls is enough to fertilise the water if there is an already healthypopulation of daphnia. If you have less, then don't use as many pellets or thebacteria population will go out of control. this is reliant on temperature, ideally inthe early 20s celsius / ~70F.

People recommend green water as the best food for daphnia. I would have to saythat I mainly agree with this, but I think that bacteria are just as nutritious. I haven'tbothered feeding green water to daphnia since 1998 so draw your own conclusions.I've been maintaining two populations since June 1998 and they have nevercompletely died out. They do pulse though. If you want a recommendation for aquick fix substitute for greenwater, get yourself a bag of frozen peas and one of carrots. Mix about 80% peas and20% carrots together and then stick them in a food blender. Blend these until youhave a mulch. You're looking for the "juices", so take any liquid and squeeze themulch to get all of the liquid from it. This contains particles of a size small enoughfor daphnia to sieve from the water (less than 50 microns). It's far moreconcentrated than water with algae in it, so use it sparingly. It gives just as good aresult. I've used this a few times, but I'm just too lazy most of the time to bother withanything except rotting pellets.

One final note on pellets - don't crush them much first. If you do you'll release all ofthe nutrients at once instead of over a few days and you can get the bacteria goingout of control. I should mention that I also keep water slaters (the European freshwater louse) in my daphnia cultures because they break down solid waste andprevent the pellets from being covered in fungus and floating at the surface. Thefresh water louse is a crustaceanthat looks like a wood louse and it is not a fish louse (louse is just the name). I don'trecommend snails in the culture either because for one thing, some species can actas a parasite vector, and also because they use up calcium and that's reserved forthe daphnia!

I've heard of ground-up liver in water being recommended. In that case it's mainlythe blood that is the fertiliser. I've tried animal's blood and found it ok, but thepellets win in my opinion, followed by algae and the mixture I mentioned above.


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How do I maximise the yield?

Daphnia production is relatively simple, if not an exact science. However, there areproven measures that increase the productivity of a culture.

Good aeration (good in so far as the manner in which the water is aerated, notgood as in quantity) is probably the largest contributing factor for goodproduction. Some species prefer no aeration, but Daphnia magna seems to dowell with it. It allows you to keep more daphnia in the same container. It alsocirculates the water, (which counters stagnancy and fouling). It minimises thepossibility of algae growing on the walls of the container, and it also keepsinert food in suspension which is more conducive to most daphnia feedinghabits. The only problem with aeration is that fine bubbles can lodgeunderneath the daphnia's carapace and float it to the surface and preventing itfrom feeding. Therefore airstones should be avoided (unless used in abio-foam filter in which case the air bubbles combine together), or coarseairstones (or better yet, no airstones) should be used instead.A good method (tried and trusted) of aerating the water which I havementioned previously is the bio-foam filter (there are a number of modelsavailable, any will do). These are commonly used in fry tanks, but are idealfor daphnia. They trap larger particles in the water (they don't trap algae), andhelp break them down, releasing nutrient for the algae to feed on. The outletsare usually very good at aerating the water, but care should be taken to usethem at low to minimum flow to avoid over-agitating the water (we wantsome aeration, not a torrent). I haven't had a fouled culture yet while using abio-foam.

Carry out regular maintenance as described in the Maintenance section,especially water changes.

Cull/Harvest the culture regularly (again, see the Harvesting section). Thisencourages constant growth and also keeps the daphnia from exhausting boththe oxygen and the food in the water too fast for it to be replaced.

Some people like to keep a light on 24 hours a day for their daphnia tank asthis can encourage faster growth and reproduction. I haven't tried this myself.However, you probably won't need to do this once your culture gets going.One important note though - continuous 24 hour periods in which the daylightis less than 12 hours and with a temperature significantly below 18

Water changes: some people recommend you change up to 75% of the waterin a culture every day. This is really dependent on what rate you're "running"the culture at. The more food you feed, the faster the water will be fouled,and therefore the more frequent the water changes. This is really up to theindividual, but be aware that output levels will drop if there is a build up ofmetabolites/toxins/etc in the water. This could lead to crashing.

Harvesting

When it comes to culturing Daphnia, harvesting may be the aim of the exercise, but


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it's also essential. Overcrowding is a serious danger otherwise. Even if you have towash the culled ones down the sink because you have too many, still cull them,otherwise the culture could become unstable. If you're culturing below about 25 oC,then it's generally a good idea to begin culling only midway through the secondweek unless you started out with a large number of daphnia (or your culture isgrowing like crazy already). This is because a lot of cultures take a few days tosettle and start reproducing. When culling, try to use a net which has a large enoughmesh to let young daphnia through, but just small enough to catch the adults (somepeople prefer to drain 1/4 of the tank into a net, and replace the water with newfertilised water, and in this way you do two jobs at once). Not more than 1/4 of thepopulation should be harvested daily, but the harvest may vary according to thequality of the population. But remember to cull regularly. In daylight/roomlight,when you stop the aeration, and let the tank settle, the Daphnia will concentrate onthe surface where they're easier to harvest.

Harvested Daphnia can be kept alive for several days in the refrigerator in cleanwater. They will resume normal activity when the water warms up. The nutritionalquality will not be as good because they have been starving for several days, so asupplemental feeding is required for best effect. Daphnia can be stored for longperiods by freezing them in a low salinity water (7ppt, 1.0046 density). Of coursethis kills the Daphnia, so adequate circulation is required to keep them in suspensionduring feeding. They also will not be as nutritious as the nutrients rapidly leach outin the aquarium. Nearly all the enzyme activity is lost in ten minutes, and in an hourall free amino acids, and most bound amino acids are lost. Fish will not feed onfrozen Daphnia as readily either.

Maintenance

A daphnia culture requires very little maintenance other than partial water changes(the amount really depends on the volume of water and the number of daphnia inthe culture - more water usually needs less changing, more daphnia usually meansmore water needs to be changed, to a maximum of 50% per week). Do feed yourdaphnia on a regular basis.

The key to avoiding population fall-off/crashing is to have constantly goodconditions, and to avoid sudden changes, such as large temperature drops, culturefouling, or the addition of dangerous chemicals to the water. Remember that ifyou're keeping your colonies outside, the population will naturally decrease inwinter, but should increase again in the following season.

Should your culture die off, don't despair. Either change most of the water or takethe mulm and put it in a new container - if conditions are good, the ephippia shouldhatch within 4 to 8 days (if you accidentally poisoned the culture with chemicals,you may need to obtain a new starter culture because the daphnia may not have hadtime to produce ephippia, and even if they did, even ephippia will not survive forvery long in strong chemicals like bleach or even mild acid).

If you go on holiday for a few weeks, don't be surprised if your daphnia haveproduced ephippia and the population has decreased while you were away!


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Dos and Don'ts

This section is intended as a reminder of things to remember and a precautionagainst simple mistakes people often make without realising it.

DOs

Do make sure you age your tap water and have a good idea of what's in it:

If it contains chlorine (chloramine will also put chloride into the water),it must be left to stand or aerate the water for 24 hours to drive off thechlorine gas (fluoride is usually very low in concentration and isn'treally something to worry about).

If your water contains lots of ammonia, this will inhibit the populationgrowth of your culture - again, aerating the water vigourously helpsdrive off ammonia (although it takes a lot longer than with chlorine).

Any metals in the water can often be toxic to daphnia. Some can inhibitpopulation growth (see the section on Physical Requirements).

Do carry out regular partial water changes.

Do feed regular modest amounts of food (this will depend on the culture size).

Do make sure you have adequate water hardness for your daphnia, otherwisethey will not reproduce at a high rate, and will probably just produceephippia.

Do try to maintain a constant temperature (about 20oC is ideal for mostspecies).

Do cull/harvest your cultures at least once a week to avoid overcrowding.

DON'Ts

Don't wash your hands with soap/detergent just before you put your hands ina daphnia culture unless you've _thoroughly_ rinsed your hands because soapand detergents are toxic to daphnia.

Don't overfeed - if anything, underfeed your daphnia to avoid fouling andtoxic build-up of ammonia.

Don't put your daphnia in a container of dense algae (and don't change toomuch water from the tank for algae water at one time) because algal bloomstend to raise pH to very high levels (over pH 9), and coupled with even a lowammonia concentration, this could be disastrous for the daphnia, killing themin short order. Ammonia toxicity increases with higher pH.

Don't keep all your eggs in one basket (or daphnia in one container). Even thebest of us will have accidents on occasion or have an emergency, etc, and ourcultures may be poisoned or die off for no apparent reason. To counter this, it


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is best to seed as many water vessels, aquariums, and even flower windowboxes with daphnia when the culture is first obtained. This will ensure youwill be able to "restart" without too much fuss.

Don't use insecticides near your daphnia containers, and don't leave yourdaphnia container in a room that was just painted/varnished/etc, because thefumes/gas can be toxic, and even if it doesn't kill the daphnia, the fish youfeed them to may be slowly poisoned.

Don't use airstones in a daphnia culture. Use an open airline tube or abio-foam filter (the latter contains an airstone inside in the apparatus, but thebubbles are not fine enough to harm the daphnia when the bubbles emergeinto the tank. Note however, there should only be a weak flow of air throughthe filter to avoid too much water flow).

Don't add miracle grow, etc, directly to the culture. It won't be much use, andit could also poison the culture, in high concentrations.

Don't add fresh tap water to a daphnia culture unless you want to kill them allwith the chlorine.

Don't keep your daphnia in the dark for days at a time as this can stimulatethem to produce ephippia.

Contacts

This section is a list of addresses/phone numbers of suppliers and information inEurope and America. These will usually stock D. pulex, and some will also stock D.magna.

Suppliers

Europe

Blades Biological (Daphnia pulex only)Kent,England,UK.Ph: 01342 850242

Living Lunch (mixed species)50 Hazel Close,Bemerton Heath,Salisbury,Wiltshire,SP2 9JJ,UK.

North America/Canada


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L. F. S. Cultures (see Links section)Internet Department,Post Office Box 607,University,MS 38677,USA.

Ph: 601-236-4687

Blue Spruce Biological Supply (see Links section)701 Park Street,Castle Rock,CO 80104,USA.

Ph: 800-825-8522

LarvaTech (see Links section)P.O. Box 641541,Los Angeles, CA 90064-1541,USA.

Ph: 1-877-603-4085

Information

Europe

Freshwater Biological Association (see Links section)The Ferry House,Ambleside,Cumbria,LA22 0LP,UK.

Windermere - 015394 42468

Daphnia Related Links

The links section is divided into mailing list links, then suppliers, and then information(daphnia/daphnid specific links and more general ones).

The Live Foods mailing list is very informative and the subscribers are immensely helpful,no matter what the question is (even though it's not the most active list on the net, it morethan makes up for this with its quality). The address is [email protected]. Tosubscribe, send a message to [email protected] with the line "subscribelive_foods" in the message body.

Living Lunch, based in southwest England. I've ordered various live foods and they're


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always friendly and helpful.

Blades Biological, based in England, supply laboratories but they also supply privateindividuals.

Blue Spruce Biological Supply are a good supplier of biological specimens and equipment.

LFS Cultures supply live foods, including Daphnia magna as well as other Daphniaspecies.

LarvaTech also supply Daphnia cultures.

Jan Parmentier and Wilm van Egmond's Web Site at Microscopy-UK is well worth a look.

The Krib has a lot of fishy information, including a collection of Daphnia articles (whichincludes the Daphnia FAQ by Kai Schumann).

Information on non-indigenous crustaceans in the US (specifically Daphnia lumholtzi).

A study of the ecological genetics of Daphnia and the genetic structure of Gammaruspopulations.

A good intro to Daphnia culturing (Kai Schumann's Daphnia FAQ).

The Journal of Plankton Research is published online and occasionally has some articleson Daphnia. It is a fascinating publication and back issues can be found in the onlinearchive.

Some good information about Moina.

A study of Daphnia retrocurva reproduction - quite interesting as it details the influence ofenviromental factors and predators on Daphnid morphology.

Population Structure and Daphnia - this paper, written by Sky Sterry, is a detailed study ofdifferentiation between isolated colonial groups of the same species of daphnia, and theoverall changes over time. Gives a good insight into the development of new/differentstrains of a species.

About.com's "Feeding Your Fish Links": Some links to Daphnia sites among other things.

Viviparous's Daphnia Page: Very well worth reading.

Actwin's Live Food FAQ.

The Daphnia Parasite Picture Gallery: And you thought Daphnia were weird enoughwithout having to worry about their parasites!

The Soil & Water Conservation Society of Metro Halifax: Information on Daphnia in theMetro Halifax region.

Daphnia Physiology: A little information on Daphnia Physiology.

Nutritional Value of Daphnia.


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Daphnia: A nice site on culturing Daphnia.

Genetic Analysis of Daphnia magna ephippia at Hull University.

The Freshwater Biological Association is an independent association founded in 1929.They are not only extremely helpful, but members have access to their library, one of thefinest freshwater libraries in the world. They also carry out research and publish manyhelpful species keys as well as articles in scientific journals. Membership is open toanyone, anywhere in the world.

The Fish INformation Service (FINS) has an online archive of many mailing lists(including a live-foods list, dating back more than three years), as well as FAQs on livefood.

References/Bibliography/Credits

Pennak, Robert - Freshwater Invertebrates of the US (1978).

Scourfield, DJ & Harding, JP - A key the the British Species of Freshwater Cladocera withnotes (1957-1966).

Schumann, Kai - Daphnia FAQ.

The subscribers to the Live Foods mailing list (see the Links Section).

Many of the sites mentioned in the links section

Sterry, Paul - Pond Watching (198x).

Clegg, John - The Observers book of pondlife.

Many snippets of information from a variety of Zoology and Limnology books, toonumerous to mention. I have been lucky in my life to have attended Trinity College Dublinfor my Bachelor's degree. Legal Deposition meant I was able to find books in the librarythere that are very rare.

-John Clare, August 1998, December 1999, May 2000, March 2001, July 2002.

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