Daphnia. All things aquarists would want to know!

Daphnia is a small crustacean that lives mostly in the fresh waters of the planet. With their miniature size, they have a rather complex structure and serve as an important element of the ecosystem – they multiply quickly and allow fish and amphibians to feed, so without them, the ponds would be much more empty. They also feed the fish in the aquarium.

A quick table of notes about Daphnia:

ITEMCHARACTERISTIC
Scientific nameDaphnia
NameDaphnia
Common namesDaphnia, Daphnia magna. water flea, zooplankton
Rangefreshwater lakes, ponds, and rivers all over the world
Size0.2-0.4 inch or 0.5mm to 1cm
Tank sizeas small as 2 gallons
Life spanvaries greatly 20-150 days
Temperature18-21C or 64-70 Fahrenheit
pH6.5 - 9.5
Colorgreen, yellow, white or salmon-pink
Foodciliates, seaweed, bacteria, detritus, microorganisms
Breeding5-10 days
Temperamentpassive, peaceful
Maturity5-10 days
Eggsextremely small and resilient,

A brief description of the species and color forms

Mostly located in the water column, moving with the help of jumps, sometimes crawl along the bottom of the reservoir or the walls of the aquarium. Often they move depending on what time of day it is: when it’s light, they go deeper into the water, and at night they are at the very edge. A lot of energy is spent on these movements, therefore they must have a reason. However, it was not yet possible to find out exactly her. There are several most likely assumptions. For example, large daphnia are forced to sink deeper during the day to become less noticeable for predators – after all, the deep layers of water are less illuminated. This assumption is confirmed by the fact that in water bodies in which there are no daphnia feeding fish, such migrations occur much less frequently. There is a simpler explanation – that daphnia simply aspire to that layer of water, where the temperature and light are optimal for them, and during the day it moves up and down. From species to species, their lifespan varies greatly. Usually the pattern is simple – the largest and live longer. Small Daphnia have 20-30 days, the largest up to 130-150 days.

Types of daphnia can vary greatly: the shape of their body, as well as its size, is determined by the conditions of the environment in which they live. Nevertheless, some common features can be highlighted. So, their body is covered with a chitinous shell with transparent valves – internal organs are clearly visible. Due to transparency in water, daphnia is less noticeable.

Water Fleas (Daphnia) in Slow Motion

The shell does not cover the head. There are two eyes on it, although often they merge into one complex eye as they grow, and sometimes Daphnia has a third, but usually, it clearly stands out and has a smaller size. On the sides of the antennae, Daphnia constantly waves them, and with their help, they move in leaps.

On the head, the rostrum is an outgrowth resembling a beak, and under it, there are two pairs of antennas, the rear ones being larger and have bristles, due to which their area increases. Swinging these antennas, they sharply fly forward, as if making a jump. These antennas are well developed and have strong musculature.

The body is flattened from the sides, the legs are flattened and underdeveloped because they are not used for movement. Mainly used, to drive fresh water to the gills and food particles to the mouth. The digestive system is quite complex for such a small crustacean: there is a full esophagus, stomach, and intestines, in which the liver outgrowths are located.

Daphnia also has a heart that is contracting at a high speed – 230-290 beats per minute, resulting in blood pressure of 2-4 atmospheres. Daphnia breathes with the entire cover of the body, but primarily with the help of respiratory appendages on the extremities.

Female-Daphnia

where do they live?

Representatives of the genus can be found practically throughout the Earth. They were found even in Antarctica in samples that were taken in relict ice lakes. This means that Daphnia is able to inhabit almost any environment of those represented on our planet.

However, if a century ago it was believed that all their species are ubiquitous, then it was found that each of them has its own range. In many species, they are quite wide and include several continents, but still, there is not one that is widespread everywhere.

They inhabit the Earth unevenly, preferring the weather conditions of the subtropics and the temperate zone. Noticeably fewer of them both at the poles of the planet, and near the equator, in a tropical climate. The ranges of some species have undergone significant changes recently due to the fact that they are distributed by people.

For example, the species Daphnia ambigua came from Great Britain to America and successfully took root. On the contrary, the species Daphnia lumholtzi was introduced to North America from Europe, and became common for the reservoirs of this continent.

For daphnia, reservoirs without current, such as ponds or lakes, are preferred. Often they live in large puddles. In the slowly flowing rivers, there are much less of them, and you can hardly find them in fast streams. Most species live in fresh water.

But the ability to adapt manifested itself here: daphnia, once found in arid conditions, where only salt water bodies were available to them, did not die but developed stability. Now, the species originating from them are characterized by a preference for reservoirs with high salt content.

Best of all, they live in clean water – it should have as little groundwater as possible. After all, daphnia feed on by filtering water, and, if it is dirty, soil particles also enter their stomach along with microorganisms, which means that they die much faster in polluted water bodies due to clogged stomach.

Therefore, by the number of daphnia in a reservoir, one can judge how pure the water is in it. They live mainly in the water column, and some species live completely at the bottom. They do not like bright lighting and go deeper when the sun begins to shine directly on the water.

I recommend you to watch this fantastic old video with good narration explaining everything about Daphnia: Be careful this video has SOUND!

Daphnia - Life Story of a Water Flea - Basic Life Science

What do they eat?

They feed, filtering the water, for which they move their legs, causing it to flow. Filtration of the incoming water stream is performed by special fans on the filtering bristles. Then the absorbed particles stick together in a lump due to secretion and are sent to the digestive system.

Daphnia is noteworthy for its voracity: in one day only some species eat 6 times their own weight. Therefore, with a decrease in the amount of food, their number in the reservoir becomes smaller – this occurs when the cold weather sets in, and Daphnia becomes the largest in late spring and summer.

Detritus is fed by those species of daphnia that do not hibernate in winter. They spend the winter at the bottom of the reservoir and in layers of water close to it – it is detritus that predominates their diet, that is, particles of tissue or excreta of other living organisms.

Detritus
Detritus

They themselves are used as food for fish in the aquarium – they are very useful due to the fact that in their stomachs there is a lot of plant food. Daphnia is both fed to fish dry and or alive into the aquarium. The latter is also useful if the water in it is cloudy: Daphnia eat bacteria, because of which it happens, and fish, in turn, eat Daphnia.

In their diet:

  • ciliates
  • seaweed
  • bacteria
  • detritus
  • other microorganisms floating in the water or lying on the bottom.

An interesting fact: On daphnia, it is customary to test the level of toxicity of various solutions. They even respond to low concentrations — for example, they may become slower or sink to the bottom.

Breeding

Daphnia is very prolific, and their reproduction is interesting in two stages – they reproduce both asexually and sexually. In the first case, exclusively females participate in it, and parthenogenesis is used. That is, they reproduce themselves without fertilization, and their offspring receives the same genotype as that of a single parent. It is thanks to parthenogenesis when good conditions come that their quantity in the reservoir grows significantly in the shortest possible time: usually, this method of reproduction in Daphnia is used in late spring and summer, when there is most food for them.

Reproduction, in this case, is as follows: eggs are laid in a special cavity and develop without fertilization. After their development ends and a brood of new Daphnia appears, the female sheds, and after only 3-6 days, a new cycle can begin. By that time, the females that appeared last time are also ready to breed.

Given that dozens of new Daphnia appear in each brood, their number in the reservoir grows very rapidly, and in just a couple of weeks it can be filled – this becomes noticeable by the reddish shade of the water. If food begins to be scarce, males appear in the population: they are smaller and faster than females, they are also distinguished by some other structural features. They fertilize the females, as a result of which eggs appear in the so-called ephippia – a strong chitinous membrane that allows surviving adverse conditions.

For example, they do not care for the cold or the drying up of a reservoir, they can be carried by the wind along with dust, they do not die when passing through the digestive system of animals. Even the presence of toxic salts in solutions does not matter to them, their shell is so reliable.

Daphnia eggs

But, if Daphnia multiplies by parthenogenesis simply, bisexual reproduction requires much more effort, and in many species, the females even die after laying their eggs. After falling into favorable conditions, the next generation of daphnia is derived from eggs and propagated again by parthenogenesis. Moreover, only females appear, since males do not survive adverse conditions.

Now you know how to breed Daphnia. Let’s see what dangers await Daphnia in the wild.

Daphnia’s predators

Daphnia is extremely important in the fish food economy, being very nutritious, every type of fish, hydras, flatworms, and even bigger crustaceans love to eat it.

An interesting fact: Deciphering the Daphnia genome revealed a lot of interesting things for scientists: approximately 35% of the gene products found in the genome are unique while being very sensitive to any change in the environment. It is because of this that Daphnia adapts so quickly.

An interesting fact: Generations of daphnia can differ markedly in body shape depending on what season they develop. For example, the summer generations often have a helmet on the head and a needle on the tail. To grow them, you need to spend more energy, as a result, the fecundity of an individual decrease, but this is justified by the fact that outgrowths protect from predators.

In the summer, there are especially many predators, and due to these outgrowths, some of them become harder to grab Daphnia, sometimes they also break the tail needle, due to which Daphnia can slip out. In this case, the outgrowths are transparent, and therefore it does not become easier to notice it because of them.

 

How to culture daphnia at home?

Daphnia crustaceans (Daphnia pulex, moina, magna or hybrids) are considered one of the best live food for aquarium fish, which, moreover, will not be difficult to grow at home. In this part of the article we will tell you where to keep Daphnia, how and how to feed it, what to pay attention to, so that the colony of crustaceans flourishes and gives a plentiful “harvest”.

To begin with, we will answer the question – where to get the living culture of Daphnia? In Western Europe and North America, everything is simple, crustaceans can be ordered via the Internet and the package will be delivered the next day right to the doorstep. In other countries, such a service exists only in large cities and not all. Residents of the province can use the services of pet shops as intermediaries by buying live crustaceans from them or collect them in nature with a simple net. In summer, zooplankton lives in large numbers in almost any lake or pond. True, in the latter case, there is a great risk of catching unwanted guests, for example, hydras or any parasites that can later migrate to the aquarium with fish.

You can even culture Daphnia in a jar: Be careful this video has SOUND!

How to Culture Daphnia in a Jar
Daphnia can be cultivated in almost any tank (barrels, cans, tanks, etc.). In the article, for simplicity of calculations, a 100-liter tank is used. The water should be clean, the hydrochemical composition does not matter, the temperature is 18–21 ° С. At higher temperatures, the breeding process slows down, so you will have to find a cool place for the tank. Ordinary tap water will do. However, depending on the terrain, it may contain chlorine. It must be removed, for example, leaving water for a day in an open bowl. Additional aeration will not be superfluous.
For those who breed Daphnia for the first time, a transparent aquarium is recommended in order to better control the development of the crustacean culture, the amount of feed, etc.

What to feed daphnia for home culture:

As such, there is no specialized food for daphnia. Various sources mention a wide variety of products from manure, yeast to finely chopped trout and bacon. However, most of them are not the direct food of crustaceans but serve as the basis for the development of bacteria, fungi, which daphnia already feed on. In the subjective opinion of the author, the optimal food is:

algae

  • Spirulina and / or chlorella algae in powder form – are supplied to pet stores, are widely available in online stores. For example, you can order on ebay or aliexpress.
  • Specialized micro food for freshwater shrimp larvae – available at pet stores or on order from fish suppliers.
  • Dry baker’s yeast and regular wheat flour – sold at any grocery store.
  • A mixture of Arc – the crown of the culinary creation for Daphnia. It consists of 1 part of soy flour, 3 parts of wheat flour, 1 part of peas, crushed to flour, 3 parts of baking yeast, 1 part of paprika, 2 parts of spirulina and / or chlorella algae.

Home experiments have shown that the Doug mixture is most effective, but requires a lot of time and ingredients to prepare. A combination of baker’s yeast and chlorella powder in a ratio of 50 to 50 gives similar results – this mixture is prepared much faster and easier. If desired, you can add a little paprika (1/10 part), which stains daphnia, and is subsequently absorbed by the fish organism and enhances their color.

How to feed daphnia for culture?

Daphnia can be fed in two ways. The first is based on the transparency of water. The second – based on the density of the culture of crustaceans in the aquarium.

First way

A mixture of feed is added to the container with the crustaceans and gently mixed until the water becomes slightly cloudy. Remember the amount of feed given. After a day, the water should become crystal clear. If this did not happen, then there was too much feed. If the water cleansed faster, then the feed is not enough.
This method requires experience and a constant correlation between the amount of mixture supplied. Only suitable for a mature colony.

Daphnia

Second way

First, you need to learn how to determine the number of daphnia per unit volume. In this case, one unit is 20 ml. Get a regular 20 ml syringe from the pharmacy and leave only the flask from it. Fasten it on a stick, for example, bamboo from under sushi/rolls, vertically with the tip down, and cork it. It will turn out something like a scoop. With this scoop, you need to scoop up water from different depths and each time calculating how much Daphnia has got into it. Then it remains to calculate the average value.

The feed should be based on the number of daphnia per unit volume – the same 20 ml. Use the table below as a guideline for compiling your own. For example, if the average value is about 20 crustaceans per 20 ml in a 100-liter aquarium, then every day you need to stir 2 teaspoons (tsp) of the feed mixture.
Be sure to observe the transparency of the water as mentioned in the first method. Proportions may need to be changed.

Daphnia Density per 20 mlAmount of feed per 100 liters
20+2+ tsp / day
12-20 2 tsp / day
5-11 3/4 tsp / day
1-4 1/4 tsp / day
0-1 1/8 tsp / day

At the first stages of daphnia cultivation, when their number is very small (just brought for breeding), crustaceans are easy to overfeed. Not eaten food quickly decomposes and pollutes the water, which in the end can lead to the death of the entire colony. Therefore, feed should be in limited quantities, a few pinches.

Aquarium / Daphnia Tank Maintenance

It is necessary to replace the water (at least 25% of the volume) with fresh water of the same temperature every 2-3 days. It is advisable to combine the water change with cleaning the bottom, where various organic debris and dead crustaceans will settle. Water is drained using a siphon – often its role is played by an ordinary hose (within 1 cm) with a tube at one end. It is convenient to drive the pipe along the bottom, sucking up trash. As with a conventional aquarium, over time the walls will be covered with organic coating. It is easy to remove it with a scraper, and the fallen particles can be removed with a siphon.

If only water is replaced, then it is advisable to put on a fine mesh on the drain end of the siphon, on which several dozen daphnias settle, which inevitably fall into the hose. You can feed your aquarium fish with crustaceans caught in this way.

Equally important, and perhaps decisive, is the presence of snails in the reservoir, many snails. Those that are widely used in aquariums. They serve as excellent living cleaners and are safe for Daphnia. The remains of feed and other organics are eaten, and their shells serve as a place for the development of colonies of nitrifying bacteria involved in the nitrogen cycle. Thanks to them, labor costs for maintaining an aquarium with crustaceans are significantly reduced and the risks of increasing nitrite and nitrate concentrations to dangerous values ​​are reduced.

Daphnia

Using a biological filter and any other filter is not effective, it will quickly suck in the feed before it gets to daphnia. The result is malnutrition of the crustaceans and rapid clogging of the filter material. The only equipment used to grow daphnia is an aerator. You may also need a heater if the temperature does not reach 18 degrees. Aeration solves several problems: it enriches water with oxygen and mixes it, ensuring uniform distribution of feed throughout the volume. The latter is very important for the normal nutrition of crustaceans, since food particles should not settle to the bottom, but should always be in suspension.

If everything is done correctly, then in a few weeks the colony should reach a concentration of more than 10 daphnia per 20 ml, which means 100-150 grams (wet weight) per 100 liters per week. A smaller number will indicate a problem. In this case, carefully inspect the aquarium / tank for the presence of natural predators, such as flatworms, hydras, and others. Problems can be related to the conditions of detention, there are two main signs: crustaceans do not breed well or there is a high mortality rate. In the first case, it is likely a matter of temperature. And in the second, everything is much more complicated. You will need to check each component: the quality of the water (charming for the presence of chlorine), the composition of the feed and its distribution over the entire volume of water, how the cleaning takes place, perhaps too much loss is associated with a siphon, etc.

When? In what quantities? And how to collect daphnia?

“Harvest” is allowed to be harvested only when the concentration of crustaceans reaches 10–15 or more per 20 ml. In this case, only large individuals should be caught, so that small and medium ones continue to grow and give a new generation. As soon as the concentration reaches 10 or fewer crustaceans per 20 ml, the catch stops. If you want to know more about why to feed your aquarium fish with daphnia or other kinds of living food, please check out this article.

Your Daphnia culture tank should look like this one: Be careful this video has SOUND!

#246: Daphnia Magna Culture in the Fishroom - Update Monday
Daphnia is a small and inconspicuous inhabitant of ponds, lakes, and even puddles, performing several necessary functions at once, and besides, their study is very important for scientists. Yes, and for the owners of the aquariums firsthand – you can not only give dried Daphnia to fish but also start these crustaceans themselves so that they clean the water.