The genus Daphnia includes more than 100 known species of freshwater plankton

Daphnia is a crustacean organism. It is widely used as phytoplankton and food for aquarium inhabitants. It is quite difficult to create conditions for its breeding. Therefore, many aquarists use the services of pet stores, purchasing live, frozen or dried crustaceans in the required quantity.

• 1 Description, structure, lifestyle and natural habitat
• 2 Mr. Tail recommends: Daphnia as fish food
• 3 Value and benefits
• 4 Species of Daphnia
• 5 Daphnia in the aquarium
• 6 Nutrition of Daphnia
• 7 Catching Daphnia
• 8 Natural reproduction and breeding of Daphnia
• 9 Danger to humans

Description, structure, lifestyle and natural habitat

Daphnia belongs to the genus of planktonic crustaceans and is a cladoceran organism. The second name, Water Flea, was given due to its structure reminiscent of these insects and the ability to make sharp leaps in the water column. If you look under a microscope, you can make the following description of the appearance:

• a rounded body 2-6 mm long is enclosed in a bivalve shell made of transparent chitin;
• there are branched antennae on the head that help jumps in the water;
• There is only one compound eye in mature individuals, but there is an additional ocellus near it;
• in the front of the head there is a beak-shaped growth called a rostum, and under it there are antennae with olfactory bristles;
• 4-6 pairs of thoracic legs are covered with many setae and contain gill sacs intended for breathing and absorption of food;
• in the posterior part of the body there is a tail equipped with paired claws and an anus to cleanse the body of large foreign particles;
• Eggs form in a sac-like outgrowth on the back.

Photo gallery of Daphnia:

The size and color of Daphnia depend on its subtype and habitat. Thus, in spacious, clean reservoirs with a sufficient amount of oxygen and nutrients, light gray or greenish individuals live, and in small and polluted ponds they acquire a red-brown pigment.

The internal structure has the following characteristics:

• the brain and the nerve chain in the peritoneum are responsible for the nervous system;
• striated muscles help move the antennae, tail and thoracic legs;
• the digestive system consists of the mouth, small and middle intestines, 2 hepatic outgrowths and the hindgut with the anus;
• closer to the back is the heart, from which 2 ostia filled with blood arise;
• the respiratory organ is not expressed, oxygen enters the body through the membrane and from the growths of the legs;
• on both sides of the intestine there is a pair of ovaries in females or testes in males.

Daphnia live in freshwater bodies of standing water. They are distributed everywhere, including the lakes of Antarctica. For successful reproduction, they only need a clean environment with a minimum amount of silt and dirt at the bottom. Otherwise, there is a risk of accumulation of clogging substances in the intestines of crayfish, which leads to their death.

In the water column they exist as plankton, freely drifting with the current. They hide at the bottom when the sun shines too brightly, and the rest of the time they swim at the top. Life expectancy in a favorable environment is 22 days, and in a large individual it reaches 110-150 days.

Features of character and lifestyle

Photo: Daphnia crustaceans

They are mainly found in the water column, moving by jumping, sometimes crawling along the bottom of the reservoir or the walls of the aquarium. They often move depending on the time of day: when it is light, they dive deeper into the water, and at night they find themselves at the very edge.

A lot of energy is spent on these movements, so they must have a reason. However, it has not yet been possible to find out exactly. There are several most likely assumptions. For example, that large daphnia are forced to sink deeper during the day in order to become less noticeable to predators - after all, the deep layers of water are less well lit.

This assumption is confirmed by the fact that in reservoirs in which there are no fish feeding on daphnia, this kind of migration occurs much less frequently. There is a simpler explanation - that daphnia simply strive for that layer of water where the temperature and illumination are optimal for them, and during the day it moves up and down.

Their lifespan varies greatly from species to species. Usually the pattern is simple - the largest ones live longer. Small daphnia are given 20-30 days, the largest ones up to 130-150 days.

Interesting fact: It is customary to test the toxicity level of various solutions on daphnia. They react even to small concentrations - for example, they can become slower or sink to the bottom.

Mr. Tail recommends: Daphnia as fish food

Many aquarists and entrepreneurs prefer to grow Water Fleas as food crops for feeding small and young fish. You can also buy crustaceans in any form from them:

• live for home breeding;
• ice cream packaged in blisters;
• dry as ready-to-eat food.

This food has a number of positive aspects and has a positive effect on aquarium flora and fauna.

Increased Productivity

Producing daphnia is a relatively easy process. However, there are measures to increase cultivation productivity.

1. Good aeration (good to the extent that the water is saturated with oxygen, but not excessively strong aeration) is the main factor in increasing productivity. Some species prefer the absence of aeration, but Daphnia magna grows better in its presence. In addition, this allows you to increase the density of the culture, water circulation (which prevents stagnation and suppression of the culture), reduces algae deposits on the walls of the vessel, and also transfers food particles into suspension, which is typical for the natural diet of daphnia. The only drawback is that small air bubbles fill the carapace of the crustaceans, which float up and cannot feed. Air spray should be avoided altogether, or it should be very rough to create large bubbles. Convenient in terms of aeration is the “bio-foam” filter ( the airlift filter is shown in the photo on the right

). It is usually used in an aquarium with fry, but is ideal for daphnia. It captures large particles and promotes their decomposition to feed algae. 2. Regularly maintaining the cleanliness of the environment and replacing water 3. Regular selection/collection of culture. This event maintains constant growth of the crop and provides daphnia with the opportunity to quickly accumulate oxygen and food. 4. A 24-hour daylight period increases the productivity of daphnia, but this is not a necessary measure. Also, you should not keep daphnia in the dark for 24 hours, because this stimulates the crustaceans to form ephippia. 5. The mode and degree of water replacement depends on the nutrient medium used, but, in any case, they are necessary for purification of metabolites and toxins.

Value and Benefits

Daphnia is grown along with Bloodworm, Gammarus, Caddisfly, Amphipod, Cyclops, Prudovik and other food organisms. In terms of calorie content, they are all approximately equal, but the first has a higher protein content. Amino acids absorbed by young fish have a beneficial effect on their growth and development. Because of this, Daphnia is used commercially and added to many dry foods. In this form, 50% of their mass consists of proteins.

Live food is of particular importance in the diet of fish. It minimizes their incidence, is easier to digest during illness and facilitates adaptation to new conditions.

Crustaceans usually have a stomach filled with plant particles, so they are preferred as food by Guppies, Danios, Fire Barbs, Crucians, Carps and other aquatic inhabitants. In an aquarium, such nutrition is especially useful for fish deprived of a natural diet. The chitin shell, which is not digested, activates the intestines and starts its cleansing.

Moreover, they are unpretentious in care and multiply quite quickly. They benefit the entire aquarium by filtering the water in it. One individual eats 6 times more food per day than it weighs. This helps get rid of foreign microorganisms in a pond or tank.

Benefits and harms for the aquarium

Daphnia in the aquarium is not as common as you might think. In ecotoxicology, the daphnia test is a popular tool for detecting contaminants in water. Notable species include, for example, Daphnia magna, the large water flea, Daphnia pulex, the common water flea, Moina macrocopa, the Japanese water flea.

With small living creatures you get information about the water quality of a reservoir. They are very sensitive to pollutants: if the water is polluted, "water fleas" exhibit unusual swimming behavior, no longer reproduce and die.

Value as fish food

Daphnia are a popular fish food that is highly prized for its chitinous, high-fiber shell. Since you can not only buy water fleas as live food from a pet store, but also breed them as live food, they are very well known in the aquarium hobby.

Danger to humans

Water fleas and the human immune system have one thing in common: only when there is a real threat from an attacker do they develop certain defense mechanisms. In the human body, antibodies and immune cells take over the defense; in the case of water fleas, even the entire body changes.

Important! Daphnia cannot bite humans, and they are not related to the human or animal fleas you deal with at daycare or on pets. Therefore, the term "water fleas" is actually a misnomer. It probably comes from a jumping swimming motion.

Species of Daphnia

Their genus includes more than one hundred species of cladocerans, which belong to approximately 10 families. In Russia you can find three varieties:

• Magna is considered the largest, reaching a length of 6 mm in the female, 2 mm in the male and 0.7 in the larva. It matures in 12-14 days and gives birth in 2 weeks, laying an average of 20-30 and up to 80 eggs (ephippia) at a time. Lives approximately 110-150 days.

• Pulex is medium in size, the female grows up to 3-4 mm, and the male no more than 1-2 mm. It reproduces every 3-5 days, producing 10-25 eggs. The life cycle is 26-47 days.

• Moina is the smallest, has a soft shell and is suitable for feeding fry. It grows no more than 1.5 mm, and newborns are 0.5 mm. Maturation occurs within a day, and litters appear every 1-2 days, up to 53 ephippia each. Lives for approximately 22 days.

These three types can be bred even by amateurs, without requiring special maintenance. But the specifics of caring for them and interacting with other inhabitants are still worth knowing.

How to catch it from reservoirs yourself

Daphnia is caught from the end of spring until the end of autumn, until the reservoirs are covered with ice. It is recommended to catch in the morning or evening in cloudy, windless weather. In such conditions they rise closer to the surface of the water. For fishing, you can use a regular fabric net.

Caught specimens should be placed in a tin container and shaken periodically. It should be remembered that at high densities they may die during transportation. At home, the crustaceans are washed and passed through a sieve to sort by size.

Daphnia in the aquarium

To breed crustaceans in closed tanks, you must provide certain conditions for their existence:

• choose a clean container made of glass or plexiglass, initially with a capacity of 1-3 liters, replacing it as the number of inhabitants increases, taking into account a density of 0.3-1 kg/m³;
• use purified water or from the tap, with a hardness of 6-18° and a neutral pH of 7.2-8, without chlorine and chemical impurities, for which it can be filtered;
• place it away from direct sunlight, as crustaceans do not like excessive light;
• install a 20 W fluorescent lamp, providing light lighting for 14-16 hours every day;
• provide temperatures within +20…+24 °C for Daphnia vulgaris and +26…+28 °C for Moin; in a cool habitat the reproduction rate will decrease;
• provide complete nutrition by dissolving the fertilizer in the liquid until it becomes slightly cloudy, and adding a new portion after clearing;
• as necessary, clean and change the water so that debris and silt do not accumulate at the bottom, as well as plaque on the walls;
• use weak aeration to remove film on the surface, mix food, provide oxygen access of at least 3-8 mg/l and oxidation 14.8-26.2 mg O2/l.

First, you should purchase crustacean eggs and place them in a prepared container. Already matured individuals need to be caught with a net in order to immediately be fed, dried or frozen.

Conditions for breeding

Many people breed daphnia at home, which is quite simple. However, this process must be given due attention. The color of the water in the container plays a big role. It should be greenish or light brown.

Don't forget to add yeast to your diet

It is impossible to allow other representatives of water bodies, for example, cyclops, to get into the container with daphnia. At home, the diet of crustaceans should consist of dry lettuce leaves or grapes. Baker's yeast is added to the diet. They are ground to a powder and then strained through cheesecloth. To get them at home, you need to take water with 50 crustaceans from a natural reservoir with prepared food and only then put them into the prepared vessel.

Nutrition of Daphnia

In nature, Water Fleas feed on simple microorganisms:

• blue-green algae from unicellular organisms;
• ciliates;
• fungal spores;
• bacteria;
• detritus (remains of invertebrate animals).

A suitable environment is created in ponds with a small number of fish and a large number of phytoplankton, which creates the effect of a bloom in the water column. In artificial tanks, crustaceans should be fed with the following products:

• The bacteria are obtained from banana peels, food waste or excrement. To do this, they should be soaked in water for up to a week until it begins to become cloudy. Add the resulting liquid to the tank, 450 ml per 20 liters, every 5-6 days.
• Microscopic algae and other plankton will remove excess contaminants and serve as food for Water Fleas. To obtain them, you should scoop up the liquid from the stocked aquarium and place it in a sunny, warm place at +18...+25 °C.
• Yeast can be dried or raw, frozen to a rich color. Dilute in water at +35 °C at the rate of 1-3 g per 1 liter. They should be used 2-3 times a week, in combination, as they have less nutritional value.
• Beetroot, cabbage or carrot juice will serve as a vitamin supplement. You need to add 1 tsp to the container. for 5 liters of volume.
• Dry the elodea, nettle or lettuce, chop it, grind it in gauze, and add it to a container of water. When it turns green, introduce crustaceans there. Repeat every 10-15 days.
• A couple of times a week you can add ammonium nitrate at 1 g/100 l, phosphorus salts up to 5 mg/l, or other mineral fertilizers.
• Stale blood or water remaining from washing fresh meat (1.5-2 cm3/l), blood or meat and bone meal (0.5-2.5 cm3 per 10 l), manure (1.5 kg/m3).

During the feeding process, crustaceans create a current by raking with their chest paws. It is on them that the organs that send microelements to the esophagus are located. Inside there are organs that produce a sticky substance that collects individual food particles into clumps. Inside the esophagus, they go through all stages of digestion and only large excesses come out.

Area

The usual habitat is standing water bodies. They can live both in a pond and in a deep lake. Even cold Antarctica is no exception.

One of the main conditions is the presence of standing freshwater with a minimum amount of soil.

Groundwater promotes soil filtration and the settling of algae in the intestines.

Daphnia: natural filter.

This leads to clogging. The presence of crustaceans in the water makes it clear how clean the lake, pond, or river is. Groundwater promotes soil filtration and the settling of algae in the intestines. This leads to clogging.

Some species live on the bottom, feeding on dead parts of plant food and the remains of invertebrate animals. Sometimes they can be seen in puddles and holes with water. In bright light, crustaceans hide in depth.

Catching Daphnia

Water fleas can be collected independently from small lakes, ponds with waterfowl, pits, ditches and other bodies of water with minimal aquatic life. They do not breed in river conditions, but only in standing water. They are quite easy to detect by coloring the thickness in a gray-green or brownish tint.

You should not look for them in heavily dammed reservoirs or lakes with many fish and predators. The presence of the latter will affect not only the quantity of plankton, but also its quality, and will also increase the risk of the spread of diseases to aquarium fish.

To catch bioplankton, you need to take a fine-mesh net or muslin sieve. The scooping motion should follow a figure eight shape and be slow. Rapid scooping leads to increased pressure on the crustaceans and to their death.

The best time for this is during the period of water bloom, when the concentration of algae in it increases. Moreover, it is easier to do this in a shaded area of ​​shallow water, in the evening or on a cloudy day. After all, the attitude of crustaceans to bright sunlight is negative; under them, plankton-like creatures tend to go deeper closer to the bottom.

Where does it live?

Found throughout the globe. Scientists have discovered some representatives even in Antarctica. This fact indicates how well they adapt to various living conditions and the possibility of transformation into other species.

Daphnia adapts to a new environment, with each species living in its own habitat.

Some species prefer subtropics and temperate zones to live. The smallest number inhabit the equator and tropical climates. A number of species inhabit America and Great Britain, Europe and Asia. Crustaceans prefer standing water and do not like currents. Therefore, a pond or lake, as well as small puddles, are considered a favorite habitat. Mostly the number inhabits fresh water.

Arthropods that find themselves in drought conditions can move to a salty body of water. The ability to adapt keeps them alive.

Clean water with minimal soil content is considered the best habitat.

The crustacean feeds by filtering, so the cleanliness of the reservoir comes to the fore.

Natural reproduction and breeding of Daphnia

Water fleas are not asexual creatures, as evidenced by the presence of ovaries in females and testes in males. They also differ in the size and structure of the antennae. But in them, like all cladocerans, reproduction occurs through cyclic parthenogenesis. Same-sex reproduction is especially important when only female individuals remain in the population. Moreover, in warm summer weather, young females develop from their unfertilized eggs. In autumn and when water bodies dry up, males emerge from such ephippia. Their embryos are born under the shell and wait several molts before emerging.

When fertilization is complete, smaller and faster males mate with females, attaching themselves to the rear edge of the shell. During parthenogenesis, all litters are the same sex. After colder weather and decreased daylight hours, bisexual reproduction occurs. In this case, some individuals give birth to males, while others lay ephippia, which are dormant until fertilization. They spread with the wind, on the legs or feathers of birds, the fur of mammals, and in the intestines of fish. In winter, they are found on the water surface or in the upper layers of silt. They are resistant to frost or drying out, and when placed in a favorable environment, embryo development begins.

For cultivation, dry eggs are taken and placed in a suitable environment. They grow and multiply quickly, which makes it possible to obtain 30-50 g of crustaceans from 1 m3 of ephippia. Feeding has two directions:

• Joint, in which food is brought into the tank with Daphnia. The negative is rapid contamination and the need for frequent fluid replacement.
• Separate is convenient for mass breeding. At the same time, algae is grown in a separate container, which is introduced into the tank 1-2 times a day during feeding.

Industrial cultivation of forage crustaceans in large pools and dams is now popular. In this case, the producer changes the water and replants the crop every few weeks or months to prevent it from aging.

How does it reproduce

They have an amazing ability to reproduce. Daphnia breed offspring without fertilization. The female has a brood chamber on her body. If conditions are favorable, the adult female lays from 10 to 50 eggs. They then develop in the brood chamber. After three days, the breeding cycle repeats. The water of the reservoir turns red when it is teeming with a huge number of crustaceans. In autumn, the breeding process takes place with the participation of males. With their help, the egg shell becomes denser and able to withstand cold temperatures. With the onset of warm weather, the breeding cycle repeats.

Danger to humans

Because of their association with insects, many people believe that Water Fleas bite. But they do not have the corresponding organs, which means that such bites are excluded. Daphnia can cause harm only by causing an allergic reaction in people predisposed to it. As they absorb food, they also accumulate dangerous pollen, the concentration of which increases in dried organisms.

According to statistics, crustaceans cause allergies in almost every fourth person. It manifests itself in the following symptoms:

• itchy skin rashes, like hives;
• dryness and congestion of the nasal sinuses, runny nose;
• frequent involuntary sneezing;
• allergic conjunctivitis with tearing;
• difficulty breathing due to bronchospasm;
• bronchial asthma.

To diagnose the condition, doctors analyze a skin test. In case of positive results, antihistamines are prescribed and contact with Daphnia is avoided.

What types to use as fish food

Fish species such as guppies and other viviparous species love to eat water fleas such as daphnia within seconds. Many species of fish particularly enjoy eating live food. This challenges their hunting instinct and is therefore the most natural type of food available. Daphnia fish food provides particularly high amounts of proteins and nutrients that cannot be absorbed from plant-based foods alone.

For many fish species, feeding water fleas or mosquito larvae also increases their readiness to spawn. This is why live daphnia food is often used to support breeding in the aquarium. All types of daphnia are suitable as food, but you need to decide on the size of the fish. For large aquarium fish you can use magna, and for feeding fry of freshwater fish - moina.

How to cook

The shelf life of dry daphnia is from 6 months to 1 year.

But regardless of feeding regimen, the use of live food has been repeatedly shown to significantly enhance the immunity, digestion, growth, coloration and overall health of captive species. In addition, this makes it possible to observe the natural reaction of aquatic animals to feeding.

How to feed

Harvesting your live daphnia from your aquarium is a very simple method. To feed your fish and other aquatic animals you need to collect the daphnia, you can transfer them directly to the tank for feeding or put them in a tiny jar of water to feed the fish for an hour.

Daphnia allergy

A person may have an allergic reaction to daphnia. This can be especially dangerous for children, as allergic shock can lead to respiratory blockage and death. There are tests for allergies to daphnia (cost about 630 rubles). However, allergies occur in rare cases and not in all aquarium fish lovers.

Daphnia

Daphnia are predominantly small crustaceans belonging to the Daphniidae family. This family, in turn, is included in Cladocera, which also includes Gammarus, Artemia and others. Due to its peculiar sudden movements it is often called a “water flea”. Not to mention the peculiarities of movement, daphnia is also similar in appearance to a flea. However, the latter belongs to insects and has a very distant common ancestor with crustaceans, since both classes are included in the phylum arthropods. All Daphnia species have different variations, and sometimes members of the same species are very different from each other. The characteristics of the phenotype, body size and shape depend on the area of ​​​​origin and specific environmental conditions. Representatives of the genus Moina have significant similarities with daphnia.

It is important to distinguish the Daphnia crustacean from other "water fleas" such as copepods, Cyclops species and barnacle crustaceans, which often live in the same places. Abrupt movements, body shape and, to a lesser extent, coloration are the best criteria for discrimination without the need for microscopic examination.

The genus Daphnia has a very wide distribution, including Antarctica, where Daphnia studeri, previously assigned to the genus Daphniopsis, was discovered in the relict salt lakes of the Vestfold oasis. At the beginning of the 20th century, the prevailing opinion was that most species had a cosmopolitan distribution, but it later became clear that the faunas of different continents differ greatly. Some species, however, have very wide ranges and are distributed on several continents. The smallest number of species is typical for equatorial regions, where daphnia are rare. The most diverse fauna is in the subtropics and temperate latitudes. In recent decades, the ranges of many species have changed due to human dispersal. Thus, a species from the New World, D. ambigua, was introduced into Europe. In many reservoirs in the southern United States, D. lumholtzi, which was previously found only in the Old World, has become common.

In ponds and puddles in central Russia, the following crustaceans of the genus Daphnia are often found, and therefore the most popular among aquarists. Daphnia magna (D. magna), female - up to 6 mm, male - up to 2 mm, newborns - 0.7 mm. They ripen within 10-14 days. Litters in 12-14 days. There are up to 80 eggs in a clutch, but usually 20-30. The lifespan of this crustacean is up to 3 months. Daphnia pulex (D. pulex), female - up to 3-4 mm, male - 1-2 mm. Litters in 3-5 days. There are up to 25 eggs in a clutch, but usually 10-12. Pulex live 26-47 days. In the lakes of the temperate zone of Eurasia, D. cucullata, D. galeata, D. cristata and several other species are often found.

Daphnia are small crustaceans, the body size of adult individuals is from 0.6 to 6 mm. They inhabit all types of standing continental bodies of water and are also found in many slow-flowing rivers. In puddles, ponds and lakes they often have high numbers and biomass. Daphnia are typical planktonic crustaceans, spending most of their time in the water column. Various species inhabit small temporary reservoirs, littoral and pelagic zones of lakes. Quite a few species, especially those inhabiting arid areas, are halophiles, living in brackish, saline and hypersaline continental water bodies. These species include, for example, D. magna, D. atkinsoni, D.mediterranea, as well as most species previously classified in the genus Daphniopsis.

They spend most of their time in the water column, moving in sharp leaps due to the flapping of the second antennae, which are covered with special feathered bristles. Many daphnia are also capable of slowly crawling along the bottom or walls of vessels due to water currents created by the thoracic legs; the antennae are motionless during this method of movement.

Perhaps the elusiveness of quickly jumping crustaceans reminded scientists of the legend about the nymph Daphne, who was almost overtaken by Apollo, but was never caught by him? Or maybe the mustaches of the crustaceans seemed to someone like the branches of an evergreen laurel into which a beautiful nymph had turned.

Ovid in his poem “Metamorphoses” told how once the golden-haired god of light Apollo carelessly laughed at Aphrodite’s son Eros (or, as the Greeks also called him, Eros). The offended god of love struck the silver-faced patron of the muses in the very heart with a golden bow. Having once met the beautiful Daphne, the daughter of the river god Peneus, Apollo fell in love with her at first sight, but the beautiful nymph, whom Eros struck with an arrow that kills love, began to run away from him with the speed of the wind. Then Apollo chased after her, but the nymph only ran faster and faster from the beautiful god. When her strength began to dry up, Daphne began to beg her father to deprive her of the appearance that brought her only grief. Old Penei took pity on his daughter. And at that moment, when it seemed that Apollo had already caught up with the beauty, she turned into a laurel tree.

The saddened Apollo did not want to part with his beloved. He decorated his quiver and cithara with laurel leaves, and placed a wreath of laurel branches on his head, the scent of which always reminded him of the elusive Daphne.

Reproduction in nature

During the summer months, daphnia are often found in blooming ponds and lakes that have high concentrations of algae. The fertility of daphnia is simply amazing, which is associated with the implementation of parthenogenesis.

Parthenogenesis is the ability of self-reproduction without the need for fertilization, when the offspring completely repeats the genotype of the parent, and any differences in the physiological state are determined by environmental conditions. Parthenogenesis allows daphnia to reproduce rapidly under favorable conditions, shortly after they emerge from the eggs. In nature, in late spring, summer and early autumn, depending on temperature, food availability and the presence of products of their metabolism, Daphnia reproduces parthenogenetically, giving birth to an average of 10 nauplii for each adult. During this period, only females are present in the reservoir. The developing embryo is often visible inside the mother's body without a microscope. Females of the next generation are capable of parthenogenesis after 4 days of development, with births occurring every three days. During her life cycle, a female can give birth 25 times, but in practice this number is slightly less and the female tends to produce no more than 100 offspring.

When there is a lack of food, some eggs develop into males, and females begin to produce eggs that must be fertilized. The latter develop into small embryos, which then go dormant and become covered with a dark brown/black saddle-shaped shell known as the ephippium. In this form, daphnia can tolerate harsh environmental conditions, short-term drying out of the reservoir and even its freezing. Females born to form an ephippium are easily distinguished from parthenogenetic individuals because the developing ephippium is present in them as a black spot at the posterior end of the body. When environmental conditions become favorable again, a generation emerges from the eggs, which, in turn, gives birth to only females, while all males die before the onset of unfavorable conditions.

Fishing in natural reservoirs

They catch daphnia with a net. A special net is needed for this - with a long handle up to 2-3 meters, usually made of several screwed sections, with a diameter of about 25-30 cm and a fabric cone about 50-60 cm long with a rounded end. The net ring is made of durable material, for example stainless wire with a diameter of 3-5mm. If you make it from a thinner one, it will bend easily, and considering the possible snags on the bottom... But the most difficult thing is to choose the fabric for the net. Here, synthetic materials are preferable, such as nylon, which do not rot from prolonged contact with water. The mesh size of the net depends on what you are going to catch; very fine fabric greatly slows down the net in the water, so it is better to have several interchangeable rings with different fabrics for catching food of different sizes.

They operate the net calmly, smoothly, without much effort, moving it with a figure of eight in places where daphnia accumulate. We did it a couple of times, took it out, shook out the catch, and began to fish further. If you push a full net, many daphnia will crumple and die, so it is better to take it out more often with small portions of prey. Otherwise, greed, you know, does not lead to good. For fishing, it is better to prefer smaller bodies of water, for example, puddles - there daphnia are more accustomed to oxygen starvation and will more easily endure further transportation. True, it is difficult to catch in small puddles with a standard net; there you have to use a net with a shorter cone - otherwise it begins to cling to the bottom and create turbidity. In order not to catch hydra with daphnia, you should try to catch prey away from thickets of aquatic plants or objects in the water to which it can attach. And in no case is it recommended to catch food in reservoirs where fish live - with such food you can easily introduce pathogens of various diseases.

The caught daphnia are placed in a container - a can or a special can for transportation. Before pouring, it is advisable to strain the catch through a thin mesh to remove any trapped debris and any large unwanted guests - swimming beetles or large dragonfly larvae. It is very desirable to have a battery-powered compressor in the transport container - it will keep most of the catch alive during the journey home.

At home, caught daphnia are poured into a wide flat vessel, for example a white enamel basin. There, for some time, all the unwanted organisms settle on the bottom and walls; on a white background it is easy to spot the larvae of dragonflies and leeches, and everything else that has nothing to do with daphnia. There, at the bottom, dead crustaceans accumulate. When feeding, daphnia are caught with a net; the water in which they are located cannot be poured into the aquarium! These crustaceans are best suited for feeding small aquarium fish such as guppies or neons. For larger fish, it is more convenient to use live or frozen bloodworms.

In nature, daphnia live in ponds and large puddles, where they feed on various bacteria and phytoplankton. However, such reservoirs are often polluted with industrial waste or fish are found in them. Both can lead to diseases of aquarium inhabitants.

Daphnia can also pose a danger to aquarists themselves. In spring and early summer, the diet of crustaceans often includes pollen from flowering plants, carried by the wind into water bodies. Daphnia caught at this time and dried for future use when feeding fish can cause a painful reaction in people suffering from pollen allergies. This fact, in particular, can explain the often-found opinion that an aquarium is harmful to health. In fact, the reason is pollen, with which crustaceans are literally “stuffed” during the period of mass flowering of grasses.

Breeding at home

A 15 liter plastic container or any other is perfect for growing daphnia. In this case, several recommendations can be noted. Avoid container materials that are water soluble or release harmful chemicals. If a metal container is used, it must be made of stainless steel. Aluminum oxides form a film, but some aluminum is still released. As in the case of a regular aquarium, a large area of ​​​​contact with air is required for gas exchange, because daphnia are very demanding of oxygen content. If the container is located outdoors, in strong sunlight or other lighting, it is recommended to use larger than 40 liter volumes to ensure a stable water environment. In addition, when black pond material is used, it will heat up more than clear or yellow material, which must also be taken into account.

For those who wish to have a small number of daphnia per week, the culture can be maintained in a two-liter bottle. For aquarium cultivation, a good idea is to connect the lights via a timer, which can be purchased at an electrical store. It was found that Daphnia magna prefers weak aeration. In theory, aeration not only supports gas exchange, but also stabilizes water conditions and prevents inhibition of cultural development. Daphnia pulex also likes light aeration. It is necessary to avoid small air bubbles that can get under the carapace of daphnia, raise them to the surface, interfere with feeding and ultimately lead to death.

The best nutrient medium for the culture is blue-green algae. Typically, these are free-floating species of green algae that tend to turn water into "pea soup", yeast (Sacromyces spp and similar fungi) and bacteria. The combination of the above objects makes the process of maintaining the culture successful; yeast and algae complement each other.

Microalgae are consumed by daphnia in huge quantities, and an abundance of crustaceans is observed in places where water bodies bloom. There are a number of ways to ensure algae development that require minimal effort.

Placing the culture container in direct sunlight will ensure algae development within two weeks, usually sooner. Their spores are airborne and colonize water bodies, but, as a rule, some algae is added to the water to speed up flowering. Using plant fertilizers such as Miracle grow. Once a week, add 1 teaspoon of fertilizer to a 4-liter container. The container should be in direct sunlight. Aeration and slow movement of water are necessary. A system should be built according to which the first container with algae is already green, the second will acquire this shade within two days, the third within another two days, etc. When the first container becomes light green (after 2 weeks), it is poured into the daphnia culture. The empty container is refilled with the mixture with the addition of a small amount of water from the second container. Thus, every two days the aquarist has 4 liters of flowering water at his disposal, ready to be fed to daphnia.

The advantages of algae are the ease of preparation and the extremely rapid development of the culture of daphnia that consume them. There are no disadvantages, except for the need to constantly restart the tanks. Daphnia should not be placed in an environment that is too algae-rich because algae tend to raise the pH as high as 9. High alkalinity is associated with increased ammonia toxicity, even at low concentrations.

Baking, brewing and almost all other types of yeast are suitable for culturing Daphnia, but it is recommended to apply no more than 28 g per 20 liters of water as a daily rate. If you use yeast, you can additionally add algae to the water, which will prevent environmental pollution. It is important not to overdo it with adding yeast; excess will pollute the environment and destroy the daphnia culture.

Some baker's yeast comes mixed with active ingredients such as calcium sulfate, ascorbic acid, which stimulate the development of fungi. These components themselves are harmless to the culture, but ascorbic acid can lower the pH of the medium to 6, which is far from the ideal value for daphnia. This usually occurs when overfeeding.

The advantage of yeast as a nutrient medium is its ease of acquisition, and minimal effort in preparing and maintaining the culture. However, they are not as valuable from a nutritional point of view for daphnia as algae. Crustaceans need to consume more yeast than algae to obtain the same nutritional value.

Daphnia lives in a wide range of temperatures. The optimal temperature is 18-22 CD pulex feels great at temperatures above 10 0C. Moina can withstand even harsher fluctuations, 5-31 C; the optimum is 24-31 C. Moina's increased resistance to temperature makes it a preferred cultivation object when the optimum for D. magna under natural conditions is reached only once a year.

Daphnia are tolerant of dirty water, and dissolved oxygen levels can vary from almost zero to super-saturated. Like Artemia, Daphnia's ability to survive in oxygen-poor environments is due to its ability to form hemoglobin. Hemoglobin production may accelerate with increasing temperature and population density. Just as in the case of artemia, daphnia does not tolerate active aeration with small air bubbles, which can destroy it.

Producing daphnia is a relatively easy process. However, there are measures to increase cultivation productivity. Good aeration, good to the extent that the water is saturated with oxygen, but not excessively strong aeration, is the main factor in increasing productivity. Some species prefer the absence of aeration, but Daphnia magna grows better in its presence. In addition, this makes it possible to increase the density of the culture; water circulation reduces algae deposits on the walls of the vessel, and also transfers food particles into suspension, which is typical for the natural diet of daphnia. The only drawback is that small air bubbles fill the carapace of the crustaceans, which float up and cannot feed. Air spray should be avoided altogether, or it should be very rough to create large bubbles. Convenient in terms of aeration is the “bio-foam” filter. It is usually used in an aquarium with fry, but is ideal for daphnia. It captures large particles and helps them break down to feed algae.

Regular selection/collection of culture. This event maintains constant growth of the crop and provides daphnia with the opportunity to quickly accumulate oxygen and food. A 24-hour daylight period increases the productivity of daphnia, but this is not a necessary measure. Also, you should not keep daphnia in the dark for 24 hours, because this stimulates the crustaceans to form ephippia. The mode and degree of water replacement depends on the nutrient medium used, but, in any case, they are necessary for purification of metabolites and toxins.

When it comes to cultivating daphnia, collecting them can be a real challenge, but it is an integral part of the entire breeding process. Otherwise, overpopulation becomes a serious problem. Even if you have to shake the crustaceans into the sink, this must be done because the culture can become unstable. If the aquarist cultivates daphnia at temperatures below 25 0C, it makes sense to start catching in the middle of the second week. This is because most crops take several days to adapt and begin reproducing. When culling/catching, a net is used that has cells large enough to allow young crustaceans to pass through, but small enough to catch adults. Some aquarists recommend pouring ¼ of the container through the mesh and then filling the volume with a new portion of water with nutrient medium. No more than ¼ of the population can be caught daily, which also depends on the quality of cultivation. Catching can be done during the day when aeration stops, when all daphnia rise to the top layer of water.

Caught crustaceans can live for several days in a fish tank with fresh water. They show normal activity when the temperature rises. However, the nutritional value of daphnia gradually decreases because they are starving and must be provided with food for the best effect. Crayfish can be stored frozen for a long time if they are frozen in water with a low salt content (0.007 ‰, density - 1.0046). Of course, this will kill the daphnia, due to the leaching of nutrients their value will decrease, almost all enzymatic activity will be lost within 10 minutes, and after an hour ½ of the free amino acids and all bound ones will be lost. Fish are not so willing to eat frozen crustaceans.

PROTECTING DAPHNIAS FROM PREDATORS

Daphnia are prey to a variety of vertebrate and invertebrate predators. The role of predators on the population ecology of D. pulex has been extensively studied and has been shown to be a major axis of variation in shaping population dynamics and habitat distribution. In addition to the direct population ecological effects of predation, this process contributes to phenotypic evolution in the opposite way: large D. pulex are more visible to vertebrate predators, but invertebrate predators are unable to cope with them. As a result, the largest daphnia are more often found in habitats of invertebrate predators, while smaller sizes are found in habitats of vertebrate predators.

Like other Daphnia species, Pulex morphology exhibits a plastic response to the presence of predators. For example, the larvae of coretra mosquitoes secrete certain kairomones—chemical signals that cause the formation of small, jagged projections on the head known as “neck teeth.” Neck teeth increase survival in the presence of invertebrate predators, but there are also disadvantages to this - for example, a longer development time for daphnia.

Kairomon is a substance that stimulates adaptation - for example, substances secreted by predatory invertebrates and causing the formation of spines in invertebrate prey (rotifers)