The smallest crustacean Daphnia has received the second name of the flea aquatic among the people for its external resemblance to a parasite insect and its ability to jump. But, besides this, they have nothing in common, because these are representatives of completely different classes.
Features of the external structure
Daphnia is the most famous and numerous representative of the Daphniidae family. The skin of this organism is bicuspid, with two hooks at the end of the body and one spherical, moving eye, which sets in motion three pairs of oculomotor muscles. The body of Daphnia is transparent and allows you to see everything that happens in her body. Even the smallest muscle contraction of a crustacean can be examined under a microscope if desired.
Features of the internal structure
Despite its miniature size, a fairly amazing organism is a water flea. The description of the species notes many interesting features in its internal structure. The kidneys of daphnia are located near the mouth, the brain is near the esophagus, and the heart is on the back of the body. The blood is yellowish in color, contains white bodies - phagocytes, which, if necessary, protect the body of the crustacean from bacteria, fungi and foreign microorganisms.
A water flea has five pairs of legs, but they serve not so much for movement as for directing the flow of water to the mouth, which it filters for nutrients. Breathing is carried out directly through the integument of the body.
Distribution and living conditions
Daphnia is widespread throughout almost the globe. Most of them are in the subtropics and in latitudes with a temperate climate. Mostly flea aquatic lives in stagnant water bodies (lakes, ponds, rivers with a slow course), as well as in puddles. It multiplies rapidly, is extremely tenacious, therefore its number is quite large. Usually located in the water column, moves irregularly or crawls along the bottom (due to pectoral legs).
In summer, Daphnia swim quickly, but when unfavorable times come, they freeze. Even if the puddle in which they were located dries up, then they return to life immediately after it is filled again.
Most daphnia are herbivores, but predators are also found. Water flea processes phytoplankton, fungi, bacteria, and also rotting remains of animal tissue after use by large predators.
The most common types
The Daphnia family is quite numerous. About 150 species of these crustaceans live in Europe and North America alone. In Russia, some of them are especially common - magna, puleks, kukulata, galeat, crest. All of them live in a variety of reservoirs.
The largest water flea is daphnia magna. Its female has a length of up to 6 mm, the male is three times less. The maturation period of newborn Daphnia lasts two weeks. The female also lays eggs every two weeks (about three dozen eggs). First, newborns are microscopic in size. But then they are actively growing. This species lives for about three months.
Another common species is Daphnia puleks. Representatives of it are slightly smaller - females about four millimeters, males are half as much. They are very prolific - laying of fifteen eggs occurs once every five. These water fleas live for a relatively long time - the life cycle can be up to one and a half months. It varies depending on the conditions of existence. For example, an increase in temperature shortens life due to the fact that the metabolism of crustaceans increases.
Breeding
Water fleas are unusually prolific. At all Daphnia egg laying is divided into winter and summer. Eggs in a certain period have their own characteristics. So, for example, in winter masonry, they are covered with a denser shell and their number is small (about 2 pieces), and in summer they are much larger. All these features are no longer due to the changing seasons and living conditions, but to the presence of males. In the summer, when the male population is very small, Daphnia eggs appear and lay without fertilization. Eggs fertilized by males are laid only once a year - in the fall. During its life cycle, the female is able to give offspring up to 25 times.
Daphnia harm to humans
Despite the fact that daphnia is called the flea, it has nothing to do with bites. Nevertheless, it can cause harm to humans. Everything lies in a high degree of allergenicity. This is due to the fact that during the period of violent flowering of plants, pollen enters the water in which daphnia are located, and those, in turn, filtering it, can capture the same particles of pollen. Then, when the crustaceans are dried, this pollen remains and can cause a strong allergic reaction in the human body, which is often mistaken for a bite of a water flea.
Allergy symptoms are often typical - inflammation of the conjunctiva of the eye (conjunctivitis), lacrimation, frequent sneezing, nasal congestion and difficulty breathing.
Sometimes rashes on the body may also appear, accompanied by severe itching.
Human use of daphnia
In turn, daphnia serve as a universal food for aquarium fish. To this end, they are bred at home.
It is only necessary to catch Daphnia in a standing reservoir and provide them with living conditions close to natural. Catching crustaceans is in bodies of water where there is little or no fish, since in the absence of predators Daphnia will be more and less likely that they are affected by any infection.
Breeding conditions
Water fleas in the aquarium should be kept in the water in which they live, because there is no feed in tap water that they feed on. You also need to carefully consider the choice of containers in which the crustaceans will be contained. After all, materials such as, for example, polypropylene, can come into contact with water when they release harmful substances, and Daphnia simply die.
Daphnia kept in aquarium conditions need a lot of light. In a well-lit room they feel great and give good offspring. In addition, Daphnia cannot tolerate crowding. Since they multiply rapidly, you need to constantly ensure that they have enough space and periodically transfer part of the water fleas to another aquarium. This can be explained by the fact that crustaceans are very sensitive to a lack of oxygen and quickly die, lacking it.
Many daphnia aquarists have noted that baker's yeast is the best food for them. You only need to feed Daphnia carefully - if you feed too much, the water will become cloudy and the crustaceans will not have enough oxygen. A five-liter aquarium needs a quantity of yeast equal to the size of a match head. It is necessary to stir them in a teaspoon of water and gradually pour into the aquarium. Also, algae, including Euglena green and Chlorella, serve as food for crustaceans.
It is important to note that they also need a certain temperature. This, according to experts, from 22 to 25 degrees. It is in such conditions that water fleas multiply in the pool of a natural reservoir.
It is necessary to prevent water from boiling and change the water (one third of the total volume) at least once or twice a week.
Daphnia crustaceans perfectly filter water from bacteria. Therefore, many aquarists breed them for water treatment - it does not bloom and remains clean for a long time.
At first glance, it may seem that breeding daphnia at home is a very painstaking, time-consuming process. Nevertheless, these crustaceans are a year-round ecological clean food for most fish species (both fry and adult individuals).
Water flea is very sensitive to environmental pollution and changes in its ionic composition (sodium, magnesium, calcium, and so on). For this reason, crustaceans are often used to determine the quality of water (both tap water and water from open reservoirs).