The smallest crustacean daphnia was popularly called the water flea for its external resemblance to a parasitic insect and the ability to move by jumping. But other than that, they have nothing in common, because they 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, movable eye, which is set in motion by three pairs of oculomotor muscles. The body of Daphnia is transparent and allows you to see everything that happens in her body. Even the slightest muscle contraction of a crustacean can be viewed under a microscope if desired.
Features of the internal structure
Despite its diminutive size, the water flea is a rather surprising organism. The description of the species notes many interesting features in its internal structure. Daphnia's kidneys are located near the mouth, the brain is near the esophagus, and the heart is on the back of the body. yellowish blood,contains white bodies - phagocytes, which, if necessary, protect the body of the crustacean from bacteria, fungi and foreign microorganisms.
The 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 integuments of the body.
Distribution and living conditions
Daphnia have a wide distribution almost all over the globe. Most of them are in the subtropics and in latitudes with a temperate climate. Basically, the water flea lives in stagnant water bodies (lakes, ponds, slow-flowing rivers), as well as in puddles. It multiplies rapidly, is extremely tenacious, so its numbers are quite large. Usually found in the water column, moving in jumps or crawling along the bottom (due to the pectoral legs).
Daphnia swim fast in summer, but when bad times come, they freeze. Even if the puddle they were in dries up, they come back to life as soon as it fills up again.
Most daphnia are herbivores, but there are also predators. The water flea recycles phytoplankton, fungi, bacteria, and rotting remains of animal tissue after being used by large predators.
The most common types
The Daphnia family is quite numerous. Only in Europe and North America there are about 150 species of these crustaceans. In Russia, some of them are especially common - magna, puleks, cuculata,galleata, cristata. All of them live in a variety of water bodies.
The largest water flea is daphnia magna. Its female has a length of up to 6 mm, while the male is three times smaller. The maturation period of newborn daphnia lasts two weeks. The female also lays eggs every two weeks (about three dozen eggs). At first, newborns are microscopic in size. But then they grow rapidly. This species lives for about three months.
Another common species is Daphnia pulex. Representatives of its slightly smaller size - females are about four millimeters, males are two times smaller. They are very prolific - a clutch 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.
Reproduction
Water fleas are unusually prolific. In all Daphnia, egg laying is divided into winter and summer. Eggs in a certain period have their own characteristics. So, for example, in winter laying, they are covered with a denser shell and their number is small (about 2 pieces), and in summer they are much more. All these features are no longer due to the change of seasons and conditions of existence, but to the presence of males. In summer, when the male population is very low, Daphnia eggs appear and lay without fertilization. Eggs fertilized by males are laid only once a year - in autumn. During her life cycle, the female is capable ofgive offspring up to 25 times.
Daphnia harm to humans
Despite the fact that Daphnia is called the water flea, it has nothing to do with bites. However, it can cause harm to a person. Everything is 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 they, in turn, filtering it, can capture those same pollen particles. Then, when the crustaceans are dried, this pollen remains and can cause a severe allergic reaction in the human body, often mistaken for a water flea bite.
Allergy symptoms are often typical - inflammation of the conjunctiva of the eye (conjunctivitis), watery eyes, frequent sneezing, nasal congestion and difficulty breathing.
Sometimes there may also be rashes on the body, accompanied by severe itching.
Human Use of Daphnia
In turn, daphnia serve as a universal food for aquarium fish. For this purpose, they are bred at home.
You just need to catch Daphnia in a stagnant pond and provide them with living conditions close to natural. It is worth catching crustaceans in water bodies where there are few or no fish, since in the absence of predators there will be more daphnia and less likely to be affected by any infection.
Breeding conditions
Water fleas in an aquarium should be kept in the water in which they live, because there is no food that they feed on in tap water. Also needpay attention to the choice of containers in which the crustaceans will be contained. After all, materials such as, for example, polypropylene, upon contact with water, can release harmful substances, and daphnia will 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 quickly, you need to constantly make sure that they have enough space and periodically move some 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, not getting it.
Many daphnia aquarists note that the best food for them is baker's yeast. Only you need to feed the daphnia carefully - if you pour too much food, the water will become cloudy, and the crustaceans will not have enough oxygen. For an aquarium of five liters, you need an amount 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, green algae serve as food for crustaceans, including Euglena green and Chlorella.
It is important to note that they also need a certain temperature. This, according to experts, is from 22 to 25 degrees. It is under such conditions that water fleas breed in the pool of a natural reservoir.
Don't let the water boil and change the water (a third of the total volume) at least once or twice a week.
Daphnia crustaceans perfectly filter water from bacteria. Therefore, many aquarists breed them to purify water - 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 year-round ecological clean food for most fish species (both fry and adults).
The water flea is very sensitive to environmental pollution and changes in its ionic composition (sodium, magnesium, calcium, and so on). It is for this reason that crustaceans are often used to determine the quality of water (both tap water and water from open water).
