Daphnia lives. Big daphnia (lat.

Herbst, 1968

External structure

Unless otherwise noted, this section describes the structure of females. The integuments consist of a head shield and a bivalve carapace. Usually they have a well-marked pattern of rhombuses and polygons - reticulation. Each such cell of the integument is formed by one cell of the hypodermis. There are spines on the edge of the valves, and a tail needle covered with spines at the posterior end. Many species have rows of feathered setae on the inner margin of the valves in its middle part; males of all species have the same setae and additional setae on the anterior-lower corner of the valves.

On the head, most species have a beak-shaped outgrowth - the rostrum. Under it are the first antennae (antennules) - short outgrowths bearing 9 olfactory setae - aesthetasci (aesthetics) at the end, and one additional seta on the lateral surface. In males, the first antennae are larger, mobile; in addition to aesthetasci, they carry a large bristle (“flagellum”) at the distal end.

On the lateral surface of the head there are protrusions of the cuticle - fornixes. Their shape, as well as the shape of the posterior edge of the head shield, is an important diagnostic feature of subgenera and groups of species. Under the fornixes, the second antennae (antennae) are attached to the head with a complex "joint". They consist of a base and two branches - an internal three-segmented and an external four-segmented. At the ends of the segments of the branches there are two-segmented swimming bristles covered with flattened hairs, forming "oars" when swimming. There are five of them on a three-segmented branch (four only in D. cristata), on a four-segmented one - four. There are several small sensitive bristles on the base.

A large upper lip extends from the back of the head. Inside it are several giant polyploid cells that secrete a secret that glues food into a food bolus.

On the border between the head shield and the carapace, mandibles are located under the valves. They have a complex shape, are asymmetrical and have highly chitinous chewing surfaces covered with ridges and outgrowths. In the process of feeding, the mandibles transport food to the mouth opening.

Under the carapace are small first maxillae (maxillae), bearing four setae. Maxillae II are reduced in Daphnia. There are five pairs of biramous thoracic legs of complex structure. The legs of the first and partly of the second pair differ in structure in males and females. On the first pair of legs of males there are hook-shaped outgrowths that allow them to cling to females during mating. The third and fourth pairs carry fans of filtering bristles. Each leg has a respiratory appendage - the epipodite.

Behind the thoracic region there is a reduced abdominal region, the presence of which is “marked” by dorsal abdominal outgrowths that close the exit from the brood chamber. There are usually four of them, they are well developed in mature females and reduced in males of most species.

The posterior part of the body is a large mobile post-abdomen homologous to the telson of other crustaceans. On its dorsal side are two rows of teeth, between which is the anus. In males of some species, these teeth are partially or completely reduced. At the end of the postabdomen there are paired claws covered with spines. According to some sources, they are homologous to the furca, according to others, they are a pair of large modified setae. There are spines on the outer and inner sides of the claws, usually there are three groups of spines on the outer side, and two on the inner side. The postabdomen serves to clean the filtration apparatus from large foreign particles.

Internal structure

The integumentary system of daphnia is represented by a typical hypodermis. The hypodermis of the carpax consists of large cells forming rhombic-shaped cells.

Central nervous system consists of the supraesophageal ganglion (brain) and the ventral nerve cord with several paired ganglia. The brain is clearly visible in living individuals, which is extremely rare. It consists of a large, bisected optic ganglion and the supraesophageal ganglion proper. From the anterior part of the optic ganglion, the optic nerve departs, connecting the brain with a complex compound eye. The unpaired compound eye in Daphnia is formed from a paired primordium (embryos have two eyes) and contains exactly 22 facets (ommatidia). It is located in a special cavity inside the head, to the walls of which it is suspended with the help of two ligaments (ligaments) and is set in motion by three pairs of oculomotor muscles. In living individuals, an eye tremor is noticeable, larger jumps (saccades) of the eye are observed from time to time. Nerves also depart from the brain to the ocellus (simple eye), the first antennae (at their base there is a sensitive ganglion, the cells of which innervate the olfactory bristles - aesthetes), as well as nerves to the sensitive occipital organ of unknown purpose. A simple eye (ocellus, nauplial eye) adjoins the lower part of the supraoesophageal ganglion. In most species, it contains pigment and is visible as a small black dot. There are 4 groups of sensitive cells around the pigment spot.

Daphnia has a complex system of striated muscles that move the second antennae, postabdomen and pectoral limbs, as well as muscles that move the eye, upper lip, etc. The muscles of the digestive tract are also striated.

The digestive tract begins with a mouth opening, which is covered by a large upper lip. Giant highly polyploid cells located inside the lip secrete a secret that glues food into a food bolus. With the movements of the mandibles, it is transported to the thin esophagus, the dilator muscles of which create peristalsis, ensuring the transport of food through the esophagus. Inside the head, the esophagus passes into the wider midgut, which extends to the middle part of the postabdomen. Inside the head, two curved hepatic outgrowths depart from the midgut. In the posterior part of the postabdomen is a short hindgut.

The heart is located on the dorsal side of the body, in front of the edge of the brood chamber. Blood (hemolymph), the flow of which is clearly visible due to the presence of colorless cells in it - phagocytes, enters the heart through ostia - two slit-like lateral openings. When the heart contracts, the ostia close with valves, and blood is ejected through the anterior opening to the head. There are no blood vessels, the regular direction of blood flow is provided by transparent partitions between different parts of the mixocoel.

Breathing occurs through the integument of the body, primarily the pectoral legs, on which there are respiratory appendages - epipodites. The latter are also involved in osmoregulation. An additional organ of osmoregulation in newborns is the large occipital pore (occipital organ), which disappears after the first postembryonic molt.

The excretory organs are complex-shaped maxillary glands, which are located on the inner surface of the valves in their anterior part.

Paired ovaries (in males - testes) are located on the sides of the intestine. At the posterior end there is a zone of reproduction of oogonia, the rest of the ovary is filled with maturing oocytes. The eggs, as they mature, move to their posterior third, where narrow oviducts are located that open into the brood chamber. In males, the vas deferens open on the postabdomen in its distal part, in many species on special papillae.

Moult

When molting, the cervical suture, the line between the head shield and the carapace, diverges, and the animal crawls out of the exuvia. Together with the carapace, the covers of the body and limbs are shed. Moulting is periodically repeated throughout the life of the individual. Usually molting occurs in the water column, ephippial females of some species molt, sticking from below to the surface film of water. Several molts occur during embryonic development, in the brood chamber.

Spreading

Genus Daphnia has a worldwide distribution (including Antarctica, where in the relict salt lakes of the Vestfold oasis ( Vestfold Hills) was found Daphnia studeri, previously assigned to the genus Daphniopsis). At the beginning of the 20th century, the opinion about the cosmopolitan distribution of most species prevailed, but later it turned out 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 characteristic of the equatorial regions, where daphnia are rare. The fauna of subtropics and temperate latitudes is the most diverse. In recent decades, the ranges of many species have changed due to their dispersal by humans. Thus, a species from the New World was introduced into Europe (England) D.ambigua. In many reservoirs in the southern United States, it has become common D. lumholtzi, which until then had only been found in the Old World.

In ponds and puddles of central Russia, the following crustaceans of the Daphnia genus are often found (and most popular among aquarists):

daphnia magna (D. magna), female - up to 6 mm, male - up to 2 mm, newborns - 0.7 mm. Ripen within 10-14 days. Litters in 12-14 days. In laying up to 80 eggs (usually 20-30). Life expectancy - up to 3 months.

daphnia pulex (D.pulex), female - up to 3-4 mm, male - 1-2 mm. Litters in 3-5 days. In laying up to 25 eggs (usually 10-12). They live 26-47 days.

In the lakes of the temperate zone of Eurasia are often found D. cucullata, D. galeata, D. cristata and several other types.

Biology

Daphnia are small crustaceans (body sizes of adults are from 0.6 to 6 mm). They inhabit all types of stagnant continental water bodies, they are also found in many rivers with slow flow. In puddles, ponds and lakes, they often have a high abundance and biomass. Daphnia are typical planktonic crustaceans, most spending time in the water column. Various species inhabit small temporary reservoirs. littoral and pelagial lakes. Quite a few species, especially those inhabiting arid regions, are halophiles living in brackish, saline and hypersaline continental water bodies. These types include, for example, D. magna, D. atkinsoni, D.mediterranea, as well as most of the species previously assigned to the genus Daphniopsis.

locomotion

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 (hence their common name - “water fleas”, often referred to as all cladocerans). Many daphnia are also able to slowly crawl along the bottom or walls of blood vessels due to water currents created by the pectoral legs (the antennas are motionless during this method of movement).

Food

The main food for daphnia are bacteria and unicellular algae. Species that survive the winter in an active state (in deep, non-freezing water bodies) spend it in the bottom layers of water, feeding mainly on detritus. They feed by filtration, creating currents of water with the rhythmic movements of the pectoral legs. Food is filtered out by fans of filtering setae, which are located on the endopodites of the third and fourth pairs of pectoral legs. Large particles stuck in the filtration apparatus (for example, filamentous algae) are removed using the postabdomen and its claws. From the filter fans, food enters the abdominal food groove, is transmitted to the maxilla of the first pair and then to the mandibles, the movements of which transport it to the esophagus. In front, the mouth opening of Daphnia is covered by a large upper lip, inside which salivary glands of giant polyploid cells are located. Their secret glues food particles into a food bolus.

At an average concentration of food in water, adult daphnia various kinds filtered at a rate of 1 to 10 ml/day. Adult daily food intake D. magna can reach 600% of her body weight.

Gas exchange

On the thoracic legs are saccular respiratory appendages - gills. It is likely that Daphnia obtain a significant part of their oxygen through the thin integuments of the body and limbs, and the respiratory appendages, like the occipital organ of newborns, play an important role in osmoregulation. Some types (for example, D.pulex, D. magna) with a reduced oxygen content in the water, they begin to synthesize hemoglobin, so that their hemolymph and the whole body turn red.

Cyclomorphosis

Many species of daphnia (mostly living in lakes) have cyclomorphosis - their different generations, developing in different seasons of the year, differ sharply in body shape. In temperate latitudes, the summer generations of such species have elongated cuticle outgrowths - a tail needle and a helmet of the head shield. In spring and autumn generations, the tail needle is shorter, the helmet may be shorter or absent altogether. It is shown that the growth of outgrowths requires energy costs and leads to a decrease in fertility. Of the factors causing the growth of outgrowths of the covers, the influence of increased water turbulence, high temperature, etc. was demonstrated. Later it was shown that kairomones, signaling substances released different types invertebrates and vertebrate predators. Many hypotheses have been put forward about the adaptive role of cyclomorphosis: facilitating soaring in less dense and viscous water, accelerated swimming in a horizontal direction, etc. Most of them are either not proven or refuted. Now, the theory of the role of outgrowths in defense against predators is accepted as the main explanation for cyclomorphosis. Transparent outgrowths increase the actual size of the body and thus protect against small invertebrate predators - larger prey with outgrowths is more difficult to grab and not release when manipulated - "stuffed into the mouth." Sometimes the tail spine breaks off, which may play the same role as tail autotomy in the lizard. At the same time, transparent outgrowths do not increase the visible size, which is important for protection from large visual predators - fish.

Vertical migrations

During the period of bisexual reproduction, some females give birth to males, while others at the same time form resting, or ephippial, eggs. They are formed by meiosis and require fertilization for development. After fertilization, they also enter the brood chamber, the integuments of which thicken and form a special chitinous chamber - ephippium (ephippium). Most Daphnia species have two eggs in their ephippium; in some Australian species, often separated into a separate genus Daphniopsis, there is one egg in the ephippium. In species of the subgenus Daphnia the long axes of the eggs are perpendicular to the dorsal margin of the ephippium; in species of the subgenus Ctenodaphnia- parallel to it or inclined at a slight angle. Egg development continues until the gastrula stage, then they fall into anabiosis. During the next molt, the female sheds the ephippium, which in some species usually sinks to the bottom, while in others it floats on the surface of the reservoir. When laying the effipia of the female of some species (for example, D.pulex) often die. Together with ephippiums, daphnia eggs are carried by the wind, spread on the paws of mammals, on the paws and feathers of birds, as well as in their intestines. It has also been shown that floating ephippiums can stick to the body of smooth bugs flying up from the surface of the water and be carried by them, and more often smoothies carry smaller ephippiums. Eggs in a chemically resistant shell inside the ephippia can remain viable after passing through the intestines of birds and fish. They usually also withstand freezing and prolonged drying. It has been shown that resting daphnia eggs can long time survive and develop in solutions of toxic salts (for example,) at a concentration of poisons thousands of times higher than the MPC; after the rupture of the egg shell, the hatched embryos in such solutions immediately die.

Use in scientific research

Daphnia are used as model organisms in many environmental, toxicological and genetic studies.

Deciphering the genome

In recent years, a partial decoding of the Daphnia genome has been carried out. Daphnia pulex, in 2011 its draft was completed. Daphnia genome consists of 200 million nucleotides, but it contains at least 30.9 thousand genes - more than in other multicellular animals studied so far (for example, there are about 20-25 thousand genes in the human genome). The Daphnia genome was characterized by a high rate of gene duplications, which led to the creation of numerous gene clusters. More than a third of the gene products found in the Daphnia genome have no known homologues in the proteomes of other organisms. The largest amplified gene families are also characteristic only of this evolutionary line. Many paralog genes are expressed differently depending on environmental conditions; genes unique to daphnia are most sensitive to changes in conditions. It can be assumed that gene duplications increased the ecological plasticity of Daphnia, allowing them to adapt to the conditions of different water bodies and to changing conditions in one water body.

Breeding

The cultivation of daphnia as a food object is widespread, as in industrial purposes and amateur aquarists. Under favorable conditions, daphnia multiply and grow easily and quickly, which makes it possible to obtain 30-50 (in some cases up to 100) grams of crustaceans per day from one cubic meter of culture.

The initial culture can easily be obtained from natural reservoirs. It is advisable to catch crustaceans in small reservoirs, where the population of daphnia can be practically free from the admixture of other animals. In winter, a Daphnia culture can be obtained from ephippial resting eggs collected in advance from the surface of the water or from the upper layer of silt. Collected ephippiums are well preserved in a dry state in a cool room.

Depending on the required number of crustaceans, daphnia can be cultivated both in small vessels and in major basins and ponds. The optimum culture density is 300-1000 g/m³. Periodically, once every few weeks or months, the culture is replanted. The aging of a culture is associated with the accumulation of metabolic and decomposition products in it and with clogging it with other organisms. By changing the water, the life of the culture is extended.

The optimum growing temperature is 15-25°C, the reaction of the medium is neutral (pH 6.8-7.8), the oxygen content is not less than 3-6 mg/l, the oxidizability is 14.8-26.2 mg O 2 /l.

When growing daphnia, both joint and separate cultivation of crustaceans and food for them is used.

When co-cultivated, organic fertilizers are added to the crop, for example, manure applied in an amount of 1.5 kg / m 3. It is possible to grow on mineral fertilizers, the addition of which causes the rapid development of unicellular algae.

The disadvantage of joint cultivation is severe water pollution, rapid aging of the culture and rapid overgrowth of the container with filamentous algae.

Separate cultivation of daphnia and food for them is devoid of these shortcomings, but is technically more difficult and is used mainly in the conditions of mass industrial cultivation of food crustaceans. At the same time, an algal culture is grown separately, which is added 1-2 times a day to a container with daphnia.

In the laboratory and at home, it is convenient to keep a culture of daphnia on yeast, introduced daily a little at a rate of 15-20 g per cubic meter of culture (15-20 mg / l). . Standardized Methods laboratory cultivation of daphnia are described in manuals on toxicology and bioassays.

Other facts

Live, dried and frozen daphnia are often used as food for aquarium fish or insects kept in terrariums. In industrial fish farming, the cultivation of daphnia for food is of great importance.

Daphnia is one of the standard objects for toxicity testing. aqueous solutions chemical compounds used in the study of pollution aquatic environment. Daphnia are sensitive even to small concentrations of some salts, for example, the addition of copper salts at a concentration of 0.01 mg / l causes a slowdown in the movements of crustaceans, they either sink to the bottom or freeze at the surface water film.

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Notes

1. // Encyclopedic Dictionary of Brockhaus and Efron: in 86 volumes (82 volumes and 4 additional). - St. Petersburg. , 1890-1907.
2. , With. 119.
3. , With. 123.
4. Keonho Kim, Alexey A Kotov, and Derek J. Taylor. Hormonal induction of undescribed males resolves cryptic species of cladocerans//Proceedings of the Royal Society B: Biological Sciences. 2006 January 22; 273(1583): 141-147.
6. .
7. , With. 555.
10. - Lenta.ru
11. , With. 128.
12. , With. 136.
13. , With. 129.
14. .
15. , With. 134.
16. , With. 48.
17. .
18. , With. 103.

Literature

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• Ivleva I.V. Biological bases and methods of mass cultivation of fodder invertebrates. - M .: Nauka, 1969. - 171 p.
• Makrushin A. V., Lyanguzova I. V.// Magazine general biology. - 2006. - T. 67, No. 2. - pp. 120-126.
• Shpet G.I. Breeding of daphnia as live food in fish farming // Proceedings of the Ukrainian Institute of Pond. and lake-river. fish household - 1950. - T. 7.
• . - M .: REFIA, NIA-Priroda, 2002.

Links

• - database of genomes of representatives of the genus Daphnia(English) (Retrieved March 5, 2011)

An excerpt characterizing Daphnia

At three o'clock, no one had yet fallen asleep, when the sergeant-major appeared with the order to march to the town of Ostrovna.
All with the same accent and laughter, the officers hurriedly began to gather; again put the samovar on the dirty water. But Rostov, without waiting for tea, went to the squadron. It was already light; The rain stopped, the clouds dispersed. It was damp and cold, especially in a damp dress. Leaving the tavern, Rostov and Ilyin both in the twilight of dawn looked into the doctor's leather tent, glossy from the rain, from under the apron of which the doctor's legs stuck out and in the middle of which the doctor's bonnet was visible on the pillow and sleepy breathing was heard.
"Really, she's very nice!" Rostov said to Ilyin, who was leaving with him.
- What a lovely woman! Ilyin replied with sixteen-year-old seriousness.
Half an hour later, the lined up squadron stood on the road. The command was heard: “Sit down! The soldiers crossed themselves and began to sit down. Rostov, riding forward, commanded: “March! - and, stretching out to four people, the hussars, sounding with the slap of hooves on the wet road, the strumming of sabers and a low voice, set off along the large road lined with birches, following the infantry and the battery walking ahead.
Broken blue-lilac clouds, reddening at sunrise, were quickly driven by the wind. It got brighter and brighter. One could clearly see that curly grass that always sits along country roads, still wet from yesterday's rain; the hanging branches of the birch trees, also wet, swayed in the wind and dropped light drops to the side. The faces of the soldiers became clearer and clearer. Rostov rode with Ilyin, who did not lag behind him, along the side of the road, between a double row of birches.
Rostov in the campaign allowed himself the freedom to ride not on a front-line horse, but on a Cossack. Both a connoisseur and a hunter, he recently got himself a dashing Don, large and kind playful horse, on which no one jumped him. Riding this horse was a pleasure for Rostov. He thought of the horse, of the morning, of the doctor's wife, and never once thought of the impending danger.
Before, Rostov, going into business, was afraid; now he did not feel the least sense of fear. Not because he was not afraid that he was accustomed to fire (one cannot get used to danger), but because he had learned to control his soul in the face of danger. He was accustomed, going into business, to think about everything, except for what seemed to be more interesting than anything else - about the impending danger. No matter how hard he tried, or reproached himself for cowardice during the first time of his service, he could not achieve this; but over the years it has now become self-evident. He was now riding beside Ilyin between the birches, occasionally tearing leaves from the branches that came to hand, sometimes touching the horse's groin with his foot, sometimes giving, without turning, his smoked pipe to the hussar who was riding behind, with such a calm and carefree look, as if he were riding ride. It was a pity for him to look at the agitated face of Ilyin, who spoke a lot and uneasily; he knew from experience that agonizing state of expectation of fear and death in which the cornet was, and he knew that nothing but time would help him.
As soon as the sun appeared on a clear strip from under the clouds, the wind died down, as if he did not dare to spoil this charming summer morning after a thunderstorm; the drops were still falling, but already sheer, and everything was quiet. The sun came out completely, appeared on the horizon and disappeared in a narrow and long cloud that stood above it. A few minutes later the sun appeared even brighter on the upper edge of the cloud, tearing its edges. Everything lit up and sparkled. And along with this light, as if answering it, shots of guns were heard ahead.
Rostov had not yet had time to think over and determine how far these shots were, when the adjutant of Count Osterman Tolstoy galloped up from Vitebsk with orders to trot along the road.
The squadron drove around the infantry and the battery, which was also in a hurry to go faster, went downhill and, passing through some empty, without inhabitants, village, again climbed the mountain. The horses began to soar, the people blushed.
- Stop, equalize! - the command of the divisional was heard ahead.
- Left shoulder forward, step march! commanded ahead.
And the hussars along the line of troops went to the left flank of the position and stood behind our lancers, who were in the first line. On the right, our infantry stood in a dense column - these were reserves; Above it on the mountain, in the clear, clean air, in the morning, oblique and bright, illumination, on the very horizon, our cannons were visible. Enemy columns and cannons were visible ahead beyond the hollow. In the hollow we could hear our chain, already in action and merrily snapping with the enemy.
Rostov, as from the sounds of the most cheerful music, felt cheerful in his soul from these sounds, which had not been heard for a long time. Trap ta ta tap! - clapped suddenly, then quickly, one after another, several shots. Everything fell silent again, and again crackers seemed to crackle, on which someone walked.
The hussars stood for about an hour in one place. The cannonade began. Count Osterman and his retinue rode behind the squadron, stopped, spoke with the regimental commander, and rode off to the cannons on the mountain.
Following the departure of Osterman, a command was heard from the lancers:
- Into the column, line up for the attack! “The infantry ahead of them doubled up in platoons to let the cavalry through. The lancers set off, swaying with the weathercocks of their peaks, and at a trot went downhill towards the French cavalry, which appeared under the mountain to the left.
As soon as the lancers went downhill, the hussars were ordered to move uphill, to cover the battery. While the hussars took the place of the uhlans, distant, missing bullets flew from the chain, screeching and whistling.
This sound, which had not been heard for a long time, had an even more joyful and exciting effect on Rostov than the previous sounds of shooting. He, straightening up, looked at the battlefield that opened from the mountain, and wholeheartedly participated in the movement of the lancers. The lancers flew close to the French dragoons, something tangled up in the smoke there, and after five minutes the lancers rushed back not to the place where they were standing, but to the left. Between the orange lancers on red horses and behind them, in a large bunch, blue French dragoons on gray horses were visible.

Rostov, with his keen hunting eye, was one of the first to see these blue French dragoons pursuing our lancers. Closer, closer, the uhlans moved in disordered crowds, and the French dragoons pursuing them. It was already possible to see how these people, who seemed small under the mountain, collided, overtook each other and waved their arms or sabers.
Rostov looked at what was going on in front of him as if he were being persecuted. He instinctively felt that if they now attacked the French dragoons with the hussars, they would not resist; but if you strike, it was necessary now, this very minute, otherwise it would be too late. He looked around him. The captain, standing beside him, kept his eyes on the cavalry below in the same way.
“Andrey Sevastyanych,” said Rostov, “after all, we doubt them ...
“It would be a dashing thing,” said the captain, “but in fact ...
Rostov, without listening to him, pushed his horse, galloped ahead of the squadron, and before he had time to command the movement, the whole squadron, experiencing the same thing as he, set off after him. Rostov himself did not know how and why he did it. He did all this, as he did on the hunt, without thinking, without understanding. He saw that the dragoons were close, that they were jumping, upset; he knew that they would not stand it, he knew that there was only one minute that would not return if he missed it. The bullets squealed and whistled so excitedly around him, the horse so eagerly begged forward that he could not stand it. He touched the horse, commanded, and at the same instant, hearing the sound of the clatter of his deployed squadron behind him, at full trot, began to descend to the dragoons downhill. As soon as they went downhill, their gait of the lynx involuntarily turned into a gallop, becoming faster and faster as they approached their lancers and the French dragoons galloping after them. The dragoons were close. The front ones, seeing the hussars, began to turn back, the rear ones to stop. With the feeling with which he rushed across the wolf, Rostov, releasing his bottom in full swing, galloped across the frustrated ranks of the French dragoons. One lancer stopped, one on foot crouched to the ground so as not to be crushed, one horse without a rider got mixed up with the hussars. Almost all French dragoons galloped back. Rostov, choosing one of them on a gray horse, set off after him. On the way he ran into a bush; a good horse carried him over him, and, barely managing on the saddle, Nikolai saw that in a few moments he would catch up with the enemy whom he had chosen as his target. This Frenchman, probably an officer - according to his uniform, bent over, galloped on his gray horse, urging it on with a saber. A moment later, Rostov's horse struck the officer's horse with its chest, almost knocking it down, and at the same instant Rostov, without knowing why, raised his saber and struck the Frenchman with it.
At the same moment he did this, all the revival of Rostov suddenly disappeared. The officer fell not so much from a blow with a saber, which only slightly cut his arm above the elbow, but from a horse's push and from fear. Rostov, holding back his horse, looked for his enemy with his eyes in order to see whom he had defeated. A French dragoon officer jumped on the ground with one foot, the other caught in the stirrup. He, screwing up his eyes in fear, as if expecting every second of a new blow, grimaced, looked up at Rostov with an expression of horror. His face, pale and splattered with mud, blond, young, with a hole in his chin and bright blue eyes, was the most not for a battlefield, not an enemy face, but the simplest room face. Even before Rostov had decided what he would do with him, the officer shouted: "Je me rends!" [I give up!] In a hurry, he wanted and could not disentangle his leg from the stirrup and, without taking his frightened blue eyes off, looked at Rostov. The hussars jumped up and freed his leg and put him on the saddle. Hussars from different sides were busy with the dragoons: one was wounded, but, with his face covered in blood, did not give up his horse; the other, embracing the hussar, sat on the back of his horse; the third climbed, supported by a hussar, onto his horse. Ahead ran, firing, the French infantry. The hussars hastily galloped back with their prisoners. Rostov galloped back with the others, experiencing some kind of unpleasant feeling that squeezed his heart. Something obscure, confused, which he could not explain to himself in any way, was revealed to him by the capture of this officer and by the blow that he inflicted on him.
Count Osterman Tolstoy met the returning hussars, called Rostov, thanked him and said that he would present to the sovereign about his valiant deed and would ask for the St. George Cross for him. When Rostov was demanded to Count Osterman, he, remembering that his attack had been launched without orders, was fully convinced that the boss was demanding him in order to punish him for his unauthorized act. Therefore, Osterman's flattering words and the promise of a reward should have struck Rostov all the more joyfully; but the same unpleasant, vague feeling morally sickened him. “What the hell is bothering me? he asked himself as he drove away from the general. - Ilyin? No, he's whole. Did I embarrass myself with something? No. Everything is not right! Something else tormented him, like remorse. “Yes, yes, that French officer with the hole. And I remember well how my hand stopped when I picked it up.
Rostov saw the prisoners being taken away and galloped after them to see his Frenchman with a hole in his chin. He, in his strange uniform, sat on a clockwork hussar horse and looked around him uneasily. The wound on his hand was almost not a wound. He feigned a smile at Rostov and waved his hand in the form of a greeting. Rostov was still embarrassed and somehow ashamed.
All this and the next day, Rostov's friends and comrades noticed that he was not boring, not angry, but silent, thoughtful and concentrated. He drank reluctantly, tried to remain alone and kept thinking about something.
Rostov kept thinking about this brilliant feat of his, which, to his surprise, bought him the St. George Cross and even made him a reputation as a brave man - and could not understand something. “So they are even more afraid of ours! he thought. “So that’s all there is, what is called heroism?” And did I do it for the fatherland? And what is he to blame for with his hole and blue eyes? And how scared he was! He thought I would kill him. Why should I kill him? My hand trembled. And they gave me the George Cross. I don't understand anything!"
But while Nikolai was processing these questions in himself and still did not give himself a clear account of what so embarrassed him, the wheel of happiness in the service, as often happens, turned in his favor. He was pushed forward after the Ostrovnensky case, they gave him a battalion of hussars, and when it was necessary to use a brave officer, they gave him instructions.

Having received news of Natasha's illness, the countess, still not quite healthy and weak, came to Moscow with Petya and the whole house, and the entire Rostov family moved from Marya Dmitrievna to their house and completely settled in Moscow.
Natasha's illness was so serious that, to her happiness and to the happiness of her relatives, the thought of everything that had caused her illness, her act and the break with her fiancé passed into the background. She was so sick that it was impossible to think how much she was to blame for everything that had happened, while she did not eat, did not sleep, noticeably lost weight, coughed and was, as the doctors made her feel, in danger. All he had to think about was helping her. Doctors went to Natasha both individually and in consultations, spoke a lot of French, German and Latin, condemned one another, prescribed the most diverse medicines for all diseases known to them; but not one of them came up with the simple thought that they could not be aware of the disease that Natasha suffered, just as no disease that a living person was possessed by could be known: for every living person has his own characteristics and always has special and its own new, complex, unknown disease to medicine, not a disease of the lungs, liver, skin, heart, nerves, etc., recorded in medicine, but a disease consisting of one of the innumerable compounds in the suffering of these organs. This simple thought could not come to doctors (just as the thought cannot come to a sorcerer that he cannot conjure) because their life's work was to heal, because they received money for that, and because they spent the best years of their lives on this business. But the main thing is that this thought could not come to the doctors because they saw that they were undoubtedly useful, and were really useful for all the Rostovs at home. They were useful not because they forced the patient to swallow mostly harmful substances (this harm was not very sensitive, because harmful substances were given in small quantities), but they were useful, necessary, inevitable (the reason is why there always are and will be imaginary healers, soothsayers, homeopaths and allopaths) because they satisfied the moral needs of the sick and people who love the sick. They satisfied that eternal human need of hope for relief, the need for sympathy and activity that a person experiences during suffering. They satisfied that eternal, human need, which is noticeable in a child in the most primitive form, to rub the place that is bruised. The child will be killed and immediately runs into the hands of the mother, the nanny in order to be kissed and rubbed sore spot, and it becomes easier for him when the sore spot is rubbed or kissed. The child does not believe that the strongest and wisest of him do not have the means to help his pain. And the hope for relief and the expression of sympathy while the mother rubs his bump consoles him. Doctors were useful for Natasha in that they kissed and rubbed the bobo, assuring that it would pass now if the coachman went to the Arbat pharmacy and took seven hryvnias of powders and pills in a pretty box for a ruble, and if these powders were sure to be in two hours, nothing more and no less, the patient will take in boiled water.
What would Sonya, the count and the countess do, how would they look at the weak, melting Natasha, doing nothing, if there weren’t these pills by the hour, drinking warm, chicken cutlets and all the details of life prescribed by the doctor, observing which was a lesson and comfort for others? The stricter and more complex these rules were, the more comforting it was for those around. How would the count endure the illness of his beloved daughter, if he did not know that Natasha's illness cost him thousands of rubles and that he would not spare thousands more to do her good: if he did not know that if she did not recover, he would not he will spare thousands more and take her abroad and hold consultations there; if he had not been able to tell the details about how Metivier and Feller did not understand, but Freeze understood, and Wise defined the disease even better? What would the countess do if she could not sometimes quarrel with the sick Natasha because she did not fully comply with the doctor's prescriptions?
“You will never recover,” she said, forgetting her grief in annoyance, “if you do not obey the doctor and take your medicine at the wrong time!” After all, you can’t joke about this when you can get pneumonia, ”the countess said, and in the pronunciation of this one word, incomprehensible to more than her, she already found great consolation. What would Sonya do if she didn’t have the joyful consciousness that she didn’t undress for three nights at first in order to be ready to fulfill exactly all the doctor’s instructions, and that now she doesn’t sleep at night so as not to miss the clock in which it is necessary to give harmless pills from a golden box? Even Natasha herself, who, although she said that no medicines could cure her and that all this was nonsense - and she was glad to see that so many donations were made for her that she had to take medicines at certain hours, and even she was happy was that she, neglecting the fulfillment of the prescribed, could show that she did not believe in treatment and did not value her life.
The doctor went every day, felt the pulse, looked at the tongue and, not paying attention to her dead face, joked with her. But on the other hand, when he went out into another room, the countess hurriedly followed him, and, assuming a serious look and shaking his head thoughtfully, he said that, although there was danger, he hoped for the effect of this last remedy, and that we had to wait and see. ; that the disease is more moral, but ...
The countess, trying to hide this act from herself and from the doctor, put a gold piece into his hand and each time returned to the patient with a calm heart.
The signs of Natasha's illness were that she ate little, slept little, coughed, and never perked up. Doctors said that the patient should not be left without medical care, and therefore they kept her in the stuffy air in the city. And in the summer of 1812, the Rostovs did not leave for the village.
Despite the large number of swallowed pills, drops and powders from jars and boxes, from which madame Schoss, the hunter for these gizmos, gathered a large collection, despite the absence of the usual village life, youth took its toll: Natasha's grief began to be covered with a layer of impressions of her life, it such excruciating pain ceased to lie on her heart, it began to become past, and Natasha began to recover physically.

Natasha was calmer, but not more cheerful. She not only avoided all external conditions of joy: balls, skating, concerts, theater; but she never laughed so that her tears were not heard because of her laughter. She couldn't sing. As soon as she began to laugh or tried to sing alone with herself, tears choked her: tears of repentance, tears of memories of that irrevocable, pure time; tears of annoyance that so, for nothing, she ruined her young life, which could have been so happy. Laughter and singing especially seemed to her a blasphemy against her grief. She never thought of coquetry; she didn't even have to refrain. She said and felt that at that time all men were to her exactly the same as the jester Nastasya Ivanovna. The inner guard firmly forbade her any joy. And she did not have all the former interests of life from that girlish, carefree, hopeful way of life. Most often and most painfully, she recalled autumn months, hunting, uncle and Christmas time spent with Nicolas in Otradnoe. What would she give to bring back even one day from that time! But it was over forever. The foreboding did not deceive her then that that state of freedom and openness to all joys would never return again. But I had to live.
It was comforting to her to think that she was not better, as she had thought before, but worse and much worse than everyone, everyone, who only exists in the world. But this was not enough. She knew this and asked herself: “What next? And then there was nothing. There was no joy in life, and life passed. Natasha, apparently, tried only not to be a burden to anyone and not to interfere with anyone, but for herself she did not need anything. She moved away from everyone at home, and only with her brother Petya was it easy for her. She liked to be with him more than with the others; and sometimes, when she was with him eye to eye, she laughed. She hardly left the house, and of those who came to see them, she was glad only for Pierre. It was impossible to treat her more tenderly, more carefully, and at the same time more seriously than Count Bezukhov treated her. Natasha Osss consciously felt this tenderness of treatment and therefore found great pleasure in his company. But she was not even grateful to him for his tenderness; nothing good on the part of Pierre seemed to her an effort. It seemed so natural for Pierre to be kind to everyone that there was no merit in his kindness. Sometimes Natasha noticed Pierre's embarrassment and awkwardness in her presence, especially when he wanted to do something pleasant for her or when he was afraid that something in the conversation would bring Natasha to painful memories. She noticed this and attributed it to his general kindness and shyness, which, according to her, the same as with her, should have been with everyone. After those inadvertent words that, if he were free, he would ask her hands and love on his knees, said at a moment of such great excitement for her, Pierre never said anything about his feelings for Natasha; and it was obvious to her that those words, which then so comforted her, were spoken, as all sorts of meaningless words are spoken to comfort a crying child. Not because Pierre was a married man, but because Natasha felt between herself and him in the highest degree that force of moral barriers - the absence of which she felt with Kyragin - it never occurred to her that she could get out of her relationship with Pierre not only love on her part, or still less on his part, but even that kind of tender, self-confessing, poetic friendship between a man and a woman, of which she knew several examples.
At the end of the Petrovsky post, Agrafena Ivanovna Belova, the Rostovs' Otradnenskaya neighbor, came to Moscow to bow to the Moscow saints. She invited Natasha to go to bed, and Natasha seized on this idea with joy. Despite the doctor’s prohibition to go out early in the morning, Natasha insisted on fasting, and not fasting as usual in the Rostovs’ house, that is, listening to three services at home, but in order to fast as Agrafena Ivanovna used to, that is, all week without missing a single Vespers, Mass or Matins.

There are more than 150 species. Any self-respecting aquarist knows what Daphnia crustaceans as they are a popular food for many types of aquarium fish.

Features and habitat of daphnia

Depending on the kind daphnia, their size can vary from 0.2 mm to 6 mm, so study structure of daphnia only possible under a microscope. The body of these crustaceans has an oval shape, it is covered with a special shield of two valves (carapace), which protects the internal organs.

The head is also covered with a chitinous shell and has a beak-like outgrowth (rastrum), under which the anterior antennae are located, which perform an olfactory function.

The size of the rear antennas is much more impressive than the front ones, their main task is the movement of daphnia. Waving both antennas at the same time, daphnia pushes off the water and swims, making sharp jumps. For this feature common daphnia often referred to as the "water flea".

On the head of the crustacean is a compound eye - an unpaired organ responsible for vision. The number of facets depends on the species and ranges from 22 to 300. In predatory representatives, the structure of the eye is more complicated and there are more facets. A naupliar ocellus is located just below the faceted ocellus.

Thoracic legs of Daphnia, covered with many bristles, serve as a kind of filter through which the crustacean passes single-celled algae and bacteria suspended in water. The legs make up to 500 strokes per minute.

Daphnia photo made at high magnification, allow a good view and internal structure crustacean. Thanks to the translucent shell, the heart, intestines are clearly visible, and in females, the brood pouch with several embryos.

Daphnia of one kind or another can be found in almost any stagnant body of water - from a small pond to a deep lake. There are some representatives of this genus of crustaceans in Eurasia, and South and North America, and even in Antarctica.

An important factor in their normal existence is stagnant water, in which there is a minimum number of soil particles. Getting into running water, daphnia filter the soil along with algae and gradually clog their intestines.

Eaten grains of sand accumulate and do not allow the crustacean to move normally, it soon dies. Daphnia is extremely sensitive to environmental pollution, so it is often used to test the quality of water in reservoirs.

The nature and lifestyle of daphnia

Daphnia prefer to spend most of their lives in the water column, where they continuously filter water saturated with single-celled microorganisms. Some species stay near the bottom, feeding on the remains of invertebrates and dead parts of plants. In the same way, daphnia survives the winter cold if it does not hibernate.

Food

Blue-green algae, yeast and bacteria are the main food of Daphnia. The highest concentration of unicellular algae is observed in "blooming reservoirs", where, in the absence of a large number of fish, daphnia lives perfectly and reproduces especially intensively.

Reproduction and lifespan

interesting breeding daphnia - class crustaceans are characterized by such a feature as parthenogenesis. This is the ability to reproduce offspring without direct fertilization.

When the living conditions of this genus of crustaceans are sufficiently favorable, Daphnia females reproduce through parthenogenesis, while giving birth only to females.

On average, one individual gives offspring in the amount of 10 nauplii, which in turn become capable of reproduction already on the 4th day after birth. During the period of life, the female daphnia brings offspring up to 25 times.

With the deterioration of environmental conditions, males are also born, and the next generation of crustaceans will reproduce eggs that need to be fertilized. daphnia eggs, formed during such a period, grow into small embryos, they are covered with a special protective shell and go into hibernation.

In this form, Daphnia embryos are able to survive both drought and severe frost. When environmental conditions return to normal, they develop into adults. The next generation will again reproduce only females that will be capable of parthenogenesis.

Another interesting feature of Daphnia is cyclomorphosis. In different seasons of the year, individuals with different body shapes are born in the same population.

Thus, the summer generations of daphnia have an elongated tail needle and an outgrowth on the helmet. Among the many hypotheses about the appropriateness of such changes, the main one is protection from predators, which are more active in summer period.

The life span of daphnia is short and ranges from 3 weeks to 5 months, depending on the species. Large species such as Daphnia magna outlive their smaller counterparts.

The lifespan of daphnia also depends on the temperature of the water - the higher it is, the faster the metabolic processes proceed, the body develops faster, ages faster and dies.

The price of daphnia in the form of feed

Along with others crustaceans, daphnia and gammarus are bred commercially. Daphnia breeding at home does not bring much trouble.

It is enough to take a plastic or glass container, connect aeration and create conditions for good reproduction of blue-green algae - good illumination and stable temperature.

In the photo, dry daphnia for fish

Live daphnia, frozen and dried, is an excellent food for aquarium inhabitants. Dry daphnia for fish serves as a good source of protein, because its content exceeds 50% of the total feed weight.

gammarus, brine shrimp, daphnia - food more than affordable. So, a package of dried gammarus or daphnia with a volume of 100 ml will cost no more than 20-50 rubles, a frozen one - a little more expensive - 80-100 rubles.

Live foods are also not uncommon in modern pet stores, but they do not last long and differ little in nutritional value from frozen counterparts.

Daphnia is the most famous and numerous representative of the Daphniidae family. The skin of this organism is bivalve, with two hooks at the end of the body and one spherical, movable eye, which is set in motion by three pairs. The body of Daphnia is transparent and allows you to see everything that happens in its body. Even the slightest contraction of the muscles of a crustacean can, if desired, be examined under a microscope.

Features of the internal structure

Despite its miniature size, the water flea is a rather surprising organism. Description of the species notes a lot 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. 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.

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 the presence nutrients. Breathing is carried out directly through the integument of the body.

Distribution and living conditions

Daphnia are widespread throughout almost the entire globe. Most of them are in the subtropics and in latitudes with 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 located in the water column, moves in leaps or crawls along the bottom (due to the pectoral legs).

In summer, daphnia swim quickly, but when unfavorable 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, pulex, cuculata, galeata, 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 able to give offspring up to 25 times.

Daphnia harm to humans

Despite the fact that daphnia is called a 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, which is 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, daphnia will be more 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. You also need to be careful about 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.

Contained in aquarium conditions Daphnia 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 without 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, including Chlorella, serve as food for crustaceans.

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.

It is necessary to prevent water seething 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 reservoirs).

Daphnia belong to the genus of planktonic crustaceans. Branched antennae are located on the head, which is why taxonomists classify them as a branched mustache superorder. They live everywhere, including Antarctica. You can meet their populations in any body of water, be it a puddle, a pond, a lake, a river. The water flea spends the cold season in the bottom layer. With the onset of heat, it activates and, under favorable conditions, begins to multiply rapidly.

There are more than 150 species of daphnia, which can have a different color, body length. In the CIS, such species as galeata, cristata, pulex, magna are common. The sizes of daphnia vary in the range of 0.5-6 mm. The body is covered with a transparent sheath fastened on the back. Antennae, covered with bristles, help the water flea to move and make vertical movements in the water column.

In addition to the antennae, there is one movable eye on the head, consisting of several small eyes, a cranberry-shaped outgrowth - the rostrum. Due to the transparency of the body, it is possible to examine the internal structure in detail with a microscope or in a photo. The heart of Daphnia is located on the dorsal part, the kidneys are in the upper part of the body, and the brain is located near the esophagus.

Interesting!

The heart rate of Daphnia magna reaches 180 beats per second. Weak heart contractions indicate a painful condition of the crustacean.

Water fleas in the photo, even if they belong to the same species, may differ in color. The color of daphnia depends on how oxygenated the reservoir is. With its excess, they are light yellowish or gray in color. If there is a lack of oxygen in the reservoir, the body becomes dark brown.

What do water fleas eat

AT natural environment crustaceans feed on the simplest organisms: ciliates, bacteria, fungal spores, free-floating algae. In summer, they can be found in blooming water, abundant with phytoplankton. In winter, water fleas feed on detritus.

With the help of the legs, the crustaceans make rhythmic movements and create a water current. Setae located on the pectoral legs filter food. Then it enters the groove, after which it is redirected to the esophagus. Due to their nutritional habits, the culture of daphnia is often added to an aquarium to purify water from algae.

Interesting!

During the day, one individual is able to filter from 1 to 10 ml of food in water and consume an amount of food that is 6 times its own weight.

Reproduction of water fleas

In the presence of a food base, the eggs of the female develop without the intervention of the male. Embryos develop in a special chamber located under the sink. You can examine them in the body of a female even without a magnifying glass. The number of young individuals varies from 5 to 10. During her entire life, the female is able to give life to 100 crustaceans. During the period of stay in the chamber, the embryos undergo molting.

Interesting!

The generation of the female during partherogenesis always has one sex. In the summer, young females flood the reservoirs, and in the autumn, mainly males develop.

It takes 3-4 days for a newborn female to replenish the reservoir with her offspring, and given that only female individuals are born during the hot period, population growth is rapid.

The process of bisexual reproduction is possible with a decrease in temperature and insufficient food. Embryos are in the chamber and are protected by a dense chitinous cover. During the molt, the female drops the capsule with eggs, and it either sinks to the bottom or floats in the upper layer of water. The dense shell preserves the viability of the embryos when frozen, high temperatures, in toxic solutions.

The benefits and harms of water fleas

Contrary to the erroneous opinion, daphnia are not able to bite a person, their mouth apparatus is absolutely not adapted for this. Water fleas are used as food for aquarium fish. Depending on the species and nutritional conditions, crustaceans contain from 50 to 70% of protein. They are given to fish fresh, frozen or dried.

You can catch "live food" in any reservoir using a net or set up production at home. Water fleas in the aquarium will serve not only as food, but also purify the water.

The harm of crustaceans lies in their allergenicity. During the flowering of plants, pollen is carried by the wind and enters the water bodies. Daphnia pass it through themselves during the filtration process, as a result of which the allergen accumulates in them. During the drying process, pollen remains and provokes severe allergic reactions that are mistaken for bites.

Daphnia allergy symptoms:

• the appearance of a rash on the body, similar in nature to urticaria;
• severe itching;
• sneezing, nasal congestion;
• labored breathing;
• lacrimation, inflammation of the eyes.

An accurate diagnosis can only be made by a doctor based on a skin test. Depending on the severity of the symptoms, antihistamines, inhalers are prescribed.

Growing water fleas

To provide the inhabitants of aquariums with environmentally friendly food, daphnia is grown at home:

1. First of all, it is necessary to prepare a tank in which crustaceans will breed. It can be any plastic container suitable for food products often used plastic drinking water bottles.
2. The crustaceans are not particularly demanding on the composition of the water. The main thing is that it does not contain impurities of salts, metal compounds.
3. Yeast, green algae are used as feed. The latter actively develop in sunlight. It is enough to place a bottle filled with water with microalgae culture in warm place, as after 10-14 days it will be possible to feed water fleas with "own" grown food.
4. In order for the crustaceans to actively multiply, it is necessary to create favorable conditions for them: a temperature of 23-25 ​​° C and a 24-hour daylight hours.
5. Periodically, the culture of daphnia and water are renewed.

The highest nutritional value of fresh water fleas. In the frozen state, they lose some of the enzymes and amino acids.

Freshwater organisms, which have long been widely used as high-quality universal food for. In nature, these individuals inhabit ponds and lakes, but it is also quite possible to grow them indoors.

Description and types for home breeding

Daphnia are predominantly small crustaceans that are traditionally classified as "living dust". Let us dwell in more detail on the structure of daphnia. In all individuals of this group, the body is tightly compressed on the sides and has a chitinous bivalve cover - a shell attached to the back.

Two eyes are located on the head, often merging in sexually mature organisms into one compound eye, and in some specimens, another auxiliary eye can be observed next to the compound eye. In addition, there are two pairs of peculiar antennae on the head of the crustacean. The posterior pair is larger and is equipped with auxiliary bristles. It is thanks to the volume of the rear antennae that individuals move in the water.

Often in reservoirs you can find the following types of microscopic crustaceans:

• magna - largest representative culture (the body of the female grows up to 6 mm);
• puleks - individuals of medium size (the female reaches 3-4 mm);
• moina is the smallest type of crustacean (the maximum size of a female is 1.5 mm).

Did you know? It is curious that with a change in the level of pollution of the reservoir in which daphnia live, like a litmus test, the color of the bodies of these small organisms also changes.

How Do Daphnia Reproduce?

The breeding process of Daphnia is quite interesting. On the body of the female (on the back) one can observe the so-called "brood chamber". This cavity is securely guarded by the upper end of the shell. In summer, under the right climatic conditions, the female lays unfertilized eggs in this space, the number of which varies from 50 to 100 pieces. Only females hatch from these eggs. The young then leave the mother's cavity. A few days later, this phenomenon repeats itself. During these days, the young have time to grow up and connect to the breeding procedure. Ideally, this process proceeds in an avalanche-like manner.

At the end of the summer season and in early September, due to the deterioration of the climate, males hatch from a row of eggs. The males then inseminate the females. In females, new eggs are formed, wrapped in a dense coating (ephippium). The shell of eggs is able to tolerate fairly low temperatures. With the advent of spring, thanks to the warmth and moisture, ephippia awaken to life. Females emerge from them, and the cycle repeats. During her life cycle, a Daphnia female can have time to “give birth” 25 times, but in practice this number is usually less.

Did you know? Among all the multicellular organisms whose genome has been deciphered and studied, Daphnia are the owners of the largest number of genes. If the human genome contains approximately 20-25 thousand genes, then the genome of a microscopic crustacean has more than 30 thousand. Moreover, more than 10 thousand of these genes have no analogues among other living organisms. Due to this fact, daphnia, along with mice, yeasts and fruit flies, is used for laboratory tests as a "model" organism.

How to independently catch in reservoirs

It is customary to catch Daphnia from the spring season until the end of autumn, until an ice crust forms on the reservoirs.

It is better to catch small crustaceans with an ordinary canvas net. Then they are passed through sieves, sorting individuals by size.

It is necessary to go fishing in the most calm and cloudy weather. Usually it should be in the morning or evening. In such conditions, crustaceans rise closer to the surface of the water.
In the process of catching daphnia, they are periodically shaken out into a special tin vessel. In the same cans, the crustaceans are then transported. Do not forget that at very high density, individuals may die during transportation.

How to breed at home

When starting to grow freshwater organisms, you should first prepare a suitable container. In addition, you must know how to create all the necessary conditions for these individuals. It is about how to properly breed daphnia at home that will be discussed later in the article.

Vessel or aquarium for growing

For growing "live food" a container with a volume of 15-20 liters is excellent. When choosing a vessel, consider the following guidelines:

• choose a material that does not release hazardous substances into the water chemical substances(for example, synthetic polymers). The ideal container is a glass vessel or aquarium;
• if you use a simple glass vessel, the area in contact with air should be extremely large. This condition is required for natural gas exchange and supply of small crustaceans with oxygen;
• if you nevertheless chose a metal container - it should not be made of stainless steel;
• if you plan to keep a container with crustaceans indoors with bright lights or outdoors under the bright rays of the sun, take a container with a minimum volume of 40 liters.

Physical conditions

• Temperature . Crustaceans adapt to a wide range of temperatures. The ideal temperature is +18-22 °C. Daphnia pulex perfectly withstands fluctuations above 10 ° C. For the magna crustacean in nature, the optimum temperature is reached only once a year.
• Salinity . Daphnia is a freshwater living organism. The genus of planktonic crustaceans to which it belongs does not include marine representatives. 99% of crustaceans are freshwater, while the rest live mainly in brackish and sea ​​water. Individual specimens have been found in water with a salinity of over 0.004 ppm.
• pH and ammonia . The optimal pH is 6.5-9.5. Ammonia, even in low concentrations, is toxic to all living organisms. However, in an alkaline environment, the level of toxicity of ammonia rises sharply, which does not affect the health of daphnia, but negatively affects the reproduction of individuals. So, the insignificant content of pH and ammonia does not pose a threat to the successful breeding of Daphnia. A significant increase in the hydrogen index increases the toxicity of dissolved gases and minerals.
• Oxygen . Crayfish do well in dirty water. In this case, the dissolved oxygen index can vary from almost zero to supersaturated level. Such endurance of the culture is due to the ability to form hemoglobin. The crustaceans do not withstand intensive air exchange with small air bubbles. These bubbles can kill small individuals. However, very slow aeration can also kill small crustaceans. Slow air exchange forms a foaming layer harmful to these living organisms on the surface of the water.

• Dissolved Minerals . Crustaceans are very vulnerable to changes in the chemical component of their environment. They die when magnesium, potassium, zinc, sodium and calcium are added. A low phosphorus content activates the reproduction process, however, saturation exceeding 0.001 ppm is fatal to young animals. Even the lowest content of copper causes a decline in the mobility of these organisms. To the content of dissolved toxins (pesticides, bleaches, detergents), small organisms are also very susceptible. In turn, nitrogen, which stimulates the growth of algae, does not affect daphnia. To get rid of chlorine in the aquarium, aeration or dechlorination should be applied. You can also add a small dose of tuff stone (in powder form). City or natural waters are usually too polluted. You can not use distilled water, as it does not contain the required minerals. For daphnia, it is better to take water that is drawn from an aquarium with fish. Filtered lake water or rainwater can also be used.

A home for aquarium fish and other aquatic life needs quality clean water, because otherwise your swimming pets will not be very happy and, most likely, they will not live with you. Read how to choose and how to use an aquarium conditioner.

As for what Daphnia eats, then in natural conditions the diet of this culture consists of bacteria, yeast and microalgae.

Bacteria of small crustaceans are extracted from banana peel and other food waste. In addition, bacteria can be obtained from ordinary excrement. If you decide to use excrement, soak it in water beforehand and insist for several days. The water will begin to turn cloudy, indicating bacterial growth. After 6-7 days, pour healthy water into a vessel with fish in a ratio of 450 ml per 20 liters. Repeat the procedure every 5-6 days.
Yeast is suitable for ordinary bakers. The daily norm for crustaceans is 28 g per 20 liters of water.

At the same time, add microalgae, which prevents clogging of water and serves as another source of nutrition for the culture. Algae supply in large enough quantities. To do this, scoop up water from a populated aquarium, place it under the rays of the sun, so that the "sea hay" is intensively formed.

To diversify the diet of daphnia, as well as provide them with vitamins, periodically add cabbage, beet or carrot juice to the aquarium (1 tsp per 5 liters of water). An excellent effect is also given by liquid manure, added in small quantities.

Important! As food for small crustaceans, it is not recommended to pour milk or hay decoction into the aquarium - these components inhibit the development and reproduction of individuals.

As you can see, growing small crustaceans indoors is quite easy. These small organisms make excellent food for your home aquarium inhabitants.