Life cycle of daphnia. Large daphnia (lat. Daphnia magna) is a small cladoceran crustacean used in biotesting. Growing water fleas

The body of Daphnia is laterally compressed and everything, except for the head, is covered with a bivalve shell (carapace). Inside the shell, the body fits freely, being attached to it only by the front part.

Between the walls of the shell valves and the dorsal surface of the animal, females have a brood (embryonic) chamber. The edge of the shell on the dorsal side is elongated into a long spine (spina). The head is bent to the ventral side, the frontal part is extended into the rostrum directed downwards and backwards. The large median eye, formed by the fusion of two compound eyes that are embryonic, is equipped with special muscles that determine its mobility inside the eye chamber. Some species of daphnia also have a small unpaired eye. Short antennules, which are sensory organs, are articulated in females motionlessly with the head behind the rostrum; at the end they bear a bunch of sensitive bristles.

The antennae, which are the only organ of locomotion, are well developed, consisting of a large protopodite and two branches, the outer or exopodite and the inner or endopodite, armed with long feathered swimming setae. Strong musculature is visible inside the antennae. Each antenna is driven by three abductors, three adductors and one levator; the first two abductors and the levator are attached to the chitin of the dorsal part of the head with their conspicuous fan-shaped widened ends. The antenna rises due to the contraction of the adductors and the levator, the abductors are their antagonists.

The mandibles, clearly visible in living organisms by their peculiar movements, are devoid of a palp, on the inside with a large chewing surface, consisting of chitinous plates armed with spines. Maxillules are reduced. Maxillae are completely absent. In total there are five pairs of pectoral legs, which are turgor limbs.

On the dorsal side of the abdomen (abdomen) there are several abdominal outgrowths that serve to close the brood chamber behind; behind these outgrowths there is a pair of feathered swimming or caudal setae. The posterior part of the abdomen behind the caudal setae is called the postabdomen or cauda. It is bent under the body of the organism so that its upper, or dorsal, edge, on which the anus opens and the anal teeth are located, becomes, as it were, the lower edge; at the end of the postabdomen is a furca formed by two strong and slightly curved claws called furcal or caudal claws.

The mouth, bounded from above by the upper lip, and from the sides by mandibles, leads to a short esophagus, passing into a long midgut, of the same diameter throughout its length; in the anterior part of the midgut there are paired hepatic outgrowths, which look like short and curved blind appendages located in the head.

The heart looks like a rounded bag with one pair of lateral awns. Heart contractions are made with great speed, at room temperature, up to 200-290 beats per minute, which is the limit for animals. Blood from the heart enters the lacunae of the body. The osmotic pressure of the blood under normal conditions is two to four atmospheres. This circumstance is of great importance for maintaining the shape of the body and the elasticity of the limbs (turgor limbs).

The respiratory organs are the epipodites of the limbs, which are washed by currents of water caused by the rhythmic movements of the legs.

The excretory organs are paired armored (shell) glands located in the thickness of the shell valves, between the outer and inner layers, and are clearly visible after the valves are separated from the body of Daphnia.

The clearly visible brain consists of two merged halves. From its anterior part, nerves extend to the compound eye, and on the underside there is often an unpaired (naupliar) ocellus.

The female reproductive organs extend along the sides of the intestine from the first pair of legs to the postabdomen; short oviducts open on the dorsal side of the body in the back of the brood chamber.

All embryonic development of juveniles takes place in the brood chamber during the period between two molts. Daphnia form parthenogenetic and latent eggs. The latter are enclosed within the highly modified and dark-colored upper part of the shell valves, which forms the so-called ephippium (saddle).

Daphnia males differ from females in the absence of a brood chamber, the presence of large and mobile antennules, and other leg armament of the first pair.

A—B—Daphnia magna, female (A), male (C), female post-abdominal (C), D, E—Daphnia longispina, female (D), female post-abdomen (D); B - Dap cucullata, female; F, 3 - Daphnia cristata, female (F), antenna (3).

The five most common species of Daphnia differ from each other in the following ways.

Caudal claws armed with large spines at base

Upper (dorsal) postabdomen straight, without notch - D. pulex

Upper edge of postabdomen with notch - D. magna

Caudal claws lack large spines at base

Unpaired eye available - D. longispina

Unpaired ocellus absent

The rostrum is sharp, the setae of the antennules do not go beyond its end - D. cristata

The rostrum is obtuse, the setae of the antennules extend beyond its end - D. cucullaia

Genus: Daphnia = Daphnia

Daphnia is the common "popular name" for all types of cladocerans (CLADOCERA). Under this name, there are about 420 different species of cladocerans belonging to about 10 families. The most common are: daphnia magna, daphnia pulex, daphnia longispina, moina, bosmina, hidorus, sida, simocephalus, ceriodaphnia. The body of most cladocerans is strongly compressed from the sides and enclosed in a bivalve chitinous shell, fastened on the back and diverging on the ventral side. Daphnia periodically sheds this shell and replaces it with a new one. Daphnia's head is elongated in front into a pointed "beak" or "proboscis". There are two eyes on the head, which in fully developed specimens merge into one compound eye. In many species, there is another small eye next to it.

There are two pairs of antennae on the head. The anterior antennae are rod-shaped, very small. But the rear antennae are disproportionately large compared to the body. They are branched, with each branch of the antenna provided with long feathery setae. The posterior antennae serve as the main organ of locomotion in cladocerans, simultaneously waving both posterior antennae, the crustaceans are repelled by them and thus swim in short leaps. By adjusting the frequency of the flapping of the antennas, daphnia can not only "hover", but also rise to the upper layers of the water or, conversely, go to the depths. Thus, they make vertical movements (migrations) associated with the search for food, changes in water temperature or time of day. The thoracic section of the cladocerans is shortened and consists of 4-6 segments, each of which is equipped with a pair of legs. In females, between the dorsal surface of the body and the dorsal edge of the shell, there is an extensive cavity that performs the task of a brood chamber. Eggs are laid in this bag, where they develop.

In summer, in warm weather, unfertilized eggs are formed in the female's brood chamber (50-100 pieces for each individual), from which only females emerge, leaving the mother's body very quickly. Therefore, as a rule, all daphnia caught in the summer turn out to be females. Throughout the summer, females reproduce parthenogenetically. With the onset of cold weather, males are born from some eggs, and eggs begin to form in females, which can develop only after fertilization by the male. Daphnia males are rare, usually appear by autumn and are always much smaller than females. After fertilization of females by them, eggs are formed (usually no more than two), rich in yolk and completely opaque. The shell with eggs forms a saddle, or ephippium. Ephippia are free-floating or sinking to the bottom, they tolerate freezing and desiccation. Dried ephippia are carried by the wind. Heat and moisture awaken the eggs to life; females are bred from them, capable of reproducing in the virgin way for many generations. The color of daphnia depends on the composition of the food consumed and the oxygen content in the water of the reservoir. Color varies from green and brown to red and black. Branched crustaceans feed on unicellular algae, bacteria and ciliates, which they suck into their mouths with a stream of water created by the movement of their legs. Usually, in nature, there is a sharp increase in the number of daphnia after the death of phytoplankton.

Cladocerans are present in almost every reservoir. But the greatest number of daphnia is found in stagnant waters (ponds, lakes, ditches, water pits) rich in decaying plant organic matter with a small population of fish. The peak of the maximum number of daphnia in water bodies occurs in spring and summer. Sometimes there are so many of them that the water from their number becomes red-brown.

The largest representative of the genus Daphnia magna (Daphnia magna Straus). Lives in shallow water bodies (ponds, pits, forest puddles). Females reach 5 - 6 mm in length, males - 2 mm, larvae - about 0.7 mm. Ripens at the age of 4 - 14 days. Give up to 20 litters every 12 - 14 days. Clutch up to 80 eggs. Life expectancy - 110 - 150 days. Daphnia pulex (Daphnia pulex De Geer) is widespread in shallow water bodies. Crustaceans of medium size, their size is up to 4 mm; Give up to 12 litters every 3 - 5 days. Each clutch contains up to 25 eggs. Life expectancy 26 - 47 days.

Daphnia longispina (Daphnia longispina Muller) their size is up to 4mm. Lives in both shallow and deep waters. It has a number of different forms.

Simocephalus (Simoctphalus) - flat crustaceans, often painted red. Habitat shallow ponds with stagnant water. Their body length ranges from 2 to 4 mm.

Ceriodaphnia (Ceriodaphnia), the shape and size is similar to the previous species. The habitat is the same.

Moina - "live-bearer" - (Moina macrocopa, M. rectirostris). Females reach a length of up to 1.7 mm, males - up to 1 mm, larvae - about 0.5 mm. They ripen in 3-4 days. Give up to 7 litters every 1 - 2 days. Clutch up to 53 eggs. Life span 22 days. Moina as a food object has a number of advantages over other Daphnia species. The size of an adult moina rarely exceeds 1 mm, which makes it possible to use it when feeding fry, while the size of other Daphnia species reaches 4 mm. The chitinous shell of the moina is much softer. Juveniles of various species of aquarium fish grow much faster when fed with moina and reach puberty earlier than when fed with other types of food. Biochemical analysis showed that the nutritional value of Moina macrocopa is 20% higher than that of Daphnia magna. Moina's body contains more than 50% protein. Its reproduction rate is approximately three times higher than that of Daphnia pulex.

Bosmina (Bosmina) is one of the smallest representatives of cladocerans with long beak-like appendages on the head. Bosmins are often caught when catching daphnia - they are very similar to them, but twice as small. These black crustaceans are found in large numbers along the coast and in clusters of aquatic plants.

Chidorus (Chydorus) are small crustaceans, characterized by their rounded shape and small size. Cladocera is one of the best aquarium food for medium-sized fish species, as well as juveniles of almost all species. Fish eat them willingly, with appetite, and grow much better on them than on many other types of food.

Some species of daphnia are specially cultivated in fish farms as a highly valuable food for juvenile fish. Daphnia are one of the most complete aquarium foods. The high protein content, a large number of trace elements and vitamins, the optimal amino acid composition of the protein - all this makes daphnia a very popular food for aquarium fish among aquarists around the world.

Large daphnia (lat. Daphnia magna) is a permanent inhabitant of any fresh water body.

It is sometimes referred to as the freshwater or water flea and is familiar to many aquarium hobbyists as it is an excellent food for aquarium fish. It belongs to the family Daphniidae (Daphniidae) from the order Leaf-legged crustaceans (Onychura).

Habitat

The ideal place for the settlement of daphnia are village ponds, in which there is a lot of manure and oxygen-depleted water. Water fleas are resistant to changes in the amount of oxygen in the water. This is due to the fact that they are able to independently synthesize hemoglobin.

With a decrease in oxygen, hemoglobin in daphnia increases. They turn bright red and increase in number. With a normal oxygen content, the crustaceans have a yellow-pink color.

Small crustaceans are permanent inhabitants of fresh water bodies, deep lakes, and small puddles. Many of them move along the bottom of the reservoir or the leaves of aquatic plants, and some scurry along the surface, periodically waving their antennae.

Small puddles and roadside ditches serve as a good habitat for the water flea. In them, the water temperature is close to atmospheric and enriched with oxygen. The drying up of shallow reservoirs threatens the death of all its inhabitants.

reproduction

The reproduction of Daphnia is accompanied by a process of heterogony. In the case of favorable conditions in the form of rainfall and filling all the hollows with fresh water, only females emerge from the fertilized eggs. After a week, they reach puberty and proceed to procreation.

Up to a hundred eggs are laid in the female's brood chamber. The higher the ambient temperature, the faster they develop. Young daphnia are born into the world in a brood chamber. After that, the mother molts and lays the next batch of eggs. After one week, a new generation of juveniles is ready to breed.

Two months later, the water in the puddle is already teeming with water fleas. Such overpopulation often leads to the death of a large number of daphnia. Then the surviving females begin to lay eggs, from which individuals of different sexes emerge.

After mating, the female lays 2 eggs. Cells appear under their shell, which surround the eggs in a dense layer, and a chitinous shell is created on top of these cells, which leads to the appearance of ephippium in the brood chamber.

Eggs placed in such a capsule are supplied with a huge supply of nutrients and look larger than usual. They can stay for a long time in a dried-up reservoir or frozen in ice, while maintaining their viability.

Sticking to the paws of birds, clinging to the fur of animals, to frogs or aquatic insects, they are easily transferred from one reservoir to another. Under favorable conditions, a new generation of females emerge from them, which give birth to a new population of water fleas.

Daphnia are excellent food for freshwater fish and other creatures living near the water. They reproduce at an astonishing rate. If all her offspring survived, then in just one season it would reach 30 million individuals.

Behavior

Daphnia large in large quantities inhabit reservoirs, briskly scurrying through the water column. They move in short nets, simultaneously waving their antennae. For the spasmodic way of moving in the water, they received the name of water fleas.

Daphnia are active all day long. At night, they swim closer to the surface of the water, and during the day they sink to the very bottom. They have from 4 to 6 pairs of pectoral legs equipped with bristles. Such a filtering apparatus is used to obtain food.

The main food of water fleas is protozoa, algae, detritus particles and bacteria. Daphnia do not use sight while hunting. Their eyes can only distinguish between light and shadow. During the movement of the legs, food enters the filter chamber along with the flow of water.

Morphology

The pectoral lobes of the pectoral legs are turned into gills. Small claws are designed to clean the shell, and the back of the body is bent towards the abdomen. The transparent body of daphnia allows you to see under a microscope its internal organs - the esophagus, circulatory system, blood circulation and brood chamber.

The size of the female is about 6 mm, and the male is up to 2 mm. The round head does not have a neck interception. One compound eye was obtained by merging two lateral ones. The first pair of antennas is small. The rear antennae are more developed and are used as oars. The body is strongly flattened laterally. The double-leaved oval shell hides the entire body, leaving the head free.

The brood chamber is located on the back. The shell ends tail spike.The life expectancy of large daphnia does not exceed 19 days.

Daphnia- this is an ordinary small crustacean with a size of 3-5 mm.

External structure

The body of Daphnia is flattened from the sides and enclosed in a transparent chitinous shell - a shell. The head is not covered by a shell; a large compound eye is visible in front of it. On both sides of the head there are large branched antennae directed forward and upward. The antennae constantly wave up and down and, accordingly, the crustacean itself also jumps in the water (therefore, Daphnia has a second name - a flea). Daphnia have flattened legs like a leaf.

Lifestyle

When feeding, daphnia jumps all the time, staying almost in one place.

Through the transparent flaps of the shell, one can see the constantly working pectoral legs, they drive water under the shell. The water washes the gills located at the base of the legs, and the microorganisms present in the water are used to feed the daphnia.

Reproduction and development

In summer, usually all daphnia living in a reservoir are females. On the dorsal side, under the shell, you can see the brood chamber with eggs. The hatching of the young takes place here, then they go outside, and new eggs appear in the chamber. Development is very fast, every 2-4 days a new generation is formed - several dozen young daphnia. They are all also females and after 6-12 days (depending on the temperature) they also begin to breed. Therefore, it is not surprising that the number of daphnia is increasing so rapidly that in the middle of summer the water is literally teeming with them.

This method of reproduction from unfertilized eggs is called parthenogenesis(virgin reproduction).

Daphnia males emerge from fertilized eggs only when the water gets colder. In autumn, with the advent of males, females lay fertilized eggs. There are few eggs (usually 2), but they are large and very resistant to various adverse conditions - freezing, drying. In the spring, only females appear from them again, and the cycle of alternating parthenogenetic and dioecious generations is repeated again. material from the site

Position in systematics (classification)

Daphnia belongs to the type Arthropoda, subtype Crustacea, class Gills, subclass Leafy.

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 - the largest representative of the 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 body 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 chemicals into the water (such as 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 vessel 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 used. 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 high-quality clean water, because otherwise your swimming pets will not be very happy and, most likely, will not live with you. Read how to choose and how to use an aquarium conditioner.

As for what daphnia eats, 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 teaspoon 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.