Sturgeon from the sturgeon family is one of the oldest fish, the appearance of which dates back to the Silurian period. Outwardly, the sterlet is similar to related biospecies: sturgeon, stellate sturgeon or beluga. It belongs to the category of valuable fish. Due to a significant reduction in numbers, its catch in its natural habitat is strictly regulated.
Origin of the species and description
The history of the species refers to the end of the Silurian period – about 395 million years ago. It was during this period that an important evolutionary change in prehistoric fish-like occurs: the transformation into the jaws of the anterior gill arches. First, the gill arch, which has an annular shape, acquired an articular joint that helps it fold into a double semicircle. It turned out some semblance of a grasping claw. The next stage is the connection of the cranium with the upper half ring. Another of them (the future lower jaw) retained mobility.
As a result of the changes that have occurred with the fish, they have become real predators, their diet has become more diverse. While the ancestors of sterlets and other sturgeons only filtered plankton. The appearance of sterlets, the one with which they have survived to this day, was formed 90-145 million years ago. We can say that these fish are contemporaries of dinosaurs. Only, unlike prehistoric reptiles, they successfully survived a number of global catastrophes and reached the present day practically unchanged.
This indicates the ecological plasticity of fish, the ability to adapt to environmental conditions and use the resources allotted by nature to the maximum. The heyday of sterlets and other sturgeons dates back to the Mesozoic era. Then some of the bony fish pushed aside. However, unlike armored species, sturgeon survived quite successfully.
Appearance and features
Sterlet belongs to the subclass of cartilaginous fish. The appearance of the scales resembles bone plates. The spindle-shaped elongated body is completely covered with them. A sign of sturgeons is a cartilaginous chord, which forms the basis of the skeleton. Vertebrae are absent even in adult fish. The skeleton and skull of sterlets are cartilaginous, there are 5 lines of bone spines on the body.
The mouth is retractable, fleshy, teeth are absent. Below the spine is the swim bladder, which is connected to the esophagus. Sterlet and other sturgeons have spiracles – holes that go from the gill cavities to the covers. The great white shark has something similar. The number of main gills is 4. Gill rays are absent.
The sterlet has an elongated body and a relatively large triangular head. The snout is elongated, conical in shape, the lower lip is bifurcated. These are the distinguishing features of the fish. In the lower part of the snout there are fringe whiskers, which are also found in other sturgeon species. There are 2 varieties of sterlets: sharp-nosed (classic version) and blunt-nosed, with a somewhat rounded nose. As a rule, individuals that are not able to reproduce, as well as cultivated ones, which are bred artificially, belong to the blunt-nosed ones. The eyes of sterlets are small and bulging.
On the surface of the sterlet's head there are bony shields fused together. The body is covered with ganoid (containing an enamel-like substance) scales with comb-like protrusions that look like grains. A feature that distinguishes sterlet from most other fish is the dorsal fin, shifted towards the tail. The shape of the tail is typical for sturgeons: the upper lobe is longer than the lower one. As a rule, sterlets are painted gray-brown, sometimes with light yellow areas. The lower part is lighter than the back, in some individuals the abdomen is almost white.
Of all sturgeon fish, the sterlet is the smallest. The length of adults is rarely more than 1.2-1.3 m. Most cartilaginous and even less – 0.3-0.4 m. Males and females are completely identical in color and size. The type of scales they also practically do not differ.
Where does the sterlet live?
The habitat of sterlets is rivers that flow into the seas: Black, Caspian and Azov. This fish is also found in the Northern Dvina. From the Siberian rivers – in the Ob, Yenisei. The range of the sterlet also extends to the rivers located in the basin of lakes: Onega and Ladoga. These fish were settled in the Oka, Nemunas (Neman) and some reservoirs. More details about the living conditions in the largest reservoirs.
- The Northern and Western Dvina – sterlet acclimatized artificially to preserve the species.
- Ob. The most numerous populations were recorded near the mouth of the Barnaulka River.
- Yenisei. The sterlet is found, as a rule, below the mouth of the Angara, as well as in the tributaries of the river.
- Nemunas (Neman), Pechora, Oka, Amur — fish were artificially introduced.
- Don, Ural — sterlets are rare, literally single specimens.
- Sura. Since the middle of the 20th century, the population, previously numerous, has become very thin.
- Kama. The sterlet population has increased significantly due to the reduction of deforestation and the fact that the water in the river has become much cleaner.
- Kuban. It is considered the southernmost point of the sterlet range. The number of sterlets is small, but gradually increasing.
- Irtysh. The most numerous flocks fall on the middle course of the river.
The sterlet lives only in clean water bodies, prefers soil covered with sand or pebbles. Females stay closer to the bottom of the reservoir, while males are more active and spend most of their time in the water column.
What does a sterlet eat?
Sturgeon – predator. The basis of its diet is made up of small invertebrates. It mainly feeds on benthic animals: small crustaceans, soft-bodied organisms, worms, insect larvae. Sterlet and caviar of other fish regale themselves. Adult large individuals feed on medium-sized fish, avoiding large prey.
Since females stay near the bottom, and males mainly swim in the water column, their diet is somewhat different. The best time to hunt sterlets is at night. The diet of young individuals and fry is microorganisms and plankton. As the fish grows, its “menu” becomes more diverse.
Peculiarities of character and lifestyle
The sterlet is a predator that settles only in clean rivers. Sometimes sterlets swim in the sea, but at the same time they stay close to the river mouth. In summer, sterlets stay on the shallows, the young go into small channels or bays near the mouth. With the onset of autumn cold, the fish goes into the depths, looking for the so-called holes. She uses them for winter quarters. In the cold season, sterlets are inactive, do not eat anything, do not hunt. After the river breaks up, the fish leaves the deep-water places and rushes to the upper reaches of the river to spawn.
Starlets, like all sturgeons, are long-lived among fish. Their life expectancy reaches 30 years. However, it cannot be called a champion of longevity among sturgeons. Lake sturgeon live over 80 years.
Social Structure and Reproduction
Most sturgeons are solitary. In this regard, sterlet is an exception to the rule. Their peculiarity is that the fish stray into large flocks. She even hibernates not alone, but with numerous brothers. The number of sterlets waiting out the cold in the bottom pits is measured in hundreds. They are so tightly pressed to each other that they can hardly move their fins and gills.
Males are considered sexually mature at 4-5 years of age. Maturation in females occurs by 7-8 years. 1-2 years after spawning, the female is again ready for breeding. This is the period necessary for the body of the fish to recover from the grueling process of spawning. The breeding season for sterlet falls in late spring or early summer, most often from mid to late May, when the temperature of the river water is set at 7-20 degrees. The best temperature for spawning ranges from 10 to 15 degrees. The spawning period may be earlier or later, depending on the water temperature and its level.
Volga sterlets do not spawn at the same time. Spawning in individuals that settle in the upper reaches of the river begins somewhat earlier. The reason is that the river overflows in these places earlier. Fish spawn in clean areas with a fast current, a bottom with pebbles. The number of eggs laid at one time by a female sterlet exceeds 16,000. The eggs are oblong, dark in color. They are covered with a sticky substance with which they are attached to the stones. After a few days, the fry hatch. The yolk sac in young animals disappears on about the tenth day. By this time, young individuals reach a length of 15 mm. The fertility of an individual depends on its age. The younger the sterlet, the fewer eggs it lays. Fish older than 15 years of age lay about 60 thousand eggs.
The appearance of fry differs from adults. The head is covered with small spines. The mouth is small, transverse. The coloration is darker than in adult fish. The tail has a particularly dark shade. Young starlets grow in the same place where they hatched. Only by autumn, 11-25 cm young growth rushes to the mouth of the river.
An interesting feature: the sterlet can interbreed with other sturgeon fish: beluga (hybrid – bester), stellate sturgeon or Russian sturgeon. Besters grow quickly and gain weight. At the same time, puberty of besters, like sterlets, occurs quickly, which makes these fish profitable for captive breeding.
Natural enemies of sterlet
Since the sterlet prefers to stay closer to the bottom of the water, it does not have very many enemies. And they do not threaten adults, but fry and eggs. For example, beluga and catfish are not averse to eating sturgeon caviar. More effective predators that massively destroy fry and teenage sterlets are pike perches, burbots and pikes.
In unfavorable living conditions, fish often get sick.
The most common diseases:
- gill necrosis;
- gas bubble disease;
Species population and status
A few decades ago, the sterlet was considered quite prosperous and numerous species. However, the unfavorable ecological situation, pollution of rivers by runoff, as well as uncontrolled fishing led to a sharp decrease in the number of the species. Therefore, this fish received the status of a vulnerable species according to the international classification. In addition, the sterlet is listed in the Red Book as an endangered species.
Until the middle of the last century, these fish were actively caught. Currently, the trapping of sterlets is strictly limited. However, fish often appears on sale in smoked, salted, canned, fresh or frozen form. The reason for this is that sterlets are actively bred in captivity, on specially equipped farms. Initially, these measures were taken to preserve the biospecies. Then, with the increase in the number of fish in captivity, the revival of the traditions of ancient Russian cooking began.
There are several ways to grow sterlets in cage farms:
- Settling adult fish in cages.
- Growing fry. At first, young animals are fed with crustaceans, and, as they grow older, they diversify the diet with minced fish and compound feed.
- Incubation of eggs is keeping them in special conditions, which leads to the appearance of fry.
Of course, sterlet grown on farms is inferior in taste to fish grown in the natural environment. And yes, they are quite expensive. However, the development of fish farms is a good chance not only for the survival of the sterlet as a biospecies, but also for the return of its commercial status. Unpretentiousness to food makes it possible to successfully grow fish in artificial conditions. It is also beneficial to breed new species of sturgeons – the same bester.
The peculiarity of the hybrid is that it combines the advantages of both “parent” species: rapid growth and weight gain – from the beluga, early maturation, like in sterlets. This makes it possible for the rapid reproduction of offspring in farm conditions. The most difficult problem is accustoming fish to compound feed. If you create favorable conditions for them, then in 9-10 months it is possible to grow a commodity-demanded specimen from a five gram fry, the net weight of which is 0.4-0.5 kg.
The problem of declining sterlet populations is mainly associated not with climate change, but with anthropogenic activities.
- Effluent discharge into water bodies. Sterlet cannot live in polluted, non-oxygenated water. Dumping of chemical compounds and production waste into rivers negatively affects the number of fish.
- Construction of hydroelectric power stations on large rivers. For example, after the creation of the Volga hydroelectric power station, about 90% of the spawning grounds were destroyed, since the fish are not able to overcome artificial obstacles made of concrete. An excess of food for fish in the upper reaches of the Volga led to obesity and impaired reproductive function of sterlets. And in the lower sections of the river, the eggs died from lack of oxygen.
- Unauthorized fishing. Catching sterlet with nets has led to a decrease in their number.
In Russia, there is a state program aimed at preserving the species. One of the successful events is the reacclimatization of fish in water bodies. The rules for catching sturgeon are strictly regulated. Obtaining a special license gives the right to catch a certain number of adult fish. The permitted type of tackle is zakidushki (5 pcs.) Or, alternatively, 2-set nets. The allowable number of fish caught under a one-time license is 10 pieces, for a monthly one – 100 pieces.
The mass and size of fish are also regulated:
- Length – from 300 mm.
- Weight – from 250 g.
The period when fishing is allowed is from July to September. The number of licenses is limited, so those wishing to take care of their registration in advance.
Fortunately, sterlets are ecologically plastic species. To restore the number of this fish, all that is needed is the creation of favorable living conditions, the protection of spawning grounds and restrictions on fishing. A positive point is the hybridization of sturgeons, which allows obtaining viable stable forms. You need to save the sterlet. The extinction of a biological species inevitably leads to a violation of the ecological system, which negatively affects, among other things, people.