Sturgeon fish: anatomy and structure of cartilaginous fish

Description, structure and characteristics

Sturgeon is a big fish. The body length of large species can reach about 6 meters. The maximum weight of the fish is 816 kilograms. This is exactly the body mass of the world's largest white sturgeon. But the average commercial fish weighs 12-16 kilograms.

The fish has a small head and an elongated snout, spatulate or cone-shaped. Retractable mouth, 4 antennae at the end of the snout. The lips are fleshy, the lower lip is torn, there are no teeth. The fry grow small teeth, but disappear over time. The gill openings of sturgeons are the same as those of sharks; regular gill rakers are located on their inner surface.

The sturgeon's skeleton consists of cartilaginous tissue, there are no vertebrae, the notochord is preserved throughout the life of the fish. The body is spindle-shaped and highly elongated. The fish has no scales, but its body is covered with five rows of special scutes-bugs - diamond-shaped bony scales. Each species of sturgeon is characterized by a certain number of bone bugs.

The sturgeon has a hard pectoral fin, its front ray, similar to a spine, is especially thick and pointed. As a rule, the age of the fish is determined by the transverse cut of the front ray. The dorsal fin has from 27 to 51 rays. The anal fin may contain from 18 to 33 sharp rays.

The sturgeon is most often gray in color. The color of the back can be light gray, light brown, grayish-black, yellowish or green. The fins are characterized by a dark gray tint, the sides are brownish, the belly is white, gray with blue or grayish with yellow.

Sturgeon is one of the long-living fish. On average, fish live 40-60 years, while the lifespan of some fish can reach 100 years.

Description

Sturgeons are among the oldest group of fish on earth. To this day, 19 species have survived, 11 of them are found in Russian waters.

The Sturgeon family is one of the largest in the ichthyofauna. A prominent representative is the sturgeon. Its spindle-shaped, elongated body is covered with five rows of bone spines. Two of them are located on the belly, the other two are on the sides, and one is on the back. Between them are bone plates.

The sturgeon fish has an elongated snout that resembles a cone. The skin is thick, rough, diamond-shaped scales. On the underside of the head there are fleshy lips, the mouth opening is on the lower part of the snout, surrounded by four antennae. The fish's jaw is toothless and retractable. The ray fin on the chest is large, thickened, and resembles a spine in shape. The fin on the back is removed from the head, slightly pushed back. The swim bladder, located at the bottom of the spine, connects to the esophagus. The bony skeleton is a chord-shaped structure. Four gills are attached to the throat by membranes, connected to each other in the throat area, and there are two more accessory gills.

Sturgeons are classified as anadromous, semi-anadromous and residential. Migratory fish include sea-dwelling fish. They come in spring and winter varieties. In the spring, spring fish swim into rivers with fresh water only for spawning. Winter crops move into rivers in the fall, go into hibernation, wait out the winter cold, and spawn in the spring.

Semi-anadromous sturgeons do not like the high salinity of the sea, but swim in water areas where sea water is diluted with river water. They rise to spawn in the upper reaches of rivers flowing into the sea.

Residential freshwater species are found in rivers and lakes. There they spawn without going out to sea.

Male sturgeons reach sexual maturity at 5-18 years of age. Females are ready to breed at 8-18 years of age and spawn 3-5 times throughout their lives.

Population and species status

In the 21st century, the sturgeon is especially at risk of extinction, the reason for this is human activity: environmental degradation, overly active fishing, which continued until the 20th century, poaching.

The trend towards a reduction in the number of sturgeon became obvious back in the 19th century, but active measures began to be taken only in recent decades: to fight poachers, raise fry on fish farms and then release them into the wild. Today in Russia it is strictly prohibited to catch almost all types of sturgeon.

Types of sturgeon

In Russia, sturgeon live in places from the White Sea to the Caspian Sea. Fish are found in the basins of Siberian rivers, in the east - in the Pacific Ocean, in the west, sometimes in the Baltic Sea.

Amursky

It is found in the basins of the Amur River, including in floodplain lakes: Kizi, Boloni, Orel-Chle. The Amur sturgeon is distinguished by the presence of smooth gill rakers with 1 apex. An endangered species. The length of the Amur sturgeon reaches 3 meters and weighs about 190 kilograms, the average weight does not exceed 56-80 kilos.

Representatives of sturgeon are distinguished by their pointed, elongated snout. The fish feeds on larvae of mayflies, caddis flies, lampreys, various crustaceans, and small fish. During the spawning period, schools of fish go up the river to the Nikolaevsk-on-Amur region.

Kaluga

A fish belonging to the beluga genus. It is a large fish, the length of which reaches more than 4 meters and weighs up to 1000 kilograms. Kaluga is considered a long-liver, because with a weight of about 600 kilograms it can live up to 50 years. The diet includes fish: pink salmon, silver carp, carp, chum salmon. Small individuals feed on minnows and lampreys. Puberty occurs late - by 18-20 years.

Inhabits the Amur basin along its entire length. Found in Lake Orel, Ussuri. Does not go into the Sea of ​​Okhotsk.

Atlantic (Baltic)

A large fish, the length of which can reach 6 meters. The maximum recorded weight of the fish is 400 kilograms. The Atlantic sturgeon has large bugs and has three pairs of large fused scutes on its tail. The back color of the Atlantic sturgeon is grayish-olive, the sides are lighter than the back, and the belly is white.

The habitat is the Black Sea and the Bay of Biscay, where no more than 300 individuals are found. A small number of fish are found only in France in the Garonne River.

The Atlantic sturgeon prefers to feed on small fish (gerbil, capelin, anchovies), worms, crustaceans and mollusks.

Stellate sturgeon

A large fish, the length of which reaches 2.2 meters and weighs about 80 kilograms. It is characterized by an elongated, narrow, slightly flattened snout. The back of the sturgeon is black-brown, the belly is white, the sides are lighter than the back.

Stellate sturgeon prefers to feast on mysids, crustaceans, various worms and small fish. The stellate sturgeon lives in the basins of the Black, Azov, and Caspian seas. During the spawning period, the fish goes to Kodori, Volga, Inguri, Ural, Southern Bug, Kura, Dnieper, Kuban, Don.

Sterlet

The natural habitat of the sterlet is the rivers of the Baltic, Black, and Azov seas. Fish is found in the following rivers: Ural, Dnieper, Sura, upper and middle Kama, Yenisei, Irtysh, Ob, Volga, Don. Previously, sterlet was found in Lakes Onega and Lake Ladoga. The fish is considered a vulnerable species.

Sterlet is a medium-sized fish. Puberty occurs early: males are ready for spawning at the age of 4-5 years, females - at 7-8 years. Another difference between the sterlet and other sturgeons is the presence of fringed antennae and a large number of lateral bugs: there are more than 50 of them.

Sterlet is a freshwater fish, but there are few semi-anadromous forms. The maximum length of the sturgeon variety reaches 1.25 meters and weighs 16 kilograms. The average size of a sterlet is 40-60 centimeters. The snout of the fish is sharp or blunt, the color varies from brownish-gray to brown. The belly is white with yellowish tint.

Sterlet feeds on insect larvae, leeches, other bottom organisms, and small fish in small quantities. A valuable hybrid form of sterlet and beluga is bester.

Read about breeding sterlet at home here.

Thorn

The advantage of the sturgeon is that it thrives equally well in both fresh and salt water, due to which its habitat extends over many kilometers. Representatives of this species are found in the Black, Caspian, Azov, Aral Seas, and in river basins adjacent to these reservoirs. Many individuals live in the Sefidrud River, the Urals, and the Kura.

Adult spiny fish can reach more than 2 meters in length, but many representatives of this species are smaller. The spine is characterized by an elongated body with cone-shaped spines on the back. Unlike other representatives of sturgeon, the sturgeon has fringed antennae located near the lower lip.

The color of the thorn varies from light gray to greenish, the belly is light. There are star-shaped scales on the surface. Thorn is a fish listed in the Red Book of Russia.

Ozerny

The lake sturgeon is a large fish with a blunt snout. The maximum size officially registered is 2.74 meters with a weight of 125 kilograms. The sturgeon's body color can be greenish-brown, black with a gray tint. The belly is white or slightly yellow.

The diet of the lake sturgeon includes all kinds of bottom microorganisms; the sturgeon feeds less often on fish. The fish's habitat is the Great Lakes system, Lake Winnipeg, and the basins of the Saskatchewan, Mississippi, and St. Lawrence rivers.

Russian (Caspian-Black Sea)

A valuable species of sturgeon, which has gained popularity due to the exceptional gastronomic qualities of its meat and caviar. An endangered species. The fish has a blunt, short snout and antennae growing towards the end of the snout. The maximum length of an adult reaches about 2.36 meters and weighs 115 kilograms. But usually the weight of Russian sturgeon is 12-24 kilograms with an average length of 1.45 meters. The color of the back is grayish-brownish, the sides are with a yellow tint, and the belly is white.

The Russian sturgeon lives in all major water areas of Russia. Found in the basins of the Caspian, Azov and Black Seas. During the spawning period, fish go to the Mzymta, Psou, Volga, Rioni, Terek, Danube, Don, Dnieper, Kuban, Samur and other rivers.

Depending on the habitat, the diet of representatives consists of worms, mysids and amphipods. Russian sturgeon prefers to eat fish: shemaya, mullet, herring, sprat. Under natural conditions, the sturgeon produces hybrid offspring with thorn, stellate sturgeon, sterlet and beluga.

Persian (South Caspian)

The Persian sturgeon is an anadromous species that is a close relative of the Russian sturgeon. Conservation status: critically endangered. The maximum size of a sturgeon is 2.42 meters and weighs 70 kilograms. Representatives are characterized by a large, long, slightly curved snout and a gray-blue back, blue sides with a metallic tint.

The fish's diet consists of benthos and small fish. Sturgeon is found in the middle and southern regions of the Caspian Sea, areas of the Caspian Sea and off the Black Sea coast. During spawning they go to the Rioni, Volga, Enguri, Ural, Kura.

Beluga

A large fish, the weight of which can reach 1500 kilograms and a length of more than 4 meters. The fish's snout is similar in appearance to that of a pig. The mouth is large, sickle-shaped, the lips are thick. The eyes are small and blind. The body is covered with large scales. The back is grayish-brown in color, the belly is light, almost white.

Beluga lives in the Black, Azov and Caspian seas. Rarely found in the Adriatic Sea. It goes to spawning in the Dniester, Volga, Dnieper, Don, and Danube. Slightly less common in the Terek, Ural or Kura rivers.

Beluga fry feed on river plankton, caddis and mayfly larvae, eggs and fry of other fish. Having matured, the fish eat juvenile sturgeon and stellate sturgeon, crustaceans, mollusks, gobies or sprat, carp and herring.

Sakhalin

A rare species of sturgeon. The average length of adult individuals reaches 1.5-1.7 meters and weighs 35-45 kilograms. The largest individuals can reach up to 2 meters and weigh about 60 kilograms. Adult Sakhalin sturgeons have a large, blunt snout and a greenish-olive color.

Sturgeons feed on various bottom inhabitants: snails, insect larvae, small shrimp, mollusks, crustaceans, and small fish.

The habitat covers the cold waters of the Seas of Japan and Okhotsk, the Tatar Strait. The sturgeon goes to spawn in the Tumnin River, located in the Khabarovsk Territory.

The most famous representatives

The sturgeon family includes 17 species , most of them are extremely rare, some are listed in the Red Book:

1. Siberian sturgeon. A native Russian species of the sturgeon family. A very large freshwater fish, up to two meters, weighing about 200 kg. Lives in Siberian rivers: Ob, Lena, Angara and Lake Baikal.
2. White sturgeon. A large representative of the sturgeon genus. With a length of 6 meters, individuals weighing about 800 kg are found. Only the beluga is larger than it. White sturgeon is found in the Pacific Ocean off the western coast of America and is classified as semi-anadromous because it can spawn in both salt and fresh streams and rivers.
3. Russian sturgeon. As a result of the arbitrariness of poachers, this species was almost completely exterminated. It is distinguished by the high taste of meat and caviar, is the main source of their production and is bred artificially for these purposes. Main habitats: Black, Caspian and Azov Seas. To restore the Russian sturgeon population, special fish farms are being opened. As they grow older, fry raised in artificial reservoirs are released into the natural environment to replenish the supply of valuable and tasty fish. The average weight of a Russian sturgeon is 20 kg, length - 2 meters.
4. Sakhalin sturgeon. A rare species, little studied, listed in the Red Book. Outwardly it differs from its relatives in its greenish color and blunt muzzle. The fish is migratory. It constantly lives in the Sea of ​​Okhotsk and the Sea of ​​Japan; it swims to the fresh waters of the Amur to spawn.
5. Beluga. The largest sturgeon fish, due to depletion of stocks, is listed in the Red Book. There is information that there were individuals reaching a weight of 75 pounds (1200 kg), only one caviar in them was about 150 kg. Its main habitat is the Caspian Sea.
6. Sterlet. A breed of sturgeon fish, completely exterminated and restored based on descriptions and drawings through selection, living in the seas of the Arctic Ocean, rivers of central Russia and the Caspian Sea. Small (up to two kg) fish of commercial value, more often than other species used for breeding in artificial ponds and lakes.
7. Thorn. A valuable, but almost destroyed species of sturgeon. The sizes are medium, the taste is high. Found in the Caspian Sea, spawns in the Volga. Actively reproduced artificially.
8. Stellate sturgeon. An anadromous deep-sea fish that lives at a depth of 100 meters and is of great commercial importance. The sizes are average, weight is 5-10 kg.
9. In addition to the most famous ones listed, there are 9 more breeds of sturgeon fish that live in the northern seas of Russia, on the west coast of North America, in the seas of Korea, China and Australia.

Habitats, migrations and distribution

Sturgeons are freshwater, anadromous and semi-anadromous. Migratory fish are those that live in the sea and then in rivers. During spawning, they migrate from the sea to rivers or vice versa, which is much less common. Semi-anadromous fish are a group of fish that live in coastal zones of seas or in sea-lake areas. During spawning they migrate to the lower reaches of rivers.

The natural habitat of the sturgeon passes through the water bodies of the Northern temperate zone of Europe, northern Asia and North America. Over millions of years of evolutionary development, the sturgeon has adapted well to living in a temperate climate zone; the fish tolerate low water temperatures well and can go hungry for a long time.

Sturgeon is a bottom-dwelling fish, swimming at depths from 2 to 100 meters. Migratory species of sturgeon live in the coastal waters of seas and oceans, but they spawn in fresh river water, where the fish enter by swimming against the current, covering impressive distances. After breeding, schools of fish go back to the sea.

Semi-anadromous species of sturgeon live in the salty coastal waters of the seas and oceans, spawning at the mouths of rivers, without going upstream. Many freshwater species of sturgeon do not undergo long migrations; they prefer to lead a sedentary lifestyle in the waters of rivers and lakes, where they feed and reproduce.

All sturgeons spawn in the spring and summer, but migrate to the spawning grounds at different times. Because of this, sturgeon are divided into seasonal races - winter and spring. Spring birds go to breeding grounds before spawning, in the spring. Winter crops - in the autumn, when the eggs have not yet ripened.

Types of sturgeon and their classification

Species of sturgeon include:

• beluga,
• Kaluga,
• sturgeon
• sterlet,
• stellate sturgeon,
• Shoveler

Beluga

Beluga is the largest migratory fish from the Sturgeon family. Its weight sometimes reaches a ton, and its length is 4 m. The thick and round body is ash-gray or greenish in color, the belly is white. The fish looks like a pig. The predator's mouth is the entire head, a thick, fleshy lip is surrounded by antennae that perform the function of smell. The yellowish nose is upturned and slightly translucent.

Beluga is an omnivore, eating small fish. From the sea - sprat and anchovy, from the river - roach, bream, carp and others. The age of the king fish reaches 40 years. It spawns in April - May, laying up to 8 million eggs at a depth of about 15 m. After spawning, the beluga goes to the sea. Lives in the Black Sea, the waters of the Caspian and Azov seas. In winter it hibernates.

Kaluga

Kaluga is a fish from the beluga genus and belongs to freshwater. It has enormous weight, large body size, and lives in the river basins of the Far East.

Lopanos

Shovelnose, a freshwater fish, is found in the tributaries of the Amur.

Stellate sturgeon

Stellate sturgeon is found in the Black, Caspian and Azov seas. The body is elongated, blue-black on the sides, the lower lips are poorly developed, and the nose is long. The size of the stellate sturgeon is up to 6 m, and its weight is up to 60 kg.

Sterlet

Sterlet differs from other sturgeons in size and appearance. Its length on average is 40-60 cm, weight - about 2 kg, but larger individuals are also found, weighing 6-7 kg. The sterlet has a spindle-shaped body of a gray, yellowish tint, without scales, with a long narrow nose. Mouth with bipartite lower lip, elongated. There are protective bone shields (50-70 pieces) on the sides and along the back.

The fish lives in cold, fast-flowing rivers of Western Siberia, and in lakes with clean water. Leads a gregarious lifestyle. In winter, they hibernate in groups to a depth of 15-20 m. Sterlet spawns in the spring, in May, and lays about 150 thousand eggs in the upper reaches of fast-flowing rivers. It feeds on invertebrates, larvae, eggs of other fish, and eats mosquitoes and midges. Young animals eat benthos. Unlike other sturgeons, the sterlet leads a sedentary lifestyle and does not go to sea to spawn.

Spawning

Puberty in sturgeon occurs between the ages of 5 and 21 years. Females spawn approximately once every 3 years, several times during their lives, males - more often. Spawning of various sturgeon fish can take place from March to November. Peak spawning occurs in mid-summer.

A prerequisite for a successful reproduction process and further maturation of the offspring is freshness of water and a strong current. Sturgeons will not be able to reproduce in stagnant or salty water. The temperature of the water is also important; the warmer it is, the worse the caviar will ripen. Embryos will not be able to survive when heated to 22 degrees.

During one spawning, female sturgeon are capable of throwing up to several million eggs, the diameter of which ranges from 2 to 3 millimeters, and their weight is up to 10 mg. Females lay eggs into crevices of the river bottom, into cracks in large boulders, and between stones. Sticky eggs adhere firmly to the substrate, due to which they are not carried away by river currents. Embryos develop from 2 to 10 days.

What does sturgeon eat?

The sturgeon prefers to feast on various bottom organisms and fish. The composition of the diet directly depends on the age of the fish and its habitat:

• Sturgeon fry prefer zooplankton (Daphnia, Bosminamia, Cyclops), but can feed on very small crustaceans and worms.
• Juveniles feast on insect larvae, small shrimp, snails and crustaceans. In the stomachs of fry there are often inedible particles, most likely absorbed from the muddy bottom.
• An adult eats 85% protein foods. Sturgeons become especially voracious before breeding: they eat almost everything they can find on the bottom, including various crustaceans (usually amphipods) and representatives of the order Cladocera. They love to feed on the larvae of insects, caddis flies, and mosquitoes. They feast on clams, mussels, leeches, shrimp, and worms.

When the amount of protein food is limited, sturgeons eat algae. The fish diet consists of sand lance, herring, sprat, gobies, anchovies, sprat, pike perch, silver bream, mullet and other types of small and medium-sized fish.

During the spawning period and after the breeding process, the sturgeon stops feeding and switches to eating vegetation. Within a month, the fish recovers, its appetite returns, after which it again goes in search of food for further survival.

Sturgeon nutrition

The noble sturgeon is a predatory fish that feeds on protein foods, although it is omnivorous. Food for young individuals in the waters of the seas and oceans:

• worms,
• shellfish,
• crustaceans,
• echinoderms,
• insect larvae.

As they grow older, they begin to eat shrimp. Fresh water for young animals also contains insect larvae, worms, leeches, etc.

Adult sturgeons love to eat fry. During the breeding season before spawning, they consume a lot of small fish. If there is not enough protein food, the predator is not averse to eating algae. During spawning, the sturgeon practically does not eat. Only after a month the appetite is restored and the fish begins to eat its usual food again.

Places of residence of the Siberian sturgeon:

• Ob,
• Yenisei,
• Lena.

Spawning takes place in July.

Sturgeon caviar

Sturgeon caviar is one of the most elite and expensive delicacies in the whole world. The cost of 1 kilogram of product often reaches up to 6 thousand dollars. The high price of fish is due to the annual decline in their population. Taking into account that industrial fish production is prohibited in many countries, the main suppliers of the product are artificial fish.

Real black caviar has a refined, lightly salted taste with a slight aroma of seaweed. The color of caviar varies from light gray to dark brown. Due to the high cost of the product and its unique color, caviar was called “black gold”.

The delicacy is used as a cold appetizer with sparkling wine, vodka and dry champagne. The delicacy is served pure in crystal vases or in turtle shells with small silver spoons. Many people prefer to make sandwiches with butter and caviar. The product is also combined with onions, hard cheese, vegetables, eggs and herbs.

To prevent caviar from losing its unique taste and attractive appearance, it is served 15 minutes before consumption. Until this point, the snack is stored in the refrigerator. In addition to its excellent gastronomic properties, sturgeon caviar is especially valued in natural medicine. It contains at least 30% easily digestible proteins, 12% fatty acids, 6% vitamins and mineral salts.

It is useful to use caviar for the following problems:

• atherosclerosis;
• iron deficiency anemia;
• nervous system disorders;
• chronic fatigue;
• osteoporosis.

It is useful for pregnant women and breastfeeding mothers to eat sturgeon caviar, due to the vitamin E and choline it contains. It is recommended to consume the product during the post-rehabilitation period (after operations) - it has a general strengthening effect.

To get maximum benefit from the product, only high-quality caviar is consumed.

Biological differences between sterlet and sturgeon

In addition to belonging to different classes, there are a number of biological characteristics of sturgeon and sterlet that help to understand the difference between these two representatives of the same genus.

1.Size of the individual. Most fish of the sturgeon family are impressive in size (up to 6 meters in length) and gain a lot of weight (more than 100 kilograms). Sterlet is an exception in this series. The length of an adult fish rarely exceeds 125 centimeters, and the maximum weight is 6 kilograms.

2.Shape and size of the head. You can distinguish a sturgeon by its large and wide head and short nose. The sterlet's head is small, and its nose is very long and pointed, with a mustache in the form of a fringe. Such differences can be seen even in photographs of these sturgeon representatives.

3.Color and body structure. The color of sturgeon fish can be from light gray to black, and there is practically no difference in the color of sterlet and sturgeon. But the number of lateral bony scutes (bugs) that both sturgeon and sterlet have will help to accurately determine which class the individual belongs to. The sturgeon can have up to 70 bugs, while the sterlet has 10-15 fewer scutes.

Moreover, all sturgeons belong to one of the most ancient zoological branches, which is called cartilaginous. Their main difference from other known species of fish is the absence of a bony spine, the function of which is performed by a cartilaginous chord. Fry of any type of fish have a similar structure until their skeletal system becomes stronger.

Breeding and rearing

In nature, many species of sturgeon fish easily form crosses, due to which a hybrid of sterlet and beluga - bester - was artificially bred for commercial cultivation. Today, many people are increasingly resorting to breeding sturgeon at home. If all stages of the technological process are followed, it is possible to obtain products that will be no worse in quality than livestock caught in natural reservoirs.

Features of cultivation (subject to permission from the state):

• To grow sturgeon, you will need to select a plot of land whose area will be at least 30 square meters. It is recommended to choose a location away from roads, because sturgeons are shy fish. It is very important to take care of heating in winter.
• Professional sturgeon farming on a large scale requires about 5-7 tanks where adult fish will be sorted. But beginning breeders can use one small container, 2-3 meters in diameter and at least 1 meter deep. Such a pool will allow you to grow about 1 ton of fish.
• For good fish growth, filters, pumps, compressors, and pipelines are installed in the pools. It is advisable to purchase an automatic feeder and incandescent lamps. When using plumbing to supply water, the fish farmer must ensure that no residual chlorine enters the pool. The volatile compound can be eliminated by installing a carbon filter.
• Take care of the fish regularly. Be sure to keep the pool clean: change 10% of the water daily, remove silt from the walls, monitor the temperature and serviceability of the equipment. The optimal water temperature in cold weather should be at least 17-18 degrees, in summer – 20-24 degrees.
• It is difficult to calculate the rate of future growth of the fry, so the fish are sorted weekly into different tanks. At the same time, the cultivation of strong specimens takes no more than six months, medium – 7 months, strong – up to 9 months.

Successful sturgeon breeding directly depends on the nutrition of the individuals. They are fed nutritious high-calorie food, which should contain the following components:

• protein – at least 45%;
• crude fats – 25%;
• dietary fiber – 2%;
• phosphorus and lysine – 1%.

When choosing food for sturgeon, it is recommended to give preference to water-resistant food that swells and sinks in water. Fry are fed 5-6 times a day, adults - 4 times a day. At the same time, equal time intervals must be maintained between feedings, otherwise the fish may refuse to eat.

Read more about sturgeon breeding here.

Anatomy and structure of cartilaginous fish

Introductory remarks.

Cartilaginous ganoids (order Acipenseriformes) retain a number of primitive features in their structure. Externally, this can be seen in the structure: rostrum and squirter; paired fins horizontally located in relation to the body; heterocercal caudal fin; the anus, which is located near the ventral fins.

Of the internal organs, a primitive structure can be observed in: the cartilaginous axial skull; the jaw arch, represented by the palatoquadrate and Meckel's cartilages; conus arteriosus in the heart and spiral valve in the intestine.

These features bring cartilaginous ganoids closer to elasmobranchs (Elasmobranchii).

At the same time, they have characteristics that make them classified as bony fish.

The skeleton of cartilaginous fish contains ossifications of the integumentary bones of the skull and vomer; parasphenoid and secondary jaws; operculum; collarbone

The combination of cartilaginous and bone elements in the skeleton determined the first name of these fish - cartilaginous. The presence of remains of ganoid scales and fulcra on the upper lobe of the tail (evidence of antiquity of origin) determined the second name - cartilaginous ganoids.

External building.

Sturgeons have a torpedo-shaped body.

Like all fish, it is divided into the head, body and tail. The head has the shape of a cone. Snout shape

(rostrum) can be conical, blunt, pointed, xiphoid, rounded or spatulate.
This is a species characteristic. On the underside of the snout in front of the mouth are two pairs of antennae
, or
tentacles
(cirri). Their shape varies among different species of sturgeon.

In sterlet and thorn they are fringed, in stellate sturgeon they are without fringes, and in kaluga they are flattened laterally, without leaf-like appendages. Antennae are a species characteristic.

The mouth (stoma) of all sturgeons is lower. In representatives of the genus Acipenser it is in the form of a small transverse slit, and in belugas (genus Huso) it is a large semilunar one. The mouth is surrounded by fleshy lips in the form of ridges on the upper and lower jaws.

It is retractable, and if you pull the upper jaw, the oral funnel extends along with the jaw apparatus. This has adaptive significance for the absorption of food from the bottom.

The nasal openings are located on the sides of the head

, or
nostrils
(naris), behind them
is the eye
(oculus).

The operculum covers the gill apparatus on the sides of the head. It is bordered by a gill membrane, which in sturgeons is attached to the intergill space isthmus, and in belugas it forms a free fold.

The spiraculum, in the form of a small pin hole, is located behind the eyes, on the upper edge of the gill cover.

It is absent in shovelnoses and pseudoshovellings.

of bone bugs run along the body of sturgeons

. One row is located on the back, two on the sides and two on the ventral side of the body. The number of bugs and their sizes are an important systematic feature. So, the sterlet has 57-71 side bugs, the Russian sturgeon has 24-50. Between the rows of bugs there are bone plates of various shapes and sizes. In the Siberian sturgeon, the plates between the dorsal and lateral bugs are small, star-shaped, while in the Russian sturgeon they are larger; in sterlet - in the form of sharp conical shields.

The pectoral fins are located behind the gill cover, almost horizontal to the body.

The first ray of the fin has the appearance of a bony spine, the degree of development of which varies in different species. It is highly developed in the Atlantic and Amur sturgeon, and weakly in the Sakhalin sturgeon. The remaining rays of the fins (lepidotrichia) are bony and of dermal origin.

The pelvic fins are somewhat shifted back towards the caudal region, just like the pectoral fins, they consist of lepidotrichia.

The dorsal fin is carried back to the caudal fin and is located above the anal fin.

The anal fin is located behind the anus.

The caudal fin is heterocercal, epibate.

Its upper blade is covered with ganoid scales, and along the upper edge of the blade there are fulcra.

The anal (anus) and genital (foramen genitale) openings are located between the ventral fins, one after the other.

Internal structure.

On an opened fish, you can see the arrangement of organs in the body in their natural state (Fig. 23). To do this, place the fish in the bath on its side with the ventral side facing you and lift the flap of skin upward, attaching it to the paraffin with pins.

Figure 23 – General topography of the internal organs of the sterlet:

1

- heart;
2
– abdominal cavity;
3
– liver;
4
– gallbladder;
5
– cardiac section of the stomach;
6
– pyloric section of the stomach;
7
– pyloric gland;
8
– duodenum;
9
– spiral valve;
10
– rectum;
11
– anus;
12
– pancreas;
13
– swim bladder;
14
– spleen;
15
– testes;
1
6 – genital duct;
17
– genital opening.

Internal organs are placed in the pericardial and abdominal cavities.

The pericardial cavity lies closer to the head and is separated from the abdominal transverse septum.

It contains the heart

(cor).

liver is visible in the anterior abdominal cavity.

(hepar), covering
the stomach
(gaster) from the front and sides so that only its back part is visible.
The intestine, differentiated into sections, departs from the stomach
.
In its anterior part there is pyloric gland
(glandula pyloriс), to which is adjacent a large Y-shaped spleen (lien).

The swim bladder lies on the dorsal side of the body above the digestive tract.

.

It can be seen by retracting the anterior loop of intestine. kidneys stretch along the spine

(ren).
A significant part of the body cavity in adult fish is occupied by gonads
.

Having examined the topography of the internal organs, we move on to a more detailed acquaintance with individual organs. Using tweezers and a dissecting needle, we consistently examine the internal structure of sturgeons.

Digestive system.

The retractable toothless mouth (only the larvae have teeth) of the sturgeon mouth leads into
the oropharyngeal cavity
(cavum oropharyngeus), consisting of the anterior oral and posterior gill cavities.

It is followed by the esophagus

(oesophagus) (Fig. 24), the beginning of which can be seen by turning away the stomach and liver.
The esophagus passes into the stomach
(gaster), which consists of two sections: the anterior - cardiac (gaster cardium) and the posterior - pyloric (gaster pylorus).

The pylorus leads to the midgut. The pyloric gland is located at the border of the pyloric region and the beginning of the midgut.

(glandula pylorica).

It is believed that it consists of numerous pyloric appendages connected by connective tissue and blood vessels into one organ, opening into the intestine with a wide opening.

Figure 24 – General view of the digestive organs of sterlet:

1

– esophagus;
2
– cardiac section of the stomach;
3
– pyloric section of the stomach;
4
– pyloric gland;
5
– duodenum;
6
– spiral intestine with a spiral valve;
7
– rectum;
8
– liver;
9
– gallbladder;
10
– pancreas;
11
– swim bladder;
12
– opening of the swim bladder;
13
– spleen.

Anterior part of the midgut - duodenum

(duodenum).

In the posterior part of the midgut - spiral colon

(colon) there is a spiral valve with 7-8 turns.
It is formed by a rounded fold of the mucous membrane of the intestinal tube. Next is the rectum
, or short section ending in
anus
.

Of the digestive glands in the anterior part of the abdominal cavity is the multilobular liver

(hepar).

The gallbladder is located in its anterior lobe

(vesica fellea), which opens through the bile duct into the duodenum at the base of the pyloric gland.

Pancreas

(pancreas) is not always differentiated from the lobes of the liver, so it is often called hepatopancreas.

In large sturgeons, the pancreas can be separate and located in the form of two longitudinal lobes at the junction of the pyloric stomach with the duodenum.

Respiratory system.

The respiratory organs of cartilaginous ganoids, like those of other fish, are gills of ectodermal origin.

Externally, the gill cavity is covered by the operculum

.
Under the operculum lie the gills. Each gill consists of a gill arch
(arcus branchialis), along the outer edge of which
gill filaments
(fulum branchialis) are located in two rows, separated from each other by gill septa.

Unlike elasmobranchs, in which the gill septa extend to the edges of the gill openings, in cartilaginous ganoids they are reduced and do not reach the edge of the gill filaments.

Gill rakers extend from the inside of the gill arches

, arranged, like the petals, in two rows. On the inner surface of the operculum you can see the opercular gill (branchia opercularis) - the semi-branch of the hyoid arch.

The cardiovascular system.

On an opened representative of sturgeon, you can see
the heart
(cor), which is located in the pericardial cavity, enclosed in the pericardial sac and consists of four sections.

Anterior section - conus arteriosus

(conus arteriosus) (Fig. 25), from which
the abdominal aorta
(aorta ventralis) extends forward.
The second section of the heart is a thick-walled ventricle
(ventriculus), the outer surface of which, like the surface of the arterial cone, is covered with vesicular extensions.
This is a lymphoid gland
, typical of sturgeons.
Under the ventricle there is an atrium
(atrium), which communicates with the most posterior part of the heart -
the venous sinus
(sinus venosus), which looks like a thin-walled sac.

Figure 25 – Sturgeon heart:

A

– in section;
b
– side view;
1
– arterial cone;
2
– ventricle;
3
– atrium;
4
– venous sinus;
5
– lymphoid gland.

The hematopoietic organ visible on dissected fish is the spleen

(lien) is a large organ that goes around the loop of the duodenum on the right and left and underlies it, which can be seen by lifting the intestine.

Genitourinary system.

The genitourinary system of sturgeons retains the structural features of cartilaginous fish and bears new ones - bony ones.

Like cartilaginous animals, they have oviducts with funnels opening into the body cavity (Fig. 26). They are similar to teleosts due to external fertilization, high fertility and the absence of a cloaca.

Figure 26 – Male genitals ( a

) and female (
b
) sterlet:

1

– testes;
2
– ovary;
3
– oviduct funnel;
4
– oviduct;
5
– seed tube;
6
– urogenital canal.

Kidneys

(ren) in the form of paired flat elongated bodies lie on the sides of the spine, merging behind the swim bladder.

They are penetrated by blood vessels that form the renal portal system.

Ureters

(ureter) and
deferens
(vas deferens) are the primary renal ducts.
Starting at the anterior edge of the kidney with separate tubules, they form a common duct. The oviduct funnel
, formed in sturgeon fish by the mesonephric canal, is attached to it at the level of the posterior end of the swim bladder

Through this funnel and the outlet channel, the whole liquid is discharged out.

Ovaries

(ovarium) - paired gonads of the female - are located on the sides of the body cavity and attached to its dorsal wall by mesenteries.
The excretory ducts of the ovaries are the oviducts
(oviductus), which lie on the outside of the gonads in the form of wide tubes. They open into the body cavity with wide funnels at the level of the lower half of the gonad. The oviducts open externally through a common opening behind the anus.

Testes

(testis) - paired sex glands of males - are also located on the sides of the body cavity.

In contrast to the granular structure of the ovary, the testes have a lobular structure. The seminiferous tubules a extend from the testes

(vas efferens), flowing into the upper part of the kidney.

Nervous system and sensory organs.

Using a prepared specimen of the sturgeon brain and using tables, the general topography of the nervous system in the cranial region is examined.

The brain of cartilaginous ganoids consists of five sections (Fig. 27).

Figure 27 – Sterlet brain:

A

- view from above;
b
– bottom view;
1
– forebrain;
2
– diencephalon;
3
– pineal gland;
4
– funnel of the diencephalon;
5
– pituitary gland;
6
– midbrain;
7
– cerebellum;
8
– medulla oblongata;
9
– nerves.

Forebrain

(telencephalon) small, not divided into hemispheres.

Paired olfactory lobes extend from it in front, the posterior upper section is covered by the roof of the diencephalon

(diencephalon).
epiphysis
extends forward from the diencephalon on a stalk .
At the bottom of the infundibulum of the lower part of the diencephalon is the inferior cerebral gland, or pituitary gland
(hypophysis).
Behind the diencephalon is a poorly differentiated midbrain
(mesencephalon) with the optic lobes, to which
the cerebellum
(cerebellum) is adjacent at the back, which is a thickened anterior wall of the medulla oblongata and its rhomboid fossa.

The last part of the brain is the medulla oblongata

(myelencephalon) passes into the dorsal. The roof of the medulla oblongata is covered on top by a pear-shaped lymphoid organ.

In different species of sturgeon, parts of the brain are developed differently, which is associated with their lifestyle and the activity of individual sense organs. The sterlet brain is characterized by a strong development of the olfactory sacs and olfactory nerves. Accordingly, the forebrain, where the olfactory centers are concentrated, is also significantly developed.

The midbrain and cerebellum are well developed. The stellate sturgeon has a well-developed forebrain and diencephalon, while the optic lobes in the midbrain are less developed than the sterlet.

The main sense organs that allow sturgeon to navigate in the environment are the organs of the lateral line system and the organs of smell, while the organs of vision are poorly developed. The organs of the lateral line system are represented by canals and pits, or follicles.

Side channel

(canalis lateralis) runs in the lateral rows of beetles along the entire body. It opens to the surface through holes in the spaces between the bugs. On the head, the skin sensory organs are very complex and are represented by sensory channels, tubercles and pits (Fig. 28).

Figure 28 – Diagram of the location of the skin sensory organs of the lateral line on the head of a sterlet, etc.:

1

– sensory canals with neuromasts immersed in them;
2
– sensory tubercles;
3
– lateral line of the body;
4
– sensory pits.

The sturgeon's olfactory organ, in the form of paired nasal openings, is located in front of the eyes.

The olfactory sacs are well developed. On the outside, the olfactory sac is covered with a leathery film with two openings - the nostrils.

The organs of vision - the eyes - have a structure typical of fish.

The organs of touch are the antennae, on which taste buds are located.

The benefits and harms of sturgeon

Sturgeon is rich in easily digestible proteins, due to which the product is quickly digested and is often recommended by nutritionists for various diets. The composition of sturgeon meat is rich in rare beneficial acids, including glutamic acid, as well as vitamins A, C, PP and group B. Sturgeon meat is a delicious product that contains useful macro- and microelements: potassium, fluorine, phosphorus, iodine, calcium, nickel , magnesium, molybdenum, sodium, chromium, iron, chlorine. The calorie content of sturgeon is 160 calories per 100 grams of product.

The calorie content of 100 grams of sturgeon caviar is about 200 calories. The product is rich in healthy proteins and lipids. It is useful to eat caviar for people who are in poor health after a serious illness and for those who have undergone aggressive treatment.

With regular consumption of sturgeon, which contains healthy fatty acids, blood vessels and heart muscles are strengthened, which helps lower cholesterol levels in the blood and reduce the risk of myocardial infarction. Caviar has a beneficial effect on the growth and strengthening of bone tissue and improves skin regeneration.

Consumption of sturgeon caviar and fish meat has a beneficial effect on human health and well-being:

• Sturgeon fat helps improve brain function and strengthen the cardiac and vascular systems.
• When consumed, fish fights stress and depression.

The most valuable caviar is stellate sturgeon, beluga and Russian sturgeon. The product differs in color and size.

The danger for humans is that sturgeon caviar and meat itself can be contaminated with botulism pathogens. Because of this, fish are purchased only from reliable suppliers. When purchasing, a thorough visual inspection of the product is carried out.

People suffering from diabetes and obesity should consume fish carefully to avoid the risk of deterioration in health.

Fishing for sturgeon is against the law

According to paragraph 1 of Article 258.1 of the Criminal Code of the Russian Federation, fishing for sturgeon listed in the Red Book is prohibited. Species of sturgeon that are not included in the list of endangered fish cannot be fished during spawning (we are talking about recreational fishing). But more and more often there are reports in news feeds that it is prohibited to catch sturgeon (regardless of the species) almost everywhere. This indicates a critical decline in the number of sturgeon in the world.

Species of the Red Book sturgeon

There are nineteen species of fish that are included in the sturgeon family, and most of them are found in Russia. Most often, sturgeon is found in the Caspian, Azov and Black Seas, as well as in rivers in the North of Russia and the cold waters of the Sea of ​​Japan and Okhotsk.

So, sturgeon is listed in the Red Book of the Russian Federation:

• Amursky;
• Atlantic;
• Sakhalinsky;
• Siberian;
• Russian.

Such specimens of the sturgeon family as sterlet, stellate sturgeon, thorn, kaluga and beluga are also in the Red Book of Russia.

The International Union for Conservation of Nature and Natural Resources (IUCN) list of critically endangered fish also includes sturgeon:

• Blunt;
• Korean;
• Adriatic;
• Persian;
• Chinese;
• White.

What threatens violators?

Only those species of sturgeon that are listed in the Red Book fall under Article 258.1 of the Criminal Code. Catching Red Book species of fish is punishable throughout the year, and not only during the period of protective measures during spawning or migration.

If brought to criminal liability, they face correctional labor for up to 2 years, forced labor or imprisonment for up to 4 years and a fine of up to 1 million rubles.

For posting on the Internet evidence of their catch of Red Book sturgeon, the offender is given up to 6 years in prison + a fine of up to 2 million rubles.

If the crime is committed by a group of persons, then the fine will be up to 2 million rubles and imprisonment for 5-8 years.

Appearance

Sturgeon caviar
The body has an elongated and spindle-shaped shape. The dorsal and anal fins are very strongly displaced towards the tail. There are antennae on the muzzle. There are no scales. Instead there are bone stripes. They are called "bugs". Small bone plates are scattered between the bugs throughout the body. The bugs stretch from head to tail. One stripe is on the back. Two are located on the sides. And also two plates stretch along the belly. They are not connected in the tail section. Coloration varies depending on the species and region of habitat. In most cases, the back is dark with a grayish tint. The sides are light brown and the belly is gray or white.

The largest are considered to be Atlantic and white sturgeon. The first lives in the Baltic, North and Mediterranean seas. Previously found in the Black Sea and White Sea, near river mouths. Currently listed in the Red Book, as it is on the verge of destruction. Its length reaches 6 meters, and its weight reaches 400 kg. Such a fish weighing 200 kg produces up to 80 kg of caviar. The second species lives off the west coast of North America from Alaska to California. It is also called the “California beluga” due to its enormous size. The largest representative of this species was caught off the coast of British Columbia (Canada). It reached 6.1 meters in length and weighed 499 kg.

The Siberian sturgeon is a purely Russian fish that lives in rivers over a vast territory from the Ob to Indigirka. Grows up to 2 meters. Normal weight is 65 kg. The maximum recorded weight is 210 kg. The Russian sturgeon is the original inhabitant of the Caspian, Azov and Black Seas. Accordingly, it can be found in the Volga, Kama, Dnieper, Danube and on the Don and Kuban rivers. It differs from other species by its rounded short snout. Maximum length 2.35 meters and weight 115 kg. But given the fact that fish grow slowly, such giants are impossible to find these days. They are all caught at a young age, when representatives of the species weigh 15-20 kg. The Amur sturgeon lives in rivers such as the Amur, Argun, Shilka, and Ussuri. The usual body length is 1.5 meters. Weight is 8-10 kg. Can reach a weight of 60 kg. They say that individual specimens weighing up to 160 kg have been caught. The lake sturgeon is native to North America. He lives in the Great Lakes, St. Lawrence River, Mississippi. Can weigh up to 190 kg with a body length of 3 meters. But for this, the fish needs to live for many years, which is not always possible due to the excessive appetite of people.

Interesting Facts

Sturgeon is one of the oldest and most popular fish on earth. Archaeological finds dating back to 3 thousand years BC indicate that already in those days sturgeon caviar was successfully used by sailors in canned form. In the army of Alexander the Great, sturgeon caviar served as food for soldiers.

In the 20th century, one French woman managed to notice that women who process sturgeon caviar, despite their hard work, have very beautiful and smooth skin on their hands. After this, they began to study the miraculous properties of black caviar and launched a line of cosmetics, which enjoyed incredible success. Today they have stopped producing such cosmetics due to the fact that it is not profitable.

In the middle of the 20th century, an Atlantic sturgeon weighing 213 kilograms was caught in the Neva, and 80 kilograms of caviar were obtained from it.

Sturgeon is a unique fish that has gained popularity for its large size, elongated body and amazing exterior. All sturgeon fish are in great demand, because the value of their healthy meat is very high. You can earn a huge fortune not only by selling meat, but also sturgeon caviar.

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Habitats

Sturgeon fishing
Sturgeon can be found in almost every major Russian or Siberian river. In European Russia, in the northern rivers, despite the particular abundance in the Yenisei and Ob, Russian sturgeon. anyway, he is a very rare guest and swims in by accident. Once, near Ust-Tsylma, like a huge curiosity, an Ob sturgeon was caught. This Siberian sturgeon has some differences from sturgeon from the Black Sea or Caspian basins, and Siberian fish can reach a weight of up to 210 kg. The beluga can reach the same gigantic size.

The Volga is considered the most numerous sturgeon; this river rises quite high, and already in the Urals and in the reservoirs of the Black Sea basin, sturgeon is already found in much smaller quantities. Sturgeon are sometimes found in the Volga River up to the city of Rzhev, but after Yaroslavl small sturgeon become quite common, this proves that the fish comes to these areas to spawn.

The sturgeon belongs to the family of migratory fish, like pink salmon, and in the open sea it is a very rare occurrence and tries to stick to river mouths and freshwater parts of the sea; and in the Caspian Lake - its northern part. But, despite this, the bulk of sturgeon live in the Caspian Sea itself. From here, from April, sturgeon begin to swim into rivers to spawn. He most often walks in small schools and tries to stay in the fastest and deepest places in the reservoirs; It swims slower than the sturgeon, but faster than the thorn. From the Dnieper in May the return journey begins, but in the Volga and the Urals the sturgeon remains much longer, and along the Yenisei (along Krivoshapkin) it turns down only by August 25th.

The course of the sturgeon, like all migratory fish, depends on a fair wind: in the opposite wind direction, the fish will crowd near the shallows in front of the mouths and wait for the long-tailed fish to return to the river at the same time as the waves.

The number of sturgeon increases significantly from mid-May. But the fish entering the river at this time no longer spawn here, but remain on the Yatovs for the whole winter and will spawn only a year later. In the Volga, from the city of Rybinsk to the city of Samara, sturgeon spawn almost at the same time as sterlet or a little later - in early May. In the lower reaches of the Volga, near Sarepta and Tsaritsyno, and in the Kura River, sturgeon spawn at the end of June or July (mostly).

Sturgeon spawning is very short and lasts only 3-4 days. Maturation and spawning is a fairly quick process; all eggs ripen simultaneously in each individual fish, and they are all spawned together.

Small sturgeon live for a long time where they hatch from the eggs, and then migrate to the sea, where they remain until they reach puberty - up to five years, or even more. It is not known for certain how long sturgeon live in the river. Most likely, they swim away as soon as they turn one year old, but sometimes two-year-olds are also found in rivers. It is noteworthy that these osterata, as experienced fishermen say, stay in the same flock with sterlet. this suggests that the bulk of young fish go to sea, most likely in the same autumn or during high water, before reaching one year of age.

Young sturgeons at first feed on small crustaceans, and as they mature they begin to eat shells. Shells are the main food of adult sturgeons, which only when they reach a significant size of about 1.5 meters begin to eat other fish.

Unfortunately, despite the extreme fertility of sturgeon, the number of this fish species is significantly decreasing from year to year. Today in the upper Volga, for example, sturgeon is very rare. The main destroyer of sturgeon is man, since predatory fish or birds are dangerous to him only at first. Most often, sturgeon becomes prey for catfish. One of the sturgeon's enemies is the small parasitic crustacean Dibcelestium sturionis. It is found on almost all representatives of sturgeon fish.