Biological characteristics and commercial significance of pink salmon and sockeye salmon

The pink salmon spawn occurs in August and lasts until mid-September. The eggs are 6 mm in diameter. At the end of April, larvae enter the water column and drift downstream.

After reaching the sea, the juveniles stay in shallow waters for about a month, feeding actively on small crustaceans. After a year or a year and a half of marine life, the pink salmon returns to its native rivers for spawning.

Homing (the instinct to return to the native river) in pink salmon reaches a maximum length of 76 cm and a weight of 5.7 kg. Usually, pink salmon entering rivers for spawning are between 32 and 64 cm long, with a prevalence of individuals 38–59 cm long and weighing 1.4–2.3 kg.

Pink salmon have one surprising biological feature: all of their larvae are initially female. Only shortly before they emerge from the soil does a sex change occur in approximately half of the individuals, and they become males.

This species has the highest population density in the western part of the Pacific basin and accounts for the bulk of the Far Eastern salmon harvest.

Figure 2 – "Nuptial coloration" of Pacific salmon:

• 1 – chum salmon; 1a – spawning chum salmon;
• 2 – pink salmon; 2a – spawning pink salmon

Sockeye salmon (red salmon) slightly resembles another salmonid species – chum salmon – in its shape and size. They differ in the number of gill rakers on the first gill arch:

The weight of an adult sockeye salmon reaches 3 kg, with a body length of 80 cm. This species reaches sexual maturity quite late – in the 5th or 6th year of life.

A distinguishing feature of sockeye salmon compared to other salmon is that it prefers to spawn in lakes fed by springs. Interestingly, most fish return not only to the same lake where they were born but also to the exact same spawning ground, i.e., homing is very well developed in sockeye salmon. This fish begins entering rivers at the end of spring and continues to do so until the end of July or the beginning of August.

The so-called nuptial coloration of sockeye salmon is a bright red body color and a green head (which is why the second name for sockeye is "red"). After hatching, juvenile sockeye salmon live in fresh water for a long time (2–3 years), and only a few migrate to the sea.

Another fundamental difference between sockeye salmon and other salmonids is that its flesh is a deep red color, whereas the others have pale pink flesh.

This species is widespread along the American coast, and there is a great deal of sockeye in Alaska. In Asia, it is found on Hokkaido Island in the south and in the Anadyr River in the north. However, it is most numerous off the coasts of Kamchatka and Sakhalin.

There is also a self-sustaining lake-dwelling form of sockeye salmon. In some rivers, besides the anadromous form, there is a dwarf resident form of sockeye. Dwarf fish are found in lakes in Japan, North America, and Kamchatka. They do not migrate to the sea, reach sexual maturity in fresh water, and participate in spawning alongside the anadromous sockeye. This form is created from a portion of the offspring of anadromous fish under favorable feeding conditions in lakes.

Chinook salmon (king salmon) is the largest and most valuable of the Pacific salmon. The average size of a migrating chinook is 90 cm, but significantly larger specimens are encountered, reaching over 50 kg in weight. Americans call the chinook "king salmon," and the Japanese have bestowed upon it the title of "prince of salmon."

Chinook salmon differ from other salmon by a larger (greater than 15) number of branchiostegal rays. Its back, dorsal, and caudal fins are covered with small, round black spots. The nuptial coloration is less pronounced than that of chum, pink, or sockeye salmon; only the male becomes somewhat blackish with red spots during spawning.

Chinook salmon are distributed along the American coast of the Pacific Ocean, where they travel south as far as California. There are few on the Asian coast, although they individually enter many rivers from the north of Hokkaido Island in the south to the Anadyr in the north. In Russia, chinook salmon most often enter the rivers of Kamchatka, and they go to spawn earlier than other salmon, starting from mid-May. Being strong fish, they are not afraid of rapid currents (1–1.5 m/sec) and use their tails to dig spawning pits in coarse gravel and boulders.

The female lays up to 14 thousand or more eggs, which are as large as those of chum salmon. The hatched fry remain in the river for quite a long time, just like sockeye fry; some of them, especially males, mature there, reaching 75–175 mm in length. True resident forms are also found in American rivers.

Chinook salmon live in the sea for 4 to 7 years. Like sockeye, it is a rather cold-loving species and feeds primarily in the waters of the Bering Sea adjacent to the Komandorski and Aleutian Islands ridge. In the sea, Chinook salmon feed mainly on small fish. Its commercial significance for us is negligible due to its scarcity.

Coho salmon is a large fish, reaching a length of 90 cm and a mass of 14 kg. Coho differs from other salmon in the bright silvery color of its scales (hence the Japanese and American name "silver salmon" and our old name "white fish").

Along the Asian coast, it inhabits the area from the Anadyr River along the Kamchatka coast to the rivers of the northwestern part of the Sea of Okhotsk. It is occasionally found in eastern Sakhalin and Hokkaido. It is more common on the North American coast of the Pacific Ocean, where it lives from Alaska to California (Sacramento River). The dimensions of North American fish are larger than those found in the Asian part of the range. Asian representatives of the species reach a length of no more than 88 cm and a mass of no more than 6.8 kg.

It reaches sexual maturity at the 3rd–4th year of life. Premature maturation of a portion of males in fresh water has been noted. The run into rivers continues from the end of June to December. In Kamchatka, three forms of coho are distinguished by spawning timing:

• summer – spawns in September – October;
• autumn – spawns in November – December;
• winter – spawns in December – February.

Life cycle and specific features of reproduction of Pacific salmon

Coho salmon does not spawn in lake conditions, choosing other parts of water bodies for reproduction. During the spawning period, the fish acquire a characteristic dark crimson color, after which all spawned individuals die. The bulk of the juveniles go to sea in the second year of life, and only in rare cases does the downstream migration occur in the third or fourth year. Marine feeding lasts about a year and a half, with anadromous coho wintering directly in the ocean. In a number of lakes in the Magadan Region, Lake Sarannoye on Bering Island, and Lake Kotelnoye near Petropavlovsk-Kamchatsky, the fish form isolated resident forms that reach sexual maturity in the fourth year of life.

Juvenile coho in fresh water actively feed on various live feed:

• caddisflies and other insects;
• insect larvae;
• fish roe and fry.

Masu salmon externally resembles coho or small Chinook, but is distinguished by larger and more numerous black spots on the body and fins. During the spawning period, the fish acquires a bright breeding dress with transverse red and crimson stripes. This is the only species of Pacific salmon that lives exclusively along the Asian coast, entering the rivers of Kamchatka, Sakhalin, Hokkaido, and Honshu, and to the south along the mainland — up to Pusan and the Tumen River. The juveniles spend a year or more in fresh water, and the marine feeding period takes from 2 to 3.5 years depending on the age of the migrated juveniles. Masu salmon becomes sexually mature at the 3rd–4th year of life, while in the sea it feeds on crustaceans and fish fry, and enters rivers for its spawning run in June and July.

Juvenile masu salmon spend a year or more in rivers, where it is known by local names:

• "pestrushka";
• "kamenka";
• "podkamenka".

Biological potential of noble salmon: Atlantic salmon, brown trout, and trout

Representatives of the genus of true salmon differ from Pacific salmon by a shortened anal fin, containing from 7 to 10 branched rays. In young individuals, teeth are located on the back of the elongated vomer bone of the skull. The main difference for fish farming is that noble salmon do not die after the first spawning and are capable of reproducing repeatedly. They are widely distributed in the northern parts of the Atlantic and Pacific Oceans, as well as in the basins of the Baltic, Black, and Caspian Seas (with the exception of Siberia, where resident forms are absent).

Atlantic salmon is a most valuable object of commercial fishing and artificial reproduction. In the sea, it feeds intensively on small fish and crustaceans, but upon entering rivers for spawning, it completely stops feeding and loses significant weight. The spawning run occurs during the summer and autumn periods, when fish enter the rivers of the Barents, White, and Baltic Seas. Due to the sharp reduction in the natural population, the reproduction of Atlantic salmon is now supported mainly through hatchery breeding.

• Maximum length of Atlantic salmon — 1.5 m
• Maximum weight of Atlantic salmon — 40 kg
• Age of sexual maturity of Atlantic salmon — 5–6 years

The brown trout is easily distinguished from the Atlantic salmon by its coloration: its body is covered above and below the lateral line with numerous black spots, often shaped like the letter "x". This anadromous fish enters European rivers from the Iberian Peninsula to the Pechora, and is also found in the White, Baltic, Black, and Aral seas. In the sea, the brown trout actively gains weight, the parameters of which are shown in the table.

The Black Sea salmon is a special subspecies of brown trout with a high caudal peduncle and an increased number of gill rakers. This subspecies has become rare; it enters the rivers of the Black Sea coast for spawning in the spring (in the Sukhumi area — starting from February), and spawning itself takes place in the winter. Lake trout lives exclusively in cold bodies of water with clear water, migrating to spawn in fast, riffle-filled rivers. During the feeding period, its coloration is similar to that of the brown trout, but during the spawning season, females darken to a dark grey color, and males acquire orange stripes and bright fins.

Lake trout migrate from lakes to rivers for spawning and lay large (up to 5 mm) orange-colored eggs on gravel-bottomed riffles. Like brown trout and Atlantic salmon, they bury their eggs in mounds. The fry that hatch from the eggs migrate down into the lake; however, a significant portion of the juveniles mature in streams and brooks, even the smallest ones, turning into brook trout.

Brook trout are small fish (usually 25–35 cm long and 200–500 g in weight, extremely rarely up to 2 kg) with very bright coloration. The back of the brook trout is dark, the belly is white or golden-yellow, and small spots are scattered on the sides and fins – black, orange, and red, often surrounded by a light rim.

It has been noted that the coloration of brook trout depends on the color of the water and the soil of the water bodies. Their sizes are also determined by environmental conditions. The larger the stream in which the trout lives, and the more food objects it contains – such as small crustaceans and insect larvae – the larger sizes it can reach. Trout also feed on insects that have fallen into the water; larger ones can feed on small fish and frog tadpoles.

List of salmonid species:

• 1 – Atlantic salmon
• 2 – brown trout
• 3 – lake trout
• 4 – brook trout

They are characterized by the presence of a Weberian apparatus (an organ in some teleost fish that connects the swim bladder to the inner ear, making it possible for the ear to perceive changes in the volume of this bladder and its vibrations. The level of hearing development in fish is determined by the presence or absence of the Weberian apparatus. Fish possessing it perceive sounds with a frequency of up to 13 kHz, while fish without it perceive only up to 2.5 kHz), and the swim bladder is connected to the intestine. These are mainly freshwater fish.

The number of species in the order accounts for about 15% of all bony fish. Among cyprinids, there are herbivorous, carnivorous, and omnivorous species; many are of great commercial importance. They are specifically bred in many fish farms. In the fresh waters of Russia, there are about 110 species of cyprinids.

Cyprinids can be divided into two large groups:

• the first group unites fish that lack barbels and possess single-row and double-row pharyngeal teeth;
• the second group includes fish with three-row or two-row pharyngeal teeth, many species of which have barbels at the corners of the mouth.

Fish of the first group – dace, roach, minnows, asp, nase, bream, and others – are distributed mainly in Europe and Asia north of the mountain ranges of Central Asia and the Amur basin.

Fish of the second group – carp, crucian carp, barbel, gudgeon, schizothorax, Amur bream, yellowcheek, and others – are found mainly in Southeast Asia and Africa, with a few species in Europe. If we proceed from the widely accepted position that the center of origin of a particular group is considered to be the region where this group is represented by the greatest number of species, then for cyprinids, such a center is the southeastern part of Asia.

The family Cyprinidae is the richest in the number of species among freshwater and marine fish. It brings together predominantly freshwater and semi-anadromous fish that are quite diverse in their lifestyle, reproductive ecology, feeding habits, and other biological characteristics. Many cyprinids are very valuable objects for artificial fish farming.

Some are capable of tolerating fairly high water salinity, yet they reproduce only in fresh water. Cyprinids are predominantly thermophilic fish. They are characterized by the presence of a small number of pharyngeal teeth located on the lower pharyngeal bones.

There are no teeth on the jaws. The swim bladder is usually large, freely situated in the abdominal cavity, and divided into two parts. The oral opening is bordered above by the premaxillary bones, which are movably articulated with the maxillary bones, making the mouth generally more or less protractile. Barbels are present only in a few species, with no more than 2 pairs.

The digestive tract of cyprinids is not differentiated into segments and is a round tube, the length of which is highly variable and depends on the nature of the consumed food: in predators and benthophages, it is equal to or sometimes shorter than the body length, while in herbivorous species, it exceeds the body length by 2–4 times or more.

In most species, the body is covered with large, dense cycloid scales; less often the scales are small, and even more rarely, they are absent entirely. The fins of cyprinids consist of many articulated rays, of which the first (1–4) are unbranched, and all others are branched at the ends. The last unbranched ray, most often in the dorsal fin, may be thickened, sometimes appearing as a spine, and is serrated along the posterior edge. The pelvic fins are located far behind the pectoral fins, always on the belly. The caudal fin is homocercal and forked, as a rule, having 19 large rays, of which the outermost are unbranched.

Body coloration is uniform, predominantly limited to shades of bright silver, gold, and olive-brown. In the waters of European rivers, fish with silver coloration predominate. The fins usually have a grayish, yellowish, or reddish hue of varying intensity.

Coloration is closely linked to the behavior and habitat of the species. Thus, fish that stay in the water column have a silvery tint, while golden, olive-brown, and spotted coloration is characteristic of fish living in the bottom layers. A stripe along the body is found in many small fish that lead a schooling lifestyle. In most, the coloration changes with age. In older fish, it usually becomes brighter. In many species, during the breeding period, the coloration also becomes brighter, and sometimes the nuptial coloration changes completely.

Length varies from 6 cm to 1.7 m. They inhabit all continents except Antarctica. Representatives of the Cypriniformes order are distributed in the waters of Africa, North and South America, Europe, Asia, and Australia.

Biological characteristics and breed groups of carp

Carp is a freshwater omnivorous fish with a thick, moderately elongated body, large, densely set golden-brown scales, and developed lips with two pairs of short barbels on the upper lip. The fish is distinguished by high viability, a maximum age of up to 30–35 years, and a potential mass of more than 20 kg at a length of over 1 meter. The main mass gain occurs in the first quarter of life, as by 7–8 years, growth rates slow down significantly. In fish farming, there is a resident form that lives in one water body, and a semi-anadromous form that migrates for spawning from brackish parts of seas and lakes into rivers.

• Temperature of initial feeding — from 7 °C
• Spawning temperature — +18…+20 °C
• Development of fertilized eggs — 3–4 days
• Female fecundity — 700–800 thousand eggs

Carp reaches sexual maturity at the 3rd–5th year of life. Spawning takes place in spring in shallow, vegetated areas, predominantly in the morning hours after quiet and warm nights. The diet of underyearlings changes in stages: the juveniles start by feeding on zooplankton, move to zoobenthos (primarily chironomid larvae), and by autumn, begin to consume aquatic vegetation. Adult individuals feed continuously on mollusks, small crustaceans, worms, insect larvae, and plant feed.

In aquaculture, three main breeds of carp are used, differing in the structure of the scaly cover:

• Scaled (common) carp — the first domesticated variety of wild carp with the highest growth rates and viability. It is distinguished by lighter scales, a smaller head, a high back, and a branched dorsal fin. It is successfully grown both in shallow ponds with stagnant water and in flowing rivers or deep quarries from Siberia to warm regions.
• Mirror carp — a breed of German selection with large silver scales arranged in rows along the back and lateral line. The fish is more demanding of its diet (it prefers cereals and mollusks), but with sufficient feeding with grain feeds, it produces record weight gains.
• Leather carp — practically devoid of scales (individual scales may be found near the tail, gill cover, and dorsal fin). It is characterized by a reduced number of dorsal vertebrae, possible fin deformations, and a slower growth rate.

Biological characteristics of Prussian and crucian carp

Crucian carp (gold) is common in shallow lakes, oxbow lakes, bays, and stagnant water bodies with slow currents. The species possesses high resistance to adverse factors: it tolerates acidic water, withstands a drop in dissolved oxygen levels down to 0.5–0.6 cm³/l, and complete freezing of the water body to the bottom. In drained or dried-up water bodies, the crucian carp survives by burying itself in the silt for the winter.

• Critical oxygen minimum for crucian carp — 0.5–0.6 cm³/l
• Spawning temperature for crucian carp — 17–18 °C
• Fecundity of crucian carp — 140–207 thousand eggs
• Fecundity of Prussian carp — 300–400 thousand eggs

Crucian carp reaches sexual maturity at the age of 2–4 years and spawns at a water temperature of 17–18 °C, laying 140–207 thousand eggs. It feeds on benthos, detritus, and parts of aquatic plants. Maximum growth indicators are 45 cm in length and 500–600 g in mass, although individual specimens reach 3 kg.

Prussian carp has an angular body shape and silvery sides; sexual maturity occurs at 3–4 years of age with the laying of 300–400 thousand eggs on vegetation. There are two biological forms of this species in water bodies, externally indistinguishable from one another:

• Bisexual form — consists of females and males.
• Unisexual form — represented exclusively by females. The separation of forms is carried out genetically by the number of chromosomes.

This number of chromosomes corresponds to a triple set of one germ cell of a diploid Prussian carp, for which reason the unisexual form is also called the triploid form.