European perch (Perca fluviatilis) is a freshwater fish of the family Percidae. Length up to 50 cm, weight up to 1.5 kg, sometimes more. Scales small, ctenoid, on the jaws, scutellum and palatine bones multi-row teeth. Spike on the gill cover. There is a black spot on the first dorsal fin. Inhabits fresh waters of Europe and Asia. Occurs in brackish waters. In large lakes is represented by two forms: coastal, slowly growing and feeding on small invertebrates, detritus and large, fast-growing, feeding on fish and occupying deep areas of the reservoir. Sexual maturity is reached in the third to fourth year of life. Spawning in May-June at water temperatures of 6-8°C. Eggs hang in long mucous ribbons on last year's vegetation, snags, bushes, tree roots. Fecundity reaches 300 thousand eggs and more.

     European perch is widely distributed in fresh water bodies of Europe and North Asia (up to the Kolyma basin in the east and water bodies of northern Iran and Afghanistan in the south), and has been introduced to Africa, Australia and New Zealand. Earlier it was believed that the range of the European perch includes the water bodies of North America, which according to modern ideas is inhabited by an independent species Perca flavescens. European perch belongs to predatory fish. In the diet of adult perch a significant proportion of other freshwater fish. European perch prefers to stick to flat water bodies, it can be found in rivers, lakes, ponds, reservoirs and even in brackish parts of the sea. Spawning in fish occurs in early spring. Female perch lays eggs in the form of a long (up to 1 m) gelatinous ribbon. European perch is a popular object of recreational fishing, in some reservoirs has an important commercial value. European perch is characterized by high intraspecific variability of morphological features depending on ecological conditions. Rays in the first dorsal fin and skeletal structure are most often used as morphometric indicators. The system of non-metric traits of the perch skeleton includes 61 traits. Perch forms are also described, with the number and length of gill stamens, the shape of the body and its separate parts, and the number of scales in the lateral line as differences. In addition, the character of appearance of pigmented zones on the fish body is used to analyze morphometric differences.

     As a rule, the length of European perch does not exceed 50 cm, and the mass - 2 kg, although individuals can reach larger sizes. The maximum size in each water body varies considerably. The average size of an adult perch is 15-20 cm. The maximum recorded life expectancy of European perch is 23 years. This age was recorded for a perch caught in Lake Khubsugul (Mongolia), 44.7 cm long and weighing more than 2 kg. The life expectancy of perch, as well as their size, also depends on the specific water body. The European perch has a laterally compressed body that is covered with dense fine ctenoid scales. The body has a greenish-yellow coloration with black transverse stripes on the sides, which can be from 5 to 9; the belly is white. European perch has two dorsal fins located very close to each other, with the first dorsal fin higher and longer than the second. The first dorsal fin begins above the base of the pectoral fins or slightly in front of them. At the end of the first dorsal fin is a black spot, which is a distinctive mark of the species. The pectoral fins are slightly shorter than the pelvic fins. The first dorsal fin is gray, the second dorsal fin - greenish-yellow, anal and pectoral fins - yellow, sometimes red, pelvic fins - light with a bright red border. Caudal fin dark color at the base and red on the sides and at the end. In the first dorsal fin in European perch from 12 to 16 barbed rays, in the second - 1-4 hard and 12-17 soft rays, in the anal fin 2-3 barbed and 7-11 soft rays. The European perch has a blunt snout and a small hump behind the head. The upper jaw usually ends vertically in the middle of the eye. The iris is yellow in color. The lid bone is covered with scales at the top, there is a spike (sometimes double) on it, and the forewing is serrated. There are bristle-like teeth arranged in rows on the jaws, scutellum and palatine bones; there are no fangs. The gill membranes are not fused together. There are 53 to 77 scales in the lateral line of the European perch. Above the lateral line there are 7-10 rows of scales, below - from 12 to 21. Cheeks are completely covered with scales, on the caudal fin there are no scales. Fry have delicate scales, but with age they become extremely strong and hard. The number of vertebrae is 38-44. Gill stamens 16-29. At the beginning of the intestine in European perch are placed three blind outgrowths (pyloric appendages), the intestine is quite short, its length is approximately equal to the length of the body. The liver is divided into two parts. The gallbladder is quite large, the spleen has an oblong shape. Coloration of European perch can vary depending on the body of water, for example, in peat lakes it acquires a darker coloration. Outwardly, European perch males do not differ much from females, except for the spawning period, when the abdomen of European perch females is filled with eggs.

     The European perch inhabits mainly flat water bodies: rivers, lakes, ponds and reservoirs, but it is also found in high mountain lakes (at an altitude of 1000 m). Classification of European rivers by typical ichthyofauna classifies European perch to the so-called barbel zone (barb zone) and bream zone (bream zone). In some water bodies European perch is the only fish species. European perch can also live in brackish water, so it is found in coastal areas of seas, in particular, in the Baltic Sea (Gulf of Bothnia, Gulf of Finland, Curonian Bay), White Sea (Kanda-guba) and Caspian Sea, in brackish lakes of the Barabinsk lowland. Earlier it was considered that for normal development of eggs water salinity of 5-7 ‰ is acceptable, but recent studies have shown that the maximum value of salinity is 2-2.5 ‰. The presence of fry in saltier water is due to the fact that juvenile fish migrate to brackish water due to more favorable conditions for feeding. European perch is a widespread fish and is found in most water bodies of its range. European perch mainly adheres to the coastal thicket zone of a water body, as well as artificial or natural obstacles, likes areas with an abundance of aquatic vegetation. European perch tries to avoid areas of water body with low temperature and fast current, it is absent in the upper reaches of rivers with cold key water. Favorable pH value - 7.0-7.5, water hardness in German degrees (dH) - 8-12, water temperature - 10-22 ° C. Water temperatures above 30-31 °C are unfavorable for European perch reproduction. Within a large body of water perch can form isolated populations: such cases are described for Lake Windermere (England), Lake Constance (in each of these lakes all European perch are divided into two large populations), Bratsk Reservoir.

     In summer, small European perch prefer to stay in overgrown aquatic vegetation in backwaters and bays. During this period perch form small flocks (about 10 fish), only in young individuals flocks can reach the number of about 100 pieces. Perch likes to be near the piles of ruined mill dams, large stones and snags. Due to their greenish patronizing coloration, perch successfully hunt small fish by ambushing them among aquatic plants. Large perch live in deeper places: pools, pits, often marshy, from where they come out in the morning and evening to hunt. The average speed of movement is 0.66 m/s. Young perch are characterized by gregarious hunting, only the largest individuals begin to hunt alone. European perch uses a very aggressive hunting pattern, it actively pursues the victim, sometimes jumping out after it even on the surface of the water. Sometimes so keen on pursuit that in pursuit can jump out on the shoal and even on the shore. During the attack, his dorsal fin flares. Larger perch may wait for their prey in ambush, like pike or pikeperch. The European perch is a crepuscular diurnal predator that hunts during daylight hours with peak activity at the day-night boundary. At night, activity declines sharply. The main factor affecting perch activity and growth is water temperature. Also perch activity is influenced by the length of daylight hours, the structure of the food ration, and the oxygen content of the water. In perch, there is a significant change in the intensity of metabolic processes both with increasing and decreasing oxygen content in the water. In deep lakes, even large perch try to stay at shallower depths in summer than in winter. In summer perch prefer places where the decrease in oxygen levels in the water is less sensitive. In summer perch may make short feeding migrations. At the onset of winter, perch return to rivers with more favorable conditions. In the fall perch gather in large flocks (up to a thousand or more individuals in large reservoirs), which migrate to deeper and more open areas. During the cold season perch stay in the bottom part of the water body. The depth at which the fish settle in winter can be quite significant. Mortality among juvenile river perch during winter compared to yellow perch is less well understood, but is known to be higher than that of European perch. Winter perch are also active during daylight hours with increased activity at dusk and no activity at night. European perch use a short shot as a danger signal during their hunt for fry.

     European perch spawn once a year at approximately the same time. The main factor determining the timing of spawning is water temperature. In the Northern Hemisphere, spawning occurs in early spring immediately after the ice drift at a water temperature of 7-8 ° C, in the southern regions in February - April, in the northern regions - in May - June. In Australia spawning occurs in August - October, in New Zealand in September - November. Large individuals begin spawning later than small ones. Before spawning perch can migrate, perch inhabiting desalinated areas of the seas go to spawn in rivers. In reservoirs and lakes, the fish migrate to the littoral (shallow coastal) zone. In some lakes, a part of the population may go to spawn in rivers and another part may stay to spawn in the lake. Males arrive at the spawning site earlier than females. Fecundity, depending on the size of females, is 12-300 thousand eggs. The number of eggs increases with increasing length of fish, also more eggs have perch females living in warmer climates. External changes in European perch during spawning, unlike many other fish (bersh, pink salmon, salmon), are not observed. Spawning period in perch is not distinguished by duration and on average lasts 4-5 days (up to a maximum of 9). The female during spawning is accompanied by several males, the number of which can reach up to 25. Spawning is done once, and during spawning female perch lays eggs in the form of long (up to 1 m) mesh ribbons of gelatinous substance on the past year's vegetation, submerged bushes and snags, fishing nets, and accompanying males fertilize it. In exceptional cases, in the absence of such objects, the female may take eggs to the sandy or muddy bottom at a depth of 0.2 to 1.5 meters. The size of the ribbon depends on the size of the female. European perch eggs are highly watered (water content - 56%), with a diameter of 2-2.5 mm (sometimes 1 mm). At the end of spawning, unlike other species of perch fish, the female never has any eggs left. Laying eggs on vegetation and other objects, as well as unattractiveness of eggs by their taste for other species of fish allow for high survival rate. Unlike pikeperch, the male perch does not guard the eggs.

     110 hours after fertilization at a water temperature of 15-17 °C, the embryo has distinguishable eyes, tail section and body segmentation. 180 hours after fertilization, the embryo responds to changes in light intensity and shaking of the egg. Egg development usually lasts two weeks (one to three weeks in other cases), after which time larvae about 6 mm long hatch. A sharp increase in water temperature is fatal for perch, as the larvae hatch insufficiently viable. At hatching, the larvae are 4.5-6 mm long. The yolk begins to resorb at a body length of 6-6.5 mm. In the early stages of development, larvae are practically indistinguishable from larvae of other fish of the family - common pikeperch, common ruff, so it is relatively easy to confuse them. Distinguishing features of larvae include increased pigmentation, vertical position of pectoral fins (in perch larvae they immediately take a vertical direction, while in ruff and pikeperch larvae the first days they have a horizontal position), as well as different character of movement in the water. In addition, larvae hatch somewhat earlier than pikeperch larvae and grow faster than ruff larvae, so they tend to be larger. Initially, the larvae swim in an inclined position. After hatching, the larvae feed on phytoplankton (only in the first few days), rotifers and crustacean larvae. After a few days, copepods and daphnia appear in their diet. Remains of the yolk sac and fat drop disappear about 14 days after hatching. Favorable water temperature for egg development and larval survival is at least 12-20 °C. Soon after emergence, larvae migrate to a deeper, pelagic zone, where they feed mainly on zooplankton. In this case, the larvae adhere mainly to the upper layers of water. After 3-4 weeks, almost all of them return back to the coastal zone, which is explained by more favorable conditions for the development of young fish (water temperature, food base), as well as the fact that as they grow, they become more and more attractive to pelagic predators. At a length of 7 mm begins to form a caudal fin, swim bladder filled with air, the lower jaw becomes longer than the upper. At a length of 8-9 mm begin to lay the rays of the caudal fin, there are barely visible pelvic fins, formed anal and second dorsal fins, teeth are formed. At a body length of 10-11 mm become visible pelvic fins, rays are formed in the second dorsal and anal fins, the first dorsal fin appears. At a length of 12-15 mm finally formed rays in all fins, disappear remnants of the fin fold. Scales begin to form at a late stage of larval development at a length of 15-17 mm. The laying of cartilaginous and bony skeletal elements begins from the moment of larval hatching. The duration of perch skeletal development is about 53 days (at water temperatures between 9 and 20 °C). In general, the development of the perch skeleton corresponds to that of other perch fishes. At a body length of 15-20 mm, the larva becomes a juvenile; characteristic dark stripes begin to appear only when the juvenile reaches a length of 20-25 mm.

     Initially, perch fry feed on zooplankton, as they grow they switch to feeding on benthos organisms, and when they mature, they begin to hunt young fish (mainly carp and perch). As a rule, fish begin to feed on fry in the second year of life, in some reservoirs - in the first, after reaching 4 cm in length. Most often the transition to fish consumption coincides with the onset of sexual maturation. In some reservoirs, the transition to a predatory lifestyle occurs much later. With age perch switches to hunting for larger and more mobile objects. According to the way of feeding European perch is attributed to facultative predators, that is, it is a predatory fish, but in large quantities also consumes other animal food. Sometimes perch of separate populations (e.g., lake perch) are classified as typical predators. This is due to the fact that depending on the water body, the food of perch of the same age can vary significantly due to the different composition of the food base. The diet of perch differs not only in different water bodies, but can also vary significantly throughout the year in the same water body due to changes in the availability of prey organisms. The fish can switch from one food to another quite easily. European perch mainly consume narrow-bodied fish. The most frequent victims of adult perch are fish of little value from the point of view of commercial fishing: sticklebacks, minnows, juvenile roach. Secondary objects of food among fish are bleak, ruffs, bullheads, bullheads, young pikeperch, bersh, crucian carp and gouster. In New Zealand rivers, the native small fish Gobiomorphus cotidianus has become the primary food item. The perch is characterized by cannibalism: adults often eat young. Cannibalism is most common in the fall, when juveniles leave the coastal zone, moving to deeper waters for the winter. Young are rarely found in the stomachs of adult perch during the summer. Cannibalism is most characteristic of water bodies inhabited exclusively by perch. Insect larvae, frogs and crayfish are also frequent food targets of adult perch. Depending on the season, the frequency of occurrence of benthos and certain fish species in the perch diet varies. No significant differences in the diet structure of females and males within one water body were observed. A higher level of fat accumulation in the body cavity in the autumn period is characteristic for perch of northern water bodies. Under prolonged starvation perch lose weight faster and die earlier than other freshwater predators (pike and catfish).

     The growth rate and timing of sexual maturation of European perch in different water bodies can vary greatly. The growth rate of perch is primarily influenced by climatic peculiarities of the water body and provision of available fish food, which allows them to switch to a predatory lifestyle earlier. In general, the growth rate of perch is low. In small reservoirs, as well as in conditions of a scarce food base perch for the first year grows up to 5 cm, and by 6 years - up to 20 cm. In large lakes, reservoirs, deltas of large rivers perch can reach 12 cm in length by the first year, and a five-year-old can be 35 cm long. In the Southern Hemisphere (Australia and New Zealand) perch grow faster than in most bodies of water in the Northern Hemisphere. The growth rate of perch may accelerate when they adopt a predatory lifestyle. The growth rate of perch depends on environmental conditions and can vary significantly from year to year in the same body of water.