The northern pike (Esox lucius) is a freshwater fish of the pike family. It has an elongated, arrow-shaped body and a large, flat head with a strongly elongated and flattened snout. The mouth has numerous sharp teeth. The dorsal fin is carried well back, above the anal fin. Occurs in the fresh waters of North America, Europe and Asia. Tolerates the acidic reaction of water well, can live comfortably in waters with a pH of 4.75. When oxygen levels drop to 3.0-2.0 mg/l, respiration is impaired and pike often die in frozen waters.

Length up to 1.5 metres, weight up to 35 kilograms (usually up to 1 metre and 8 kilograms). The body is torpedo-shaped, the head is large and the mouth wide. The colouration varies according to the environment: it can be grey-greenish, grey-yellowish, grey-brown, darker on the back, with large brown or olive spots on the sides, forming transverse stripes, depending on the type and degree of vegetation. Unpaired fins are yellowish-grey, brown with dark spots; paired fins are orange. It feeds mainly on fish. Silver pike can be found in some lakes. Males and females can be distinguished by the shape of the urogenital opening, which in males has the shape of a narrow elongated slit, coloured in the colour of the womb, and in females - an oval depression surrounded by a roller of pink colour. The body of the pike is elongated and arrow-shaped. The head is strongly elongated, the lower jaw protrudes forward. The teeth on the lower jaw vary in size and are used to catch the prey. The teeth on the other bones of the mouth are smaller, with sharp ends directed into the throat and can sink into the mucous membrane. If the prey tries to escape, the pharyngeal teeth lift up and hold the prey.

Pike are characterised by a change in the teeth on the lower jaw: the inner surface of the jaw is covered with soft tissue, under which are rows of 2-4 replacement teeth, which adjoin each active tooth from behind, forming a single group (tooth family) with it. When a working tooth is lost, a neighbouring replacement tooth from the same family takes its place. At first it is soft and unstable, but then the base becomes firmly attached to the jawbone and becomes stronger. Teeth in pike do not change at the same time. At the same time, some groups of teeth end at the edge of the jaw with an old tooth that is already resorbed, others with a strong working tooth and others with a still mobile young tooth. In some reservoirs, the change of teeth in pike increases during certain seasons, and then pike in these reservoirs stop taking large prey because it can escape from the jaws of the predator. It is difficult to catch pike at this time as they are unable to grab the bait.

In natural reservoirs, female pike begin to reproduce in their fourth or, more rarely, third year of life, and males in their fifth. Pike spawn at temperatures of 3-6°C, immediately after the ice melts, near the shore at a depth of 0.5-1 metres. During spawning the fish move into shallow water and splash noisily. Usually the smallest fish spawn first and the largest last. At this time, pike swim in groups: 2-4 males near a female, up to 8 males near large females. The female swims in front and the males swim behind her, about half a body behind. They either cling to the sides of the female or try to stay just above her back. The dorsal fins and upper part of the back are always visible above the water at this time. During spawning pike rub against bushes, roots, reed and cattail stalks and other objects. Fish do not stay in one place for long, moving around the spawning area and spawning eggs all the time. At the end of spawning, all individuals in the spawning group rush in different directions, causing a loud splash; females often jump out of the water into the air. A female pike can lay between 17.5 and 215,000 eggs, depending on her size. Eggs are large, about 3 mm in diameter, slightly sticky: they can stick to vegetation but fall off easily when shaken. After 2-3 days the stickiness disappears, most eggs roll off the plants and their further development takes place on the bottom. Normal development of pike eggs on the bottom in non-flowing water is possible only because in spring at low temperatures the water is relatively saturated with oxygen, and as the water warms up the oxygen concentration in it quickly drops. The earlier pike start spawning, the fewer eggs will die. If the water drops rapidly after pike spawning, this results in mass mortality of eggs, a phenomenon often observed in reservoirs where water levels are variable.

In a pond, the pike hides in the thickets of aquatic vegetation. Usually it will lie still and, after lurking, suddenly pounce on its prey. Caught prey is almost always swallowed from the head - if the pike has grabbed it across the body, it will quickly turn the prey's head into its throat before swallowing. In addition to the fangs with which the predator grabs and kills its prey, the pike has brush teeth on the palate, tongue and partly on the cheeks, which can bend and take up a horizontal position, pointing towards the throat. These sharp teeth are necessary for the pike not only to hold the prey but also to facilitate swallowing. When the prey tries to escape from the mouth, the pike's teeth, with their sharp ends, rest against the prey, preventing it from slipping out and pushing it further down the throat. When attacking, the pike orientates itself by means of vision and the lateral line, whose organs are developed not only on the midline of the body, but also on the head (mainly on the front of the lower jaw). The basis of the pike's diet is made up of representatives of various fish species, including: roach, perch, ruff, minnow, gouster, gudgeon, gudgeon, char, minnow, bullhead, etc. As described above, the pike is not squeamish and is a member of its own species. In spring and early summer this predator eagerly eats frogs and crayfish. There have been known cases of pike grabbing ducklings and dragging them underwater, as well as their prey of small mammals such as moles, mice, rats and squirrels caught in the water. Large pike can even attack adult ducks, especially during the moulting season when these birds are out of the water and in the air. Pike victims are often fish that are 50% and sometimes 65% of the length and mass of the predator itself. The diet of medium-sized pike - about half a metre in length - is dominated by numerous and low-value fish, so pike are a necessary component of rational lake fishing; their absence from lakes leads to a sharp increase in the numbers of small rudd and perch.

A special species, Esox reicherti, lives in the Far East, Sakhalin and the Amur basin. It is a lake and river fish. It reaches a length of 135-150 cm and a weight of up to 35 kg. Matures individually at the age of 3 years, in schools a year later. Spawning is annual, beginning in early spring at water temperatures of 4-6°C. It hatches large eggs (2.5-3.0 mm) in one go on last year's vegetation at a depth of 0.5-1 metre. The fecundity varies from 14.5 to 215 thousand of the largest up to 1 million eggs. Predator. Besides fish, it eats worms, tadpoles, frogs, small water birds, small mammals (shrews, water rats, squirrels). Commercial fish. It is bred and cultivated in pond and lake farms to control inferior fish (perch, capelin, roach, ruff).