EXTERNAL CHARACTERISTICS AND BODY CONSTRUCTION
In terms of the variety of shapes, the fish are not inferior to other groups of animals. There are twelve main types (Abel, 1912), each of which includes a great variety of forms peculiar to each species. The well-known spindle shape characterizes species that swim perfectly among the spatial areas of open water. Most often in the bottom zone, fish that are strongly flattened or - like eels - are elongated, a slippery body, capable of digging into silt. Among the coral reefs, and also in overgrown coastal areas, forms with the trunk tightened at the sides dominate, adapted to slipping between obstacles.
Pike (Lynx. 5) it represents a relatively less widespread type. The name "arrow-shaped" reflects well its characteristic features. The torso is elongated and slightly tight at the sides and ends with the largest narrowing of the body in front of the caudal fin.. Head, flattened in front, brings to mind the blade of an arrow. The lines of the back and belly run almost parallel. Only in individuals, whose stomach is filled with freshly swallowed food, and in mature spawns before spawning, the belly is drawn with a more pronounced convexity. Dorsal fin (VI — X hard rays, 13—16 soft), far back above the anal fin (III — VIII, 11—15/16/), strengthens the tail part of the body. Right behind the head, already on the abdominal steep, at the very edge of the gill covers, the pectoral fins are embedded (I(II), 12—16), while ventral (I — II, 7—11(12) ) are even lower, approximately halfway between the thoracic and the anus.
The similarity to the arrow is manifested in the pike not only in structure, but also in action. Long, not very flexible body does not allow you to make sudden turns, neither in vertical, nor in the horizontal plane. When forced to change direction, it usually flows in a wide arc. Thus, he almost always gives up the pursuit of a more agile victim. A successful hunt usually depends on one throw from the stand forward, on which he is motionlessly waiting. The strength needed not only to achieve the right speed, but most of all to overcome - within a fraction of a second - the inertia of your own weight, deliver perfectly developed (the muscles of the torso, while the entire caudal part of the body, with the lobes of the three odd fins spread wide, performs the function of a driving device. About energy, how the tail hits the water, mighty turmoil is evidenced, that can be watched, when a pike attacks a prey from a position just below the surface.
The participation of paired fins - thoracic and pelvic - in regulating the speed of swimming is negligible. However, they play a very important role during long periods of waiting for prey. Pike belongs to the fish, whose center of gravity is located above the swim bladder - an organ that helps to keep the body static in the aquatic environment. To avoid the constant threat of turning your back down, must make continuous corrective movements with its paired fins, allowing you to keep your balance.
The edge of the gill covers delimits the posterior border of the head. The distance between the beginning of the mouth and the rearmost point is approximately 3.5 to 4 times the total length of the body.. The foam line through the eye divides the head into two nearly equally long parts. The rear part, not much lower than the height of the torso, it is composed of the bones that cover the brain and the gills. The gill membrane, stretched at the bottom on strong bone rays, facilitates the suction of water while breathing. Strongly flattened front part, cutting through the water helps to overcome the resistance it creates. Due to this flattening, a pike's mouth is sometimes compared with a crocodile's or a duck's beak. Its size is worthy of a predator. The slit extends well beyond the front rim of the eye, that is, roughly half needle. Lower jaw, made of massive dental bones, it moves slightly forward in front of the upper jaw. Janec-Susłowska (1957), giving a detailed description of pike osteology, draws attention to the specific structure of the mandibular joint, which allows for an extremely wide opening of the jaws. The gaping maw can accommodate - and sometimes does indeed do - a prey not much smaller than an attacker.
Inside the mouth, as well as the throat, it is armed with teeth, whose number is estimated at over 700 pieces. They are scattered on the bones that make up the mouth of the mouth (blade and palatine bones), surrounding the rims of the mouth (dental and premaxillary bones), on the tongue, in the throat, on the gill arches and bone elements, by which these arches are connected. Individual groups of teeth differ in size, shape, way of seating and purpose. Biggest, straight and pointed - located on the lower jaw, especially in the posterior and middle parts of both teeth, with which they are strongly associated. Their task is to catch and hold the victim, which henceforth has little chance of escaping. Minor, sharp and oblique teeth on the palate, curved towards the esophagus (Lynx. 6) prevent her from escaping.
Lynx. 6. Bones of the pike's jaw vault: 1 - pre-maxilla bone, 2 - jaw bone, 3 - palatine bone, 4 - ploughshare (according to Norman).
Loose connection with bone, with the help of connective tissue, makes, that they easily bend under pressure towards the inside of the mouth, however, resisting pressure in the opposite direction. As a result, the swallowed fish can only travel deeper into the digestive tract. It is helped by small teeth - embedded in the epithelium of the throat and on the inside of the gill arches, where they are grouped in groups within separate tooth fields.