ORGANS OF THE SENSES
Unlike demersal fish, which have achieved high specialization of the senses perceiving chemical stimuli, predators hunting mainly during the day are typical visuals. So the eyes of the pike - set at the top of the head near the site, where the line marking the flattening of the mouth comes from - they are an organ that works with high precision. A spherical lens next to the cornea (Lynx. 9) provides a wide field of view.
Lynx. 9. Cross-section through the eye of a pike: 1 - iris, 2 - lens, 3 - the cornea, 4 - choroid, 5 - optic nerve (from Hegemann).
Characteristic grooved indentations run forward from each eye. Lines drawn from them, [intersecting in the extension in front of the head, create an angle that marks the boundary, beyond which both side fields of view overlap. So a binocular vision arises there, giving a three-dimensional image important in assessing the distance (Layers inside, 1962). Pike eyesight is primarily adapted to the perception of objects situated in front, as evidenced by three times greater image brightness in the front part of the field of view than in the back (Sroczyński). Focusing on distant objects is accomplished by contraction of the muscle pulling the lens backwards. The ability to recognize details with the help of eyesight is surprising in pikes - after all, they often jump on a piece of shiny sheet metal - it is even surprising.. In the experiments carried out by Gimmy (1953) juveniles, "Trained" by the method of conditioned reflex, were able to distinguish popular in aquaristics "peacocks" - of the same sex and similar shape - only by slight differences in color.
The sense, which interacts with sight in perceiving food, there is an organ of the lateral line. It is composed of the sensory bodies arranged along the sides of the torso, it is designed to perceive any - often very slight - changes in pressure arising around the fish. If it is in motion, water pressure changes occur in the vicinity of passing obstacles and prevent collisions. If it is standing still, such changes are caused by objects moving within the sensitivity range of the organ. In pike, the system of lateral receptors is perfectly developed and covers not only the area marked with the name. Sensory bodies, scattered over almost the entire surface of the torso and head, they form individual, uncovered groupings or are arranged inside the channels filled with mucus substance (Lynx. 10).
Lynx. 10. The system of the lateral organ of a young pike (by Disler).
They maintain contact with the environment through holes piercing the skin or - on the lateral line - the scale, and signaling nerves also pass through tubules that pierce some bones in the head. The lateral line organ also has a warning function. During the larval period, when young pikes can only see objects that move no further than 1-1.5 cm from the eyes, each wave of the water outside the field of view triggers an escape reflex (Disler, 1967). Later, the signals noted by the sideline are already monitored by sight and take on the role of informing about the approaching catch. They also play a significant role in locating its location accurately. According to Wunder (1936), the blinded pike was able to catch the fish that was dropped into the aquarium, provided, that his lateral organ was not damaged. Otherwise, he was completely unresponsive to her movements.
The other senses are of less importance in the nutritional process. It's hard to guess, so that the pike takes into account the taste of the food, since he swallows objects completely devoid of it, and also - as Hegemann reports (1964) - fish supersaturated with it to an unnatural degree (for example quinine). The sense of touch in the form of receptors scattered on the lips and tongue certainly plays a role - especially when rotating the captured victim.. The simplicity of its structure seems to prove the low usefulness of the olfactory organ (Lynx. 11).
Lynx. 11. Pike olfactory organ (A - due to Frischa, B - due to Teichmanna.)
It is a depression lined with folded epithelium, in which the olfactory cells are distributed. Water, directed into the cavity through a partition separating them from the top, it flows in through the front hole and the rear hole out, however, there is no device, which would regulate the water change over periods, when the fish is stationary.