Fish will be painful. The early view was that fish did not have a mammal-like cerebral cortex, so they did not feel pain. However, experiments have found that fish injected with acetic acid are slow to avoid falling unfamiliar objects, and after morphine injection, they will return to normal levels. When fish are dissected, they have nerve cells called nociceptors that can detect potential damage, such as high temperature, pressure and corrosive chemicals.
1. Vision: The eye of a fish is a transparent sphere. It has no elasticity and cannot adjust its curvature. It can only adjust the distance between the lens and the retina through the mirror-like bulge behind the lens. Therefore, it can only see things that are near clearly. If it is far away, it cannot see clearly. But this animal has a very wide field of vision, up to 180 degrees.
2. Hearing: Fish have good hearing. Although these animals do not have external ears, they have special sound receivers that transmit sound waves to the inner ear. The tubes of the inner ear contain cilia, which transmit sound through complex mechanisms to the brain. It is worth mentioning that the otoliths in the auditory system can be used to judge their age.
3. Smell: Fish have olfactory sacs, which allow them to smell food and distinguish between different fish in case they are attacked by enemies. In addition, it can also identify water quality through olfaction, as well as return movement. Unlike many land animals, their sense of smell is not volatile odor, but amino acids in water.
4. Taste: There are taste buds on the lips, mouth and tentacles of fish, which can make it perceive the taste of things. Usually, when eating, it will repeatedly swallow and vomit to judge whether the food is edible. Usually with some training, they can distinguish between sweet, sour and bitter tastes.
