People taste with their tongues, while fish taste with their beards, that is, fish whiskers. Catfish use whiskers to feel the taste. Taste cells have a protein that accepts various flavors, which is called receptor protein. Generally speaking, the reaction process of taste is that when one of the substances such as acid, sweet, bitter and spicy comes into contact with the taste cells, it is stimulated by the taste in the container to generate current and transmit the taste information to the brain. Through the analysis and synthesis of the central nervous system of the brain, we can distinguish the types and strengths of taste. According to this principle, scientists isolated a taste receptor protein from catfish whiskers which are sensitive to taste, and put it in a special device to maintain its biological activity, thus making a taste sensor. When all kinds of smells stimulate the taste sensor made of catfish whiskers, the taste sensor immediately generates bioelectric current, which is connected with the computer, and the computer can immediately judge the taste type.

The principle is as above. Simply put, a fish's beard is almost the same as a human tongue.

There are two small holes outside the fish's mouth, so the injected water can't get in. This small hole is the fish's nose, indicating that the fish's "nostrils" have no obvious connection with the mouth, cheeks and stomach.

Fish have no eardrums. In fact, most fish's ears are not connected with the outside world, but are protected in bags on both sides of their heads. The capsule is located directly behind the eyes.

Sound travels much easier in water than in air. Like other animals, fish has a lot of water in its body, and sound can directly pass through the fish's body to reach its ears.

Many kinds of fish can collect sounds in another way. Their ears are connected to the swim bladder, and the sound in the water makes the swim bladder wall vibrate, just like the eardrum vibrates through the sound of air. Then, this vibration is usually transmitted to the ear along a series of small bones connected to the swim bladder. Some fish do not transmit vibration through small bones, but through tubular organs extending from the swim bladder.

Sound is very important to fish. Many fish can make powerful calls to each other, which can be heard from several kilometers away. Some fish make sounds by grinding their teeth, and some fish make sounds by rubbing their fins on their bodies. Many fish use the swim bladder to distinguish sounds. Special percussion muscles vibrate the swim bladder to make a sound.

Fish have two sets of auditory mechanisms. There are a series of small organs on the surface of fish, which can hear low-frequency sounds (below 200 Hz) and feel the water flow. Usually, these fine sensory cells are wrapped in small tubes under the skin of fish, and these small tubes form a lateral line-lateral line. The lateral line can feel the flow and vibration of water at close range, and can also judge the direction and distance of disturbance. Fish has a relatively perfect inner ear. As a receiver of sound, sound can be transmitted from the skull through the bone or from the swim bladder to the inner ear. Some fish have small bones in their bodies, which connect the swim bladder with the fluid in the inner ear. The swim bladder is particularly important in the process of fish listening to sound, because the whole fish is almost transparent to sound in water, and only the swim bladder is the reflector of sound. After experiments, the average fish can hear the sound below 500 ~ 600 Hz. Beyond this frequency range, the fish's hearing is very poor.