How do fish find food? Not just visually.

Fish have two big eyes that can never be closed. This is because compared with our eyes, fish have no eyelids, so they have to keep their eyes open all their lives, even when they sleep.

Fisheye is one of its important organs, but compared with us, fish can only be considered nearsighted at most. This is because fish's eye structure is relatively simple, and it is difficult for them to adjust the distance between the lens and retina, which leads them to see nearby objects clearly. Once it's far away, it's blurred.

However, most of the fish eyes are distributed on both sides of the fish head, which makes them see the angle of view close to 180 with one eye, and there are only a few visual dead angles before and after. When the light is good and the water is clear, their eyesight is good. With these eyes, they can find bugs and other food in the water.

Of course, most fish's eyes are only auxiliary organs for feeding, because on the one hand, because fish grow in different environments, such as some deep-sea fish, their eyes can only be regarded as decoration, and fish living in turbid water have little effect, and fish also need to feed at night, so they must have more important senses. Let's look at the important senses of fish foraging.

An Ankang fish whose eyes are degraded and "fish" by glowing.

The first is listening.

We often say hertz to summarize the hearing ability of animals. For example, human ears can hear the sound frequency of 20hz-20000Hz, while dogs can hear the sound frequency of 15-50000Hz, which means that dogs can hear infrasound (below 20 Hz) and ultrasonic waves (above 20000Hz) that we can't hear.

But judging from the frequency of sound waves, fish are actually in the world of infrasound waves, and the frequency of sound waves that most fish can hear is between 2-3000HZ.

In other words, it is very important that fish can hear infrasound that even dogs can't hear. Most fish rely on otoliths to capture sound. The main component of otoliths is calcium carbonate, which is denser than water, and the density of water is much higher than that of air, which leads to a small sound propagation speed and loss rate. Research shows that the speed of sound propagation in water is 4.8 times that in air.

Speaking of which, it seems to have little to do with fish foraging. In fact, it has a lot to do with it, because creatures can make sounds, from microorganisms to fish, and they all make sounds when they move. The smaller the sound produced by aquatic animals, the less we can hear it, but fish can.

By capturing these low-frequency vibrations with otoliths, fish can judge whether the sound source belongs to their prey, its general orientation and so on. That is to say, when we slowly approached the fish with small steps, they actually heard it long ago, but this sound may not be included in the category of dangerous sounds by them, so it was too lazy to pay attention to us.

Therefore, hearing is one of the important organs for fish to find prey, and light and environment can be ignored.

The position of otolith

The second is the sense of smell.

Hearing alone is obviously not enough, because some debris on the land will be blown into the water by the wind, which will produce sounds, so that fish are likely to be happy in vain, and the role of smell is reflected at this time.

Fish have nostrils like us, but unlike us, fish have four nostrils, which communicate with each other.

Although its nostrils are small, don't underestimate it, because this fish will let the water flow through its nostrils continuously when swimming. Inside the nostrils is the olfactory sac (composed of olfactory plate and olfactory chamber) of the fish, which is covered with sensory nerves. These nerves can accurately capture odor particles contained in running water, especially their ciliated sensory nerves, which can play a very good role in capturing amino acids.

Theoretically, fish can obtain food information within the range of Fiona Fang 10 meter by analyzing water information, but the live bait such as earthworm we use has a very high protein content, not to mention the professional bait we use. Once these baits enter the water, they will spread to the surrounding water and be analyzed by nearby fish.

With this ability, when there is sound or fluctuation in the water, they can tell the direction by hearing, then swim to the sound source, and analyze it by smell during this period, and finally know whether it is food or not.

At the same time, sense of smell also has a very important ability. During the breeding period, fish can quickly find a mate by analyzing pheromones released by other fish of the same species in the water.

Finally, the side line.

In fact, the lateral line of fish is more obvious. When we look at the side of the fish, we see a line (some obvious, some not obvious) in the middle, extending backwards from the gills to the tail. This is actually a side line, also called a fishing line. When dealing with fish, in order to reduce its fishy smell, many people are used to cutting a knife behind the gills and then finding the lateral line (thin white round line) to pull it out.

Lateral line is a unique organ of fish and amphibians. It belongs to one of the skin receptors and is the most advanced one. Although it looks like a simple line, it actually has two important components: Lauren's ampulla and neural mound.

Lauren ampulla, also known as electroacupuncture, can help fish sense the changes of electric field, magnetic field and temperature in water, and the neural mound is composed of a cluster of sensory cells and supporting cells, among which a large number of sensory cells can feel the weak fluctuation of water flow, thus generating nerve impulses and transmitting them to the brain.

The lateral line of fish plays a very important role in foraging, in which Lauren's ampulla can feel the changes of magnetic field and electric field. Simply put, as long as the prey moves, the original magnetic field and electric field will be destroyed. It can judge whether the size of prey is suitable for itself by the degree of sensory change, and a large number of sensory cells in the neural mound further strengthen the perception ability.

So fish can still feed even in turbid or dark water, which is why we can take the bait when fishing at night. This is due to the complete and complementary perception system of fish. They have a keen sense of hearing (infrasound) and a keen sense of smell. With the blessing of the lateral line, they can still eat and survive well even if they lose their eyes.