Sensory organs of aquarium fish

Fish sensory organs

Have you ever wondered how your fish communicate with each other? Do aquarium fish have olfactory organs? You will find all the answers to these questions in today's post.

It turns out that aquatic animals have highly developed senses, and these are differently developed in different species. Thanks to sensory organs, the fish is able to hide from other fish or can see other fish behavior in surrounding water. If you've only heard about the lateral line system, take a look at our article, because there is much more to say about fish sensory systems.

So let’s take a look at fish eyesight first.

As reported in the aquarium technical literature - the fish eyes are one of the best developed organs of the body of underwater vertebrates. It turns out that very well-developed eyeballs in fish inform their brain about all the qualities of the surrounding world - colors, shape and movements. It is surprising that the depth of color in fish is probably much better developed than in humans. They do not need any vitamins for eyesight or a supplement to improve fish eyes. After all, there are many functions related to the ability to perceive - some fish species, thanks to their eyesight, change their body color depending on the surrounding environment. The fish eyesight is developed the best comparing to other senses.


What about sense of smell in fish?

I don't think I should surprise you if I say that the sense of smell is also as well developed as other senses. The unit that perceives the smell is the olfactory fovea, thanks to which the fish is able to detect, for example, a dead individual in surrounding environment, and then escape from the place of danger. But the sense of smell and taste used by fish mainly to detect and locate food. Sensitivity of these two senses to different dissolved substances is superimposed, which is why we are talking about the so-called chemical sense (smell + taste). The sense of smell of fish consists of two pouches located on the head, under the skin, right in front of the fish eyes. Each of them has two openings: the front (inlet) through which the water flows in, and the rear (outlet). Some fish spicies, such as the stickleback, have only one opening each leading to the olfactory chamber.

Ok, let's move to other senses.


Do the fish taste the food?

Fish, like other vertebrates, perceive taste thanks to their taste buds, but they are located not only in the mouth, but also on the skin of the whole body and fins of these aquatic animals. Carps and catfish and other similar fish species, for example, have a lot of taste buds on the skin, even 90%. Due to the fact that the taste buds of fish are located in the mouth and on the surface of the skin, they perceive two types of taste - the so-called internal and external taste. The inner taste examines the food that has already been grasped. The fish decides whether to swallow it or spit it out, and the external taste is used to locate food when the fish is close to it.

Fish have no voice? The sense of hearing

Most fish we know do certainly not. However, freshwater aquaristics has registered the fact that in some fish species there are audible tones that are perceived by the organ of hearing of the fish and mainly of the lateral line of its body. Usually they are sounds similar to slamming or grunting and are caused by the rubbing of muscles against the swim bladder. Hearing, however, has marginal importance for fish and is not as perfectly developed as sight. Fish, unlike mammals, do not have an outer ear. On the other hand, they have an inner ear located in the head, which also acts as an organ of balance that allows them to maintain the correct position of the body when making turns. The ability to perceive sounds in many fish species is enhanced by the swim bladder and the Weber apparatus. The Weber apparatus is made of cubes that connect the fish's swim bladder to the inner ear. Water vibrations and sound waves picked up by the fish's body are transmitted to the swim bladder and then to the ear.


Sense of touch

Fish are sensitive to vibrations and water swirls. Water thickens in one place and dilutes in another, creating waves, which changes the pressure as a result of the water movement. These changes in pressure are perceived by the fish via the lateral line. The lateral line can be seen in fish as a darker strip located on the sides of the body. The lateral line is made up of dozens of small holes leading into the lateral line canals, which are connected by a common wire from the gills to the tail. Inside, cells are embedded with microscopic cilia. If the body of the fish is struck by a wave caused by other fish passing by, the cilia begin to twitch and the vibrations travel through the lateral line system to the fish's brain. The fish then feel that something has moved. Thanks to the lateral line, the fish navigate, look for food, protect themselves from danger, distinguish water vibrations caused by various water movements, including sound waves.

Electroreceptive species vs electrogenic species

Mother Nature decided to equip some species with premium skills. Electrogenic fishes are fishes with ability to generate an electic field. Its function is mostly self-defence and communication but some fishes use it for navigation . Some fish species like shark, skate, ray and catfish can also detect electric fields in the environment, and are thus electroreceptive, but they don't generate an electric field so such species are not classified as electric fishes.

As you can see, fish have very well developed sensory organs. Thanks to these organs fishes can live safely among other animals in surrounding environment. Remember about it when your next guest will knock on the glass to say ‘hello’ to fish living in your tank :) Stress is not welcome in aquatic environment. Believe me, most fish don't like it. Remeber that fishes are extremely sensitive animals with extremely sensitive sensory systems!