Fish

Even if you don't know it, fish are the largest group of vertebrate animals, with almost 28000 species in the world. The vast majority of them live in the sea, but they are also in fresh water.

But what do you know about fish? As they are? What types of fish are there? In this section you will find all the information that a lover of these animals would want to know.

what are fish

Fish are a large group of animals that live in an aquatic environment. Their size can vary greatly, because they can measure from 8 millimeters to more than 12 meters. Reason why you find a wide variety of them. Besides, They are adapted to different temperatures in the water, being able to live in areas ranging from 40 degrees to -2.

In general, fish are animals that live in water. Anatomically, they have the area of ​​the brain protected through a cranial box and in that part of their body they house the eyes, teeth (mouth) and sensory organs.

They are vertebrate and ectothermic animals. That is, they can regulate their body temperature by guiding themselves with that of the environment.

Because they live in the water, they do not need to get out of it to breathe, but use the gills to do so (with them they are able to absorb the oxygen that is dissolved by the water). In addition, its entire body is covered by scales, which in a way protect it, and it has fins that are the ones with which it can move faster or less through the aquatic environment.

A curiosity that we can tell you about fish is about their age. Like the trees, the fish also leave a clear sign of how old they are. And it is that growth rings are formed that are those that determine the years that that fish has.

the senses of fish

Like humans, fish also have senses. While some are more developed than others.

The sense of sight is not one of its best assets, since, although the eyes have them adapted to see in the water, they do not manage to transmit to the fish a well-defined form of what they see. In fact, the more they live at the bottom, the worse eyesight they have, contrary to what happens with those who are near the surface.

However, it will also depend on the type of fish it is, since, for example, bony fish can clearly distinguish the colors of the objects it sees.

However, and in general, no fish can clearly see the colors and shapes of the objects around them, which is why, when fishing for them, it is easier because they cannot really distinguish well.

The sense of touch in fish is based on a sensory apparatus called the lateral line. These are sensory corpuscles that are all over its body, forming a visible line between them on the sides. This serves both to know the sense of direction and, through the shock waves in the water, to know if there are objects around it, other fish, etc.

One of the most developed senses in fish is smell. This is located in the front part of the head, where it has nostrils (except in the case of cartilaginous fish that have them under the face, in the mouth area). What is it for? Well, they use it to distinguish enemies as well as to look for food.

The sense of hearing is another of those that have been better developed, since it has an internal ear that connects with the swim bladder. This is the one that emits vibrations since, being full of gas, when the ear transmits sound waves, the gas moves.

In fact, even if you don't know it, there are some fish that can make sounds. These are very similar to squeaks, which is why when it is said that a fish squeals, it is not a joke, it is that they really can.

In addition, fish communicate through sound, it is a means of communication, both to establish relationships with other fish and to intimidate their enemies.

Finally, the sense of taste is not only present in the mouth, but also in the head, part of their body, in their chins...

The origin of the fish

Fishes are known to have evolved from chordates in the Cambrian period. But it is not really known what their origin is, only the most primitive group of them, the so-called ostracoderms, from which the agnaths (lampreys and mixines) were born. These fish had armor that protected their head and part of their trunk, which is why it is thought that they evolved that way. Their goal was to defend themselves from other predators with whom they lived in the same area.

Ostracoderms arose and reproduced very quickly, inhabiting not only the sea, but also rivers and lakes. It was in the Devonian period when they began to become extinct. But, instead, the first fish arose, more similar to those we know now.

Kinds of fishes

As we have said before, There are almost 28000 different species of species. But all of them can be classified into three large groups. These are:

ciclostomata

They are better known as jawless fish They have a very primitive shape, especially in the skeleton. And they are perhaps the first to emerge and have continued to be in our day to day. They are characterized by having an eel-shaped body and a motionless mouth. But full of sharp horny teeth, capable of attacking their prey and attaching themselves to them thanks to a suction cup that they use to, with their teeth, give a good account of their victim.

chondrichthyans

Better known as cartilaginous fish. This means that they have a skeleton made of cartilage, which makes them very flexible. It has two pairs of fins, the scapular (or anterior) and the pelvic (or posterior) fins.

Like the previous one, they also have teeth and the vast majority are carnivorous, but they do not usually float like other fish. This is because they do not have a swim bladder.

Osteichthyos

called bony fish. They are fish that have a complete skeleton, and are the most numerous of all species. The truth is that in terms of body shape they are quite varied, as well as with the head, fins, scales...

Of course, these fish do not have teeth.