What is the purpose of nostrils in fish?

The fascinating physique of the fish

The fish - how does it actually work?

You can recognize some body features of yourself, others not at all, because the fish is prepared for a completely different life than animals living on land.
He has two eyes and a mouth on his face - and that is where the similarities to us humans or other rural creatures are.

In geological terms, the fish is much older than the mammal.
Fish-like animals developed in the sea over 400 million years ago (that's 400,000,000!). When the first mammals evolved is not exactly known, but it was about 200 to 240 million years ago. So they are comparatively young, and the fish-like primal animals were their ancestors.
But to go ashore, many adjustments were necessary that now make us and all other mammals so different from fish.

Perfect for aquatic life

What do you notice immediately about the fish's body?
It is smooth and mostly spindle-shaped. No bulky arms and legs interfere with moving forward in the water. Only very delicate fins, which the fish can also fold up and put on the body, stand out from the otherwise simple body shape.

The shape varies between long spindle-shaped like a herring, cylindrical like a catfish or disc-shaped like a discus - but all fish have one thing in common: from the front they have very little surface. Because that is the surface with which they have to swim against the water. As the saying goes, they are "streamlined". This means that if you imagine the water flowing in from the front as lines, these slide gently along the shape and do not suddenly encounter vertical resistance against which they would press.

The fish moves forward with its fins. Most fish move sideways with the body, which ends in the caudal fin in a powerful flap of the fins. The dorsal and anal fins are there to stabilize so that the fish does not accidentally turn around. The pelvic and pectoral fins serve as oars in addition to the caudal fin. The fish uses these “paired” fins, i.e. those that exist once on each side, in order to gain momentum from a standing position and to steer them in the desired direction. Take a closer look - the pectoral fins usually move slightly meandering when standing in order to float stably in the water. And when it is about to start, they are fanned out so that they protrude and are then quickly thrown backwards. Just like when you do the breaststroke, pushing yourself forward by swinging your arms back with your hands up.
The fins consist of so-called rays, between which a skin is stretched. It's like a fan, and that's exactly how they can be folded up to save space.
So this is the fish's musculoskeletal system.

The surface

What is special about the surface of a fish? Clearly - the scales! Most fish have them. Scales are small platelets made of bone-like substance that grow out of the fish skin in a regular pattern. They are tough and protect the fish like armor. But since they are not firmly connected to each other, they can slide over each other and thus allow unrestricted freedom of movement. Man even recreated this type of tank, it's that ingenious.
But why does a fish feel smooth and slippery when you touch it? Because the scales lie under the transparent, thin top layer of skin, and the fish is also covered with a layer of mucus, which also protects it from external influences such as parasites or being attacked by predators.
If a fish loses scales, for example in a fight, they grow back like a hair that has fallen out.

Internal organs

Outwardly, fish look very different, but in the body many things are similar to humans. The internal organs perform the same functions as in mammals.

You usually have a good idea of ​​the skeleton of a fish. Simply put, it just consists of a skull, in which the brain is safely housed, and the spine. It runs like a chain through the fish from the front to the tail fin. From the individual vertebrae go up the spinous processes, down the ribs that enclose the abdominal cavity.
The fins have a bony base that is connected to the skeleton by small joints or muscle strands.

If you go through the organs from front to back, the first thing you will find is the mouth. On the side of the head are the gills - the fish's respiratory organ. The gills consist of several layers of very fine gill leaves that filter the oxygen from the water. They are protected by the gill cover, the “cheeks” of the fish, so to speak. When inhaling, the fish takes water into its mouth, which it then pushes out through the gills by closing its mouth.
In addition, a short esophagus leads from the mouth and opens into the stomach.
In the abdomen are distributed from front to back: the heart, liver, gall bladder, on top of the kidneys, underneath the swim bladder and underneath the intestines and the gonads, i.e. ovaries or testicles.
The internal organs have the same functions as in vertebrates. The heart pumps the blood, the liver detoxifies and, with the help of bile, digestion takes place in the intestines. The kidneys give off waste in the urine - most fish do not have a proper bladder. After all, you don't have to wait to find a good place to urinate - you just go into the water where you are. 😉
The swim bladder is a special feature of the fish. The organism itself is heavier than water. Therefore, in order for fish to float in the water, they need a kind of inner swim ring. This forms in the early development of the young fish from a protrusion of the intestine. This bladder is filled with oxygen and thus balances the weight of the fish in the water - it can swim.
Fish that do not have a swim bladder, such as gobies, cannot. To get to the top, they have to actively swim and once they stop they sag back down.

Sense organs

Sense of sight

The eyes of the fish are usually very well developed. But there are also some who only have weak, very small eyes because they specialize in other senses.
Most of the time, the eyes are set on the sides of the head, so the fish has an all-round view. Only some hunting fish have placed their eyes closer to the front so that they can better target their prey.


Fish definitely have ears, even if you can't see them from the outside. Sound is transmitted very well in water, as you may have noticed when you immersed yourself in the bathtub or while swimming. Therefore, hearing organs embedded in the fish's body are sufficient without an external auricle.

Taste and smell

Fish can smell and taste great. In fact, it's the same in water. On land, the difference is between smell in the air and taste in direct contact with the tongue.
There is no difference between them in water. Chemical substances are dissolved in the water and reach the sensory cells provided on the fish.
Fish have small nostrils that are equipped with very sensitive olfactory cells. Odors spread very quickly in water. So with their super noses, fish can find their food much faster than if they relied on seeing it. Have you ever fed in the dark at night? You will notice that even fish that are sleepy will immediately start looking for and targeting food, even if they cannot see it.
They can also taste good, after all they have to be able to distinguish whether something they want to eat is good for them or not. Exciting: fish have odor / taste cells not only in their mouth but also on their fins, skin and barbels! So you can decide before you put something in your mouth whether it is tasty or not.
The sense of smell also helps them with orientation. They recognize places by their smell and can, for example, go hiking up the rivers without getting lost.
And the great thing about it: the sense of smell also works in cloudy water! Crystal clear water like in our aquariums is rarely found in nature - turbidity is always stirred up by water movements and you can often see only a few centimeters. It is no different for the fish, which is why they have developed the senses that help them even when visibility is zero.
That leads us to a very fantastic sense.

The lateral line organ

This ingenious organ enables the fish to perceive the movements of other beings from a distance without seeing them - it is a pressure sensor!
This only works under water because there is too little pressure in the air for such an organ to function.
The name describes very clearly where the organ can be found: it is a line that runs across the sides of the fish from front to back. Most of them show it quite clearly. Do you have fish to spot the sideline on?
And what's behind it now?
What you can see from the outside is a series of tiny holes called pores that connect to a channel embedded in the fish skin. In this channel there are sensory cells embedded in a gelatinous mass that react to bending. Now imagine that the fish Anton is standing in the water at a certain point. A little further away from him another fish, Berta, is moving towards him. This fish pushes a “pressure wave” in front of it - the water has to avoid it and is shifted.
The pressure wave now reaches Anton long before the fish Berta. It is the first to reach Anton's head area, where it penetrates the pores and displaces the fluid in the channel. The sensory cells in front bend first, in front of those further back. And from this Anton can see that someone is approaching from this direction, even if he cannot see them. The fish can also sense stationary obstacles in this way and organize itself in a school with its colleague within a very short time. The lateral line organ is also an all-round perception and not, like the field of vision, restricted to a certain direction. Great isn't it?

We humans have nothing like it. Stand in the room with your eyes tightly closed. Can you still somehow perceive your environment? You may hear familiar noises - the ticking of a clock, for example. But if you move carefully now, you will find that you instinctively stretch out your hands so as not to bump into anything. Our hands are our “feelers”, but they only work when they really touch something.

In some fish, cells have even formed in the lateral line organ that perceive electrical impulses - even the tiny electrical impulse that comes from the muscle movement of another animal.

So fish can also “see” perfectly blind, in murky water - several other senses draw an exact picture of the environment for them, which actually contains much more information than what can only be seen.

Special organs

Some fish have developed extra organs in order to adapt to difficult conditions and thus to conquer habitats that other fish remain closed.
For example the labyrinth of the labyrinth fish:
These fish have developed an organ to breathe air. This enables them to survive in small, often warm, oxygen-poor waters.
The labyrinth, hence its name, is a finely angled bony structure in the head area, above the gills. It is covered with a strongly perfused mucous membrane that can absorb oxygen.
The fish breathes by taking in an air bubble through its mouth, which is then distributed in this labyrinth. Once the oxygen has been absorbed, it is pushed out again via the gills.
A very well-known representative of this fish species is the fighting fish, the Betta splendens.
Their skill in handling air bubbles has even led them to get out of it
Build nests.

Intestinal breathing

Some fish can also breathe through a specially designed area in the intestine - these are mostly catfish, as well as the popular armored catfish. You have to swim to the surface to swallow an air bubble.
They can also survive in waters in which the oxygen content is sometimes too low to be able to breathe with their gills alone.

Alternating warmth

Mammals are so-called "warm-blooded animals". Metabolic processes take place in our body that require a very specific temperature.
Fish, amphibians and reptiles are cold-blooded animals. Your metabolism could also use a certain temperature to function optimally. But they cannot regulate their temperature themselves. They have no fur or clothing to protect them from cooling down. Instead, your metabolism has adjusted to function at different temperatures - everything is slower when it's cold, faster when it's warm. Therefore, your fish will become more active when you raise the water temperature and more sluggish when it is low. But since every fish is set to a certain temperature range, we have to offer it exactly this so that it does not get sick. After all, it depends on the ambient temperature being right.

So you see, the organs of fish serve the same purposes as ours, their sensory perception is even broader, but at the core we are not that different.

If you compare it with a reptile, it looks much more similar. This is no coincidence either, because reptiles such as lizards and snakes evolved from fish-like creatures in the distant prehistoric times.
The early fish first became amphibians, who live in and around water, but can leave the water thanks to their legs. Amphibians depend on water for reproduction because they lay their eggs in it and the eggs and young animals cannot survive in drought conditions (e.g. frog / tadpole). The reptiles are, so to speak, a further development of this - they have eggs with solid shells that do not lose moisture and can therefore also mature on land.

But why do we mammals look so completely different and what are the differences exactly?
There are some characteristics of the fish that reptiles have retained but mammals do not, and therefore they have evolved very differently as a result, even when both live on land. Reptiles lay eggs and are cold-blooded, which means that their bodies cannot produce and regulate a temperature that is particularly good for them. Fish and reptiles have to put up with it and become sluggish when they get cold. In addition, on land they could not spread into areas where the temperature can also drop below freezing and thus stop any metabolism of a more complex animal. Here the birds and mammals have developed a trick: They can regulate their body temperature themselves. When it is cold around them, they generate warmth in themselves and protect themselves from cooling down with fur and feathers. This enabled them to colonize cold areas of the earth, and this is why their appearance is so different from that of scaled fish and lizards.

But now comes the fantastic: Since we developed from the same fish-like ancestors, our bodies basically go back to their structure. Our arms and legs have developed over millions of years from the pectoral and ventral fins of the primeval fish to what they are now.
You don't think so? Then watch a painted frogfish!