Hot Water Fish

Parts of a Fish

Fish are vertebrate animals whose body and system are clearly adapted to the aquatic environment . To live in water, they have fins to move around, and gills that allow them to breathe.
They are cold-blooded animals, they can easily change their temperature through behavioral thermoregulation. Their body is covered in scales that offer them protection and isolation. Although there is a great variety of fish whose morphologies and habitats can vary , the parts of a fish are common to all:

  • Body
  • head
  • gills
  • fins

Next, we are going to delve a little into the anatomy of the fish.


The body of fish has many characteristic aspects:

  • It is made up of a head, torso and tail.
  • On the head they have eyes, muzzle and gills.
  • In his body there is no neck because his head is directly connected to his abdomen.
  • They are covered by scales with a composition similar to that of bones.
  • On the torso they have fins, which have different names depending on their location and allow them to move through water.
  • Fish defecate and mate through the same tube , called the cloaca.
  • Although they have separate sexes, which are obvious in terms of their body shape, some species tend to reverse their sex by changing their appearance with them.
  • The body of fish is generally bilateral, which favors its movement, although it can vary in shape according to the places to which they correspond and their biological needs.

The spindle-shaped fish, that is, slightly compressed on the sides and elongated horizontally, are continuously swimming in the water. However, on the seabed, species whose anatomy is more flattened tend to predominate.
There are compressed fish , (from the sides), depressed fish , (elongated on the sides but flattened vertically), among other very characteristic forms of each species.
The skeleton of a fish is strongly ingrained with the musculature, with respect to its functioning. Their body is segmented, and both their bones and muscles are connected by tendons and ligaments that make it possible for them to swim.
The skull, ribs and spinal column belong to the axial skeleton, while the bones of the waist and pectoral fins belong to the perpendicular skeleton.


The head of the fish, like the shape of its body, varies depending on its mode of feeding.
The snout of the fish goes from the eye to the lower part of the jaw, however it should be noted that although all fish have a mouth, not all have a jaw.
Depending on the location of the mouth, it can be terminal (in front), superior (upwards) or inferior / subterminal (downwards).
Fish do not have an eyelid, but that does not mean that they cannot sleep. The reason is that these animals need to keep half their brain awake while they sleep in order to breathe. Failing that, they have a nictitating membrane around them that protects the eyeball.
Unlike humans,the shape of his eye is completely spherical and his iris does not adapt to the passage of light , that is, it does not expand or contract.
Between the mouth and the eyes are the nostrils, which are small holes similar to the nose of humans, but their function belongs to the roof of the mouth.
The cheek is between the eyes and the preopercle, which is the fin that protects the gills and where the boundary between the head and the trunk is located.
Before reaching the trunk are the gills, protected by the operculum , which make up the respiratory organ.


The gills belong to the respiratory system of the fish, they are in charge of extracting the oxygen dispersed in the water.
They are external organs, since a more complex organ would be counterproductive to the movement of swimming. In addition, water is much denser compared to air, and therefore requires direct friction with the epidermal cells of the gills.
In the most common aquatic vertebrates, the gills are located between grooves that connect the digestive tract with the exterior . In this way, the water enters through the mouth of the fish and oxygenates the blood of the partitions that are between these indentations. This is how the water comes out of the gills, having already transformed oxygen into carbon dioxide.


The fins make up the swimming system. Depending on their location, they have different names and functions, which involve the way they move, their feeding, reproduction and defense.

  • Dorsal fins
    As the name implies, they are located on the back of the fish. They take care of stability and balance.
  • Caudal fin
    Found on the tail, giving it momentum when swimming
  • Anal fin
    It is also a stabilizing fin. It is located in the belly, close to where the fish’s anus is located.
  • Fins
    They are small fins that lie behind the dorsal and anal fins.


The scales cover the body of the fish, and serve the function of isolating bacteria and fungi, and even provide protection.
These have a composition very similar to that of bones. However, not all fish have scales, or at least they are not bone-like like most.
An example of such fish are eel, cat fish , catfish, among others, who its outer structure is cartilaginous, unlike bone. This type of fish, despite the absence of scales, are also adapted to the aquatic environment and have particularities in the rest of their body to survive it.
The epidermis of the fish is covered by glands that protect the skin and give the animal a sliding layer, called mucilaginous glands. They also have secondary layers with cells that provide a variety of colors to the different species.

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