General characteristics of fish

Author: Peter Berry
Date Of Creation: 15 February 2021
Update Date: 26 September 2024
Anonim
Characteristics of Fish
Video: Characteristics of Fish

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Normally, all aquatic vertebrates are called fish, although this classification is wrong since other aquatic vertebrates, such as whales, are mammals. But the curious thing is that fish and terrestrial vertebrates share the same ancestor. Fish are a group that, despite being very primitive, achieved great evolutionary success, as the aquatic environment allowed them to survive a large amount of habitats. Their adaptations gave them the ability to colonize from salt water areas to freshwater regions in rivers and lakes, through species capable of living in both environments and overcoming rivers (as in salmon, for example).


If you want to keep learning about the general characteristics of fish, a very diverse group that inhabits the planet's waters, keep reading this article by PeritoAnimal and we'll tell you all about them.

Main characteristics of fish

Despite being a group with very variable shapes, we could define fish by the following characteristics:

  • aquatic vertebrates: according to the most diverse vertebrate taxon currently. Their adaptations to aquatic life allowed them to colonize all types of aquatic environments. Its origin dates back to the late Silurian, more than 400 million years ago.
  • bone skeleton: they have a bony skeleton with very few cartilaginous areas, this is their biggest difference with chondric fish.
  • Ectotherms: that is, they depend on the ambient temperature to regulate their body temperature, unlike endotherms.
  • gill breathing: they have a respiratory system where the main breathing organs are the gills and are covered by a structure called the operculum, which also serves to delimit the head and the rest of the body. Some species breathe through lungs that are derived from the swim bladder, which also serve to float.
  • terminal mouth: they have a terminal mouth (not ventral, as in the case of cartilaginous ones) and their skull is composed of several articulated dermal bones. These bones, in turn, support the teeth. that have no replacement when they break or fall.
  • Pectoral and pelvic fins: Have anterior pectoral fins and smaller posterior pelvic fins, both pairs. They also have one or two dorsal fins and a ventral anal fin.
  • Odd homofence caudal fin: ie that the upper and lower lobes are equal. Some species also have a dificult tail fin, divided into three lobes, present in coelacanths (sarcopterygeal fish) and in lung fish, where the vertebrae extend to the end of the tail. It forms the main organ for generating the thrust by which most fish species move.
  • Dermal scales: they have a skin that is usually covered by dermal scales, with the presence of dentin, enamel and bone layers, which vary according to their shape and may cosmoid, ganoid and elasmoid scales, which in turn are divided into cycloids and ctenoids, which are divided by their smooth edges or incised like a comb, respectively.

Other fish characteristics

Within the characteristics of the fish, it is also worth mentioning the following:


How do fish swim?

Fish are able to move in a very dense medium such as water. This is mainly due to your hydrodynamic form, which together with its powerful musculature in the trunk and tail area, propels its body forward by a lateral movement, usually using its fins as a rudder for balance.

How do fish float?

Fish face the difficulty of staying afloat because their bodies are denser than water. Some fish, such as sharks (which are chondricte fish, that is, they are cartilaginous fish) do not have a swim bladder, so they need some systems to maintain a height in the water column, such as maintaining a continuous movement.

However, other fish have an organ dedicated to buoyancy, the bladderswim, in which they hold a specific amount of air to float. Some fish stay at the same depth throughout their life, while others have the ability to fill and empty their swim bladder to regulate their depth.


How do fish breathe?

Traditionally, we say that all fish breathe through the gills, a membrane structure that allows the direct passage of oxygen from water to blood.However, this characteristic is not generalized, as there is a group of fish closely related to terrestrial vertebrates, and this is the case of lung fish or Dipnoos, which are capable of performing both branchial and pulmonary respiration.

For more information, you can refer to this other article on How do fish breathe?

Osmosis in fish

Freshwater fish live in an environment with few salts, while in their blood the concentration of these is much higher, this occurs because of a process called osmosis, the massive ingress of water into your body and the massive outflow of salts to the outside.

That's why they need several adaptations to regulate this process, so that absorb salts in your gills (which are in direct contact with water, unlike their hermetic, scale-covered skin) or releasing very filtered and diluted urine.

Meanwhile, saltwater fish face the opposite problem, they live in means very salty, therefore they are at risk of dehydration. To get rid of excess salt, they are able to release through the gills or through very concentrated urine, almost unfiltered.

Trophic behavior of fish

The diet of fish is very varied, from a diet based on the remains of animals on the bottom, vegetable matter, to the predation of other fish or molluscs. This last feature allowed them to evolve their visual ability, agility and balance to obtain food.
Migration

There are examples of fish that migrate from fresh water to salt water, or vice versa. The best known case is that of Salmonids, an example of anadromous fish that spend their adult life in the sea, but return to fresh water to spawn (ie, lay eggs), being able to use certain environmental information to find the river in which they were born and lay their eggs there. While other species, such as eels, are catadromous, as they live in fresh water, but migrate to salt water to reproduce.

Reproduction and growth of fish

Most fish are dioecious (they have both sexes) and oviparous (with external fertilization and external development), being able to release their eggs into the environment, bury them, or even transport them in the mouth, sometimes also giving a vigilant behavior to the eggs. However, there are some examples of ovoviviparous tropical fish (the eggs are stored in the ovarian cavity until they hatch). On the other hand, sharks have a placenta by which the offspring is nourished, being a live-bearing pregnancy.

The later development of fish is usually associated with environmental conditions, mainly the temperature, with fish from more tropical areas that have a faster development. Unlike other groups of animals, fish continue to grow into their adult stage without limits, reaching enormous sizes in some cases.

For more information, also read this other article on How do fish reproduce?

General characteristics of fish according to their group

We can't forget the fish characteristics according to your group:

agnate fish

They're jawless fish, it's a very primitive group and includes minnows and lampreys. Despite not having vertebrae, they are considered vertebrates, due to characteristics observed in their skull or their embryonic development. They have the following characteristics:

  • Angiliform body.
  • They are usually scavengers or parasites, living next to other fish.
  • They do not have vertebrae.
  • Do not undergo internal ossification.
  • It has bare skin, as it lacks scales.
  • Lack pairs of fins.

gnathotomized fish

This group includes all the rest of fish. Most of today's vertebrates are also included here, as are the rest of fish, amphibians, reptiles, birds and mammals. They are also called fish with jaws and have the following characteristics:

  • They have jaws.
  • Even and odd fins (pectoral, dorsal, anal, ventral or pelvic and caudal).

Within this group are included:

  • Chondrites:cartilaginous fish such as sharks, rays and chimeras. Your skeleton is made up of cartilage.
  • Osteite: ie bony fish. This includes all fish we can find today (divided into fish with radiated fins and fish with lobulated fins, or actinopterygeans and sarcopterygeans, respectively).

If you want to read more articles similar to General characteristics of fish, we recommend that you enter our Curiosities section of the animal world.