Fish belong to the chordate phylum, they are exclusively aquatic animals and, a fact that we sometimes do not specify, is that they are the most abundant vertebrates on the planet, totaling nearly thirty thousand current species. These animals have conquered all aquatic environments, possessing a great variety of sizes, shapes and adaptations to develop in the water. In this article on our site we want to present an article about the types of fish so that you can learn about their classification and main characteristics. Don't hesitate to keep reading if you want to know.
Fish classification
Since fish are a group with a wide diversity, their rating has varied over time Traditionally three groups or classes were distinguished: agnathians (no jaws), chondrichthyans (cartilage) and osteichthyans (bony). However, with advances in taxonomy, this classification has been expanded and more detailed, in such a way that it is as follows:
Agnathos Superclass
Within the agnathus superclass, we can find the following classes of fish:
- Class Mixines: Hagfish have elongated bodies, a mouth with four pairs of tentacles, 5 to 15 pairs of gill sacs, and certain species are hermaphrodites. Discover 15 examples of hermaphrodite animals and how they reproduce, here.
- Class Petromyzontida: Here are the lampreys, which have gelatinous, elongated, cylindrical bodies without scales.
If you want to know more about agnathus, we recommend that you take a look at this other article about agnathus or jawless fish: characteristics and examples.
Superclass Gnathostomes
The rest of the jawed vertebrates are also included in the superclass of the gnathostomes. Therefore, we find the following classes:
- Class Chondrichthyans: characterized by a cartilaginous skeleton, the teeth are not fused to the jaw and these fish lack a swim bladder. They are divided into two groups: the Elasmobranchs (sharks, rays and torpedoes) and the Holocephalians (chimera fish or ghost sharks, for example). Check this post about cartilaginous fish, their characteristics, names and examples to learn more.
- Class Osteichthyos: corresponds to bony fish, which have a mainly ossified skeleton, with simple gill openings, and also have a swim bladder or lungs. They are divided into two groups: the Actinopterygians (ray-finned fish) and the Sarcopterygians (lobe-finned fish). Here you can learn more about Bony Fish: examples and characteristics.
As we mentioned, this is one of the many fish sorting options. Others may include some subdivisions in addition to those mentioned. It should also be noted that we have only considered living groups, without mentioning extinct ones.
Fish Characteristics
Given the diversity of fish that exist, it is not so easy to establish characteristics that encompass them all, however, below, we present certain features of the groups:
- There are two large groups: agnathans and gnathostomes. The first, lacking jaws, are the oldest and are adapted as scavengers or parasites. The latter, with jaws, integrate a great diversity of species.
- The agnates are vertebrates: although they do not have vertebrae, they do have a skull and other homologies that make them belong to vertebrates.
- gnathostomes have jaws and limbs.
- The cartilage fish underwent transformations: they changed the heavy armor of their ancestors to adopt cartilage for bone in their skeletons.
- Cartilaginous fish are strong predators: with squaliform bodies. They have also developed a complex sensory system.
- The Bony fish are the dominant today: they are characterized by their skeletal structure being made of calcified pieces rather than cartilage.
If you want to have more precise information on the Characteristics of the fish, do not hesitate to visit this other article on our site.
Kinds of fishes
We can classify fish from various points of view, let's get to know some of them.
Types of fish according to their jaw
In principle we can talk about two types of fish, those that do not have jaws and those that do.
- Jawless fishes: as we have mentioned, they are divided into a little more than 80 species, between two groups, hagfish and lampreys. Both have elongated bodies, similar to that of eels, without internal ossification, scales and paired fins, all have gill openings.
- Fish with jaws are much more diverse, within them are the rest of the species that include all sharks, rays, chimeras and the immense variety of bony fish. The sizes, shapes and habits are very different, and depend on the characteristics of each group.
Types of fish according to their skeleton
Depending on the skeleton, fish can be of two types, cartilaginous or bony:
- Cartilaginous fish: they have a skeletal structure of cartilage, generally have paired fins, also nostrils or nostrils, a body covered with scales and go from very small sizes of a few centimeters, to more than 10 meters.
- Bony Fishes: Unlike the former, their skeleton is a mainly calcified formation. Here we find the largest number of fish species. They tend to have the same pattern in the cranial conformation, paired or unpaired fins with cartilage or bone, which divide them into two groups, rayed or lobed fins. Usually with swim bladder, large number of teeth and olfactory sacs.
Types of fish according to their habitat
Another classification that we can use to determine the types of fish is according to the habitat. So, we have we can find:
- Freshwater fish: check this article on our site to learn about some freshwater fish for aquarium, types, names and photos.
- Marine Fish: Here's more information about S altwater Fish.
- Diadromous fish: these are fish capable of being in both types of environments, since it refers to migratory fish that travel between both types of aquatic environments.
In turn, diadromous fish can be of three types:
- Anadromous: spend most of their lives in the sea but travel to rivers to breed.
- Catádromos: live in fresh water and breed in s alt water.
- Amphidromous: these are fish that move between fresh and s alt water, but without reproductive purposes.
Types of fish according to the depth where they live
On the other hand, the fish according to the depth where they live, the fish can be called:
- Benthic: are fish that develop mainly on or near the water bottom.
- Pelagic: those that have almost no proximity to the seabed, being mainly in intermediate waters or near the surface, but far of the coast.
- Neritic: referring to those fish that live near the coast or coastline.
Examples of fish
As we already know, there is an immense diversity of fish, so naming them all would be a very difficult task. In this sense, let us know some examples:
Mixines
Within hagfish, we can highlight two examples of fish:
- Gregg's hagfish (Myxine greggii).
- Sea lamprey (Petromyzon marinus), a type of Petromyzontida.
Chondrichthyans
Within chondrichthyans, which are cartilaginous fish, we can highlight:
- Elasmobranchs: where we find the great white shark (Carcharodon carcharias), the common manta ray (Dasyatis pastinaca) or the marbled electric ray (Torpedo marmorata).
- Holocephalians: where we can find the leopard chimera (Chimera panthera).
Osteichthyes
Remember that osteichthyes are all those bony fish. In this way, we can see:
- Actinopterigios (ray fins): such as the Atlantic sturgeon (Acipenser oxyrinchus) or the Nile bichir (Polypterus bichir).
- Sarcopterygian (lobe-finned): such as the coelacanth (Latimeria chalumnae) or the South American lungfish (Lepidosiren paradoxa).
Other fish examples
- Anadromous: Atlantic salmon (Salmo salar).
- Catádromo: European Eel (Anguilla Anguilla).
- Amphidromous: Sardinian shark (Carcharhinus leucas).
- Benthonic: Speckled Guitarfish (Pseudobatos glaucostigmus).
- Pelagic: Bluefin tuna (Thunnus thynnus).
- Neritic: Sawfish (Pristi pristis)
