Fish are non-tetrapod vertebrate animals that can live in marine or freshwater environments. Given their great diversity, they are grouped into different classes. In this way, lampreys belong to the Petromyzonti class, mako shark, ray fish or torpedo fish belong to the Elasmobranch class, rat fish or chimeras to the Holocephalus class and others such as the sturgeon, the eel, the conger eel, the moray eel, the sardine, the barbel, the anchovy or the seahorses are part of the Actinopterigios class.
Most of these fish have scales, whose main function is to protect the animal from possible aggressions from the environment. However, some of them do not have any type of scales, as is the case of some specimens belonging to the class Actinopterigios, Petromyzonti or Holocéfalos. These fish without scales have developed characteristics throughout evolution that have allowed them to survive in the environment. We will see some examples in this article on our site.
Why are there fish without scales?
Animals have developed numerous protection mechanisms throughout evolution to defend themselves in the environment and know how to survive in it. In fish, scales emerged, which are involved in different functions, although the most important is to offer protection to the animal from everything that could harm or disadvantage it in the aquatic environment. However, some fish have not been endowed with these structures, which does not mean that they are unprotected, since these have been endowed with other characteristics that allow them to survive in water, such as the presence of more developed sensory organs or thick body layers that offer them greater protection.
Types of scaleless fish
There are many types of scaleless fish that have different morphologies and lifestyles. However, we can classify these species into different groups to better identify them. In this way, we will classify them in the group of Petromyzontiformes, Chimaeriformes, Anguiliformes, Siluriformes and Myxiniformes
- Petromyzontiformes: this group includes specimens such as the stream lamprey or the sea lamprey, considered agnathous fish because they lack jaws.
- Chimaeriformes: its representative is the well-known “rat fish” due to its peculiar appearance.
- Anguiliformes: this group is made up of fish such as eels, conger eels and moray eels, but only the latter two lack scales.
- Catfish: within this group we find specimens such as catfish or the famous dotted catfish, very characteristic for its 4 pairs of barbels or “whiskers” on their jaws.
- Myxiniformes: this is the case of hagfish species, agnathous fish such as lampreys. An example is the purple hagfish.
Examples of fish without scales
It is true that the number of fish without scales is lower than those that do have these structures. The fish that make up this smaller group can be differentiated from each other by their different morphology, distribution and way of life. However, this section will describe the type of habitat, diet and most characteristic morphological aspects of some examples of scaleless fish so that we can get to know them better.
Sea lamprey
These are the best known finless and scaleless fish. Its scientific name is Petromyzon marinus and it belongs to the order Petromyzontiformes. This animal, with a structure similar to that of an eel, can live for more than 15 years and reaches measurements of up to 1 meter in lengthIt is agnathic since it lacks jaws and is characterized by having a sucker-shaped mouth provided with a large row of horny teeth. It is anadromous, that is, its habitat is marine (Atlantic Ocean and Mediterranean Sea), but it moves to rivers to carry out its reproductive function. Regarding the way they feed, the adults are considered hematophagous ectoparasites or predators, as they adhere to the skin of their prey and produce a scraping, creating a gash wound. which suck blood. However, these wounds can become so large that the prey ends up dying and finally being devoured.
Discover more Animals that feed on blood with this other article.
Purple Hagfish
Its scientific name is Eptatretus stoutii and it belongs to the Mixine class, another group of agnathids different from the lampreys. This fish with an elongated body and no fins does not have a suction cup in the mouth area, but it does have highly developed sensory organs such as smell and touch. They present a tongue with small tooth-shaped structures, small beards that also act as sensory organs and a body color with pink, purple or brown tones generally. They inhabit the seabed where they feed on the carrion of other vertebrates in the environment.
Chimera or ratfish
Its scientific name is Chimaera monstrosa and it belongs to the order Chimaeriformes. It is one of the most popular scaleless fish, characterized by a long, highly flexible tail, large eyes, a fold that covers the openings of its gills, an upper jaw fused with the cranial area, very wide and smooth plates like teeth and only two gill openings. These fish are marine and inhabit very deep waters of the Atlantic Ocean and the Mediterranean Sea, mainly. Their diet can be based on both vegetable matter, which is the case of some algae, and other small animals such as molluscs, fish, crustaceans and/or echinoderms.
Conger
Its scientific name is Conger conger and it belongs to the Anguiliformes order. These animals, which can reach a length of more than 2 meters, have a morphology very similar to that of an eel or a snake with very thick skin and quite bright. They are characterized by having a large mouth, large eyes and a normally grayish color. They inhabit the seabed and normally feed at night on other animals such as crustaceans, molluscs and some fish. At the same time, they are considered easy prey, since they have a curious instinct for nearby sounds or movements. In addition, they have a great capacity for regeneration, causing their wounds to heal very quickly.
Meet more Animals that are prey in this other article.
Brunette
Its scientific name is Muraena helena and, like the conger eel or the eel, it belongs to the Anguiliformes order. It has a long and flattened body laterally reaching a great length, a large mouth with numerous sharp teeth and coloration in the form of irregular spots all over its body. They are sea fish without scales and inhabit rocky areas or between cracks. Regarding their eating habits, they are considered predators because they feed on other fish, cephalopods and/or crustaceans.
Spotted catfish
Its scientific name is Icatulurus puntatus and it belongs to the Siluriformes order. In addition to its dark colors with black spots, it is characterized by having a very robust body that is somewhat compressed laterally. It has a large mouth with 4 barbels or whiskers on both jaws, reminding us of the figure of a cat, two fins on its back and a series of spines that they use as a locking mechanism. defending. They prefer freshwater habitats, such as some stretches of river or lakes, and their nocturnal feeding is based on small animals such as other fish, molluscs and/or crustaceans
Black Catfish
Its scientific name is Ameiurus melas and it belongs to the Siluriformes order. It is mainly characterized by having a body covered by a large layer of mucous substance and presenting, in general, quite dark colors However, it has characteristics very similar to other species of catfish, such as the presence of eight barbels around its mouth. They are also freshwater fish, inhabiting numerous rivers such as the Ebro River where they feed mainly on other small fish (piscivorous feeding)
Channel catfish
Its scientific name is Ictalurus punctatus, it belongs to the Siluriformes order and is also part of the list of scaleless fish. It has a large cephalic region where there are tiny eyes and a long mouth with four pairs of barbelsThe ventral region presents light colors such as white, while the dorsal region usually presents bluish tones. They are sweet habitat fish and can be found in some rivers or lakes. As for their diet, which is usually nocturnal, they are omnivorous animals, since they feed on both vegetable matter and other fish, crustaceans and/or insects.
Bullhead
Its scientific name is Silurus glanis and it also belongs to the order Siluriformes. This fish is large in size and is characterized by having an elongated body, with a large cephalic region and a mouth surrounded by three pairs of barbs similar to those of catfish. Inhabits freshwater, such as some rivers and/or reservoirs, where it feeds, as a good predator, on other vertebrate animals. This can be a problem as the population of native animals is reduced. In addition, there is data that affirms that these fish have even attacked some human.
Friar
Its scientific name is Salaria fluviatilis and it belongs to the Perciformes order. This small, scaleless fish of varying colors is known for presenting dark bands along its body, a mouth with developed canine teeth and a tentacle on the upper part of the eyes. In addition, male fish develop a kind of crest on their heads that characterizes them during the heat period. They are animals of freshwater habitats, predominating in rivers where they can feed on some crustaceans, insects and other smaller fish.
Other scaleless fish
In addition to the already mentioned fish without scales, there are some more species in the world, highlighting that the great majority of them belong to the order of the Siluriformes, as is the case of species of the catfish and the catfish. Other examples of scaleless fish are as follows:
- Red-tailed catfish (Phractocephalus hemioliopterus)
- Zebra catfish (Brachyplatystoma juruense)
- Tiger Catfish (Pseudoplatystoma tigrinum)
- Atlantic Hagfish (Myxine glutinosa)
- Common sturgeon (Acipenser sturio)
- Swordfish (Xiphias gladius)
