Fish without scales - Types, names and examples

Fish are non-tetrapod vertebrate animals that can inhabit marine or freshwater environments. Given their great diversity, they are grouped into different classes. In this way, lampreys belong to the Petromyzonti class, the shortfin mako, the ray fish or the torpedo fish belong to the Elasmobranch class, the rat fish or chimeras to the Holocephalus class and others such as the sturgeon, the eel, the conger eel, the moray eel, sardine, barbel, anchovy or seahorses are part of the Actinopterygium class.

Most of these fish have scales, whose main function is to protect the animal from possible environmental aggressions. However, some of them do not present any type of scales, as is the case of some specimens belonging to the Actinopterygium, Petromyzonti or Holocephalus class. These scaleless fish They have developed characteristics throughout evolution that have allowed them to survive in the environment. We will see some examples in this AnimalWised article.

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  1. Why are there fish without scales?
  2. Types of fish without scales
  3. Examples of fish without scales
  4. Other fish without scales

Why are there fish without scales?

Animals have developed numerous protection mechanisms throughout evolution to defend themselves in the environment and to know how to survive in it. In fish, scales arose, which are involved in different functions, although the most important is to offer protection to the animal from everything that could be harmful or disadvantageous in the aquatic environment. However, some fish have not been endowed with these structures, it 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 fish without scales

There are numerous types of fish without scales that present different morphology and way of life. However, we can classify these species into different groups in order 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 agnate 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 the eel, the conger eel and the moray eel, but only the latter two lack scales.
  • Siluriformes: within this group we find specimens such as the catfish or the famous dotted catfish, very characteristic for its 4 pairs of barbels or "whiskers " in their jaws.
  • Myxiniformes: This is the case of hagfish species, agnate 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, feeding and morphological aspects most characteristic of some examples of fish without scales so we can get to know them better.

Marine lamprey

These are the best known scaleless and finless fish. Its scientific name is Petromyzon marinus and 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 measures of up to 1 meter in length. It is agnate since it lacks jaws and is characterized by having a suction cup-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 reproduction function. As for how to eat, adults are considered hematophagous or predatory ectoparasites, as they adhere to the skin of their prey and produce a scrape creating a wound from which they suck the blood. However, these wounds can become so large that the prey ends up dying and being finally eaten..

Discover more Animals that feed on blood with this other article.

Purple mixino

Its scientific name is Eptatretus stoutii and it belongs to the Mixines class, another group of agnate different from that of lampreys. This long-bodied, finless fish does not have a suction cup in the mouth area, but there are 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 coloration with generally pink, purple or brown tones. They inhabit the seabed where they feed on the carrion of other vertebrates in the environment.

Image: pezraros.org

Chimera or ratfish

Its scientific name is Chimaera monstrosa and belongs to the order of the Chimaeriformes. It is one of the most popular scaleless fish, characterized by presenting a long tail with great flexibility, 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 plant matter, being the case of some algae, as well as other small animals such as mollusks, fish, crustaceans and / or echinoderms..

Image: shark-reference.com

Conger

Its scientific name is Conger conger and belongs to the order of the Anguiliformes. These animals, which can reach a length of more than 2 meters, They have a morphology very similar to that of an eel or a snake with a very thickened and shiny skin. They are characterized by having a large mouth, large eyes and a normally grayish coloration. They inhabit the seabed and normally feed at night on other animals such as crustaceans, mollusks 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 regeneration capacity, making their wounds 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 order of the Anguiliformes. Presents a long, flattened body laterally reaching a great length, a large mouth with numerous sharp teeth and colorations in the form of irregular spots throughout its body. They are sea fish without scales and inhabit rocky areas or between crevices. Regarding their eating habits, they are considered predators because they feed on other fish, cephalopods and / or crustaceans..

Dotted catfish

Its scientific name is Icatulurus puntatus and belongs to the order of the Siluriformes. In addition to its dark colorations with black spots, it is characterized by having a very robust body and somewhat laterally compressed. Presents a large mouth with 4 barbels or whiskers on both jaws reminding us of the figure of the cat, two fins on its back and a series of spines that they use as a defense mechanism. They prefer freshwater habitats, such as some stretches of river or lakes, and their nocturnal diet is based on small animals such as other fish, mollusks and / or crustaceans.

Black catfish

Its scientific name is Ameiurus melas and it belongs to the order of the Siluriformes. It is mainly characterized by having a body covered by a large layer of mucous substance and presenting, in general, fairly dark colorations. However, it has very similar characteristics 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 it feeds mainly on other small fish (piscivorous feeding).

Channel catfish

Its scientific name is Ictalurus punctatus, it belongs to the order of the Siluriformes and is also part of the list of fish without scales. It has a large head region where there are tiny eyes and a elongated mouth with four pairs of barbels. The ventral region has light colors such as white, while the dorsal region usually has bluish tones. They are fish of sweet habitats 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 plant matter and other fish, crustaceans and / or insects.

Bullhead

Its scientific name is Silurus glanis and it also belongs to the Siluriformes order. This fish is large in size and is characterized by having an elongated body, with a large head region and a mouth surrounded by three pairs of catfish-like whiskers.. Inhabit fresh waters, as are 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 indigenous animals is reduced. In addition, there is data that affirms that these fish have attacked some human.

Friar

Its scientific name is Salaria fluviatilis and it belongs to the order of the Perciformes. This small fish without scales of variable coloration is known to present dark bands across your body, a mouth set with developed canine teeth and a tentacle at the top of the eyes. In addition, male fish develop a kind of crest on the head that characterizes them during the heat period. They are animals of freshwater habitats, prevailing in rivers where they can feed on some crustaceans, insects and other smaller fish..

Other fish without scales

In addition to the aforementioned fish without scales, there are some other species in the world, highlighting that the vast majority of them belong to the order of Siluriformes, such as catfish and catfish species.. Other examples of fish without scales are as follows:

  • Red-tailed catfish (Phractocephalus hemioliopterus)
  • Zebra catfish (Brachyplatystoma juruense)
  • Tiger catfish (Pseudoplatystoma tigrinum)
  • Atlantic Mixin (Myxine glutinosa)
  • Common sturgeon (Acipenser sturio)
  • Swordfish (Xiphias gladius)

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