The electric ray is widely known for its specific body structure, which cannot be confused with anyone. In addition, it has two deadly features: a sharp tail that can easily pierce the enemy (and in some species it is also poisonous), and the ability to generate electricity that reaches 220 volts.
View origin and description
The Origin of Rays So Far is a controversial issue. In the most common version, stingrays are descended from sharks, some of which have changed their usual mobile lifestyle to a moderate benthic habitat. As a result of such changes, the shape of the body of animals and the functioning of organ systems have changed.
If we consider in more detail the phylogenetic origin of the cartilaginous, then according to one version, a group of armored fish is considered their common ancestor. From the latter, cartilaginous separated in the Devonian period. They flourished until the Permian period, occupied both the benthic territories and the water column, and included 4 different groups of fish.
Gradually, more advanced bony fish began to take their place. After several periods of competition, the volume of cartilaginous decreased significantly, only 2 out of 4 groups remained. Presumably, in the middle of the Jurassic, the ancestors of rays separated from one of the remaining groups — real sharks.
The literature mentions the name of an ancient representative of rays — xyphotrygon, which existed about 58 million years ago. The found fossil remains testify to the great external similarity of the ancestor and modern individuals. It had a similar body shape and had a long, awl-like tail, with which the animal hit its prey or defended itself from enemies.
It is not only the question of origin that is controversial, but also the modern classification. Different scientists attribute skates to a superorder, division, or subdivision. According to the most generally accepted classification, stingrays are distinguished as a superorder, which includes 4 orders: electric, rhomboid, sawtooth-shaped and tail-shaped. The total number of species fluctuates around 330.
Representatives of electric rays are capable of reaching a two-meter size in their lifetime, while the average is 0.5-1.5 meters. The maximum weight is almost 100 kg, the average weight is 10-20 kg.
Appearance and features
The body has a rounded, flat shape, a small tail with a caudal fin and 1-2 upper ones. The pectoral fins are fused, giving the fish a more rounded appearance and forming the so-called wings. Protruding eyes and splashes are clearly visible on the head – holes designed for breathing. In most cases, vision is relatively well developed, however, in some species it is practically absent, and the eyes are buried under the skin, for example, representatives of the genus of deep-sea electric rays. For such individuals, vision is replaced by electroreception — the ability to perceive the slightest electrical impulses emanating from living organisms, and other sensory organs.
On the underside of the body are the mouth opening and gill slits. In the process of breathing, water enters the gills through the spiracles, and exits through the cracks. This way of breathing has become a distinctive feature of all stingrays and is directly related to the benthic way of life. If, when breathing, they swallowed water with their mouths, like sharks, then sand and other soil elements would come with water to the gills, injuring the delicate organs. Therefore, the fence is carried out on the upper side of the body, but the exhaled water from the cracks helps to inflate the sand in search of prey. br />The upper part of the body is distinguished by a very diverse coloration, which depends on the color background of the habitats. It helps the fish to camouflage and hide from predators. The color range is from dark, almost black, like a black electric stingray, to light, beige, like some species of the genus Narcina.
The patterns on the upper side of the body are very diverse:
- clear and bright large spots, like an ocellated electric stingray;
- small black circles, like a spotted narcina;
- variegated blurry dots, like a marbled stingray;
- blurry, large dark and light spots, like a Cape narcina;
- florid patterns, like a genus diplobatis;
- dark, almost black outlines, like a narcina;
- the lower part of the body in the prevailing number of species is lighter than the upper.
solid coloration, like that of a short-tailed gnus or black stingray;
Where does the electric stingray live?
Thanks to the protective coloration, individuals have perfectly mastered the bottom territory of almost all seas and oceans. By geographic distribution — this is a widely dispersed group. Adaptability to a wide temperature range from +2 to +30 degrees Celsius allowed electric stingrays to inhabit the salty waters of the globe, preferring the warm temperate and tropical zones. They live on various types of relief, and almost all individuals are characterized by low mobility.
Some keep to the sandy or muddy bottom of the coastal zones, where, during rest or waiting for prey, they burrow into the sand, leaving only eyes and splashes towering above their heads in sight. Others have established rocky coral reefs and surrounding areas, camouflaging themselves with their coloration. The depth range is also varied. Individuals can live both in shallow water and at depths exceeding 1000 meters. A feature of deep-sea representatives is the reduction of the organs of vision, for example, moresby stingray or faded deep-sea.
Also, some individuals have luminous spots on the surface of the body to attract prey in the dark. Shallow-water species living in coastal areas can collide with people while searching for food or migrating and demonstrate their electrical ability for defensive purposes.
What does the electric ray eat?
The diet of electric rays includes plankton, annelids, cephalopods and bivalves, crustaceans, fish, and various carrion. To catch moving prey, rays use discharges of electricity generated in paired organs at the base of the pectoral fins. The stingray hangs over the victim and, as if hugging her with his wings, at this moment he releases a discharge of electric current, stunning the prey.
In some cases, one discharge is not enough, therefore, rays are capable of producing up to several dozen such discharges, the strength of which gradually decreases. The ability to create, store and release electricity is regulated by the nervous system, so the rays control the process and make sure not to spend all the energy left defenseless.
Another way to hunt is to press the prey to the bottom and then eat it. This is how fish act with sedentary individuals who cannot quickly swim away or crawl away. In the mouth cavity of most species, the sharp teeth are so densely packed that they create a grater-like structure. In this they differ from most of their closest relatives — sharks With their teeth, they grind hard prey.
A species such as short-tailed gnus has the ability to stretch the mouth opening, due to which it hunts and eats large prey, reaching half the length of its body, and in some cases more. Despite the inert lifestyle, stingrays have an excellent appetite.
Character and lifestyle features
All stingrays are characterized by a solitary lifestyle. As mentioned above, they prefer to spend the daytime calmly, lying on the bottom or burrowing in the sand. When at rest, they scan the surrounding area using electroreception, identifying potential prey or an enemy. In the same way, they are able to communicate with each other, transmitting and capturing electrical signals, like bats.
This ability is well developed in all stingrays. Fish hunt and actively swim at night, it is then that they rely most on the perception of electrical signals, since even for those whose vision is not reduced, it is not clear enough and cannot fully convey the whole picture of the environment, especially in the dark .
In the water column, stingrays move smoothly, as if soaring in the water, they do not need, unlike sharks, to scurry quickly to maintain breathing. Movement occurs due to the synchronous flapping of the pectoral fins, or the so-called wings. Due to their flat shape, they do not have to spend a lot of effort to stay in the water column. Despite the slowness, stingrays are able to swim quickly, especially when moving away from a predator.
In some species, the pectoral fins are small and the fish move due to the pushes of a powerful tail. Another way to move is to sharply release a jet of water from the nostrils located on the ventral side, which allows the stingray to make a circular motion in the water column. With this maneuver, he scares away potential predators, but in case of approaching him, an electric discharge becomes an additional protection.
Social structure and reproduction
Stingrays — These are dioecious cartilaginous fish. The reproductive system is quite complex.
There are three ways for the embryo to develop:
- Some are characterized by live birth, when all stages of development occur in the mother's body and full-fledged individuals are born. With this method, the little rays develop and are born rolled into a tube, the only way they can fit in the uterus, especially when there are several of them. Electric rays are characterized by embryonic uterine nutrition of embryos due to special outgrowths, similar to villi, through which nutrients are supplied from the mother's body to the embryos.
- Other species use ovoviviparity when the uterus contains embryos enclosed in hard shells. Inside such eggs contain the nutrients necessary for the development of the embryo. Maturation occurs in the eggs that the female stingray bears, until the moment the offspring hatch.
- Another option is egg production, when the female lays original eggs containing a large supply of nutrients, fixing them on the substrate elements with the help of special cords .
Young, newly born or hatched fish are already capable of producing an electric current. Due to the fact that offspring are born well adapted for survival, the number of embryos in different species varies, but on average does not exceed 10 individuals. Stingrays are characterized by sexual dimorphism. Sexual maturity occurs when the rays reach a certain size, for example, in the Japanese narca, females become capable of breeding at a body length of about 35 cm, and males, at a length of 20 to 40 cm.
Photo: Electric Ray
All stingrays, including electric ones, are preyed upon by larger predatory fish. In most cases, these are sharks of different species. It is precisely because of the presence of a large number of natural enemies that camouflage coloration, demersal lifestyle, nocturnal activity and electric shock protection allow them to maintain their numbers.
Another enemy for flatfish are various types of parasitic flatworms. Stingrays become infected with them during feeding, and become their permanent or temporary hosts. This is not surprising, because stingrays eat everything they find, including dead organisms that could be the next carriers or hosts of worms.
In addition to predatory fish and parasites, there is a danger for electric skates from fishing for other fish species, which indirectly affects the population size.
Population and species status
Electric stingrays have settled around the globe, especially in the coastal regions of various seas and oceans.
They are represented by 69 species, united in the following families:
All species are capable of generating and releasing current to some extent. Most of the species have been assigned the status «with minimal risk», there are no Red Data Book among electric rays. Electric skates are rarely caught commercially because they are they are of little value.
The danger for these animals is commercial mass trapping of fish, where they accidentally fall as bycatch. Also, traps for stingrays are gill nets set for other fish species, and squid traps. Once in a huge mass of caught fish, most stingrays die, this is especially critical for deep-sea species that do not have strong protective plates on the body surface. In the general mass, the possibility of surviving such stingrays is minimized. Stingrays with strong shells are much more likely to survive.
Caught in gillnets or squid traps, they become easy prey for both large and small predatory fish, since they do not have the opportunity to swim away, and the amount of current for protection is limited. For humans, they are dangerous in case of contact with them. The resulting discharge is not fatal, but dangerous in that it can lead to immobilization and, in extreme cases, loss of consciousness. Such a meeting can occur on any coast where stingrays live. They are difficult to notice during the day, and therefore you should follow the rules for safe swimming in such places.
Amazing creatures of nature have learned to balance on the brink of survival, having developed individual and effective elements of adaptation over millions of years of development, both in the physiology of the body and in behavior. The tactics chosen by electric rays turned out to be successful, as evidenced by the maximum similarity with ancestral species, which has remained unchanged over millions of years of evolution.