Manta rays: Even if they are called "devil", they still dance gracefully on the sea

Manta rays are an ancient cartilaginous fish that appeared in the ocean as early as the Jurassic period. Since more than 100 million years ago, their appearance has hardly changed. Manta rays are very large, with a body length of between 50 cm and 1 meter, a width of up to 7 meters, and a weight of up to 2 tons.

The English name of manta rays is "manta", which comes from Spanish and means blanket. They are also called "blanket fish". Because most of their body surface is black and their swimming posture is very similar to that of bats, we also named them manta rays. In the past, people did not know about manta rays. When fishermen went out to sea, they saw huge black shadows appearing in the sea. The black shadows would jump out of the water and even overturn the boats, which made them very scared, so they also called them "devil fish". In fact, manta rays are very gentle animals. Not only will they not attack humans, they will not attack other marine animals. They are very curious and lively.

Flying on the water

They have a wide, flat body and wing-like pectoral fins. Whether in the water or in the air, manta rays are very graceful in their "flying" movements, so they are also called "flying rays". Manta rays that jump out of the sea more than 2 meters high can keep gliding for several seconds, but when they fall into the water, their abdomens often hit the water surface, making a loud noise. Why do manta rays jump out of the water? Some people speculate that it is to remove parasites from their bodies, or to communicate with their companions... To this day, this is still an unsolved mystery. However, the force of the "double wings" flapping is enough to comminute a person's fractures.

Stinger

Larger manta rays (such as those in the genus Manta) are more docile, while smaller ones are more aggressive and aggressive, using the stinger on their tails as their weapon. These stingers contain venom glands that secrete venom. When the stinger pierces another animal, the venom leaks out, causing the victim to be poisoned, with symptoms such as severe pain, convulsions, nausea, and difficulty breathing, which can lead to death in severe cases. Moreover, the wounds caused by the stinger are prone to secondary infection.

Reproduction

The breeding season of manta rays is from December to April of the following year. In order to reproduce smoothly, manta rays will rush to the breeding site in groups. Countless black "big birds" are seen moving underwater. From time to time, one or two particularly energetic manta rays jump out of the water, turn freely in the air, and then fall back into the sea, splashing huge water. After arriving at the destination, the male manta ray begins to chase the female manta ray: usually several smaller male manta rays follow the slightly larger female manta ray together. After a chase, if the female manta ray is moved, it will gradually slow down and allow the male manta ray to approach. The male manta ray will swim under the female manta ray, caress each other with its pectoral fins, and finally form a partner. After they mate successfully, the male manta ray will leave, and the second pursuer will then stage the same scene. The female manta ray will only accept the pursuit of two male manta rays at most.

The birth of manta ray babies is very special. Most fish are born, but manta ray babies are ovoviviparous. After the fertilized egg develops into an embryo, it absorbs nutrients from the yellow sac, and then indirectly obtains nutrients such as protein and fat from the uterine fluid through a special structure, and develops in the manta ray mother's body. After about 13 months, the manta ray baby will be born directly from the mother's body. When the baby manta ray is just born, it curls up like a small flower roll, and soon it will be able to stretch its pectoral fins and move freely. Moreover, the baby manta ray weighs 20 kilograms and is about 1 meter long when it is born.

Significance of Bionics

The swimming propulsion mode of fish can be divided into two types: median fin/opposite fin propulsion (MPF) and body/tail fin propulsion (BCF). The two modes have their own characteristics, but it is difficult to achieve the best in terms of cruising, acceleration, maneuverability, etc. As a typical MPF propulsion mode fish, the pectoral fin movement of manta rays can be regarded as the coupling of spanwise swing and chordwise fluctuation, which is driven and conducted by cartilage muscles and shows strong flexibility. Using this feature, researchers have conducted in-depth research and incorporated it into the design of underwater robots to solve many problems of low efficiency, high energy consumption, and high noise of traditional submersibles.

References

[1] Ren Tianwen. Elegant and mysterious manta rays[J]. Nature Life.

[2] Chen Guang. Strange manta rays[J]. Animal kaleidoscope.

[3] The underwater ghost dancing on the sea - manta ray[J]. Civilization Vision.

[4] The “devil” of the sea—the manta ray[J].

[5] Chen Lingkun, Qiao Tao, Bi Shusheng, et al. Modeling and simulation of soft pectoral fins of manta ray-like robotic fish[J]. Journal of Mechanical Engineering, 2020, 10.