Tunas rub against sharks to eliminate parasites

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Tunas rub against sharks to eliminate parasites

The high sea is the largest habitat on the planet. Interactions between marine animals remain difficult to observe. For example, in a new study published in PLOS Oneresearchers decided to leave cameras adrift to directly record and analyze the natural behavior of animals in the ocean.

Image of a tuna rubbing against a shark.
Source: sciencealert.com

Thanks to the thousands of hours of videos taken with the underwater cameras, they hope to learn more about life in the abyss. They were then amazed to find that some fish use sharks to scratch. Although several species have also served as scrapers, it seems that the fish much prefer to rub against the skin of sharks.

This phenomenon has been observed in the Pacific Ocean as well as the Indian Ocean and the Atlantic.

Shark skin is better suited for scratching

Tuna and other fish species have been seen rubbing up against sharks to eliminate parasites, dead skin and other irritants. They do this because their environment gives them little possibilities of getting rid of it. The scientists also noticed that the smaller fish were less likely to rub shoulders with the sharks for fear of being eaten.

To better understand this phenomenon, the researchers decided to study the shark skin structure. They noticed that it is made up of small tooth-like structures called dermal denticles. She looks like sandpapermaking it a particularly suitable surface for scratching.

The scratching ritual differs from one species to another

The images captured by the underwater cameras are exceptional. They showed that fish tend to scratching his head and flanks, although each species had its own way of scratching. These are areas around the eyes, nostrils, gills and the lateral line system along the body that are most infested with parasites.

Additionally, each scratching session is different depending on the species of fish. For example, tunas which are organized in nature, line up behind the shark and take turns rubbing each other against his tail. On the other hand, the rainbowfish, which are much more unruly, gather in a school around the rear end of the shark and jostle to rub each other against his body.


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