They are the talk of the town on summer beaches where they wash up in shoals, stinging a few bathers in the process. But jellyfish can also become pets.
"The Aurelia jellyfish is like the goldfish of aquariums", explains Nicolas Cagnon, marine biologist in a public aquarium, the Cité de la mer in Cherbourg, for more than ten years. This jellyfish is a hardy animal that accepts to swim in water at 7 to 30°C. In nature, they can be found all over the world, on the beaches of Normandy as well as in the tropics, and only polar waters are avoided.
Even the living rooms of private individuals are now home to a few individuals. The idea came to us while observing visitors to our workplace," says Nicolas Cagnon, co-founder of Jellyfish Concept. They were glued to the jellyfish aquariums while they were quickly passing in front of the fish ones. "These animals so feared on the coast always provoke a little shiver at their evocation but Aurelia are not dangerous for humans. The stinging cells of the Aurelia jellyfish are like miniature harpoon launchers, which it uses to subdue its prey - small crustaceans and young fish fry - but humans are not sensitive to this venom. "If you don't suffer from allergies, you can even take them by hand," says Nicolas Cagnon, who has been in charge of jellyfish breeding at the Cité de la mer since 2003.
The biologist also evokes the mystical appeal of these unusual and wild animals: no one had yet bred them for the pleasure of individuals. Not even the American company, Jelly Fish Art, which sold the first jellyfish aquariums in 2011. "Before our company was founded, these entrepreneurs would go out and fish jellyfish for individuals. So when we started, they bought our first jellyfish from us," notes Nicolas Cagnon. For a year, the two biologists have sold a hundred jellyfish at 35 euros each.
A thousand-year-old animal for a living room ornament
The Aurelia jellyfish look more like decorative animals than pets. Indeed, these primitive life forms do not have a brain and are therefore not able to interact with humans. On the other hand, the spectacle of their evolution within an aquarium is very relaxing. These translucent blue-white jellyfish change color according to the light and swim by contracting their umbrella to make the water come out. They seem to float in their aquarium. In nature, the jellyfish is unable to move from one place to another, just moving up and down to feed on plankton; it is carried by the currents.
"Contrary to what one might think, jellyfish are not more difficult to keep in an aquarium than fish," says Nicolas Cagnon. In the wild, jellyfish are often the only animals to live in polluted harbor waters. It's not that they like these conditions," warns Delphine Thibault-Botha, a biologist at the Mediterranean Institute of Oceanology. But they are dependent on currents and cannot leave polluted waters. And what is certain is that they tolerate pollution (which lowers the level of oxygen in the water, editor's note), unlike fish that flee these areas. "However, the co-founder of Jellyfish concept advises to filter tap water before using it for an aquarium. "Then you have to add salt specially designed for jellyfish," explains Nicolas Cagnon.
In the wild, jellyfish are capable of eating six times their weight per day, but for aquarium breeding, it is possible to feed them only three to four times a week. "If the jellyfish do not eat enough, they shrink", warns Nicolas Cagnon. On the menu of jellyfish, the biologist from Normandy advises to give them live plankton, to be raised in parallel. If the plankton is inert, it falls to the bottom and the jellyfish can't go and retrieve it," he says. "And dead plankton is less rich in vitamins and essential fatty acids. It's a bit like saying that people should eat fresh fruits and vegetables! "As a backup, plankton paste is available.
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