Dragging a bunch of deaths fish Around, scientists may have discovered a hidden power of one of the most important substances in biology: mucus. And what they found could even help us understand the very dawn of vertebrate life on earth.
First of all, it is important to know that the fish are covered with a thin layer of mucus. This viscous coating (it is also called “slime coat”) is known to keep fish healthy by moving away pathogens. Scientists have also found evidence that mucus can reduce drag, helping the fish to swim in the water more easily.
Noah BressmanPhysiologist at the University of Salisbury in Maryland, studied fish mucus in Hagfish, who are notorious For their mucus. But a large part of his other research focuses on amphibious fish or fish species that can move both in water and on earth – and it was curious to know if mucus could help these fish too.
“An amphibious fish that moves, which is essentially crawling army on the ground, and it is covered with mucus, this mucus probably has an impact on the way it moves on earth,” said Bressman Popular science. “Does it make things easier?” Does this lubricate and help them move more easily on earth? »»
To try to answer this question, Bressman turned north of the serpent head, a fish from Asia which has become an invasive species in fresh water habitats dispersed in the United States during the two last decades. North snake heads can reach Almost three feet long and reach up to 19 pounds – and because they can breathe air through the mouth, these impressive fish can both survive and move on land.
The first step was to catch the fish. Bressman and Francis Lopez-Chilel, a undergraduate student at the time, obtained some of their snake heads from the Maryland Natural Resources Department, which would catch fish during the bass surveys. But the two researchers had also learned to fish for snake heads, a sport that has become popular in the United States since the introduction of the species. As part of the collection of samples for this study, Bressman even entered – and won – a snake -headed fishing tournament, which, according to him, has earned him respect for other fishermen at the head of the snake .
“It led more people to let us measure their snake heads,” said Bressman.
In addition, the team gathered common carp and blue catfish, two fish that do not go up to earth, to compare themselves to the serpent’s head. The carp, like snake heads, has ladders, while the catfish has no ladders.
For this study, each fish was euthanized and attached to a force counter via a piece of fishing, which left a researcher to trace and measure exactly the strength it took for the fish to start. The fish were dragged both forward and backwards on a smooth plastic table and a piece of artificial lawn. After having measured each of these configurations, the researchers wiped each fish and led it again to take the same measures without the mucus coating. They published their results on January 29 in the journal Integrative and comparative biology.
All fish species tended to move more easily when covered with mucus. It makes sense – mucus is slippery! But on the table and on the lawn, the mucus-y snake heads were generally even more slippery than the carp mucus-y or the mucus-y catfish. (The only exception was when the fish covered with mucus were fired back on the lawn, where snake heads and catfish had no significant difference in the slide.)
Without mucus, snake heads were much more difficult to shoot than carp or catfish on the table. On the lawn, the mucus snake heads were more slippery than the carp moving backwards, but not forward. And compared to the catfish, the snake heads without mucus were more slippery in the future, without difference between the two species moving back. The team noted that when the snake heads were dried, the remaining pieces of mucus began to feel sticky while the fish dry, potentially helping to increase the amount of force necessary to shoot them.
These results may indicate that snake heads have evolved a more slippery mucus to help them move on earth, suggests the document.
“By evolving mucus which further reduces friction compared to entirely aquatic species such as carp, they may be able to considerably reduce the energy cost required for earthly locomotion, which allows them to cover greater distances”, writes Bressman and Lopez-Chilel.
Dylan WainwrightA biologist at Purdue University who has not been involved in the new research, said Popular science That it was “very excited to see” this new article, and says that the data “align in a way in a satisfactory way with what you would predict”.
“I think a lot about the areas and scales of fish and sometimes mucus in my own work, but there is very little work on it,” explains Wainwright. “And so it was really cool to see someone else think critically on mucus and what it does in different species of fish.”
The study of fish mucus could have practical applications. Some scientists, for example, are trying to develop robots modeled after amphibious fish, noted Bressman. “What if you had to reduce this robot in an artificial mucus that can help it move more easily on earth?” He said.
But perhaps even more important, this new study could offer clues to our own origins. Four hundred million years ago, no vertebrate still lived on earth – everything with a spine was still stuck swimming in the water. Then, fish that lived in shallow coastal habitats (perhaps the famous Tiktaalik) started to stop on the beach. These creatures ended up becoming the common ancestor of each frog, bird and human living today.
We do not know if the mucus played a role in this monumental moment of evolutionary history. But these first terrestrial inhabitants probably produced mucus, said Bressman, and it is possible that they had a kind of adaptation in their mucus which helped them to survive on earth, both as lubrication and to prevent the drying.
And Wainwright wants to know if other species of fish could have a unique mucus. Some fish, he suggests, live in the sediments at the bottom of the water-that is to say that their mucus also has a different friction?
“No one has ever looked at the diversity of mucus with a very close goal,” said Wainwright.
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