Fish don't have hands, so what do they do when they feel itchy? | Nature Trumpet

Welcome to the 20th issue of the Nature Trumpet column. In the past half month, we have collected the following interesting and noteworthy natural news and research:

1) The cat ignores you, but it knows you are talking to it

2) Sharks: The universal tickler of the sea

3) Right whales are getting thinner, and the world needs fat whales

4) Britain's first European bison is born

5) The heaviest bony fish ever found, but it's dead

5) Thousands of jellyfish come ashore for a snacking carnival

Cats can distinguish human voices

Cats can tell whether the poop scooper is talking to them or to other two-legged animals - whether they want to pay attention to the poop scooper is another matter.

In a new study, scientists conducted an experiment on 16 cats. They asked cat owners and strangers to record themselves saying some phrases that are used when interacting with cats, such as "Do you want to play?" and "Do you want to eat?" The same phrases were recorded twice, once in the tone of speaking to cats, and once in the tone of speaking to adult humans.

Wake me up, you better be busy | Wikimedia Commons

When the cats heard these recordings, they were able to recognize their owners' voices , and when the speaker changed from a stranger to their owner, the intensity of the cats' behaviors increased significantly, such as pupil dilation, ears turning toward the speaker, and increased movement around the room.

Moreover, cats can distinguish different tones . If the owner uses the tone of voice they use when talking to other adults, they will reduce the intensity of their activities (cat: You are not calling me anyway); if the tone is used to talk to cats, their activities will increase significantly, and they will start to move their ears and tails (cat: The poop scooper seems to have something to do with me, did I get caught drinking the water from his cup just now?).

Not calling me? Then I'll continue sleeping｜Cat Swallow

But if the voice comes from a stranger, no matter what tone is used, the cat will not change its behavior. It will only maintain its usual aloofness and be very disrespectful.

So, actually, when cats hear their owners talking to them, they know what is going on. They are just pretending to be ignorant cats .

How do fish scratch?

What do fish do when they feel itchy? How can they scratch themselves when they don't have hands?

There is a way: rub shoulders with sharks !

A tuna comes and rubs the shark's tail | Christopher DH Thompson

Scientists have carefully studied thousands of hours of underwater videos and found that fish living in the open ocean, such as tuna, will use sharks to scratch their itch. Before looking for a shark, the fish will first weigh their own weight. Too small fish generally won't scratch a big shark - otherwise you will treat it as a scratcher, and the shark will treat you as a snack delivered to its door.

Different fish have different ways of scratching each other. Tuna are very disciplined and will line up in a neat line behind the shark, taking turns to swim up and scratch its tail; double-ribbon trevally are more impolite, they will form a large group behind the shark, and then rush out one by one to collide with the shark.

Why are sharks the only ones favored and become the target of fish rubbing? The reason is their skin - shark skin is covered with tiny teeth-like structures that feel like sandpaper and are indeed very suitable for scratching itches.

A double-banded trevally corrals a shark and charges it | Christopher DH Thompson

As ticklers, sharks have become the medical stations of the ocean . Fish prefer to "scratch" their heads and sides more than other parts of their bodies because these areas are more susceptible to parasites. Tickling sharks allows them to remove parasites, dead skin and other irritants from their bodies, which is good for their health.

But the bad news is that the number of sharks in the ocean has dropped sharply, and the number of some sharks in Australia has even dropped by 92%. "Shark, you only lost a life, but I lost a large scratcher!" (Wrong...) However, for the fish in the ocean, if there are no sharks, they can no longer use this scratcher to remove parasites, and their health will indeed be affected .

The world needs fat whales

The critically endangered North Atlantic right whale is in decline again.

This large creature, which can reach 16 meters in length, is gentle by nature and swims slowly. They have been hunted in large numbers for whale oil and whale meat for more than 300 years, and by 1935 there may have been less than 100 of them. Since then, despite international protection, the number of North Atlantic right whales has not recovered and has continued to decline until recent years. The number of female right whales has dropped from 185 in 2014 to 142 in 2018, and it is estimated that only 72 females can reproduce .

North Atlantic right whale with its baby | Wikimedia Commons

In addition to the lack of female whales, the problem of body size also affects the reproductive capacity of right whales. Their body size is getting smaller and smaller, which makes their reproductive capacity gradually decline. Peter Corkeron, chairman of the Marine Mammal Conservation Project, said with great concern: "The world urgently needs more fat whales."

Right whales travel the ocean following their food and are often caught in underwater gear used to catch lobsters and crabs. In an effort to save these innocent whales, federal politics in the United States has set stricter fishing regulations for the lobster fishery . However, right whales are still on the brink of functional extinction, and hopefully the new measures will bring good news to their populations.

North Atlantic Right Whale | NOAA

The birth of the European bison

European bison (Bison bonasus) became extinct in Britain at the end of the ancient Ice Age - but they have recently re-colonized the country and given birth to their first babies.

That's it! | Donovan Wright

In July this year, three female European bison were introduced into a woodland in Kent, England. Just a few months later, one of the bison gave birth to a baby - and everyone was surprised to realize that it was already pregnant when it was released! But this cannot be blamed on people's carelessness, after all, European bison will deliberately hide their pregnancy in the wild to avoid being targeted by predators.

The staff has developed a detailed care plan for this "only cub", but because these cattle are wild, they also have to minimize interference with them . The good news is that under the careful care of other bison, the calf has begun to nibble on leaves and run around happily in the herd.

European bison | Michael Gäbler / Wikimedia Commons

The European bison is the heaviest land animal in Europe, with males growing up to one ton . In the early 20th century, due to heavy hunting, the European bison was almost on the verge of extinction, with only a few individuals left in zoos. Afterwards, they were re-bred and released into the wild in many European countries , and now their number exceeds 9,000. This introduction project will allow the European bison to return to the British woodlands after thousands of years, and the local forests will become a more natural habitat with higher biodiversity.

Largest bony fish

Last December, a large fish floated off the coast of Faial Island in the Atlantic Ocean. Researchers later discovered that the dead fish actually broke the record for the heaviest bony fish .

Record-breaking Fish | AtlanticNaturalist.org

This is a Lamar sunfish (Mola alexandrini), 3.25 meters long and weighing 2,744 kilograms . It is not the heaviest fish - whale sharks, which are cartilaginous fish, can weigh more than 20 tons. But among bony fish, this is the current record for the heaviest. The previous record holder was also a Lamar sunfish, which was discovered in Japan in 1996, 2.72 meters long and weighed 2,300 kilograms. For this record-breaking sunfish, researchers still don't know why it died. There is a huge semi-cylindrical depression on its head, which is covered with red paint commonly found on the keel of the bottom of a ship. But people don't know whether this depression appeared before or after it died.

Jellyfish Carnival

Thousands of stomolophus meleagris recently held a carnival on a beach in North Carolina, USA.

What activities are there at the jellyfish carnival? That is - eating snacks ! It is the spawning season of Sciaenops ocellatus, and freshly baked fry are the favorite snacks of jellyfish. Jellyfish gather here and eat seasonal delicacies.

Jellyfish Carnival | NPS

The English name of the crown jellyfish is cannonball jellyfish. This name is not for nothing. Each jellyfish weighs about 450 grams and is about 25 cm in diameter. It is similar in shape and size to a cannonball . When the whole beach is occupied by jellyfish, it looks very spectacular.

However, this jellyfish cannot swim, it can only go with the flow. Where it ends up is entirely determined by the current and wind. During this carnival, the jellyfish took advantage of the weather and location , and with the help of lower water temperatures, wind and currents, they were able to enjoy a buffet.

Cannonball jellyfish | Cape Hatteras National Seashore

After being washed up on the beach, the fate of the crown jellyfish is uncertain. Maybe after this carnival, they will stay there, become food for crabs and birds, and finally be buried in the sand; if they are lucky, they will be carried back to the ocean by the next tide and continue to go somewhere else.

References

[1] https://link.springer.com/article/10.1007/s10071-022-01674-w

[2] https://phys.org/news/2022-10-fishes-sharks-involved.html

[3] https://phys.org/news/2022-10-endangered-whale-decline-population-falls.html

[4] https://phys.org/news/2022-10-wild-european-bison-born-uk.html

[5] https://www.livescience.com/jellyfish-jamboree-cape-hatteras-north-carolina

[6] https://onlinelibrary.wiley.com/doi/10.1111/jfb.15244

Author: Maotun, Mai Mai

Editor: Mai Mai

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