MOSCOW, July 8, Tatyana Pichugina. Science has long been concerned with the question of how aquatic animals acquire the ability to breathe air. One of the amazing examples is the creeper fish, or climbing perch. Russian scientists are studying it in its natural environment and at the same time helping to restore traditional crafts in Vietnam.The first information about fish, spending part of their lives on land, can be found in ancient Greek authors. The best-known example is the river eel, which can crawl on damp ground. Most amphibious fish live in the tropics, so European researchers mention them from the beginning of the Age of Discovery.
At the end of the 18th century, the German naturalist Markus Bloch compiled an encyclopedia on ichthyology. From the south of India, a collection of dozens of specimens was delivered to him, in which he discovered an unusual fish with a head resembling a shell. The scientist named the new species «turtle fish». In a drawing from that time, she is depicted with blue eyes.
Approximately in the same years, the Holstein naturalist Dagobert Karl Dahldorf, according to some sources, a native of Moscow, left for India. The Society of Naturalists of Copenhagen commissioned him to collect a collection of local fauna. In one of his scientific notes, he shared his observations about a «perch» that climbed a palm tree growing near a pond using spiny fins and gill covers.
Dahldorf's message was translated into English, many European publications reprinted it, embellishing it along the way. It has been claimed, for example, that a fish climbs a tree to drink juice or even palm wine. The famous naturalist Georges Cuvier combined these cases into an independent genus, which he called Anabas (from the Greek — «ascent»). Later, a colonial official, Mitchell, wrote a note in a scientific journal based on the words of a servant who allegedly saw the climbing climbing trees many times.
Already in the 19th century, some scientists doubted this evidence. At the same time, in the Dravidian language and some Malaysian dialects, this fish is called «climbing a tree», which was noticed in the middle of the 20th century by the American ichthyologist Hugh Smith.
Since then, the climbing perch has been observed alive many times, none of the scientists has seen it climbing trees. The reasons, even theoretical ones, that could prompt him to do so are unknown. And yet, the issue has not yet been resolved, says Dmitry Zworykin, Ph.D. in Biology, senior researcher at the A. N. Severtsov Institute for Ecology and Evolution Problems of the Russian Academy of Sciences (subordinate to the Russian Ministry of Education and Science). He worked for several years at the Russian-Vietnamese Tropical Center, detailed the history of the discovery of the species in the Archives of Natural History and became the first author from Russia in this British journal.
«Inaccurate data and errors sometimes play a positive role. Rumors that accompanied reports of fish traveling on land and climbing trees encouraged scientists to study these unusual creatures,» says the biologist.
Where they crawl peranabas
Now science knows a lot of air-breathing fish, and the most interesting live in the tropics. These include the climbing perch, or creeper fish, one of the most famous amphibious fish. Small, resembling a perch, it is widely distributed in fresh water bodies of Vietnam, Taiwan, Laos, Cambodia, Malaysia, and India.
During the rainy season, climbing perches hide in small puddles along the banks of rivers. There they breed without any competition, laying many thousands of eggs. The larvae hatch within a day. The grown juveniles get out on land and spread. Most die, it's good if a dozen individuals reach sexual maturity.
«We don't fully understand how they choose a direction,» continues Dmitry Zworykin. «But this is the survival strategy of this species. They take it in quantity.»
At the end of XX centuries, zoologist Eugene Balon argued that fish for some time protect eggs from predators, that is, they demonstrate primitive parental care. This detail is included in many encyclopedias and textbooks.
“Where did he get this from?” Zworykin asks. “This behavior takes time and effort, there are fewer offspring, but it survives better. No one has seen parental care in the perch. Most likely, this is a myth.” As well as blue eyes — in fact, they are yellowish or reddish in this species.
Panabas crawl on land, relying on fins and gill covers. They have no special devices for «walking». Usually they move over short distances, but sometimes they overcome two hundred meters. In humid conditions outside the reservoir, they are able to stay for several days. But without air in the water, they die in a matter of hours.
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«This feature allows you to survive in waters where other fish cannot exist. Thus, the species avoids competition, which is important for the tropics», — explains the biologist.
Anabas breathe air thanks to the labyrinth organ located under the gill covers. «It looks like a lump of thin sinuous plates. Due to its large surface, it has a good efficiency of gas exchange,» Zworykin clarifies.
In addition to climbing perch, for example, popular aquarium fish have a labyrinth organ — cockerels, macropods, gourami.< br />Scientists have found that the ability to go on land and breathe arose in fish many times over the course of evolution, and independently in different groups. Labyrinths appeared about 50 million years ago and most likely descended from some small freshwater fish (they have nothing to do with amphibians). Anabas, on the other hand, have existed unchanged for ten million years. » data-crop-width=»600″ data-crop-height=»338″ data-source-sid=»not_rian_photo» class=»» />
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Return to traditions
Pernabas is an important part of the diet of Southeast Asians. According to archaeological evidence, it has been used since at least the Stone Age. Fish is grilled, stewed in pots with other foods, but most often boiled, as soups are eaten throughout the day.
Anabas has been bred in ponds since ancient times, often combined with rice growing. Nowadays, due to the active use of fertilizers and pesticides, this tradition has begun to fade. Now it is being revived with the support of the Food and Agriculture Organization of the United Nations (FAO).
“At the end of the 20th century, international programs focused on breeding the most effective aquaculture objects, such as tilapia and large catfish,” says Dmitry Zworykin. Over time, however, it became clear that these species are becoming invasive and threatening the native fauna. Therefore, breeding of small native fish species is now being encouraged. «It's much cheaper, easier and safer for the environment. Available to many small farms,» the biologist notes. True, there are nuances. If you breed climbing perch in ponds, you must use hormonal injections and special feeding methods. This is where the help of scientists was required.
Being a mass species, climbing perch helps to solve environmental problems. If it is caught or bred uncontrollably, it is not known what will happen to the local biocommunities.
Not least, the creeper fish is an important object of fundamental research. It helps to reconstruct the way animals land. By studying fish that can breathe air and move in a different environment, scientists are trying to understand how and why this happened to the ancestors of the first land creatures.