This fish has been swimming upside down for millions of years – now scientists know why
In 1938, a South African fisherman had a sensation in his shell. He caught a specimen of a bluefish which, according to science, had been extinct for 66 million years.
Later, the bluefish, a type of brushfin fish as it is called in the research world, has become an icon for so-called living fossils. In other words, species which have been present on the globe for many millions of years and which are more or less unchanged today.
The bluefish lives very deep in the sea. Occasionally it swims head down, just above the seabed, hoping to catch squid and fish.
Here you can see the bluefish standing vertically in the water and how it finds space in small caves. (Video: National Geographic)
A trip to the scanners in Skejby
Well, a Danish research group with members from the University of Copenhagen and Aarhus University has given the bluefish a ride in a CT and an MRI scanner at Skejby Hospital.
– This fish is iconic, extremely rare and still shrouded in a lot of mystery, says Peter Rask Møller in a press release.
– It lives in underwater caves at a depth of 150 to 200 meters, so it is difficult to observe it alive. And several of the few specimens that have been caught over the years have been cut into small pieces, so we need new methods to learn more about how it delivers. Now we know a little more.
Møller is associate professor and curator at the Statens Natural History Museum, University of Copenhagen, and one of the researchers behind the new studies.
No spine
The individual of the bluefish that forms the basis of the new study originates from the waters around the Comoros in the Indian Ocean. It has been stored at the Zoological Museum in Copenhagen for 60 years. You can read more about this copy under the article.
The result of the research is that the research group can now say something about what makes the bluefish able to hunt while it is on the edge itself. It is about how the skeleton and fat are distributed in the fish’s body.
– We discovered that the bluefish has a special skeleton with a lot of mass in the head and tail, while there are almost no vertebrae. It is quite unique. Because the heavy parts are at the ends of the fish, it is easy for it to stand with its head down. So the balance point is an advantageous mechanism, explains associate professor Henrik Lauridsen from the Department of Clinical Medicine at Aarhus University in the press release.
At Skejby Hospital, the MR scanner has been used to analyze the fat content in the organs of the fish. Based on this, it is possible to calculate the buoyancy of the fish.
How much buoyancy a fish has is related to the sea depth at which it normally lives.
The CT scanner has been used to see where the skeleton in the fish is located. Among other things, the researchers can see that it lacks vertebrae.
German researcher is excited
A researcher who knows a lot about the bluefish is Karen Hissmann. On a daily basis, she is a biologist and researcher at the oceanographic research center GEOMAR in Kiel, Germany.
She has previously observed the bluefish in its natural environment at the Comoros archipelago in the Indian Ocean and off the coast of South Africa.
Hissmann thinks the new study is “magnificent”, although in an email she is quick to highlight a point:
– The bluefish’s normal position in the water is horizontal. Sometimes it turns belly-up in its cave, something that is not unusual for fish in caves. When it is hunting, it does not only happen with its head down. It can also hunt when it is horizontal, she says.
– We observed the bluefish from a manned submarine. We saw that the fish were always balanced no matter how narrow and crowded the holes were, but we could not explain why.
– Henrik Lauridsen and his colleagues can now show why these large and massive fish can maintain their position in the water with very little energy consumption. It is fantastic.
Possibility to preserve museum objects
The method the researchers have used is valuable because you can examine expensive and rare museum specimens of endangered species without having to destroy them.
– This shows that there is quite a lot of scientific potential in collection or museum specimens if new ideas and methods are put to use. CT and MR scanners are expensive and therefore often not available in basic biological research. It is therefore very good that the researchers who are based at institutions with different disciplines can collaborate, says Hismann.
That obvious opportunities for further research
The researchers behind the new study point to obvious opportunities for further research.
In part, they will try to find out where the bluefish give birth to no one. Because it has a gestation period of a full five years and is today a rarity.
According to the researchers, the distribution of skeleton and fat in a fetus would show to what depth they were adapted.
That knowledge can be used to find out how to protect the bluefish.
Karen Hissmann agrees.
– Studies of buoyancy in eels (Anguilla anguilla) could be used in the same way. Eels are important commercially. The stock is unfortunately in continuous decline, she points out.
Option to
The other area of research is at which ocean depths other organisms live. Again, the method can be reused.
– Instead of hunting for fish that are both rare and protected, modern scanning technology allows us to carry out exciting analyzes even if the animal has been on alcohol for many years. Having museum collections of rare animals is almost like entering the world’s best vintage shop, says Peter Rask Møller.
The new study was published in August 2022 in the scientific journal BMC Biology
Source:
Buoyancy and hydrostatic balance in a West Indian Ocean coelacanth Latimeria chalumnae, BMC Biology (2022), DOI: 0.1186/s12915-022-01354-8