March 2, 2024

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These fish seem to swim upside down full time (and for good reason)

These fish seem to swim upside down full time (and for good reason)

Scientists have made a remarkable discovery in the deep regions of the world’s oceans. They came across a fish swimming upside down. This does not appear to be a crazy hobby or a mistake on the fish’s part: there is strong evidence that these fish do this full time.

You can read that in it Journal of Fish Biology. The study revolves around fish that can be classified as finned fish. These are fish that mostly live in the deep regions of the world’s oceans and obtain their food in a very remarkable way. Fish armed with fins are “fish” for their food. On their heads is an elysium (mobile fishing rod) with a fleshy end (the bait, also called isca). Prey is attracted to that fleshy end and bites it, after which the finned fish quickly grabs it and devours it.

Upside down
Now scientists have discovered several of these deep-sea finned fish that appear to swim upside down all the time. “At first glance, it seems very strange,” admits researcher Andrew Stewart in a conversation Scientias.nl. “But the more I thought about it, the more it made sense.”

Long fishing rod
Fish that researchers have seen swimming upside down can be classified as part of the genus Giganticactis. As the name suggests, they are rather large fish, equipped with fins, also equipped with a very long “fishing rod” located at the tip of their snout, and – depending on the species – two to four times longer. The fish itself. Such a long rod can be very useful for eating, but it can be quite uncomfortable when swimming. This is likely why fish swim upside down, Stewart says. “We think that by swimming upside down, they automatically move the fleshy end of the penis under themselves and out of harm’s way. If they didn’t swim upside down, they would always be at risk of having the fleshy end pushed into their mouth. In this case, that end could be damaged and it would be That’s very disadvantageous. “This fleshy end is essential for these fish if they want to find food.”

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Normal behavior
This is not the first time researchers have done this Giganticactis Swimming faces upside down. Previously, a fish belonging to the genus had been recorded three times in the waters between California and Hawaii Giganticactis It was found swimming upside down at a depth of about 5,000 metres. “These fish were photographed floating upside down directly above the sea floor, each hanging vertically down,” the researchers wrote in their study. “When the ROV (underwater robot, ed.) approached them they swam away, still upside down.” But because the observations were made on three different occasions and only one fish was found upside down each time, the researchers weren’t sure if they had observed three upside down fish or if it was just one upside down fish simply swimming over three different fish. Occasions and moments were captured. In short: it remains verbal evidence. It therefore remains unclear whether this behavior is “normal” for fish of this species or not.

In the new study, scientists examined images taken in different places – including off the coast of Australia, California and the Bahamas – with the help of underwater robots and submarines in deep regions of the ocean. So they came up with eight observations of probably four different species Giganticactis Who all swam upside down. “Based on the number of suspected species and the geographic distribution of these observations, we believe this is normal behavior for this group of fish,” Stewart said.

In this video you see a fish belonging to the genus Gigantactis swimming upside down. Video: A.L. Stewart, Beech, T.W., Moore, J., and Peng, X. (2023). Swimming upside down: in situ observations of upside down orientation in Gigantactis, with a new depth record for Ceratiidei. Journal of Fish Biology1-5.

costly?
Although swimming upside down has obvious advantages, as you might imagine, it also has disadvantages. Because it is a different way of moving than most other (deep sea) fish. However, researchers have so far found no clear indications that swimming upside down is not only not beneficial, but also in any way costly for the fish.

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The research reveals once again how little we know about life in the deep sea. According to Stewart, it also emphasizes the importance of using underwater robots. “In the past, we made inferences about the likely behavior of deep-sea organisms by examining specimens we caught in nets. It is therefore not based on direct observations of living specimens. As more and more underwater robots and submarines are being used, we are now able to collect “Combining previously acquired knowledge (based on organisms captured in the deep sea, ed.) with what we see organisms doing. What we have learned so far is that we still have a lot to learn, and that we will learn more as more robots and submarines go underwater.”