[HN Gopher] Hammerhead sharks are first fish found to 'hold thei... ___________________________________________________________________ Hammerhead sharks are first fish found to 'hold their breath' Author : gmays Score : 75 points Date : 2023-05-12 17:33 UTC (5 hours ago) (HTM) web link (www.nature.com) (TXT) w3m dump (www.nature.com) | ugh123 wrote: | What about fish that jump out of the water? | amelius wrote: | They were either not first, or they simply keep breathing | regardless of availability of oxygen. | HWR_14 wrote: | IIRC, they keep blood pumping (inefficiently) through their | gills while above water. This is less an analogue for "holding | your breath" and more for "being on top of Mt. Everest." You're | physically trying to get oxygen, it's just not working. | hutzlibu wrote: | "You're physically trying to get oxygen, it's just not | working" | | Nitpick, but not working as good, because some humans do | manage to get enough on Everest, to not need extra supplied | oxygen. | lostlogin wrote: | I understood it as thing that could be tolerated for a | short time by some humans. They will die as their | saturations are falling, but they get up and then down | within a narrow window. | | https://en.m.wikipedia.org/wiki/Death_zone | hutzlibu wrote: | You surely could not live there, but some people managed | for astonishing amount of time. | | (and before they proofed it, it was thought to be | literally impossible without extra oxygen) | dj_mc_merlin wrote: | > To understand how sharks were coping with the temperature | changes, Royer and his colleagues developed a device consisting | of instruments that measured depth, water temperature, location | and movement, as well as a probe embedded into muscles near the | dorsal fin that recorded the shark's core temperature. | | > In a paper published in Science1, the team reported that the | sharks would dive several times -- six in an evening, for one | shark -- into deep water at temperatures of 5-11 degC, around 20 | degC colder than at the surface, and remain there for 5-7 minutes | at a time before surfacing. | | > Body temperature remained constant for most of the dive until | the final stage of their ascent back to warmer waters, when it | would decline rapidly. | | > Royer suggests that the sharks are keeping their core | temperature stable by simply not opening their gills or mouth | during the dive; effectively 'holding their breath'. "If you | don't have water going over your gills, then you won't be dumping | your body heat into the environment," he says. | | So they only measured the shark's temperature, the water | temperature, and location (in 3 dimensions). Hammerhead sharks | holding their breath is a hypothesis that aligns with the rapid | heat loss as they ascend and reenter medium-temperature waters | (and start breathing again presumably). It seems a bit early to | say this is the exact mechanism, but I am no marine biologist. | | edit: ah, they have more evidence, including videos of sharks | closing their gills | https://www.science.org/doi/10.1126/science.add4445#sec-4 | dmbche wrote: | For anyone not reading the article, they close their gills to (we | assume) not lose heat when they are diving in deep and cold water | - very interesting - hadn't thought that gills are the fastest | way to exchange heat for fish. "Diving to over 1,000 metres from | tropical temperatures at the surface down to just a couple of | degrees centigrade to feed is a fairly extreme movement to do on | a regular basis," Simpfendorfer says. | | !! | kayodelycaon wrote: | It makes a lot of sense when it's explained. Gills basically | act like a heat exchanger for oxygen. Lungs work very | differently. They don't have continuous flow and humans have | mechanisms to heat up and moisturize air before it reaches | their lungs. | wil421 wrote: | Salmon sharks are warm blooded and can stand temps down to | about 36 degrees. I wonder if they have any adaptations in | their gills to prevent heat loss or if they don't care | because they warm their bodies. | soperj wrote: | > Lungs work very differently. They don't have continuous | flow | | I was under the impression that bird lungs do have continuous | flow. | reubenswartz wrote: | Water is a much more efficient heat exchanger than air. ___________________________________________________________________ (page generated 2023-05-12 23:00 UTC)