You’ve probably seen a fish swallow something up before. In a flash, a worm or lure disappears into an extended mouth and a shimmer of scales flits away. Simple right? Not quite. If you slow everything way down, there is some amazing physics involved.
In the latest video from the YouTube science channel Smarter Every Day, Destin continues his exploits at James Cook University in Australia and brings a high-speed Phantom camera to a fish feed tank. It turns out there is a lot more science involved in a fish bite:
Imagine if you were suddenly a fish, how would you eat? The simplest way to go about it seems to be to swim at a smaller fish, open your mouth, and hope that you get lucky. That’s probably what happened in the oceans of the early Earth, but the competition between predator and prey is fierce. After hundreds of millions of years of an evolutionary arms race, catching prey isn’t simple. As the video above shows, there are a few stages to an aquatic predation by a suction feeder.
First, a fish has to be stealthy. It has to get into striking distance without alerting the prey. Then, jaws fire outwards while the mouth flares out. This sudden increase in volume creates an area of low pressure, which the surrounding, higher pressure water rushes in to equalize (you can see the initial depression in the water from this rush in the video above). Hopefully that rush of water brings with it a tasty fish or insect. Your vacuum cleaner works the same way with air and debris.
But water is much heavier than air. Your vacuum can suck in a bunch of air and it doesn’t get a lot of kickback. A fish does. So in order to deal with all the momentum that comes along with a rush of water, the fish in the video above opens the gills, allowing that momentum to dissipate. And all that fascinating physics happens in the blink of an eye.
Of course, not all fish eat like this. Only a few fish are suction feeders like the barramundi in the video. But if you’ve ever had goldfish, you can see the same physics for yourself!