Can fish swim upside down?

Can fish swim upside down ? I pesci nuotano a testa in giù ? intotheblue.it

Can fish swim upside down ? I pesci nuotano a testa in giù ? intotheblue.it

The answer of course is yes. As you can see from the movie shot in Sardinia this Castagnola Nera Chromis Chromis swims in an upside-down hole, regardless of the diver, we also see it feeding upside down. Obviously it is not often that you see fish swimming upside down and the question should rather be … Why should they do it !?

Can fish swim upside down ? I pesci nuotano a testa in giù ? intotheblue.it

Searching the net, I found this nice Harrison Tasoff article, of which I report some parts and that I invite you to read directly on:
https://www.hakaimagazine.com/news/why-dont-fish-swim-upside-down/

Harrison Tasoff
November 10, 2017; Why Don’t Fish Swim Upside Down?
It is a natural question for animals that float, but few scientists have delved into the details.

(…)

“Deepening the mystery is that scientists know few reasons why a fish would swim in any particular orientation—yet they clearly have a preference. Unlike land animals, fish don’t push against the ground to move. And, while moving, fish are no more streamlined in one orientation than another. What’s more, most fish are top heavy, says Brooke Flammang, who studies fish biomechanics at the New Jersey Institute of Technology. Like a child balancing on a beach ball in the pool, gravity wants them to flip. So why don’t they?

The leading explanation is that fish began life right side up, evolutionarily speaking, and so most never had a reason to change. “Just between us, yeah, they never bothered,” says Milton Love, a semi-retired marine zoologist at the University of California, Santa Barbara.

A fish’s preferred orientation “goes back to those very early steps of building a left side and a right side, a head end [and] a tail end,” says Peter Wainwright, who studies fish morphology and behavior at the University of California, Davis.

The shrimpfish swims vertically to blend in with sea urchin spines and coral branches. Although its anatomy is highly specialized, “there’s nothing really flipped over,” says Lauren Sallan of University of Pennsylvania.

Sallan is not sure what led to the change, but it heavily influenced vertebrate evolution. “It’s an early coin flip that’s become a major constraint in fish form,” Sallan says.

The question, then, is why did fish stay dorsal side up? The answer lies in the basic tenets of evolutionary theory: if a new trait doesn’t provide a distinct advantage, things tend to stay the same.

Scientists have teased out some of the perks to swimming top side up. For example, gravity will help move blood from the brain back to the heart, says Flammang. Fish also benefit from having their eyes above their mouths, says Love, as it keeps those sensitive organs away from food and debris, and on the lookout for predators. Even their top-heaviness confers fish some benefits: it increases their maneuverability, Flammang says.

And, some fish have learned to swim upside down, while others flirt with the idea.

Many fish that live near structures such as reefs or piers will orient their bellies against vertical walls or even ceilings, says Wainwright. The fish seem comfortable swimming this way near the structures, but they will swiftly turn right side up when they swim away.

But in the vast majority of cases, says Love, “there’s no selective advantage for most fishes to be upside down.”

(…)

https://www.hakaimagazine.com/news/why-dont-fish-swim-upside-down

Can fish swim upside down ? I pesci nuotano a testa in giù ? intotheblue.it