I have been so happy that on lemmy, the copy pasta hating sunfish gets soundly criticized and rejected as anything resembling reality.

However, I still want to take the opportunity to copy/paste in the rebuttal to that copy pasta an anti-pasto of sorts. A biologist took the time on reddit to write it up, and I have it saved in markor with a few minor edits.

Sunfish

From u/tea_and_biology

Zoologist here; the majority of this is so inaccurate the guy is basically angry at a figment of his own imagination, paha. I mean there's hyperbole, and then there's hyperbole. Yikes!

They are so completely useless that scientists even debate about how they move. They have little control other than some minor wiggling. So they don't have swim bladders. You know, the one thing that every fish has to make sure it doesn't just sink to the bottom of the ocean when they stop moving and can stay the right side up. This creature. That can barely move to begin with. Can never stop its continuous tour of idiocy across the ocean or it'll fucking sink.

Sunfish are, in fact, well understood and, though clumsy when idly basking, are reasonably accomplished swimmers when diving. They stroke their dorsal and anal fins laterally and in a synchronous manner to generate a lift-based thrust that enables 'em to cruise at speeds of 2-3mph (source), comparable to a whale shark and the perfect speed for suction feeding; ploughing straight into smacks of jellyfish and gobbling 'em all up.

Where they excel amongst fish is their ability to undergo substantial vertical movement in the water column. They possess large deposits of low-density, subcutaneous, gelatinous tissue which, unlike a swim bladder (which would otherwise change volume with hydrostatic pressure), is incompressible, enabling rapid depth changes and keeping them neutrally and stably buoyant independent of surrounding water pressure.

So, yeah, their unusual bodies are basically one big paddle, capable of putting some force behind their swimming to move over considerable distances, descending very deep, very fast.

They mostly only eat jellyfish because of course they do, they could only eat something that has no brain and a possibility of drifting into their mouths I guess. Everything they do eat has almost zero nutritional value and because it's so stupidly fucking big, it has to eat a ton of the almost no nutritional value stuff to stay alive.

Dumb. Also incorrect. Jellyfish and other Cnidarians comprise only around 15% of their diet; they mostly eat young fish (including conger eelets) and crustaceans (pelagic crab, krill, copepods etc.), alongside squid, bivalves and other assorted zooplankton. They're generalist predators, not jellyfish specialists like sea turtles (source).

They have a particularly rapid growth rate amongst bony fish, owing much to their unique genetics (source).

Some scientists have speculated that when they do that, they are absorbing energy from the sun because no one fucking knows how they manage to get any real energy to begin with. So they need the sun I guess.

They spend the majority of their time actively hunting in the very cold deep (usually at ~200m, but up to 600m) and, being ectotherms, therefore regulate their temperature by basking in the sun, before pursuing another dive. Think of marine iguanas basking on hot rocks between nibble trips.

And this concludes why I hate the fuck out of this complete failure of evolution, the Ocean Sunfish. If I ever see one, I will throw rocks at it.

Sunfish have been kicking about in temperate and tropical waters worldwide for around 50 million years and, until humans arrived on the scene, were overwhelmingly successful in their ecological niche. Sadly they're under threat by human activity and human activity alone - frequently caught as by-catch; having little commercial value, like sharks, their fins are cut off before they're dumped, often still alive, back into the sea to die. If one is to start throwing rocks at terrible creatures, perhaps one should look at us humans first.

Or, there's The visual rebuttal, credit to u/iamnotburgerking