I feel like there's a pretty big jump between saying that a fish reflects light with a somewhat unexpected polarization and saying that the fish is invisible, or breaks the laws of physics. The fish is, in fact, quite visible and obeys the laws of physics just as much as any other animal.

The headline should read: "Fish Use Laws of Physics, Become Mirrors."

I thought it was going to be about fish in deep water seeing in a different light spectrum.

I had a dream last night where someone had an animated tattoo, which got me thinking about how that might be done. I figured you could have layers of tattoo ink done in different light spectrums, and then with special glasses that change spectrums slowly you could see the animation.

Well, Ray Bradbury would like to have a word with you about your dream: http://en.wikipedia.org/wiki/The_Illustrated_Man :)

What law of physics was broken here? The law of headline puffery? Cool discovery, though.

Where is the picture of the invisible fish?

right there, under the headline

This is really neat, but isn't it odd that this trait evolved in fish given that other modes of detection are effective underwater?

Traits evolve under pressure that is local to an environment and the interactions between species that inhabit it. If there were no predators of this fish that used echolocation or another method, then this trait is sufficient to survive and thrive. Evolution is haphazard and almost completely circumstantial, so the shortest answer is, because it didn't have to.

vaguely interesting, but why replace an already link-baited title with one even more misleading? what laws of physics are being broken here?

This was the headline in all aggregators (see url), I could update to my own take on it :P