The article states: "“It’s like looking at a black hole,” Mr. Davis said."

Presumably Mr. Davis is a human, and is describing the black hole-ness of these fish as he perceived them. In the sunlight. With his eyes. I would like a picture of that. Because seeing is believing.

"They aren't even black, to us." You make this whole mythology up about how the fish are. I'm not sure why. Yes they are black. Anything with that reflectivity will be black to us. But we don't have to argue about that, we can just look at this picture of a Pacific Blackdragon: https://pbs.twimg.com/media/CwGT8egWEAAtdMf.jpg