Hi Fella --
Something like 15-20 years ago, I remember going to Wholesale Tropicals and a chap there was utterly convinced one his Oscars had died because it had eaten a bumblebee goby. (Quite what they were doing in the same tank is an issue that never became clear to me.) Anyway, he believed these gobies were poisonous, hence the colours. Can't comment either way as to the validity of that statement, but perhaps if other fish think they're poisonous, it doesn't really matter whether they are or not.
Cheers, Neale
To offer a different view, I successfully kept them together for a couple of years. I reckon the black and yellow stripes warded off the baddies...
It's possible, but I'm not sure how much I'd believe it. They've got warning colouration but I would have thought one of the gobiologists would have picked up on that by now.
I once made the mistake of keeping the goby with my archer fish temporarily, and the archer ate it almost immediately. I couldn't work out why the archer ate it but nothing else would. Most logical answer I could work out was that archers probably eat wasps and hornets above the water line and aren't bothered by the colours...
http/www.youtube.com/watch?v=kkO72XBnebc
Here is a video of the old setup I had.