We have had ours 8 months, and we see him all of the time. Although he eats froze, he is a pain in the rear to feed, just watches food float by and then by the time he decided to eat it someone else has grabbed it. Don't get me wrong, he tied for my favorite fish in the tank (tied with the indigo hamlet), and he cleared out a major bristle worm infestation. I am fairly certain that he had tried to eat our very large coral banded shrimp, as a couple times he had a torn tail.... I would not try ours with any small shrimp. He is in with a small mandarin with no issue.
As far as them eating fish, it would have to be a very, very small fish to fit in their mouth, as they do not have the extending mouths like anglerfish.