I have a warmouth sunfish, who's essentially a mini freshwater grouper and can tell the difference between me and other people. Sometimes I like to freak people out a bit by getting them to hold a piece of shrimp right at the surface of the water, because warmouths are ambush predators that go from hovering a foot below the target to launching up and grabbing both the food and the fingertips holding it. She's made a grown man yelp like a startled puppy.