The pet store did not tell me that they were incompatible. I found this out after the fact, on one of the fishy message boards (Aquaria Central.)
You would think I'd have known not to listen to pet store people, keeping herps and all, but I guess I got fooled. I plan on bringing back the more aggressive of the fishes (the aratus) and trading him for a second fish of the species I like (yellow lab) that is more docile.
I love these fish; the way they creep along in the water, how they have such bright coloration. I am especially fond of the yellow lab. Anyone who is not compatible with him would have to go.