The friendliest place on the web for anyone with an interest in aquariums or fish keeping!
If you have answers, please help by responding to the unanswered posts.
I'm not super familiar with waspfish, but for atleast some, crabs are a natural food source. I keep my fiddlers with bumblebee gobies and the combo has worked out quite nicely. Neither bothers the other. Most of the larger brackish fish I can think of would likely bother the crabs.
How do you have your crab tank set up...do you have an land area or island for them?