I had a blue throat for a long time in a reef. He was pretty benign, didn't go after crabs that I noticed.
One thing I'll say about blue throats... If I had to vote a fish that's not appropriate for captivity, they'd be it. In the wild they're probably the most pelagic of the triggers, plucking most of their food from the water column. It's why they're considered so reef safe. Whereas most of the other kinds of fish we keep interact with the benthos in some way, either grazing it or hunting for food, blue throats don't. By and large the other truly pelagic fish that we keep are either social and usually kept in groups, or too small and stupid to notice otherwise.
Mine was the only fish I've ever owned that exhibited what a zookeeper would call 'stereotypical behaviour', which happens when reasonably intelligent animals are confined without enough space or mental stimulation to keep them sane. It usually manifests as some form of obsessive compulsive behaviour, like pacing an identical path in their cage for 10 hours at a stretch, pulling out their own hair/feathers, or doing weird and gross things with their faeces that their wild counterparts never ever do.
My blue throat paced. And not "I'm looking for food" pacing, pacing the EXACT same clockwise path around the top of my tank over and over and over. From the moment the lights came on in the morning, until they went out at night. It was like watching a zombie. The only time he wasn't like that was when I was feeding the tank and he could zip around chasing after food.
I just don't think there's enough going on in a tank to prevent a large, solitary, (relatively) intelligent pelagic feeder from going insane with boredom.
I've seen similar behaviours in just about every other blue throat I've seen in captivity, but people don't seem to pick up on what that pacing actually means.
