Generally, a niger trigger would consider chromises and damsels as good fun in the same way that popcorn at the movies is fun), quickly eaten, then gone.
My Niger Trigger is a bully. I have gotten lucky with mine being in the same tank with damsels (assortment) and clown fish. But he eats any new damsel I put in there.
We have a velvet damsel that is the same size as the trigger and the buddies. We just added a yellow angel which is twice the size of the trigger and he's left him alone.
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These are a couple of pictures of my niger. He's about 4" and is in a 56 with damsels, clowns, crabs and a shrimp. He prefers pellets and flakes. If I put in a raw shrimp, he'll nip at it, but my pepperment shrimp will actually take it from him. I doubt he'll mess with my crustaceans for at Leat 2 years if the crustations live that long.