Sail Fin Tang Turned Terrorist

[serpico]

i had to return my sail fin tang back to my lfs after he started nipping our undulate trigger/ a fish with quite a reputation for being the aggressor not this time he went totally submissive when the sail fin approached he swam on his side and let the sail fin nip him at will didn't even defend himself they have been tank mates around 4 months or so with no probs what turned the tang into a bully. as anyone experienced behaviour like this before.