What kind of fish is this?

[minerman]

I once swam with hundreds of these little guys in Thailand. They seem peaceful and are very nice looking. I saw him in the fish store the other day. What kind of fish is this? I think I would like to have 2 or 3 of them in reef tank if they are peaceful. Thanks!

 

[thegrilledcheesus]

It's a sergeant major, and aggression really depends, we got a guy in the local club whose sergeant major is a model citizen, but the fish is still a damsel so its up to you if you want to risk it.