i had a damsel that was kickin' ass on everything in my tank. Took me a week to catch him, but was well worth the effort. The general stress level in the tank is 1/3 what it was before.
I put a clear glass water pitcher in the tank, fed directly into the pitcher for the next several days. Most of the fish figured out how to get into the pitcher and back out once they had eaten. Then, waited for him to go in, slapped a net over the top of the pitcher and pulled his fat ass out. The net part is key. Had him trapped and he jumped for it twice before I actually caught him.
Mat