How about sending the fish to Fishy Heaven by way of hypothermia. Place him in a bowl of water and put it in the freezer where he will shortly fall asleep and die.
125gal. megaflow. Fish Residents:
Yellow Tang -(Junior), Flame Angel -(Flamey)
Bicolor Blenny -(Butch), Randall Jawfish -(Jaws)
Lawnmower Blenny -(Lenny), Talbot's Damsel -(Dottie), Tomato Clown -(Ketchup)
Nameless fish include, Neon Blenny, Singapore Shrimp Goby, Yellow Tail Damsel, 1 Skunk Cleaner Shrimps, purple pseudochromis.