This fish trap can be affixed to the side of your aquarium using a large cleaning magnet. Using bait (frozen food or nori on a clip) in the trap, stand 10' away and wait for the right fish to enter. Tug on the fishing line gently to cause the door to pivot shut, maintaining pressure on the line as you approach.
You can tilt the trap on its end to remove it from the aquarium. It will hold the water and the fish, allowing you to carry it safely to a holding tank nearby.
These are built to order, and dimensions can be discussed to fit your aquarium. Wait time is usually about three weeks.