An aquarium fish trap is usually an acrylic box with a trap door. However, the trouble is getting the fish into the trap. A feeding tube helps lure fish into the trap chamber. Suction cups attach the fish trap to the aquarium wall. A great way to trap a fish is to place the fish trap in the aquarium and only feed in the trap for a few days. Eventually, the fish will become accustomed to the trap and enter for food. Once your target fish is inside you can spring the trap and seal the fish in. Some fish traps are even designed to allow transport after the fish has been caught.