If you connect some fishing line to the bottle's cut end, you can then tug it when the fish is in. Now the funnel is in a new location because the bottle rotates almost 90 degrees. The fish can't see the clear plastic and can't find the exit quickly enough. Pull the string to lift the bottle, reach in and pull it out full of water and that fish.
You could even use fishing line to stich the two sections together, but wedging it in there may be enough. Or glue, I suppose.