There are traps you can use, basically same as minnow traps, google search and you will find one that could work. Also, one that is similar to a rabbit trap. An acrylic box that has a trap door on one side and you drop the door when it comes in. Or, you may have to break the system down and move the rock out. The sooner you can get him out the better. There is also just the net and patience method. All I have used with variant success depending on the fish. Obviously, any method you use will induce some major stress on the fish, especially the net method, but it is a necessary evil. I'm sure you will read threads or get advice saying to use a baited hook some may be joking but unfortunately there are plenty on here that has used this method and I would NEVER use that method.
