that's impossible to say. IMO
, if you have so much rock in your tank you can't fit a net, you probably have too much. how does flow get through all of that rock? i would think you have a good amount of dead zones where detritus will build up.
back to the fish, i would get a rubbermaid bin and partially fill it with water, then remove some of the rock and place it in that tub. catch the fish, and then replace the rock....or sell it.
the other option is to wait and see if it goes in the trap, decides to leave the other fish alone, or kills the other fish.