First you need to be prepared for the fact that you may catch your other fish.
You can effectively "fish" for it using a very small hook with the barb filed down.
You can build a "heart" trap out of stiff mesh. My fine artwork is below.
Basically this is a long rectangular piece of plastic mesh. There are two larger square pieces of mesh. Cable tie the long rectangular piece in basically a heart shape, and then the other square to the top.
You will place bait in the trap of some sort - cube of food, etc, and the fish will swim in but will likely have a hard time getting out.
You can also try a similar bottle trap - basically a 1 liter or so plastic soda bottle or maybe juice bottle since it has a bigger opening. Cut the top 1/3 off or so, and invert into the bottom of the bottle. then cable tie it together. Put bait in there and again the fish will likely have a hard time getting out.
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