If a fish swallows it to where its literally gone not much you can do besides cut it off, if it was swallowed and was impeding a fishes throat take some side-cuts and be sure to cut each barb off and remove the shank of the hook, if its hooked in the gills work it out very carefully using pliers, you can go from the outside of the gillplate to get a different angle. When I gill hook a fish I am very careful to remove the hook and I put them in the well with a lot of rejuvenade so that I can monitor them, or add weight clips to ensure they can maintain an upright stance, it seems to work almost always and at the end of the day the fish are healthy and ready to go!
I've read that some carbonated soda's can aid in stopping bleeding but I haven't tried that trick I usually just hope for the best, put them in the well let them chill out with some meds and let em go.
Good info