Looking for some information on recreation mounts. What measurements do I need? Do I have to keep the fish or can I just take a few measurements and let it go?

If you are talking about graphite reproduction mounts, good photos, length and girth measurements are all you need. The taxidermist will buy a pre-made replica as close to the size and species of the fish you caught, and paint it to look like your fish. Be sure to interview the person you choose to do your mount in person and see examples of his work close up. A good artist will probably charge more but in the end, it’s worth it for a quality job. 

Ok. Thanks. I’ve never done one but want to see what it would cost and I would need for them to reproduce my catch. That way I can still let the fish go at least. 

Take a bunch of pictures. If there’s any uniqueness (coloration, markings, etc) take close ups of it so they can get it as close to the real thing as possible. 

Get both length & girth & numerous photos. Tell the taxidermist you want your replica to exactly match your measurements. If he doesn't have the right blank try someone else. You can also request he paint the fish to look like your pictures regarding coloration & markings not what he may think your fish should look like. A good taxidermist will work with your wishes but might be more expensive. The best are not cheap.