Gyotaku is a remarkably striking form of art using a fish, a piece of paper or linen, and ink. This is an excellent alternative to taxidermy mounting, and way cheaper since you can do it yourself.
This won't work with catch and release, so give that thought up - I have. But, if you catch a memorable fish and want to preserve the memory, give this some thought. Say it's the first fish you child ever caught, or an extra large trout, or...what ever you may want to remember this fish for.
I'll provide a link to instructions, and photos. I'd love to post a photo but there might be copyright problems so I won't - but do take the time to follow the link to see examples of this fantastic technique - real true wall hanging results can be easily attained by anyone.
Basically you cover one side of your fish in ink. It can be any color ink that suits you and you can place different colors of ink in different places on the fish, either to imitate the fish's natural colors or not. Then place the paper or linen on top of the inked fish and rub. Carefully remove the ink/linen and let dry and yell calf rope! You're done - except for framing if that's what you want to do.
You can also use acrylic artist paint, I have a hunch the results would be even better. So check it out, here are a couple of links: