You have to be really careful with fish as many of them the colors are not in the skin but in the scales. I tried several times with blue gills unsuccessfully. I found it very difficult to skin the fish while keeping every scale perfectly intact, and if a couple scales came off, it was very noticable. The scales are too big too, so when I do get the skin right and very carefully tan it, the scales break while trying to wrap the tubes, as the arc is just too tight. That's for blue-gills, which have great colors...I haven't tried other fish.
Taxidermy is quite a bit easier...with certain fish like blue-gills, you still have to be very careful with the scales, but the bottom line is that you are not trying to bend them into a tight circle..and then trying to cut them in a straight line for a seam without scales breaking off doesn't happen, even with a brand new xacto knife. I'm still not saying that a blue-gill can't be skinned and cast, but from all the work I've tried, it seems like something not worth doing. I have no access to any other fish that have any character worth experimenting with. No doubt some work better than others.