Yes, I have done it. I'm not an expert. Fish skins are typically "bark tanned", not "brain tanned". When soaking in the tannin, you need to start with a weak solution and increase the concentration over time. Skins are often oiled as a final step. Fish skins are much more succeptable to breakdown via bacteria, so keep the whole process under 50 degrees F. Check out the book fish leather By Lotta Rhame. Basic process:
Skin fish when still fresh.
Flesh and scrape scales
soak in tannins
Work the skin until dry
oil