I restored an old 'boo rod and used Minwax Quickdry Satin Polyurethane on it. I recently built a bamboo rod for a customer. I used Olympic Gloss Marine Spar Varnish on it- two coats. I put one coat on the thread and then the two coats on the whole rod. It turned out nice. Hopefully, when things slow down, I'll have some pictures on my website.
Graphite has a resin base; no varnish is used.
FWIW, I have an old bottle of varnish from about 48 years ago when that was used before epoxies came along.