I've not been, but there are billfish, dogtooth tuna (toughest fish that swim by many accounts), giant trevally (toughest fish that swim by all the other accounts) and yellow fin tuna. There's also quite a bit of commercial fishing and some of the fish I've mentioned are seasonal.
The Australians are big fans of Fiji. One lure maker I know is fishing there right now. His name is Steve Badman (owner of Demon Jigs), and you can contact him c/o his website
www.demonjigs.com or
mjb@demonjigs.com. Steve is very generous with his time and will suggest charter captains, timing and the like.