Pike and ferox trout, trolling deadbaits or rapalas. There may be other fish present but I never bothered with them. There are rainbows present, but it is the big browns and pike which the loch is famous for. Get yourself a boat (there are a number of places there that hire them out), troll with deads or 5-7" rapalas and expect very little. But, if something does happen, be ready for it. The trout tend to get caught in 30-40 feet of water, the pike a little shallower. One big hint - islands.
If you're fishing from the bank, usual pike tactics should bring some sport. Reeds, plateaus, drop-offs etc.
Hope that helps,
Jon