My Basic fly fishing love is casting a dry fly during daylight hours to the rainbow, brook, brown and cutthroat trout populating Montana's famous Big Hole River. It's thrilling to watch an 18-inch brown roll up and take a No. 16 Humpy. Then I enjoy carefully removing the barbless hook and watching the gorgeous fish swim back to its spot to put on a couple more pounds before I hopefully take it again.

I also realize the best time to catch real trophy browns and rainbows is after the sun sets, when these otherwise wary fish abandon caution.

Browns are the most active nighttime feeders; browns also are cannibalistic, as one lady I was guiding discovered. She had just hooked a 10-inch trout when suddenly a jolt raced along her line. She performed well playing what she thought was a revitalized fish, later discovering that a 20-inch brown had come along and swallowed her smaller trout and, in the process, became hooked itself.

The two most important ingredients for nightfishing success are (1)knowing where the big trout are feeding; and (2) knowing when biggies move out to feed. I've found that choice of lure is relatively unimportant. If you know the time and place, you can throw most any kind of big, raunchy fly at them and get hits.

I first check likely spots at dusk along undercut banks and riffles bordering deep pools. If trophy trout are rising, I measure off the distance to the feeding waters, perhaps marking my fly line, so I can cast later in complete darkness without getting hung on tree limbs, rocks or snags. Such preplanning is critical when fishing in total blackness. Night fishing actually is like deer hunting or bonefishing. You stalk individual fish that you know are there.

Big trout, and I mean those five pounds or over, develop gluttonous appetites after dark, but I'm convinced they go on heavy feeding sprees every two or three days. During these active feeding periods, they will munch down minnows, small trout, mice - even ducklings.

A large, deer-hair mouse works wonders after dark. With this or other floating lures, the trick is to strike by sound. A big slurp in the darkness and you set the hook. I also use Woollybuggers, preferring them tied on a No. 4 or No. 2 hook for night action. Obviously, a wet fly is easier to fish because you strike by feel.

Most of my night fishing adventures come during the dark of the moon. It's easier to see when the moon is full, but trout will be almost as wary as during daylight hours. Although I don't nail a trophy every night I go out, those nights when I score a nine-pound brute make all the fruitless nights worthwhile.

Very few of our clients are willing to wade streams after dark. Frankly, it isn't much fun because so much of the thrill comes in seeing a fish rise to the fly. Most of our clients are too pooped after bouncing around in a raft all day. They figure the 18 or 20-incher caught during daylight hours is reward enough.

Just as nighttime flies are big and blustery, so too must the tackle be coarse and rugged. There is no call for a fine tippet. A level leader testing 12 to 15 pounds is about right. Remember, night feeders aren't finicky or selective; they will rip into whatever drifts by and bull right into the brush, once they feel the hook. A smooth reel drag and plenty of backing help ensure the catch, plus a rod built to handle a No. * or heavier line.

No finesse is required in taking bruising-big trout after dark. The game is power versus power. You also must set the hook hard. Big trout have leathery mouths and you need to drive the barb in deep. Once a cagey brown feels the hook, expect the fish to follow a pre-set route toward the nearest brush or bank, trying to break it off.

Generally, a fearless old wallhanger will take over a hole or pocket and, until disturbed, make it his home.

However, once the fish decides to move, it may go miles before stopping. A game and fish department crew electro-shocked the same 20-pound rainbow in a pool two years in a row, but something spooked the tagged fish and it eventually was caught on a worm, 30 miles downstream.

Night fishing works on any stream with lunker trout. My favorites are the Beaverhead and Big Hole, but the Beaverhead is dangerous to wade after dark, because the bottom is pockmarked with holes.

Again, the key is to get a feel for the water before you venture out in the darkness. Know where fish are lying, where the hazards are and where a hooked fish is likely to head when hooked.

Finally, be patient. Night fishing will never supplant my love for the finesse of daytime dry fly casting to rising trout, but action on raw-boned browns and rainbows which ask or give no quarter, a darkened river pool is the place to go.