A lot of times this activity can be everything but bass...trout, bluegill, etc.
If it is bass you need to match what they are chasing as close in size and color as you can...and a lot of times if they are busting on baitfish you need to work your bait faster than you may think. As stated above a fluke can be great - I think a donkey rig(dual rig fluke) fished weightless is great.