The Zonker Fly has a very nice swimming action. It’s tail actually swims in a side-to-side paddling action mimicking a live fish when stripped.
I’ve had success with the Zonker Fly in black colour when fishing for Arapaima and other Amazonian species. See this post: Fly Fishing for Monster Fish – Arapaima, Redtail Catfish, Alligator Gar
How to Fish the Zonker Fly
Use intermediate or sinking lines. Allow for the fly and line to sink all the way to the bottom, and pause-strip very slowly.
Vary the stripping between short and long strips. Often fish will take the fly on a strip after a pause suggesting that spooky or vary fish to be following the fly and strikes when thinking the prey is trying to get away.
Strikes also happens when no action is being imparted to the fly.