Leisenring Black Gnat - Soft Hackle. The Leisenring Black Gnat is reported to be one of the most effective flies that Leisenring devised. The Leisenring Black Gnat can be used for a wide assortment of fish including primarily Trout and Panfish, which can mean, Rainbow trout, Brook Trout, Brown Trout, Bass, Blue Gill, Crappie, Sunfish etc. This pattern is sure to bring great results across north america especially in Ontario, British Columbia, Montana, Washington State, Oregon and Alberta.