The invention is a Y-bone fish fillet knife, a specialized Y-bone fish fillet knife blade and methods of using same to debone fish having Y-bones. Features of the novel Y-bone fish fillet knife and its specialized knife edge include an intentionally unsharpened, or rounded edge, notched groove and an arcuate cutting edge. The rounded notched groove tracks and slides along the Y-bones during cutting. The cutting edge may have other shapes and be dual-edged according to other embodiments. The knife and its handle are designed for ambidextrous use.