Victorinox 7" Fillet Knife, Straight Blade, Flexible, Rosewood Handle, 40311. Our classic, traditional rosewood handle is designed to provide maximum comfort at all times. Renowned rosewood handles feature a carved handle design with the unique beauty of natural rosewood, extra durable. A fillet knife is like a very flexible boning knife that is used to fillet and prepare fish. The blade that allows them to move easily along the backbone and under the skin of fish.