A filleting knife is the thin, sharp, flexible knife used for removing the bones from fish — and for lifting fillets cleanly off the frame. The blade is long, narrow, and deliberately supple, bending to follow the backbone and ribs so the maximum flesh comes away with minimum waste; the sharp point works into the tight spaces around pin bones. Technique matters as much as steel: the cut runs along the bones, not through them, with the blade angled slightly down to keep the fillet intact. A stiff boning knife serves meat; the filleting knife’s flex is made for fish. From the fishmonger’s slab to the home kitchen, it is the specialist tool that turns a whole fish into neat, boneless portions — precision engineering for the most delicate butchery.