A boning knife is long and pointy so it can pierce meat easily. It is designed to cut meat away from the bone. A fillet knife is meant for deboning fish with ease. Many people do use one or the other for both, but it’s good to have one of each in your arsenal if you spend much time cutting meat and poultry and filleting delicate fish. A flexible blade can be used to fillet a fish but a stiff blade is not recommended for the delicate skin, flesh, and bones of fish.