Although there’s not much difference between the two, professional chefs suggest using a fillet knife for filleting fish, as they’re specially designed with fish filleting in mind.
Fillet knives are flexible and thinner than other available knives in the market, with a blade measuring between 15cm and 28cm. Since they are thinner, they cannot bear excessive force the way a boning knife or a chef’s knife can. However, fillet knives are perfect for taking out scales from a fish without damaging the meat.
On the other hand, boning knives are used to removing bones from the fish and meat. They have blades with a length ranging between 5-inches and 7 inches and are usually flat with a slightly sharp, curved tip. The design of the boning knife offers precise cutting for removing meat from bones or small bones from fish. A boning knife is slightly stiffer and thicker than a fillet fish knife.
The main difference between the two is that a fillet knife is designed for fish filleting, while a boning knife can be used for meat and fish. However, a boning knife won’t deliver the same performance that a fillet knife can when removing bones from fish.