Originally Posted by venturabananas

The best fillet knife is the one that works for you. When I worked in a fish market, each of us had a set of 4-5 different knives we used depending on the kind of fish were were filleting. Long-thin blades for things like halibut, butchers' knives for swordfish, etc. And don't forget a good heavy cleaver for getting through bones of big fish.

Here's a cheap knife that we used a lot. Cheap enough to ruin on mussel shells and not be worried about it.

Dexter Russell Sani-Safe Knives - Fillet, 8 in. Narrow BladeQuantity Discounts Available