I use a light weight tang construction for most knives and as already mentioned grind the blades very thin. This makes for a well balanced package. The balance plus the overall lightness of the knife provides for a very lively feel. The knife seems to float in the hand and is very controllable. This contributes to less fatigue when you have a big box of fish or a large elk to process.
The knife should naturally fit your hand and the shape should contribute to safe use. This is especially important when things get wet and slippery. All my fillet knife designs have a flared butt section to prevent the hand from slipping backward on the cutting stroke.