I looking for a really good fillet knife for a dads Christmas.  Any ideas?

Define really good...Full custom? Or great off the rack?

I still have a ton of Rapala fillet knives but the wife got me a Bubba Blade this year and I seem to like it quite a bit.

I'm talking off the rack >50$ gift for my dad.

Dexter 2333-9  but its not that much. Is a heck of a knife. Add something else nice to it.

IMHO filet knives are meant to be throwaways. Get him a nice Kershaw pocketknife. Mine is over ten years old and I use it EVERY day. I`m 63 BTW,,,and a Dad!

You haven't used a custom then.  The most popular high end fillet knife in the upper midwest, as well as southern Ontario and southern Manitoba is the Leech Lake Knife.  Tons of fishing guides choose these knives over electric knives even when faced with cleaning large amounts of fish like at Lake of the Woods resorts during ice fishing season.  These knives are flat out awesome.  
http://www.leechlakeknife.com/Home.html
https://www.reedssports.com/all-products/browse/brand/leech-lake-knives

For less money but still good steel, the kitchen aid commercial fillet knife is a pretty good choice as well.  I've cleaned 100 walleye and perch since August with my kitchen aid knife and haven't had to touch up the blade yet.  (my leech lake knife stays at the cabin.)

Maybe something like a Dexter or Rapala but a knife like a Silver Stag is something you keep, and keep a nice edge on. But for cleaning a cooler full of Mahi, I'd go with a Bubba Blade