I'm looking for the best fillet knife available. Must be manual, no electric stuff. Flexible blade at least 6 inches in length. Mainly used on fresh water fish.

I'm sure you could spend a lot more but the Rapala (about $15 from Gander) is sharp as a razor and has been that way for a couple years.  I won't mind tossing it for a new one down the road.

My grandfather had some knives that were hands down the best fillet knife ever made. He had about 9 or 10 of them and throughout the last 10-15 years they slowly disappeared. They did not have any markings so trying to find the company that made is impossible. He fished every day and even kept logs on the weather, depth, lure and how many he caught. Someday I will add up the totals and I'm sure it will be mind boggling.

Buy what the pros use.

Get a Dexter-Russel