I like to keep mine sharp enough to shave with, literally. Sharpening the blade is a skill in itself and is rewarded by making filleting much easier than hacking with a dull edge.
Use an oil stone to put a good edge on the blade then polish and hone it with either a very fine grade oil stone or a smooth ceramic “steel.” Once you have it sharpened it should only take a few strokes on the ceramic to restore the edge; do this little and often.
Diamond sharpeners are OK if you can afford a full size one, the small ones are difficult to use, and any size will take metal off the blade faster than a conventional oil stone. Be gentle with the knife, hold the back of the blade only a blades width above the oil stone and don’t put pressure on it during the last few strokes. You’ll also need to clean the stone now and again.