I have used my "EZE-Lap" (Diamond) sharpener many times in the field. "In the field" is the key note! I am of firm belief that diamond steels & diamond stones, etc. seriously "shorten" a knife's lifespan!
Honing oil and large sharpening stones, in various textures (from more coarse to finer) is the best way to sharpen knives! I use a large Norton tri-honing system, the same as the Randall shop. I am good at it and wind up sharpening many club members knives at my hunting camp.
When I ran the boats, I sharpened all of our filet knives, while my mates did all the "blood work"! We used a lot of different types of knives for those tasks. Forschner "re-grinds", along with Dexter kitchen knives were the vast majority used when we had a lot of fish to clean.
The last paragraph was geared much more towards saltwater fish than freshwater. I skin freshwater panfish and bass, etc. with an electric knife. Afterwards I de-head and remove the ribs with a Randall Model #10-5".
If you are not proficient with sharpening stones, the very best I have found (for ease of use and less blade loss) is a "Spyderco" triangle sharpening system. Consisting of white and grey ceramic sticks, triangular-shaped, this system allows you to sharpen all types of knives, including serrated edges at a variety of angles with perfect results! A phenolic block serves as the base for inserting the sticks. It also works for laying one of the sticks, flat on it's base and sharpening in a more traditional manner.
The whole outfit is under a hundred bucks and travels well, being minimal at space-taking. I have toyed with the idea of carrying sharpening equipment to my trade shows for sale on my tables and may still..."BUT"...folks want me to teach them how to sharpen knives and, as several forum members here can attest,I just don't have the time!!
One more quick word about diamond sharpeners. They do a really quick job of sharpening. This is true..."BUT"...(Ok: That's enough "buts" for one post)...they really don't "sharpen" in the true sense of the word. They "remove blade steel"! I don't mean in a tiny, small fashion...I mean a lot of blade steel! This reduces your overall size of your blade. A sharpening "stone" sharpens your knife, more by "re-shaping" your edge, salvaging more of your blade.
Of course: This is just my opinion and observation but it comes from over 50 years of hunting and fishing experience...for what it's worth.
Stay sharp, Capt. Chris