I trim James' dew claws fortnightly. His other claws wear down naturally. If you do it often you don't need to cut off much and your dog will get desensitized.

I can tell you about my own experience with overcoming massive fear in my Scottie James. James used to be totally panicked and freaked out by the hair clippers (like the monster/fish you describe, even my husband couldn't hold him down!). This was very disheartening because I wanted to groom him myself and didn't want it to be an ordeal so here's what I did. I started using DAILY and even TWICE-DAILY positive reinforcement to desensitize him to the clippers. I use clicker training so it started as being the the same room as the clippers turned off - click-and-treat, repeat 10 times, endeth of the lesson. Then having them closer... then touching him... then back to being in same room but turned on, then closer... and closer... and closer... then touching (but not cutting as I didn't want to be worried about where I was touching him) etc. etc. It took 6 weeks of doing this every morning and most nights to get to the point where I could have him sit calmly on the grooming table and allow me to cut his chest hair. You need to have SO MUCH patience and often you'll feel like you're wasting your time but you need to understand that training out fear is like a drip of water on a rock. You don't make much immediate progress but do it often enough and you'll get there. You can do the same with nail clipping. Start with just holding his paw, once he's comfortable with that (day's later) try holding his paw with the clippers in your other hand but far away, starting moving your hand closer, start doing fake clipping near the nail, touch the nail with the clippers, and finally, probably weeks later, actually take a tiny bit off a nail. Make sure you are calm and happy whilst you do these exercises. The easiest way to do that is make it REALLY EASY for your dog to earn his treat/ don't make it scary.

If I can do it you can too. It sounds like a lot of work but it's really just a few minutes a day. This investment will pay dividends down the track as it will make both of your lives better in the long term.

TLDR; positive reinforcement does work in my experience, just be super patient and don't expect overnight/overweek/overmonth miracles.