Since we are all under quarantine, might as well learn how to fillet right?
https://www.youtube.com/watch?v=GKYt9rMKT9M
I think he's using salt in the vinegar brine, and using sugar at the first step. Your choice in how you want to play it.
Don't omit the Kombu.
Alternatively you can Kombujime, or preserve fish by wrapping in kombu to draw out moisture and add flavor, but maybe plan to do that with something larger that ages well like yellowtail.
Anyways, check out that channel for some excellent knifework.