I simply oil the fish with some olive oil or grape seed oil. Though if I am cooking salmon I actually WANT it to stick. I cook salmon with the skin on. I cook it indirect and once it's roasted to what I want I depend on the skin sticking. It allows me to slide a very large spatula under the meat between the skin, pull the meat leaving the stuck skin. Once the grill cools the skin releases and I simply discard it, otherwise with other fish i,e, catfish, Mahi Mahi, Monkfish, swordfish, tuna and others I use relatively high heat, lube the fish and grill it just like meat. I actually do salmon like this as well when I am in the mood for it but mostly the kids and I like it smoke roasted and I season it with a type of sweeter BBQ rub first this
https://www.weberseasonings.com/product/weber-kc-bbq-rub is one I am fond of. I will also at the end give it a glaze with either high quality true maple syrup or my home made maple syrup. Anyway I just don't like the flavor of cedar in my food. Makes it taste like I am licking a deck