I grill lake trout often. Pretty much a milder version of salmon. I use olive oil, kosher salt, black pepper, oregano and garlic powder.
Oil your grates once they are hot, then cook meat side down for about 4 mins, while the fish is skin up add some pam nonstick spray, and then flip and cook skin side down for another 8-9 minutes intil juice is clear and it flakes easily with a fork.
Another recommendation would be to soak it in plain water overnight in the fridge and rinse it well before you season it. The grease will come out into your bowl of water.
Homemade trailer Roaster a.k.a "Hog-A-Nator"; UDS; Dual Chamber Charcoal; ECO Gasser