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I work part time at a fish market and we do a soy sauce, brown sugar, ginger, garlic and red chili flakes brine. We make that for smoked marlin. Sailfish aren't very common here but we did get some a couple of weeks ago.
You could also treat it like salmon and do a 4 parts brown sugar and one part kosher salt and dry brine it... Heck do it both ways and tell us which you like better!