In a large plastic zip-top bag, combine the brown sugar and warm water to dissolve the sugar. Add the soy sauce and cod tips. If the cod tips are not fully submerged, add enough cold water just to cover the tips completely. Refrigerate overnight.
Preheat a grill to high heat.
Remove the cod tips from the marinade and place directly over high heat. Cook until charred, 1 to 2 minutes per side. (You'll notice that the tips will produce a LOT of grease. The black cod is perhaps the oiliest fish you'll ever encounter. That's the highly-valued omega fatty acid kind of oil that is great for your body.)
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