Fish Kettle

I picked a really nice old aluminium French, fish kettle, complete with its lifting tray at a market last week. The peasants were selling it as planter ! I'm going to poach a whole salmon and I've got the various recipes for the poaching liquid. What I want to know is do you cover the fish in the liquid, gently bring to a simmer and then turn off the gas and let it cool or put about half an inch of liquid in the kettle and steam the fish? Google has not been much help.