If you are a commercial troller then gutting them and power flushing is the ONLY way to go. Use a ink pen lower portion on the washdown hose. Gotta be with salt water, though. Your fish will all be number ones unless they are a blush or have some external divots.

Personal use fishery the brining them in the round in ice and salt water sets up the rigor and they are a dream to fillet butterfly style. No need to gut them that way. I think that after they are bled and the blood and slime are washed off the brine makes them so cold the blood does not seep into the meat.