Yes, the Big E does the salt water slurry. But it is done to super cool the fish before going on ice, not really to bleed the fish. They are the only boat currently doing this on the Texas coast as far as I know.
We always stick the tuna behind the pectorial fin to bleed it. It usually cuts the heart and bleeds well. If done immediately, the tuna pretty much goes nuts without the ice.
An interesting thing I saw a deckhand do was cut the heart out of the dead tuna. He set it down and would flick it. Each time the heart would start beating again for a while. Freaky.