To bleed any fish they need to be alive. When they die, the blood begins to coagulate along the spine and in areas of dark meat. When this happens it can bitter the meat or make it smell really fishy.
Washing it out with water is bad for the meat too, so dont try to do that if you have unbled meat. The water will wash away a lot of the oils that the good flavor and taste come from. Not to mention the nutrients and omega3 fatty acids that fish are famously known for. From personal experience, fish that is washed out with water also comes out drier.
Solution?
Well if you are going to bleed the fish it should be done while is alive, or ASAP. Alot of people try to stab or lacerate the fish under the "chin" of the fish in the triangle spot between where the gills begin and the pectoral and pelvic fins. This is where the heart of the fish is and where most of the blood goes through.
Also, you can slide a knife under the gill plate and seperate the gills from the "chest" of the fish.
My favorite way is to just grab one of the gills and to rip it completely out.
I have heard of people that when they have the time will hold the fish up right diagonally in a 45 degree angle, tail up head down, so the blood can drain from the tail along the spine and from the upper sections of the meat (picture a fish swimming downward and just hold it that way). If you hold it completely straight tail up head down, the blood will collect in the "shoulder" of the fish in front of the spiny dorsal fin, which in my opinion is some of the best meat.
The deckies will bleed the fish by just ripping the gills out and throwing it in the hold. This works just as well because the heart is not cut and is still able to pump blood. The fish will continue flopping around in the hold while the heart pumps the blood right out through the broken gill.
probably the best way, but its messy as hell.
anatomy taken from
http://floridafisheries.com/Fishes/anatomy.html
Nick Lam