1. Cut the tuna behind the base of the pectoral fins with a short-bladed knife ,
2. Leave the fish to bleed for three to five minutes.
3. Make a cut, 5-10 cm-long, in the fish’s belly
4. Insert a knife behind the gill cover and cut towards the eye until the knife hits bone (the skull).
5. Remove the gills and internal organs in one piece
Bleed the tuna by making a cut in its sides with a short-bladed knife, five to ten centimetres behind the base of the pectoral fins. The cut, two centimetres deep at most, should be made perpendicular to and across the pectoral fin recess, on both sides of the fish. Blood should flow freely from these cuts. Leave the fish to bleed for three to five minutes.
To accelerate the bleeding process, you can make a cut in the membrane between the gill collar and the gills. Place a seawater hose in this cut to accelerate bleeding and rinse away all blood from the gill cavity.
Make a cut, 5-10 cm-long, in the fish’s belly, up to 1 cm in front of the anus. This cut should be made in the direction in which the scales lie, in other words, towards the anus. Pull the digestive tube through this cut. Cut off the end of the digestive tube near the anus.
Insert a knife behind the gill cover and cut towards the eye until the knife hits bone (the skull). Repeat the procedure on the other side.
Cut the membrane between the gills and the gill collar along its whole length on both sides of the fish
Cut the connection between the gills and the lower jaw. Do not cut the connection between the throat and the lower jaw (the isthmus). If this is cut or broken, it must be tied back to the jaw, using a short piece of line or rope, otherwise gaping will occur.
Cut the connection between the gills and the base of the skull
Remove the gills and internal organs in one piece through the gill opening. This stage is sometimes difficult because of the membranes connecting some organs to the abdominal wall. Remove the heart.
Separate sections of internal organs that can still be consumed like the heart and fish eggs, then discard the rest (stomach and ingsang) into the sea, the heart and fish eggs can be sold to supplement incomes.”
Carefully cut the membrane attached to the gill collar. With the knife, scrape the edge of the collar until you get down to white bone.