We deserve fresh fish long line but what happens when a ﬁsh dies? Many things happen that effect the fish and ultimately the taste.
A temporary stiffening of the body muscles occurs. This stiffening is rigor mortis, and after rigoramortis the ﬂesh once again becomes soft. Postponing or prolonging rigor mortis in seafood, which can be achieved by chilling it, is highly desirable. This is because signficant bacterial spoilage of the ﬂesh will occur after rigor mortis has passed, therefore postponing the onset of rigor mortis will assist in extending the shelf life of the ﬁsh.
When handling of a ﬁsh (Tuna) that thrashes around on the boat will use up all the oxygen in the muscles, producing lactic acid. Consequently the ﬂesh will become a dark red to purple color and this is undesirable.
When the ﬁsh dies the deoxymyoglobin molecules degrade to form brown metmyoglobin turning the color of the ﬂesh dark. By reducing the stress during harvest and handling and later by use of stunning the fish, the exercised muscle can recover and the oxygen replaced, preserving the red ﬂesh color.