Figure 1.

With the death of the fish, blood circulation, oxygen supply and defense mechanisms cease and pre-rigor mortis begins leading to glycolysis with expenditure of ATP (adenosine triphosphate) and lactic acid production. Consequently, the rigor mortis process begins when pH drops, reducing the microorganism’s growth (desirable effect) and the water retention capacity of proteins (undesirable effect). Actin and myosin bind, the muscle contracts and post-rigor mortis is initiated with the autolysis process. With the increase of microbial growth, the pH increases with the consequent softening of the fish meat. The post-rigor mortis starts after the end of the rigor mortis, which duration varies with fish species, manipulation, size, physical condition, temperature, and stress of the fish before death.