The human tongue tends to sense food that is slightly acidic as delicious, and tends to sense it as not delicious when there is alkaline. When fish is alive, the alkaline levels are low, but after dying and beginning to stiffen, the glycogen in the muscle meat turns into lactic acid and becomes acidic. However, as more time passes, the rigor morris releases and the body softens. This is when it tastes the best. After that the proteins break down increasing the amount of alkalines such as ammonia. Also, since the proteins dissolve when they become alkaline, the body breaks down as the alkaline increases. This is the reason that fish tastes worse as it loses its freshness.
Revision date: October 1, 2019