Complex sentence: The fermentation starts from a lactic acid enzyme in the spine of the fish, and so the fermentation is by autolysis; together with bacteria, pungent smelling acids are formed in the fish such as propionic acid, butyric acid and acetic acid.
Split into simpler sentences: The fermentation starts from a lactic acid enzyme in the spine of the fish, and so the fermentation is by autolysis. Together with bacteria, pungent smelling acids are formed in the fish such as propionic acid, butyric acid and acetic acid.