The foul smell of dead fish is due to the compound Sulphur compounds.
Amino compounds are the building blocks of proteins. They are not responsible for the foul smell of dead fish.
Aldehydic compounds are responsible for the sweet smell of fruits and vegetables. They are not responsible for the foul smell of dead fish.
Nitro compounds are responsible for the bitter taste of some foods. They are not responsible for the foul smell of dead fish.
Sulphur compounds are responsible for the foul smell of dead fish. They are produced when bacteria break down the proteins in the fish. The foul smell is a warning sign that the fish is no longer safe to eat.