Complex sentence: Destroying the brain and the spinal cord of the fish will prevent reflex action from happening; such muscle movements would otherwise consume Adenosine triphosphate (ATP) in the muscle produce lactic acid, making the fish sour.
Split into simpler sentences: Destroying the brain and the spinal cord of the fish will prevent reflex action from happening. Movement of the muscle consumes Adenosine triphosphate (ATP) in the muscle and lactic acid is produced, thereby making the fish sour.