From Wikipedia:
Amines have strong, characteristic odors, and are toxic. The smells of ammonia, old fish, urine, rotting flesh, and semen are all mainly composed of amines. Many kinds of biological activity produce amines by breakdown of amino acids. Many natural neurotransmitters like epinephrine, norepinephrine, dopamine, serotonine, histamine are aminesJust a little fact for the day. Smells like bleach when fresh and fishy when old. Too bad it doesn't smell like flowers or something.