Wikipedia
"Gaseous amines possess a characteristic ammonia smell, liquid amines have a distinctive "fishy" smell."
http://www.howtomendit.com/answers.php?id=4106
"Aliphatic amines have a fishy smell and are liberated when plastic electrical fittings get over-warm and particularly as they age.
Typically, 13-amp plugs are in fact unable properly to handle 13 amp loads (i.e.3Kw) and will always get warm if handling such loads. Sooner or later they will start to smell as will plastic lamp holders fitted with high-wattage bulbs. Alan Sutton (C.Chem., FRSC)"
Change lampholder and use appropriate wattage lamp.
Peccavi
July 2009