You might consider washing the inside of the fridge down with the stuff they use to sterilise baby feeding bottles and leaving it to air overnight....
As for the fishy smell - some plastics on electrical fittings degrade chemically over time and when hot. Have a good sniff around the back and at the wall socket and plug - I would suspect an electrical connection first. A poor and dirty connection in the plug for instance might be generating heat and causing the plastic to decompose.
Search on here for fishy smell...
Peccavi
February 2011
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