Bread displayed for sale in a west Belfast branch of food store Iceland was found to have been gnawed by mice.
Mouse droppings were also found on and under shelving in the Park Centre store on the Donegall Road following an inspection in September 2008.
The investigation was launched due to a complaint from a customer who alleged they had seen mice in the store.
Belfast City Council brought a prosecution against Iceland Foods Ltd.
The chain was fined £400 at Belfast Magistrates Court on Tuesday for food safety offences, and ordered to pay costs of £66.
After the inspection, which uncovered a number of serious breaches of food hygiene legislation and observed poor standards of cleaning, the store voluntarily closed.
The council's environmental health officers established the full extent of the infestation, and staff carried out a deep clean and addressed pest-proofing issues.
Belfast City Council confirmed to the court that conditions at the premises subsequently improved to their satisfaction.
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