The takeaway, which also sells kebabs, remained closed for three days until a second inspection found there was no longer an immediate risk to the public.
Owner Hamid Faqiri, 34, admitted he was aware of the mice in the premises prior to the initial inspection.
He said he was “very sorry” for failing to ensure adequate procedures were in place to prevent the infestation and that he would be “careful in the future”.
He was fined £535 and ordered to pay costs of £500, as well as a victim surcharge of £53.
A further inspection last June found improvements had been made at the fish bar, but that there was still work to be done.
The takeaway was given a food hygiene rating of two out of five.