I don't know which category to put this in.?

Last week I was in Tesco's, in The Square, in Dublin. I was buying fresh fish and it looked lovely. Unfortunately, there wasn't enough of what I wanted left and I asked the istant to go inside and see if there was anymore. He replied that what there was of it was defrosting in the sink. I thought no more about it at the time but, when I got home, I realised what the guy had said. Frozen fish was defrosting so that it could be sold as fresh fish and no warning being given that it should not be frozen again. There has to be an infringement of consumers's rights here. Many times I have frozen fresh fish after buying it. Leaving aside the fact that it could have bacteria in it, the nutritional value of twice frozen fish is zilch. Who, in Ireland, can I report this to? I am very annoyed about it but, even more so, worried, that it might be common practise across the board. Have su[permarkets, Tesco in particular, no conscience?