Yeah, but that's Derry for you. Its probably one of the worst places in Ireland for decent food. What is there, not even half a dozen good restaurants in a city with a population of over 100k? I'm from there myself and when I visit family we got to Limavady to eat in the Lime Tree, or Portrush to eat in the Ramore, or Donegal, because Derry is so dreadful for eating out. So I'm not surprised no-one eats fish.
Down here in Cork ( pop. about the same as Derry) we have apparantly got one of the longest wet fish counters in Europe in the English market, so there is buckets of the stuff being eaten here.
Here's one section of the fish market in Cork.