Does this sound like cruelty to animals to you?

I went to a pub last night and couldnt help noticing a fish tank in there quite close to where bands play in the pub etc. It was karaoke last night and it was really loud, I noticed one of the fish was just flopping on the floor of the tank and seemed distressed. Apart from this the tank was clean and the fish looked well maintained. I know fish can hear very well and cant help thinking it must be unbearable for them. Is this unaceptable do you think and what can be done about it? I am in the UK by the way.