I can't remember what sort of fish - yeah, I'm rubbish at them, too - and not a particularly good photo.
It just reminded me of the fish tanks at Stretford Arndale when I was little; there was a fish almost as big as the tank and it just lay there floating. Still gives me the creeps to think about it.
I can assure you that Kew keep their fish in better conditions than Stretford Arndale in the 1970s!