Yes, some people eat only fish on Good Friday, my late wife & I did, it wasn't a religious thing for us, more an old tradition, I believe that some restaurants still feature a special on fish dishes on that day, & I don't think it's just a Brit thing, anyway, enjoy your Easter Sunday, but remember what it is about.
I don't know if people eat fish on Good Friday here (I don't pay attention much), but I know we're not permitted to eat meat today by my religion, Christiananity.