That Friday fasting (abstinence) is mostly a lot of hoohaw, here in America. At least nowadays. Originally it came over from England with the early immigrants, if I remember right.
It started among early CHristians as a remembrance of Jesus's suffering on Good Friday and was a total fasting on that day, as well as Wednesday (the day of Christs betrayal). Later, it served as a personal penance performed throughout the year just on Friday's and in more modern times it continued with the eating of fish on Friday. No meat, eggs or fats were to be consumed on that day, just like during Lenten observations.
Friday abstinence, the "fish on Fridays" you refer to, was once such a serious obligation that it was a distinguishing mark of Catholics everywhere - so much so that it even changed restaurant menu's on that day. I remember this, as we used to go out for a big fish dinner on Fridays when I was a kid (so much for abstinence!).
Some form of abstinence is still encouraged for Catholics on Friday's, per the orignal intent. But, in truth, the whole Friday abstinence thing has been relaxed since 1966, except for all Fridays in Lent, which is still binding.
Currently, US bishops encourage Friday abstinence on behalf of world peace.