Fish is best on Frday as well:
"The sandwich was introduced by a McDonald's
franchise in
Cincinnati, Ohio, in response to declining sales at restaurants on Fridays, due to the
Catholic practice of not eating meat on Fridays at the time (a practice that the Catholic Church continues to consider obligatory on Fridays during
Lent).
[4] Created by young enthusiast
Lou Groen, it has become popular with people who cannot eat meat-based products offered, particularly
Muslims who are more inclined towards eating meat that is
Halal.
[5]"