Kashrut
Among the numerous laws that form "kashrut" are prohibitions on the consumption of certain animals (such as pork and shellfish), mixtures of meat and milk, and the commandment to slaughter mammals and birds according to a process known as "shechita". There are also laws regarding agricultural produce that might impact the suitability of food for consumption.
Fasting and abstinence in the Catholic Church
Because of this, some Catholic parishes in the United States sponsor a fish fry during Lent. In predominantly Roman Catholic areas, restaurants may adjust their menus during Lent by adding seafood items to the menu in an attempt to appeal to Roman Catholics. However, the same USCCB website says that:While fish, lobster and other shellfish are not considered meat and can be consumed on days of abstinence, indulging in the lavish buffet at your favorite seafood place sort of misses the point. Abstaining from meat and other indulgences during Lent is a penitential practice.