I'm not catholic but I found this quote :.......... Current Church Law Regarding Abstinence:That's why, under current Church law, the days of abstinence fall during Lent, the season of spiritual preparation for Easter. On Ash Wednesday and all of the Fridays of Lent, Catholics over the age of 14 are required to abstain from meat and from foods made with meat.FISH is not considered meat.
I am not catholic, and could be wrong, but the tradition of sacrificing something by denying to partake in it, is to honor the sacrifice Christ made. Most traditionally it is all other meats besides fish, but the practice is not limited to meat. I know of people who give up caffeine or sweets. Hope this helps. God bless.