So far the only answer (with a source) I've found was [this] (http://www.reddit.com/r/AskHistorians/comments/2164db/when_and_why_did_fish_become_allowed_on_fridays/cga2udx).
However, I remember learning at the Catholic High School I went to that the historical/cultural reasoning behind it was to be "clean" for Lent. Pigs and cattle were raised in unsanitary pastures and were very bloody when being butchered for meat and those were deemed unclean for the body. However, fish were seen as clean being they came from the water and aren't as bloody while being prepared for consumption.
Two other common things I've heard are (and these usually don't have a source when being said):
*Disclaimer, I was born a raised Catholic for 18 years of my 20 year life, and went to Catholic elementary and high school for a total of 12 years. However, for the past 2 years I've considered myself an empirical agnostic.
I'm this asking question because I was trying to debate with my mother that eating deep fried fish for Lent seems counter-intuitive considering how it's bad for the body in general (especially McDonald's fried fish filet sandwich). I couldn't find many sources that explain the root historical meaning to who first created these rules (and I would assume the answer would lie somewhere in the New Testament, so I would appreciate it if a Theologian could chime in on this). Thanks again for all the help and info!
Fasting during Lent can be traced back to Athanasius (a bishop in Alexandria, Egypt) who in 331CE encouraged, in his festal letters, a period of forty days of fasting preliminary to the Holy Week.
In 339CE, after Athanasius had returned from Rome, he advised that this observance of fasting for 40 days should be carried out by the people of Alexandria, Egypt that it should be universally practiced, with only one meal a day in the evening, forbidding the consumption of both meat and wine.
This is the first reference, but it was not made into common law of the Church at this time, the churches were arguing among churches over all matters of doctrine; (The Catholic Encyclopedia. Vol. 9.) and as we can see from Socrates (5th century CE) in his writing in Church History vol. 22, he indicates that there was enormous diversity in fasting ritual in terms of what people did/didn't eat by the 5th century CE:
"Some abstain from every sort of creature that has life, while others of all the living creatures eat of fish only. Others eat birds as well as fish, because, according to the Mosaic account of the Creation, they too sprang from the water; others abstain from fruit covered by a hard shell and from eggs. Some eat dry bread only, others not even that; others again when they have fasted to the ninth hour partake of various kinds of food"
The habit of fasting before Easter developed very slowly, with enormous diversity in fasting rituals for centuries. However, ~600CE Gregory the great wrote to Augustine stating:
"We abstain from flesh meat, and from all things that come from flesh, as milk, cheese, and eggs."
It is from this that the decision was finally made to have fasting during Lent enshrined in the Corpus Juris, and it became regarded as the common law of the Church, forbidding meat, milk, cheese, eggs etc for all Christians. That was until 1966 in the Apostolic Constitution of Pope Paul VI, Paenitemini. He recommended that fasting be appropriate to the local economic situation of individual countries, making numerous exceptions to the rule, in Venezuela, for example, they celebrate Lent by eating meat. The current practice of fasting through Lent, and abstaining from meat, is regulated by Canons 1250–1253 of the 1983 code of Canon law.
I would assume the answer would lie somewhere in the New Testament
Fasting before feast days was common before Christianity (as well as amongst unrelated religions) and later was not contained to just Easter, along with other 'deny the material world' guides. We're fairly self-entitled these days, though, and being slightly uncomfortable on occasion is basically beyond bearing, so we've given it up over time, and are now left with [whatever version your local area teaches]. Often times its just 'no sweets or alcohol', 'no carbs for lent!', or 'Jesus wants you to eat all your broccoli'. Abstaining from meat specifically isn't particularly special (see Loknik's answer)...