Chapter 3 - It is prohibited to trap fish from fish ponds on yom tov, as is feeding the fish, but taking an animal from an enclosure for food on yom tov is permitted. But there's a direct contradiction to this statement regarding the animals, which the Gemara needs to resolve. Likewise, an apparent contradiction about birds, and when they are considered to be in an enclosure. Also, any catch in traps that are set prior to yom tov can't be eaten on yom tov, unless it's known that it was trapped prior to yom tov as well. Plus, a story of Rabban Gamliel, who declines a gift of fish from a non-Jew, while acknowledging that it would be permissible, which includes the chain of transmission from Tannaim to Amoraim.