Fishing is not prized for consumption, although it is available in any Seawater area. It is more regarded as a game, of luck and shit.
Not known as of now.
Fish will live in any area of the sea. They are elusive though, and may even resist against your tries.
Fish must be caught with a Fishing Rod. Then they must be taken out of the Inventory and cooked in either a Campfire or Furnace (For culinary purposes this shall be refered to as the Oven.
Fish, not being actually present on the map, does not exhibit any communication.