Fish is like a hunting spot and provides a single tile that can only be exploited by one fisherpig. the fishing spot can provide a max of 8.1 fish.
Fish has a random chance of spawning in a body of water. (The size of the body of water plays no influence in fish spawn). Fish also has no bias for distance to land, some sources can be touching the land (or even be on the land) while other sources require a fisherpig lvl 4 to gather them.