You cannot fish as a shaman and you cannot get a prize if there are less than 6 mice in the room.
Lower Right Bowl (Orange Fish): Starfish Earring or Fishbone
Left Bowl (Green Fish): Clownfish Hat or Cat Hat
Upper Right Bowl (Blue/Purple Fish): Fishbowl Hat or Fish Earring
If you get something from the bowl it will show above your head. You might just get the cheese.
The map was criticized in the early stages of the April Fools' holiday event because of its extremely rare rotation. More criticism came as certain moderators and other staff members played the map in hidden/varied rooms, whilst other players were even left unaware of its existence.
If you wish to get all six items available fastest, it's a good idea to see if you can get the two from the Upper Right Bowl (Blue Fish) first as many shamans will rage over being shaman in the map and simply not make a path up there (or troll other mice).