After three months the farmers drain the paddies, netting the fattened animals. Next they bring in ducks to graze the paddies. The birds leave behind their droppings to fertilize the next rice crop. Foods for the captive animals are chosen to yield maximum growth. In recent years the diets of many cultured fish have been supplemented with vitamins.
Some water plants are as systematically cultivated as agricultural crops.
Traditionally, farmers collected amanori spores by placing long pieces of split bamboo or tree branches in shallow, muddy river water. In two weeks spores settled onto the bamboo and developed into small plants. The bamboo was then moved toward the estuaries, where the amanori thrived on a nutritious mixture of fresh and salt water. Amanori culture is tightly controlled and completely mechanized today. The spores collect on nets that hang in special hatching tanks.