Duckweed (Lemna minor) is an aquatic plant that produces one to three leaves that are 1/16-inch to 1/8-inch long. It floats on top of ponds, lakes, swamps and slow-moving streams; colonies of duckweed can cause a depletion of oxygen in the water. Also called water lentils, duckweeds are gaining international attention for their numerous uses and as a potential for aquaculture.
Duckweed is used in Southeast Asia and other parts of the developing world as feed in fish farming. Duckweed is fed to tilapia and species of carp that eat on top of the water. Carp that feed in the middle and bottom of fish ponds eat the excrement of the carp that feed on top.
The quality of duckweed depends on how it is grown. Duckweed grown slowly in water with low nutrients is high in ash, carbohydrates and fiber but contains low protein. Duckweed grown in waters rich in ammonia and minerals grows rapidly with high protein and lower fiber.
Studies by the UN have shown that duckweed is not good as a source of protein for growing boiler chickens but is useful for older chickens. Duckweed is a useful supplement for young, growing chickens if they are also allowed to scavenge for food.
The UN reports that dried duckweed is useful for chickens laying eggs and adds to the color of the yolk. It gives a higher quality protein than alfalfa meal and can be used in place of alfalfa meal for 5 percent of the diet of egg-laying chickens.
Ducks eat duckweed in the wild, hence its name. Ducks are important poultry in the developing tropical world because they are less susceptible to diseases that afflict chickens. In Vietnam, duckweed is grown from human waste, then mixed with cassava waste and fed to ducks. Ducks are also allowed to scavenge, eating duckweed and whatever else they can find.
Studies are ongoing as to the usefulness of adding duckweed to the diet of pigs. The Cuban Instituto de Investigaciones Porcinas (Institute of Pork Investigation) reports that duckweed mixed with molasses is a good source of protein in pig feed.
Researchers are studying duckweed as a potential source of mineral supplementation for feeding cattle. Farmers add duckweed to corn silage to feed Holstein heifers and to cattle feed in Bangladesh. Duckweed provides ammonia that is helpful to the digestive systems of cattle and other ruminants, animals that rechew their food in the form of a cud.
In Northern Thailand duckweed is called Khai-nam (eggs of the water). Burmese, Laotians and Thais add it to rice during the dry season when green vegetables are scarce.
Duckweed can remove phosphorus from human sewage. Sewage treatment systems using duckweed are available commercially. These systems are cheaper than microbiological and chemical treatment systems and are especially useful at the village level in the developing world.
The UN reports that continuing studies suggest that duckweeds release compounds that kill mosquito larvae. There are reports that sewage water and rice paddies filled with duckweed are free of mosquitoes. Research on the possible benefits of duckweed to control mosquitoes is ongoing.