Water hyacinth
Practical Action
In sewage systems, the root structures of water hyacinth (and other aquatic plants) provide a
suitable environment for aerobic bacteria to function. Aerobic bacteria feed on nutrients and
produce inorganic compounds which in turn provide food for the plants. The plants grow quickly
and can be harvested to provide rich and valuable compost. Water hyacinth has also been used
for the removal or reduction of nutrients, heavy metals, organic compounds and pathogens from
water (Gopal 1987).
Animal fodder. Studies have shown that the nutrients in water hyacinth are available to
ruminants. In Southeast Asia some nonruminant animals are fed rations containing water
hyacinth. In China pig farmers boil chopped water hyacinth with vegetable waste, rice
bran, copra cake and salt to make a suitable feed. In Malaysia fresh water hyacinth is
cooked with rice bran and fishmeal and mixed with copra meal as feed for pigs, ducks
and pond fish. Similar practices are much used in Indonesia, the Philippines and
Thailand (National Academy of Sciences, 1976). The high water and mineral content
mean that it is not suited to all animals.
The use of water hyacinth for animal feed in developing countries could help solve some
of the nutritional problems that exist in these countries. Animal feed is often in short
supply and although humans cannot eat water hyacinth directly, they can feed it to cattle
and other animals which can convert the nutrient into useful food products for human
consumption.
Fertilisers. Water hyacinth can be used on the land either as a green manure or as
compost. As a green manure it can be either ploughed into the ground or used as a
mulch. The plant is ideal for composting. After removing the plant from the water it can
be left to dry for a few days before being mixed with ash, soil and some animal manure.
Microbial decomposition breaks down the fats, lipids, proteins, sugars and starches. The
mixture can be left in piles to compost, the warmer climate of tropical countries
accelerating the process and producing a rich pathogen free compost which can be
applied directly to the soil. The compost increases soil fertility and crop yield and
generally improves the quality of the soil.
Compost can be made on a large or small scale and is well suited to labour intensive, low
capital production. In developing countries where mineral fertiliser is expensive, it is an
elegant solution to the problem of water hyacinth proliferation and also poor soil quality.
In Sri Lanka water hyacinth is mixed with organic municipal waste, ash and soil,
composted and sold to local farmers and market gardeners.
Fish feed. The Chinese grass carp is a fast growing fish which eats aquatic plants. It
grows at a tremendous rate and reach sizes of up to 32kg (National Academy of Sciences,
1979). It is an edible fish with a tasty white meat. It will eat submerged or floating
plants and also bank grasses. The fish can be used for weed control and will eat up to 18
- 40% of its own body weight in a single day (Gopal 1987).
Other fish such as the tilapia, silver carp and the silver dollar fish are all aquatic and can
be used to control aquatic weeds. The manatee or sea cow has also been suggested as
another herbivore which could be used for aquatic weed control.
Water hyacinth has also been used indirectly to feed fish. Dehydrated water hyacinth has
been added to the diet of channel catfish fingerlings to increase their growth (Gopal
1987). It has also been noted that decay of water hyacinth after chemical control
releases nutrients which promote the growth of phytoplankton with subsequent increases
in fish yield (Gopal 1987)
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