Organic Waste Recycling

Aquatic weeds and their utilization 331

Figure 7.8 A schematic diagram of the major pathways involving aquatic weeds in food
production (Edwards 1980) Note: Pathways which may have the greatest potential at
present are in a heavier solid line. The broken line indicates that the recycling of
livestock and human wastes could play an important role in food production (from
Edwards 1980; reproduced by permission of the International Centre for Living Aquatic
Resources Management).

Chinese grass carp

The most promising species for the consumption of aquatic weeds is the
Chinese grass carp or white amur, Ctenopharyngodon idella (Figure 6.2a). It is a
fast growing fish that feeds voraciously on many aquatic weeds and grows to
weigh as much as 32 kg in mass. It exhibits tolerance to a wide range of
temperatures, to low dissolved oxygen level, as well as to brackish water
(Mitchell 1974).Being a grazer, the grass carp feeds primarily upon submerged
plants, but also eats small floating plants such as duckweed. Submerged weeds
consumed by the fish include hydrilla, water milfoil, chara, Elodea canadensis,

Man

Plankton Slurry

Fresh Fresh

De-

Ash Fresh hydrated

Mulch,

manure

Composting manure Green digesterBiogas Fresh Silage

Aquatic weeds

Manatee,

rodent,

turtle

Herbivorous

fish

Land Livestock

crops

Plankton

feeding

fish