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Duckweed

Datasheet

Description
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Common names 

The main duckweed species are the following:

  • Lemna minor: common duckweed, lesser duckweed [English]; lenticule mineure, petite lentille d'eau [French]; lenteja de agua [Spanish]; klein kroos [Dutch]; kleine Wasserlinse [German]; لمنة صغرى [Arabic]; 浮萍 [Chinese]; ウキクサ [Japanese]; 개구리밥 [Korean]
  • Lemna gibba: fat duckweed, inflated duckweed, gibbous duckweed, swollen duckweed [English]; lentille d'eau bossue [French]; Bultkroos [Dutch]; Bucklige Wasserlinse [German]; lenticchia d'acqua spugnosa [Italian]
  • Spirodela polyrhiza (sometimes spelled Spirodela polyrrhiza): great duckweed, greater duckweed, water flaxseed [English]; spirodèle polyrhize [French]; veelwortelig kroos [Dutch]; Vielwurzelige Teichlinse [German]; lenticchia di palude [Italian]
  • Wolffia arrhiza: rootless duckweed, spotless watermeal [English]; wortelloos kroos [Dutch]; Wurzellose Zwergwasserlinse [German]

Other duckweed species include Landoltia punctata, Lemna disperma, Lemna japonica, Lemna minuta, Lemna paucicostata, Lemna perpusilla, Lemna trisulca, Lemna turionifera, Lemna valdiviana, Spirodela biperforata, Spirodela intermedia, Wolffia australiana, Wolffia columbiana, Wolffia microscopia, Wolffia neglecta, Wolffiella caudate, Wolffiella denticulata, Wolffiella lingulata, Wolffiella oblonga, Wolffiella rotunda (Hasan et al., 2009)

Synonyms 

Spirodela punctata, Spirodela oligorrhiza, Lemna punctata and Lemna oligorrhiza are now known as Landoltia punctata.

Taxonomic information 

The duckweed family, Lemnacae, is placed by certain taxonomists in the Aracaea family. There are about 40 species in five genera: Lemna, Landoltia, Spirodela, Wolffia and Wolffiella. Duckweed taxonomy is often confusing and disputed (Hasan et al., 2009).

Feed categories 
Description 

Duckweeds are tiny free-floating vascular plants found throughout the world on fresh (or sometimes brackish) waters.

Morphology

Their morphology is extremely simple as they have no stems or true leaves, and usually consist of a single or a few flat, oval-shaped and small "fronds": 2 mm or less in diameter for Wolffia species, 6-8 mm for Lemna species and as much as 20 mm for Spirodela species. Each frond may or may not have roots. Most species reproduce by vegetative propagation and are characterized by rapid clonal growth. Daughter fronds form from two pouches on each side of the narrow end of the frond and remain attached to the mother frond during the initial growth phase. Some species also reproduce by producing unisexual and monoecious flowers and seeds. The plants cluster in colonies and form green mats on the surface of the water. It is quite common for floating mats of duckweeds to consist of more than one species, e.g. Lemna and Wolffia. Duckweeds have the ability to reinvigorate when blown by wind to nutrient-rich sites (Rusoff et al., 1980Hasan et al., 2009).

Utilisation

In many parts of the world, duckweeds are consumed by domestic and wild fowl, fish, herbivorous animals, and humans (Boyd, 1968Chang et al., 1977Culley et al., 1973Rusoff et al., 1977Rusoff et al., 1978). One of the smallest duckweeds (Wolffia arrhiza) has been used as a nutritious vegetable by Burmese, Loatians, and the people of Northern Thailand for generations (Bhanthumnavin et al., 1971). Since the 1970s, duckweeds have attracted considerable attention for their high protein content, fast accumulation of biomass compared to terrestrial plants, and ability to absorb nutrients and other chemicals (see the reports and reviews of Skillicorn et al., 1993Iqbal, 1999Hasan et al., 2009Mwale et al., 2013). Duckweeds can grow very quickly in small ponds, ditches or swamps where they can extract large quantities of nutrients, making the plant a potential source of protein for humans and livestock, notably poultry and fish (Mwale et al., 2013Islam, 2002). Duckweeds have a high mineral absorption capacity, they can tolerate high organic loading and are thus being used to process waste waters and remove contaminants from it (Leng et al., 1995). 

Distribution 

Duckweed species are adapted to a wide variety of geographic and climatic zones, with most species inhabiting tropical and subtropical areas (Mwale et al., 2013). They do not grow in waterless deserts and permanently frozen areas. Lemna species, for example, are very rare in regions with high or very low precipitation and are not found in Greenland or the Aleutian Islands (Landolt et al., 1987). Temperature and sunlight control growth, with maximum growth occurring between 17.5 and 30 ºC. Growth is slower at low temperatures, and the plants tend to die when water temperature rises above 35°C. In cold weather, many species of duckweed form a specialized starchy frond (turion) that sinks to the bottom of the pond where it remains dormant until warm water triggers resumption of normal growth. Duckweeds have a wide range of tolerance for pH and survive well from pH 5 to 9, though tolerance levels depend on the species (Hasan et al., 2009). Duckweeds can grow in water of any depth but they cannot survive in fast moving water (more than 0.3 m/sec), or water exposed to wind (Leng et al., 1995; Hasan et al., 2009). Generally, duckweeds are robust in terms of survival with an extreme range of tolerance for temperature, pH, conductivity, nitrogen and phosphorus. However, they are sensitive in that they thrive within well-defined ranges of optimum requirements. Birds and floods often disperse duckweeds to different geographic areas (Hasan et al., 2009). 

Processes 

Duckweeds contain a lot of water (92-95%) and are, therefore, extremely bulky and perishable when harvested. While feeding dried duckweed is often promising from a nutritional point of view, the economic and practical aspects of drying should be taken into consideration. Drying may be too expensive and not feasible, particularly for smallholder farmers (Mwale et al., 2013Du Thanh Hang, 2013). Due to the high water content, artificial drying is costly: a trial in the Netherlands required 30 hours at 40°C to decrease moisture from 95 to 10% (Holshof et al., 2009). Natural, or less expensive methods (sun-drying, drying in the shade, air-drying) are therefore preferable. Drying methods should not diminish the levels of carotene and xanthophylls in the plant when duckweed is intended for livestock that require these pigments (Mwale et al., 2013).

Forage management 

Yields

Duckweeds are highly productive plants, capable of a level of productivity closer to that obtained with microorganisms than with other higher plants (Cross, 1994). Duckweeds can double their mass in 16 h to 2 days under optimal nutrient availability, sunlight, and water temperature. This results in an exponential growth that lasts until the plants become crowded or run out of nutrients (Rusoff et al., 1980Hasan et al., 2009). Reported yields vary widely, ranging from 9 to 38 t DM/ha/year, depending on species, climatic conditions, nutrient supply and environmental conditions (Hasan et al., 2009). In Louisiana, for instance, under summer conditions, with heavy fertilization, up to 44 t/ha/yr have been obtained (Said et al., 1979). Average yields of around 10-20 t DM/ha can be obtained where nutrients are generally not limiting and frequent harvesting is practiced to avoid overcrowding of plants (Hasan et al., 2009).

Farming

Though duckweed plants can easily be established, duckweed farming requires intensive management for optimum production, with daily attention and frequent harvesting needed throughout the year to ensure optimum productivity. Pond depth should be 20-50 cm to reduce the potential sources of stress and to facilitate harvesting. The main issues are when, how much and which fertilizers to apply and when to harvest. Urea, muriate of potash and triple superphosphate are suitable sources of N, and K and P, respectively. Any waste organic material that is readily biodegradable and has a sufficiently high nutrient content can be used for duckweed cultivation. The most economic sources of suitable waste materials are animal manure, kitchen wastes, wastes from food processing plants, biogas effluents, and slaughterhouse wastes. Solid materials, such as manure from livestock, night soil from villages, or food processing wastes, can also be mixed with water and added to ponds. Duckweed should be harvested frequently, preferably daily, the standing crop density determining the amount and timing of harvests. For instance, 10-35% may be harvested daily with the remaining plants left in the pond for further growth (Hasan et al., 2009).

Environmental impact 

Invasiveness

Duckweeds form large covers in waterways, which may negatively affect the water quality and cause odour nuisance. It is recommended to remove these covers frequently, but disposal and composting may be costly. Using duckweeds as animal feed can be a sustainable alternative (Holshof et al., 2009).

Water treatment and bioremediation

Duckweeds can reduce eutrophication effects and provide oxygen from their ability to sustain photosynthesis (Hasan et al., 2009). They are used extensively to reduce the chemical load of sewage ponds during waste water treatment. The basic concept of a duckweed wastewater treatment system is to farm local duckweed on the wastewater requiring treatment. Duckweed wastewater treatment systems have been studied for dairy waste lagoons, raw domestic sewage, secondary effluent, waste stabilization ponds and fish culture systems (Hasan et al., 2009). They have been used to remove diverse pollutants, including heavy metals, estrogenic hormones, or for bioremediation of tannery effluent or water contaminated by an oil refinery (Mwale et al., 2013). Duckweed waste water treatment systems can remove as much as 99% of the nutrients and dissolved solids contained in wastewater (Skillicorn et al., 1993). These substances are then removed permanently from the effluent stream following the harvesting of a proportion of the crop. The plants also reduce suspended solids and biochemical oxygen demand by reduction of sunlight in lagoons. Duckweed systems distinguish themselves from other effluent wastewater treatment mechanisms in that they also produce a valuable, protein-rich biomass as a by-product. Depending on the wastewater, the harvested crop may serve as an animal feed, a feed supplement supplying protein/energy and minerals, or a fertilizer (Hasan et al., 2009).

Nutritional aspects
Nutritional attributes 

The entire duckweed plant is composed of non-structural, metabolically active tissue. Most photosynthesis is devoted to the production of protein and nucleic acids, making duckweeds very high in nutritional value, typically rich in protein and minerals and poor in fibre. However, the chemical composition of duckweeds varies considerably due to the age of the plant, environmental temperature, and the nutrient content of the water. The nutritional content of duckweed is probably more dependent on the mineral concentrations of the growth medium than on the species or their geographic location. As a result, water low in nutrients generally results in reduced nutritional content in duckweed (Hasan et al., 2009).

The crude protein content of duckweeds ranges from 7 to 45% DM, depending on nitrogen availability (Culley et al., 1981). Under optimal conditions, duckweed contains considerable protein, fat, starch and minerals. Duckweeds grown in enriched waters containing minerals or effluents from agricultural and municipal waste lagoons can have a protein content as high as 30-40% DM (Chang et al., 1977Hillman et al., 1978Culley et al., 1973Rusoff et al., 1977Rusoff et al., 1978). However, the protein content of duckweeds obtained from natural waters (ponds, streams, lakes, paddy fields, and ditches) has been reported to range from 7 to 20% DM (Bhanthumnavin et al., 1971Tan, 1970). Slow growth, starvation and aging result in protein levels as low as 7% DM (Landolt et al., 1987). Duckweeds are moderately rich in lysine (about 4% of the protein) though a higher value (6% of the protein) has been reported for a leaf protein extract (Dewanji, 1993).

Though poorer in fibre than terrestrial plants, duckweeds does contain significant amounts of crude fibre. Crude fibre content is generally lower (7-10% DM) for duckweeds grown in nutrient-rich water than those grown in nutrient-poor water (11-17% DM). Duckweeds have a highly variable mineral content (up to more than 30% DM) that is directly linked to the amount of minerals available in the water. They may contain relatively large amounts of potassium and calcium (Leng et al., 1995). Duckweeds have high concentrations of pigments and xanthophylls that make this plant a valuable supplement for livestock, especially poultry, when these pigments can contribute to skin and yolk colour. Carotene contents reported in the literature are in the 600-1000 mg/kg range (Dewanji, 1993; Mwale et al., 2013).

It is important to note that the wide variability in protein and mineral content will often explain the differences observed in feeding trials and estimations of digestibility and energy values. In some cases, protein-rich duckweeds can compete with soybean meal and other sources of quality protein. However, in other cases a high mineral content and low protein content will be detrimental to the energy value, digestibility and performance, thus limiting inclusion rates. It is, therefore, recommended to assess the nutrient content of duckweeds prior to feeding them to livestock.

Potential constraints 

Pathogens, heavy metals and organic toxins

Pathogens, heavy metals and organic toxins are the main public health concerns related to duckweed farming. Pond workers (who come into direct contact with the waste materials used to fertilize the ponds), populations (particularly children) living in the vicinity and the consumers (humans and animals) of products from duckweed pond systems may be at risk. Those risks can be alleviated by adopting work routines, pond designs, such as two-pond systems where duckweeds and fish are grown separately, and food preparation guidelines that limit, if not eliminate, the transfer of pathogens from the wastewater to animals and humans. In the case of duckweeds grown on industrial wastewaters containing heavy metals and organic toxins, it is strongly advised that they are not used for feed and food production, but rather disposed of as safely as possible, for example in bottom-sealed landfills (Iqbal, 1999).

Antinutritional factors

Duckweeds may contain antinutritional factors detrimental to performance when duckweeds are fed at high levels. In particular duckweed species such as Spirodella and Lemna have large quantities of oxalic acid, which limits intake in livestock (Goopy et al., 2003). Growing duckweed in a low-calcium medium for a short period can prevent the formation of calcium oxalate (Franceschi, 1989). Phenolic compounds, tannins and saponins have been reported (Negesse et al., 2009).

Bloat

Slight bloat symptoms were observed in heifers fed fresh duckweed, probably due to the large amount of fresh plant ingested (Rusoff et al., 1978).

Ruminants 

Fresh or dried duckweeds have been fed to cattle, sheep and goats with relatively good results, provided that they are only part of the diet. In several cases, full substitution resulted in lower performance. There are contradictory values about duckweed protein degradability: some authors found duckweed protein to be highly degradable in the rumen (80%, Huque et al., 1996). Others found much lower values (50-60%, Damry et al., 2001) and described duckweed as a valuable source of escape protein.

Results of trials including duckweeds in the diets of cattle are summarized in the table below:

Country Animal type Duckweed species Trial Results Reference
Bangladesh Bulls, 317 kg Mostly Spirodela sp. with Lemna sp., Wolffia spp. Straw, fresh grass and concentrate containing 28% sun-dried duckweeds Mixed duckweeds as a component of a concentrate mixture were eaten by the cattle at 10% of their LW. Huque et al., 1996
United States Holstein heifers, 150 to 300 kg Spirodela polyrhizaLandoltia punctata, Wolffia sp. and Lemna gibba Fresh duckweed and maize silage fed at 2:1 (DM) for 28 days. Control diet based on corn, concentrate and grass pasture.  Higher average daily gain than for the control diet (900 g/d vs. 450 g/d). Rusoff et al., 1978
Mexico Crossbred ewes, 40 kg Lemna sp. and Spirodela sp. Napier grass hay supplemented with 200 or 300 g/d of sun-dried duckweeds No effect on DM intake, estrus parameters (beginning, percentage of ewes, duration), pregnancy rate and progesterone concentration. Zetina-Cordoba et al., 2012
Nigeria West African Dwarf sheep, 10-18 kg Lemna gibba Soybean meal diets with 0, 50 or 100% dried duckweeds Economical and sustainable sheep production sustained by 50% replacement of soybean meal with duck weed meal. Full substitution was detrimental to performance. Belewu et al., 2009
Australia Merino sheep Landoltia punctata Oaten chaff supplemented with fresh (1 kg/d) or sun-dried (50-100 g/d) duckweeds The sheep readily ingested the fresh or dried duckweeds. Diet had no effect on wool measurements (yield, rate of fibre elongation, fibre diameter). Damry et al., 2001
Nigeria West African Dwarf goats, 10-18 kg Spirodela polyrhiza Duckweeds offered ad libitum, fresh or dried, with or without Guinea grass Duckweeds were well accepted, fresh or dried. Intake was maximum when the diet contained 20% fresh duckweeds (440 g/d) and decreased at 40% inclusion rate. Babayemi et al., 2006
Pigs 

There have been few trials on the use of duckweeds for pig feeding. In Cuba, the inclusion of 10% duckweed (Lemna gibba) in the diet of growing pigs resulted in decreased DM digestibility but did not affect performance and energy digestibility (Gutierrez et al., 2001). In Vietnam, dried duckweed (Lemna spp.) was introduced in pig diets at up to 30%, resulting in relatively high nutrient digestibility values (OM digestibility 88%), similar, or higher, than those obtained with dried cassava leaves, stylo and sweet potato vines included at the same rate (Du Thanh Hang et al., 2009).

Poultry 

Due to their high protein content, duckweeds have been tested extensively, as a source of high-quality protein, for domestic poultry such as commercial broilers, village chickens, ducks and quails. Duckweeds are also a valuable source of pigment for meat and egg production (Mwale et al., 2013). The energy value was reported to be relatively poor.

Trials conducted on several poultry species are summarized in the tables below. 

Commercial broiler production

Results with commercial broilers tend to show that duckweeds should be fed in relatively limited amounts. High levels of inclusion (or substitution) rates tend to decrease performance, particular in young chicks that cannot consume enough duckweed due to the bulkiness of the material (Mwale et al., 2013). Though a least-cost formulation trial showed that dried Lemna paucicostata was cost-effective when included at 29.5% in broiler diets (Olorunfemi, 2006), other feeding trials with broilers suggested that the contribution of duckweed to the dietary protein should not exceed 6%. The high carotene content of duckweed has been shown to deepen the yellow colour of the broiler meat and skin (Mwale et al., 2013). Reported values for metabolizable energy are rather low (less than 7 MJ/kg).

Country Poultry type Duckweed species Trial Results Reference
Peru Broilers Lemna gibba 0, 10, 15 or 25% dry duckweed in the diet 25% duckweed resulted in a significant decrease in feed consumption and weight gain but the weight gain of broilers fed 15% duckweed was similar to that of the control diets. Haustein et al., 1994
India Vencobb broiler chicks, 8 d old Lemna minor Diets with 0, 4, 8 or 12% duckweed meal (DWM) ad libitum Body weight, feed intake, feed efficiency, protein efficiency, energy efficiency and profitability linearly declined as the proportion of DWM increased. Kabir et al., 2005
India Starbro broiler chicks Lemna minor Fish meal (12%) fully replaced with combinations of duckweed and soybean meal The full replacement of fish meal with duckweed and soybean meal is not recommended as it reduced feed intake, liveweight gain, feed efficiency, and profitability. Islam et al., 1997
India Broilers Lemna perpusilla Control diet partially replaced, either with 6% fresh duckweed or 7% dry duckweed. No effect on feed intake, weight gain, feed conversion ratio and carcass traits but the inclusion of fresh or dry duckweed reduced the feed cost. Khatun et al., 2004

Smallholder chicken production

Duckweeds have been tested as a supplementary feed in smallholder (village) chicken production, with variable results. It is important to test for the nutritional profile, toxicity and antinutritional factors that might be present in duckweeds, so that corrective measures can be taken before feeding to the chickens (Mwale et al., 2013).

Country Poultry type Duckweed species Trial Results Reference
Vietnam Luong Phuong chickens, 30 d old Lemna minor Fresh duckweed ad libitum, with a basal diet of maize and protein supplement (16% protein in DM) restricted between 60 and 90% of DM intake, or offered ad libitum. Live weight gain and feed conversion deteriorated as the level of duckweed in the diet was increased, as the chickens were unable to eat enough fresh duckweed to compensate for the restriction in the concentrate allowance. Du Thanh Hang, 2013
Cambodia Sampov and Kandong chickens Unspecified Fresh taro leaves, duckweed and water spinach offered 4-5 times a day with broken rice as source of energy. Duckweed was the most preferred green forage, followed by water spinach and taro leaf. The fresh intake of duckweed was 61-116 g/day. Kong Saroeun et al., 2010
Vietnam Tau Vang chickens Lemna minor Basal diets of differing protein content (18-22%) with or without fresh duckweed ad libitum Access to fresh duckweed increased feed intake and growth rate. Nguyen Thi Kim Kang et al., 2004a
Vietnam Tau Vang chickens, 5-15 weeks old Lemna minor Broken rice with roasted soybean partially or fully replaced with fresh duckweed ad libitum Live weight gain and feed conversion improved with duckweed, optimum at 75% substitution but 100% substitution showed the highest profit. Carcass skin of chickens fed duckweed had a deeper orange-yellow colour. Nguyen Thi Kim Kang et al., 2004b
Vietnam Tau Vang chickens, 5-15 weeks old Lemna minor Diet based on 8% roasted soybeans. Birds left to scavenge during the day. A scavenging system with supplementary duckweed and a concentrate feed containing 8% roasted soybeans gave good results under village condition Nguyen Thi Kim Kang et al., 2004b

Laying hens

Work with laying hens has been more limited than in broilers but has been encouraging.

Country Poultry type Duckweed species Trial Results Reference
United States Laying hens Spirodela polyrrhiza Diet containing 12.6% Spirodela meal Dried Spirodela fed at a 12.6% inclusion rate did not impair the performance of laying hens and could also be a means of enhancing Omega 3 levels in eggs. Anderson et al., 2011
Peru Laying hens Lemna gibba Dried duckweed included 0, 15, 25, and 40% inclusion rate Performance (egg production and weight) was maintained at all levels, though the optimal level was 15%. Eggs from hens fed 15 and 25% Lemna had higher protein content than control eggs. The addition of 15% Lemna in the diets resulted in more egg pigmentation than in controls Haustein et al., 1988
Vietnam Tau Vang hens, 19 weeks old Lemna minor Broken rice with roasted soybean partially or fully replaced with fresh duckweed ad libitum Egg production, egg quality and feed conversion were highest at 75% substitution. 100% substitution showed the highest profit. Nguyen Thi Kim Kang et al., 2004c

Ducks

Duckweeds are a natural feed for ducks (Cross, 1994) and there have been numerous trials concerning their use in duck farming. The results of feeding fresh or dried duckweed on performance, skin colour and egg colour have been generally positive.

Country Poultry type Duckweed species Trial Results Reference
Indonesia Local ducks, 1.24 kg Unspecified Diet containing 20% dried duckweed; diet with fresh duckweed, offered in wet form; dried diet and fresh duckweed offered separately ad libitum. Duckweed in different forms did not affect egg weight, egg white, yolk weight and shell thickness. Diet in wet form improved feed conversion (5.3 vs. 7.25). Fresh duckweed ad libitum improved yolk pigmentation. Indarsih et al., 2012
Vietnam Muscovy ducks Lemna minor Rice bran:fresh duckweed at 80:20 (high protein duckweed) or 70:30 (low protein), DM basis ad libitum Final live weight and daily weight gain were highest with high protein duckweed. Few differences in carcass traits except for a more attractive skin colour with duckweed. Dang Thi My Tu et al., 2012
Cambodia Muscovy ducks Lemna sp. Rice bran mixed with fresh duckweed in equal parts on fresh basis and fed ad libitum Supplementing rice bran with fresh duckweed supported growth rates of 26.5 g/d. Phongphanith et al., 2012
Bangladesh Laying Jinding ducks Lemna perpusilla Sun-dried duckweed included at 5 to 15% in the diet as a substitute for mustard oil meal Body weight gain and egg productivity showed a linear declining trend as inclusion rate increased but rates up to 15% could result in a profit due to the lower price of duckweed. Khandaker et al., 2007
Vietnam Crossbred ducklings, 28 to 63 d Lemna sp. Broken rice supplemented with roasted soybeans (0-27 g/d) and fresh duckweed ad libitum Fresh duckweed completely replaced roasted soybeans and a vitamin-mineral premix in broken rice based diets for fattening ducks without reduction in growth performance or carcass traits, though feed efficiency was reduced. Bui Xuan Men et al., 1995
Thailand Muscovy ducks Lemna minor 20% broken rice and 20% (fresh basis) of water spinach or duckweed, or a mixture (35:45) of water spinach and duckweed DM and protein intake, live weight gain and feed conversion were better when the ducks were fed duckweed alone rather than water spinach alone or mixed with duckweed. Ngamsaeng et al., 2004
Bangladesh Crossbred ducklings Lemna trisulca Fish meal (12%) partially replaced with sun-dried duckweed (8, 12 and 16% inclusion rate corresponding to 33, 50 and 67% of fish meal protein substitution) Duckweed replaced up to 50% of fish meal protein without affecting performance. Hamid et al., 1993

Japanese quails

Country Poultry type Duckweed species Trial Results Reference
Thailand Japanese quails Wolffia globosa Replacement of 20, 50 and 75% of soybean protein with Wolffia meal protein 50% of soybean protein can be replaced with Wolffia meal protein without affecting feed efficiency, performance and carcass quality of quails. Skin pigmentation increased with increasing protein replacement. Chantiratikul et al., 2010
Fish 

Use of duckweeds as fish feed is by far the most widespread application (Iqbal, 1999). Because of its attractive nutritional qualities and the relative ease of production, a significant number of studies have been carried on the potential utilization of duckweed biomass as fish feed and an extensive review of the literature up to 2009 has been produced by FAO (see Hasan et al., 2009). Duckweeds can be grown separately and then provided to the fish, or produced in the same pond. Several systems of duckweed-fish polyculture systems have been implemented, notably in Asia (Azim et al., 2003Hasan et al., 2009).

Duckweed can be fed fresh as the only feed, or in combination with other feed components in a polyculture of Chinese and Indian carp species with tilapia. Herbivorous and omnivorous fish such as grass carp (Ctenopharyngodon idella), silver barb (Puntius gonionotus) and tilapia (Oreochromis sp.) readily feed on duckweed (Iqbal, 1999). Catla (Catla catla) and common carp (Cyprinus carpio) compete aggressively for available duckweed feed and consume it directly (Ansal et al., 2010). The preference of duckweed over other aquatic plants has been reported for grass carp and other fish species (Hasan et al., 2009). 

Growth responses of different fish species fed fresh duckweed have been variable. The general trend was that carp perform better than Nile tilapia and other species and that performances obtained with duckweed as the sole feed were better than with the control diets (Hasan et al., 2009). Reviews of feeding trials have shown that duckweed included in dry diets at 13.5-40% can support growth in herbivorous or omnivorous fish, such as carp and tilapia, as well as in protein-demanding carnivorous fish, such as catfish and snakeheads (Ansal et al., 2010Hasan et al., 2009).

Carps

Feeding trials with carp receiving duckweed have been carried out since the early 1960s with generally very positive results (Hasan et al., 2009). Grass carp seem particularly adapted to feeding on Lemna (Landolt et al., 1987). The weight of grass carp could be tripled (from 100 g to 300 g) within 50 days when feeding a mixture of Lemna gibba and Lemna minor (Porath et al., 1977). The growth of hybrid carp (Ctenopharyngodon idella (Val.) X Hypophthalmichthys nobilis) was determined by feeding preference and feed consumption. The most preferred species was Lemna gibba when compared with six other species (Cassani et al., 1983).

Tilapia

Dry duckweed replaced up to 50% of the commercial tilapia feed without adverse effects on fish performance (Essa, 1997; Tavares et al., 2008). In Nile tilapia fingerlings (Oreochromis niloticus) fed diets including 0 to 100% solar kiln-dried duckweed (Spirodela polyrhiza), duckweed inclusion resulted in progressively reduced growth performance and nutrient utilization, but 30% inclusion rate was found to be cost-effective (Fasakin et al., 1999). In hybrid tilapia (Oreochromis niloticus x Oreochromis aureus) grown with duckweed (Lemna gibba) or a combination of duckweed and commercial pellets, this combination gave the best performance. When fed on duckweed alone, intake was low, feed conversion ratio good (1:1) and growth rate poor (0.67% of BW daily). 65% of the duckweed consumed was assimilated and 26% converted to tissue. When the fish were fed on pellets in addition to duckweed the rate of duckweed consumption decreased and growth rate of the fish doubled with feed conversion ratios between 1.2 and 1.8. 70% of the mixed diet was assimilated but only 21% converted. Fish grown on the mixed diet performed similarly to fish grown on pellets but had a better feed conversion ratio (Gaigher et al., 1984). In Nile tilapia fed fresh duckweed, Lemna perpusilla, optimal daily feeding rates of Lemna were 5, 4 and 3% of the total fish body weight on a duckweed-dry-weight basis for fish of 25 to 44 g, 45 to 74 g and 75 to 105 g in weight, respectively (Hassan et al., 1992). Tilapia fed diets with 20% to 40% duckweed contained significantly more ash, phosphorus and protein and significantly less lipid and dry matter than tilapia fed the control diet without duckweed (El-Shafai et al., 2004).

Catfish

Channel catfish (Ictalurus punctatus)

Channel catfish (Ictalurus punctatus) fed a diet containing 20% dry duckweed had similar weight gains and feed conversion efficiency as catfish fed a standard feed (Robinette et al., 1980).

African catfish (Heterobranchus longifilis)

In African catfish (Heterobranchus longifilis) diets, 10% of the fish meal was replaced with dried duckweed (Lemna paucicostata) without affecting growth performance (Effiong et al., 2009b).

Striped catfish (Pangasianodon hypophthalmus)

In Vietnam, with striped catfish fingerlings (Pangasianodon hypophthalmus) the nutrient and energy digestibility of duckweed (Lemna polyrhiza) was lower than for a wide range of other plant ingredients, such as soybean meal, broken rice, maize grain, cassava leaves and sweet potato leaves, which may be partly explained by the high mineral content of the duckweed (22% DM). This low digestibility may limit the possibility of using duckweed as replacement for fish meal, despite the high digestibility of protein and essential amino acids (Da et al., 2013).

Other fish species

Snakehead (Channa striatus)

With snakehead (Channa striatus), duckweed (Lemna minor) included at 50% of the supplementary diet resulted in higher specific growth rates and weight gains as well as lowering the feed cost (Raj et al., 2001).

Milkfish (Chanos chanos)

When duckweed (Lemna spp.) grown on sugar mill waste was harvested and transferred to a milkfish (Chanos chanos) pond, it acted as a fertilizer on the pond and resulted in higher fish production (820 kg/ha in 90 days in duckweed-fertilized ponds vs. 320 kg/ha in inorganically fertilized ponds) (Ogburn et al., 1994).

Jade perch (Scortum barcoo)

In Australia, jade perch (Scortum barcoo) actively consumed and gained weight (with 100% survival) on fresh duckweed alone harvested from an effluent treatment plant (Willett et al., 2003). 

Crustaceans 

In the red claw crayfish (Cherax quadricarinatus), decomposed Spirodela species supported growth equal to that from commercial pellets (Fletcher et al., 1997).

Nutritional tables
Tables of chemical composition and nutritional value 

Avg: average or predicted value; SD: standard deviation; Min: minimum value; Max: maximum value; Nb: number of values (samples) used

Various species included

Main analysis Unit Avg SD Min Max Nb  
Dry matter % as fed 5.6 1.0 4.6 7.9 13  
Crude protein % DM 29.1 4.3 24.9 38.6 15  
Crude fibre % DM 12.5 4.6 6.9 18.7 9  
NDF % DM 40.1 8.2 33.9 58.2 8  
ADF % DM 18.5 4.5 12.4 23.4 4  
Lignin % DM 5.7 4.3 3.2 10.6 3  
Ether extract % DM 6.1 3.6 2.2 13.8 9  
Ash % DM 15.9 3.9 9.5 23.3 14  
Gross energy MJ/kg DM 18.2         *
               
Minerals Unit Avg SD Min Max Nb  
Calcium g/kg DM 23.3 14.2 7.1 33.1 3  
Phosphorus g/kg DM 5.7 0.7 4.9 6.2 3  
Potassium g/kg DM 42.9       1  
Sodium g/kg DM 1.4       1  
Manganese mg/kg DM 1723       1  
Zinc mg/kg DM 75       1  
Copper mg/kg DM 20       1  
Iron mg/kg DM 0       1  
               
Amino acids Unit Avg SD Min Max Nb  
Alanine % protein 4.3 0.5 3.8 4.6 3  
Arginine % protein 4.4 0.7 3.8 5.3 3  
Aspartic acid % protein 6.8 1.0 5.6 7.6 3  
Glutamic acid % protein 7.1 1.2 5.8 8.0 3  
Glycine % protein 3.6 0.5 3.0 4.0 3  
Histidine % protein 1.7 0.5 1.2 2.2 3  
Isoleucine % protein 3.6 0.4 3.1 3.9 3  
Leucine % protein 6.6 0.7 5.8 7.2 3  
Lysine % protein 3.9 0.5 3.4 4.3 3  
Methionine % protein 0.8 0.0 0.8 0.9 3  
Phenylalanine % protein 4.1 0.4 3.6 4.5 3  
Proline % protein 2.9 0.4 2.4 3.3 3  
Serine % protein 2.6 0.3 2.3 2.8 3  
Threonine % protein 3.1 0.5 2.6 3.5 3  
Tyrosine % protein 2.7 0.5 2.2 3.1 3  
Valine % protein 4.3 0.7 3.5 5.0 3  
               
Secondary metabolites Unit Avg SD Min Max Nb  
Tannins (eq. tannic acid) g/kg DM 16.0       1  
Tannins, condensed (eq. catechin) g/kg DM 0.2       1  
               
Ruminant nutritive values Unit Avg SD Min Max Nb  
OM digestibility, ruminants (gas production) % 77       1  
ME ruminants (gas production) MJ/kg DM 6.5       1  

The asterisk * indicates that the average value was obtained by an equation.

References

Bui Xuan Men et al., 1995; Dang Thi My Tu et al., 2012; Hassan et al., 1992; Ly et al., 2002; Negesse et al., 2009; Ngamsaeng et al., 2004; Nguyen Nhut Xuan Dung et al., 2002; Nguyen Nhut Xuan Dung et al., 2002; Rusoff et al., 1980; Zaharaby et al., 2001

Last updated on 30/11/2013 00:17:09

Main analysis Unit Avg SD Min Max Nb  
Dry matter % as fed 80.2 28.8 5.1 97.8 16  
Crude protein % DM 27.8 5.6 15.5 35.6 18  
Crude fibre % DM 13.1 4.0 8.7 20.0 8  
NDF % DM 40.3 11.1 22.5 57.4 9  
ADF % DM 23.9 2.9 20.3 28.9 7  
Lignin % DM 2.3   1.3 3.3 2  
Ether extract % DM 4.0 1.0 2.2 5.1 9  
Ash % DM 18.9 8.0 3.8 35.6 17  
Gross energy MJ/kg DM 17.1 1.1 15.5 17.8 4 *
               
Minerals Unit Avg SD Min Max Nb  
Calcium g/kg DM 20.3   10.3 30.3 2  
Phosphorus g/kg DM 5.2   3.9 6.4 2  
Manganese mg/kg DM 241       1  
Zinc mg/kg DM 167       1  
Copper mg/kg DM 2       1  
Iron mg/kg DM 5405       1  
               
Amino acids Unit Avg SD Min Max Nb  
Alanine % protein 5.6   4.8 6.5 2  
Arginine % protein 5.9 0.9 4.9 6.7 3  
Aspartic acid % protein 8.0   7.4 8.7 2  
Glutamic acid % protein 11.9   7.7 16.0 2  
Glycine % protein 4.6   3.9 5.3 2  
Histidine % protein 2.2 0.3 1.9 2.5 3  
Isoleucine % protein 4.0 0.3 3.8 4.4 3  
Leucine % protein 7.5 0.6 6.9 8.0 3  
Lysine % protein 4.0 0.3 3.6 4.3 3  
Methionine % protein 1.8 0.7 1.1 2.5 3  
Phenylalanine % protein 4.8 0.5 4.4 5.3 3  
Proline % protein 4.2   3.0 5.4 2  
Serine % protein 3.3   2.8 3.8 2  
Threonine % protein 3.6 0.6 3.2 4.2 3  
Tyrosine % protein 3.6 0.4 3.1 3.9 3  
Valine % protein 5.0 0.5 4.7 5.6 3  
               
Secondary metabolites Unit Avg SD Min Max Nb  
Tannins, condensed (eq. catechin) g/kg DM 16.0       1  
               
Ruminant nutritive values Unit Avg SD Min Max Nb  
ME ruminants (gas production) MJ/kg DM 11.7       1  
a (N) % 30.5 11.4 17.8 42.1 4  
b (N) % 60.1 13.1 45.2 76.5 4  
c (N) h-1 0.057 0.014 0.042 0.074 4  
Nitrogen degradability (effective, k=4%) % 66 9 56 79 4 *
Nitrogen degradability (effective, k=6%) % 60 10 50 72 4 *
               
Pig nutritive values Unit Avg SD Min Max Nb  
Energy digestibility, growing pig % 62.7         *
DE growing pig MJ/kg DM 10.7         *
Nitrogen digestibility, growing pig % 64.0       1  
               
Poultry nutritive values Unit Avg SD Min Max Nb  
AME poultry MJ/kg DM 4.9 2.5 3.3 7.7 3  

The asterisk * indicates that the average value was obtained by an equation.

References

Anderson et al., 2011; Bui Huy Nhu Phuc, 2006; Chantiratikul et al., 2011; Da et al., 2013; Domínguez et al., 1996; Du Thanh Hang et al., 2009; Hassan et al., 1992; Haustein et al., 1988; Huque et al., 1996; Islam et al., 1997; Khandaker et al., 2007; Ly et al., 2002; Muztar et al., 1976; Nolan et al., 2001; Rusoff et al., 1980; Sakarya et al., 2005; Zetina-Cordoba et al., 2012

Last updated on 30/11/2013 00:21:19

References
References 
Datasheet citation 

Heuzé V., Tran G., 2015. Duckweed. Feedipedia, a programme by INRA, CIRAD, AFZ and FAO. http://www.feedipedia.org/node/15306 Last updated on October 21, 2015, 10:02

English correction by Tim Smith (Animal Science consultant) and Hélène Thiollet (AFZ)