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OCR for page 211
6
Aquatic Plants
INTRODUCTION
Aquatic plants occur throughout the world in oceans, saltwater marshes,
rivers, lakes, and waste-treatment ponds. Seaweeds, especially kelp, have
been used as medicinals for centuries, but little use has been made of
other aquatic plants.
These plants have been regarded more as problems than resources. A
National Academy of Sciences report pointed out that the problem of
aquatic weeds was reaching alarming proportions in many parts of the
world (National Research Council, 19761. The report pointed out the
following adverse effects of these plants: blocking canals and pumps in
irrigation projects, interfering with hydroelectric production, wasting water
by evapotranspiration, hindering boat traffic, increasing waterborne dis-
ease, interfering with fish culture and fishing, and impeding drainage,
which results in flooding. The problem seems to be more severe in tropical
areas. Aquatic plants may foster mosquitoborne diseases because small
sheltered pools formed between floating plants are well adapted for mos-
quito breeding.
Recently, aquatic plants have been recognized as potentially valuable
resources for animal feed and other uses. The production per hectare may
be quite large. Problems exist in harvesting and processing these plants
for animal feed, since they are grown in water and are very high in moisture
content. Nevertheless, they appear to be valuable resources for use as
feedstuffs for production of meat, milk, and eggs.
211
OCR for page 212
212 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
QUANTITY
Information is available on seaweed production by countries known to
harvest seaweeds (Naylor, 19761. The values by countries for 1960, 1967,
and 1973 are given in Table 59. The total tonnage harvested is not very
large, especially considering the low dry-matter content of the harvested
seaweed.
Data are not available on total quantity of other aquatic plants; however,
there is potential for very large quantities. For example, growth rates of
800 kg dry matter/ha/day have been recorded for water hyacinth (National
Research Council, 1976~. If such growth could be expected for even 6
months a year, a yield of 146 tons dry matter/ha would be achieved.
Yields of 17.8 tons dry matter/ha were reported for duckweeds, compared
to 4.4 to 15.9 tons for alfalfa for hay (Hillman and Culley, 1978~. Standing
crops of microalgae have yielded up to 1,130 g dry weight/m2 surface
pond (Boyd, 1 973a). This would amount to 1 1 .3 tons dry matter/ha.
PHYSICAL CHARACTERISTICS
The physical characteristics of aquatic plants present problems in har-
vesting and processing. Algae are small (5 to 15 ~m) and have low specific
gravity (Golueke and Oswald, 19651. Kelp varies in length, from very
small to 6 to 9 m long (Hart et al., 19784. Water hyacinths consist of a
short rhizome, roots, rosulate leaves, and inflorescence and stolons that
connect different plants (Pieterse, 19781. Duckweed is a tiny free-floating
vascular plant (Rusoff et al., 19801. Harvested plants usually consist of
a slippery, tangled mass that is difficult to handle mechanically. Water
hyacinths grow rapidly and may present problems by blocking water flow,
thus interfering with rice production. In Bangladesh, rafts of water hy-
acinths weighing up to 300 tons/ha float over rice paddies (National Re-
search Council, 1976~.
A common physical characteristic of all water plants is a low dry-matter
content, varying from 5 to 15 percent (National Research Council, 19764.
Kelp contains approximately 12 percent dry matter (Hart et al., 1978~.
The low dry-matter content of algae in ponds is an even more serious
problem; algae harvested from ponds contains only 1 to 2 percent solids
(Golueke and Oswald, 19651.
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Aquatic Plants 213
TABLE 59 Production of Seaweeds and Aquatic Plants
Thousands Metric Tons (wet weight)
Continent
Country 1960 1967 1973
Africa Egypt 3.8
Morocco17.018.08.0
Senegal- (1.0)
South Africa 43.024.1
Tanzania0.52.00.5
North and Canada13.244.139.9
Central Mexico15.528.936.9
America United States(91.0)2.31.1
South Argentina0.932.824.4
America Brazil (103.0)
Chile7.232.526.5
Peru (1.0)(1.0)
Asia China(250.0) (700.0)
India(1 5)(3 5)(5 5)
Indonesia 16.6
Japan386.1534.3654.2
Republic of Korea29.787.8224.2
Philippines(0.1)1.62.8
Thailand 0.3
Europe Denmark15.627.510.9
France45.776.360.2
Iceland(20.0) (20.0)
Ireland69.1(54.0)(44.0)
Italy (0.6)
Norway 61.0(75.0)
Spain15.536.047.0
United Kingdom(18.0)23.124.1
USSR (100.0)
Oceania Australia (7.0)
New Zealand(0.4)(0.5)(0.6)
World Total 117118862402
NOTE: Numbers in parentheses are estimates.
SOURCE: Naylor (1976). Courtesy of the Food and Agriculture Organization of the United
Nations.
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214 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
NUTRITIVE VALUE
Chemical Composition
Algae
Crude protein content of algae (see Appendix Table 1) ranges from 31 to
68 percent, dry-matter basis. The levels of essential amino acids indicate
that algae protein is of high quality (see Appendix Table 41. Algae are
also rather high in ether extract and low in crude fiber, indicating fair
energy value. Values given for required minerals indicate that algae are
good sources of these (see Appendix Table 21.
Other Aquatic Plants
The crude protein content of other aquatic plants ranges from 11 to 32
percent, dry basis (see Appendix Table 1 J. These levels would be satis-
factory for ruminants and for most classes of swine if the amino acid
pattern is satisfactory. Aquatic leaf protein was lower in lysine and me-
thionine than meat proteins (Boyd, 19681. The fiber level appears to be
lower in duckweed than in other aquatic plants. Aquatic plants are also
rich in required minerals (see Appendix Table 21. According to Bagnall
et al. (1973) 3 kg dry water hyacinths would supply an excess of the major
minerals for 450 kg steers. None of the other minerals were present at
high levels (see Appendix Table 31.
Nutrient Utilization
Algae
The protein efficiency ratio (PER) in rats was lower for dried algae than
for casein (Cook, 19621. Autoclaving algae lowered the PER, and cooking
for 30 minutes or 2 hours had no effect. However, cooking improved true
digestibility of protein and net protein utilization (NPU). The PER of
protein in three species of algae was lower than that of soy protein and
casein for chicks and rats, respectively (McDowell and Leveille, 19631.
Supplementing algae protein with methionine increased the PER for rats
but not to the value for casein. Including cellulase, diastase, and alpha
amylase at 1 percent of the diet increased the digestibility of nitrogen by
laboratory rats. In swine, digestibility of the protein in algae was 72
percent, whereas the digestibility of energy was only 34 percent (Hintz
and Heitman, 1967~. PER, biological value, and apparent digestibility of
OCR for page 215
Aquatic Plants 215
nitrogen were lower for algae protein than for casein in growing rats
(Chung et al., 1978~.
Dry-matter digestibility by sheep of dried or dehydrated algae was 54.2
percent, calculated by difference (Hintz et al., 19661. Energy digestibility
was 58.7 percent. In cattle, energy digestibility of algae was 59 percent.
Seaweed
Incorporation of 20 percent seaweed in a concentrate mixture did not
affect digestibility of protein, but lowered the TDN (67.9 versus 70.6
percent) of a calf diet (Shukla et al., 19741. Digestion coefficients in pigs
were 12 percent for energy and negative for nitrogen in seaweed residue
that had been extracted for alginate (Whittemore and Percival, 19754. The
authors indicated that the nitrogen fraction was largely insoluble. They
indicated that the low energy digestibility resulted from a loss of soluble
energy through the extraction process.
Water Hyacinth
Organic matter and crude protein digestibility were lower for ensiled water
hyacinth and dried citrus pulp (4 percent) than for pangolagrass and citrus
pulp (Bagnall et al., 19741. Values for organic-matter digestibility were
40 and 48 percent for water hyacinth silages and 54 percent for pango-
lagrass. Crude protein digestibility averaged 51 percent for ensiled water
hyacinth-dried citrus pulp for hyacinth from oxidation pond water, com-
pared with 53 percent for hyacinth from lake water. Addition of 2 percent
acetic acid, propionic acid, or a combination of these prior to ensiling
was necessary to get a pH below 5 from ensiling partially dried aquatic
plants (Linn et al., 1975a). Adding 5 percent corn grain did not lower the
pH to less than 5. Dry-matter digestibilities were 43.8 and 43.4 percent
for dried aquatic plants (two species), compared with 50.8 percent for
dehydrated alfalfa (Linn et al., 1975b). Respective values for energy
digestibility were 53.7, 47.4, and 49.2 percent. Digestibility of ensiled
aquatic plants was 41.4 percent for dry matter and 51.4 percent for energy.
Crude protein digestibility was 58.3 percent for dried material and 33.0
percent for the ensiled material.
Replacing 35 percent of alfalfa meal with dried aquatic plants depressed
dry-matter digestibility from 77 to 72 percent in sheep and 66 to 64 percent
in goats (Heffron et al., 1 9771. In vivo digestibilities of dry matter, organic
matter, and crude protein were lower for ensiled water hyacinth than
ensiled pangolagrass (Baldwin et al., 19751. Values for pangolagrass and
water hyacinth, respectively, were 54.0 and 35.0 percent for dry matter,
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216 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
53.6 and 39.6 percent for organic matter, and 76.1 and 52.8 percent for
crude protein. Digestibility of amino acids in duckweed by channel catfish
varied from 38 percent for glycine to 64 percent for tyrosine (Robinette
et al., 19801.
Animal Performance
Algae
Chicks could tolerate only up to l O percent algae meal in the diet if residual
alum was present, but could tolerate up to 20 percent of aluminum-free
algae meal (Grau and Klein, 19571. Algae was found to contain substantial
amounts of xanthophyll, which can be utilized in the chick for shank and
skin pigmentation. Performance of chicks and rats fed algae-supplemented
diets was lower than that of comparable animals fed soybean-protein and
casein-supplemented diets (McDowell and Leveille, 19631. Supplemen-
tation of algae-containing diets with seven essential amino acids increased
growth rate 49 percent and feed efficiency 47 percent in chicks, indicating
amino acid deficiency in algae protein.
Including up to 10 percent algae in swine diets did not alter rate of gain
or feed efficiency (Hintz et al., 19661. Supplementing lambs on summer
range in California with pellets in which 50 percent of the nitrogen was
supplied by algae and 50 percent by alfalfa resulted in higher weight gains
than supplementing only with alfalfa pellets. Rate of gain was similar for
pigs fed diets supplemented with algae or fishmeal if certain B-vitamins
were also supplemented (blintz and Heitman, 19671. Performance was
lowered if the diets were supplemented with only algae. In a subsequent
trial, evidence was obtained that the effect of B-vitamin supplementation
was due at least partly to vitamin By.
Seaweed
Including 20 percent seaweeds in the concentrate of a calf diet tended to
lower rate of gain, but the difference was not significant (Shukla et al.,
19741. Feeding concentrate mixtures with up to 30 percent seaweed did
not alter milk yields and fat-corrected milk yields in dairy cows (Desai
and Shukla, 19751. Body weights tended to be lower if the level of seaweed
meal exceeded 15 percent in the concentrate. Including up to 15 percent
dried seaweed meal did not affect feed intake and weight gain in sheep
(Herbert and Wiener, 1978~. Diarrhea was observed in swine fed a diet
containing 50 percent dried residue of seaweed after extraction of alginate
(Whittemore and Percival, 1975~.
OCR for page 217
Aquatic Plants 217
Water Hyacinth
Body weights and shank pigmentation score of chicks fed a diet containing
duckweed were similar to those of chicks fed diets containing alfalfa
(Truax et al., 19724.
Cattle preferred water hyacinth silage containing the highest level of
preservative, 4 kg dried citrus pulp and 1 kg sugarcane molasses/100 kg
plant residue (Baldwin et al. ? 1974J. The silage preference was negatively
related to pH and ash in silage. Cattle and sheep readily consumed com-
plete diets with processed water hyacinth (Bagnall et al., 1974J. Dry-
matter intake of pangolagrass silage by sheep was higher than that of water
hyacinth silage (Baldwin et al., 1 9751. Intake of a diet by sheep and goats
in which dried aquatic plant was substituted for 35 percent of the alfalfa
meal was similar to that of the control diet (Heffron et al., 1977~.
Rate of gain of dairy heifers fed diets containing duckweed was equal
to or higher than that of heifers fed control diets (Rusoff et al., 1977~.
PROCESSING
Harvesting and processing water plants would result in reduction of weeds
in waterways in addition to providing a resource that could be used as
animal feed. There are problems with harvesting and processing. Since
weeds are located in water, specially adapted harvesting equipment is
essential. The high water content (up to 95 percent) adds volume and
weight to the process and means some of the water may have to be
removed.
Algae
Harvesting algae involves three steps: (1) initial concentration, (2) de-
watering, and (3) final drying (Golueke and Oswald, 19654. The solids
content of pond water is increased to 1 to 2 percent in the initial concen-
tration. Chemical precipitation and centrifuging appear to be most prom-
ising for the initial concentration. Suitable floculating agents were alum,
lime, and synthetic organic polyvalent cationic polymers. Optimum pH
for alum precipitation was 6 to 7. Optimum pH for precipitation with lime
was 11.2.
Excellent dewatering was achieved by using a modified industrial grav-
ity filter with two batch-type centrifuges and with a continuous solid-bowl
centrifuge. In the gravity filtration, at maximum production of slurry of
14 m3/ha/day, a bed width of 24 m would be required to process the yield
from each 0.4 ha of pond.
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21 8 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
Golueke and Oswald (1965) suggested minimum exposure to high tem-
peratures during drying in order to maintain quality. They suggested flash
drying, a process similar to alfalfa dehydration procedures. A high-grade
product was obtained using a steam-heated drum dryer. These workers
used an inexpensive method of sand bed dewatering and drying of algae.
An area of 1,470 m2 would be required/ha of pond.
Seaweed
The greatest problem facing the seaweed industry is the need for improved
efficiency in harvesting (Naylor, 1976J. Hand collection still accounts for
most seaweed harvested. Few mechanized methods have been developed
successfully, the principal exception being the California Macrocystis
beds. Compared with the brown algae, red algae are much smaller and
occur in deeper water, making their harvesting slower and more costly.
Red algae are usually collected by hand or by using rakes or grapnels.
Along the eastern seaboard of the United States and Canada, Chondrus
crispus (Irish moss) is normally harvested by use of long-handled rakes
from small boats.
After harvesting, the bulk of seaweed must be reduced by drying before
further processing, since the wet material deteriorates in quality (Naylor,
19761. Most seaweed is dried naturally by exposure to sun and air, but
there has been increased use of mechanical dehydration. In the case of
natural drying, the washed seaweeds are spread thinly on portable racks,
wooden platforms, or areas of flat rock. Under favorable drying conditions
1 or 2 days are sufficient to reduce the moisture level to 18 to 20 percent.
The problems and uncertainties of the weather have stimulated the
development of artificial drying, especially the use of rotary flame-heated
air driers. The use of this method of drying also results in a more uniform
product.
A process has been developed to reduce water and ash content of kelp
and increase its caloric and bulk densities (Hart et al., 1978~. The process
consists of chopping the kelp in a silage cutter, then grinding in a vertical-
shaft hammermill. After addition of calcium chloride the mixture is heated
and pressed, with removal of 75 percent of the moisture and 65 percent
of the ash. The level of calcium chloride was 0.5 percent. Following
calcium chloride treatment, kelp could be pressed successfully after 15
minutes at 90°C or 30 minutes at 77°C. The process is shown diagra-
matically in Figure 14.
OCR for page 219
Aquatic Plants 219
Fresh
Kelp
AL
my=
Juice
| Aqueous I-
Chemical
Additive
Juice
to
Recovery Operations
for Organic Solids KCI
Pulp
Press Cake
Ju ice to
· Fermentation
· Marine/Terrestrial
Animal Feeds
· Human Food
FIGURE 14 Flow diagram of kelp dewatering process. SOURCE: Hart et al. (1978).
Other Aquatic Plants
Aquatic plants may be harvested from a site at the water's edge or with
a self-propelled floating harvester (National Research Council, 1976~.
Small moving boats can be used to mow aquatic plants (see Figure 15~.
A harvester for submerged plants is shown in Figure 16. Stationary con-
veyers (see Figure 17) may be used to remove aquatic plants from the
water and transport them to processing or transportation equipment (Bryant,
1973).
Approximately 50 percent of the water in aquatic plants can be removed
simply by pressing since it is on the surface or contained loosely in the
vascular system (National Research Council, 1976~. This press water
contains only about 2 percent of the plant solids. Heavier pressing is
necessary for further reduction in water. Approximately 10 to 30 percent
of the solids may be removed by further pressing. The complete process
may remove up to 70 percent of the water in hyacinth, reducing the
moisture level from about 95 to 65 percent. This moisture level would
enable ensiling of the aquatic plant. Bagnall and Hentges (1979) produced
cattle feed by harvesting, chopping, pressing, and ensiling water hyacinth.
Production energy and cost were less and the ensiled product was more
acceptable to cattle than dried feed. It appears that artificial drying of
aquatic plants is not economically feasible because of the high-moisture
content of these materials. In areas of low rainfall, solar drying may be
feasible.
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220 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
FIGURE 15 Harvester for water hyacinth. An experimental harvester lifts, breaks, and
throws water hyacinth by grasping and pulling on aerial parts of the plants, protecting the
high-speed harvesting mechanism from damage by sudden underwater obstructions. SOURCE:
National Research Council (1976).
UTILIZATION SYSTEMS
The high protein and mineral levels in algae indicate that these materials
could be dried and used in limited amounts in swine and poultry diets.
They have been used at levels of 10 to 20 percent of the diet in these
animals (Grau and Klein, 1957; Hintz et al., 19661. The lower protein
and energy value of the other materials would make them more likely to
be used for ruminants. Seaweeds are usually used as sources of minerals
and vitamins rather than of protein and energy (Stephenson, 1973~. It is
probable that ensiling would be more economically feasible than dehy-
dration.
ANIMAL AND HUMAN HEALTH
Feeding a diet containing 18.3 percent algae (Arthrospira) to male rats
for 14 days did not produce gross pathological or histopathological effects
in liver, kidney, heart, lungs, spleen, stomach, intestines, testes, or lymph
nodes (Chung et al., 19781. Feeding this diet to female rats from weaning
OCR for page 221
Aquatic Plants 221
FIGURE 16 Floating harvester for submerged aquatic plants. Large, complete floating
harvesters for submerged aquatic plants are impressive but expensive and have modest
capacity. SOURCE: National Research Council (1976).
until the second week of lactation did not alter reproduction and lactation.
The livers of these females were histologically normal. Feeding high levels
of water hyacinth (Eichhornia crassipes) for three generations affected
reproduction in rats (Chavez et al., 19761. During the first two generations
little difference was noted in number of dams that littered when fed diets
containing 0, 10, 20, and 30 percent dehydrated water hyacinth. During
the third generation 75 and 38 percent of the females littered on the 20
and 30 percent hyacinth diets, respectively. The number of offspring
weaned in the first generation was lower for females fed 30 percent hy-
acinth and was lower for females fed 20 and 30 percent hyacinths during
the second or third generations. In all three generations, gains of rats from
5 through 13 weeks of age were lowest for those fed 30 percent hyacinth.
The gains for those fed 10 and 20 percent hyacinth were lower than for
the controls during the second and third generations. The nitrate, oxalate,
and tannin content of hydrilla and water hyacinth did not appear to be a
hazard in cattle diets (Stephens et al., 19731.
Data are not available concerning pathogens in water plants. The main
potential problem appears to be in plants harvested in waste-treatment
OCR for page 222
222 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
FIGURE 17 Hyacinth control station. SOURCE: Bryant ( 1973). Courtesy of Aquamarine
Corp. Crown Copyright. 1973. Controller of Her Britannic Majesty's Stationery Office.
ponds and lagoons. Data on mineral composition do not implicate a serious
heavy metal threat (see Appendix Table 2), but this aspect needs to be
explored further.
REGULATORY ASPECTS
There are no specific regulations concerning feeding water plants except
those related to algae feeding. More data are needed before sound regu-
lations can be formulated.
RESEARCH NEEDS
More critical experiments are needed to define the utilization of protein
and energy in aquatic plants, especially seaweeds and water hyacinths.
OCR for page 223
Aquatic Plants 223
This should include research on parts of plants, aerial versus submerged;
stage of maturity; and palatability.
The most serious void is in development of economical mechanical
harvesting and processing methods. The research should be with seaweed,
algae, water hyacinths, and duckweed. In the case of algae, hyacinths,
and duckweed, equipment needs to be developed for handling plants from
lakes and waste-treatment ponds. Research should be directed toward
developing controlled production, harvesting, processing, and quality for
use as animal feed.
Research should be directed toward the health aspects of utilizing these
resources. The presence of pathogens and methods of destroying these
should be studied. Data should be collected on pesticides, mycotoxins,
and heavy metals in these resources.
SUMMARY
Aquatic plants occur throughout the world and may present problems in
irrigation projects, hydroelectric production, boat traffic, fish culture, and
drainage. They are potentially valuable resources for different uses, in-
cluding as animal feed. Yields of dry matter per hectare are usually higher
for these plants than for conventional forage and grain crops. The physical
characteristics, including varying size and high water contents, present
problems in harvesting and processing the plants.
Generally, algae are high in crude protein and ether extract, and low
in fiber. Water hyacinths are fairly high in fiber, indicating limited energy
value, and are lower in protein than algae. Efficiency of utilization of
protein in algae is good, although lower than in casein. The energy value
of water hyacinths is lower and ash content much higher than for con-
ventional roughages.
Including 10 percent algae in diets of chicks and swine did not alter
performance. Including limited levels of seaweeds in ruminant diets has
not altered performance. Water hyacinths have been ensiled successfully,
and the silage was consumed readily by cattle and sheep.
The location of water plants and their high water content present prob-
lems in harvesting and processing. Equipment has been developed for
processing various aquatic plants, but generally efficiency and capacity
are low. Drying algae and ensiling the other aquatic plants probably are
the most feasible processing methods at present.
Feeding 18 percent algae did not produce harmful effects in male and
female rats. Feeding 10 percent dehydrated water hyacinths did not affect
reproduction in female rats during three generations, but feeding 20 or 30
percent lowered reproductive rates. There is no evidence of harmful levels
of minerals in aquatic plants.
OCR for page 224
224 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
LITERATURE CITED
Anonymous. 1970. State of development of the IFP Algae Process at December 1970.
Report to FAOtWHO/UNICEF Protein Advisory Group. Institut Francais du Petrale.
Bagnall, L. O., and J. F. Hentges, Jr. 1979. Processing and conservation of water hyacinth
and hydrilla for livestock feeding. In Aquatic Plants, Lake Management, and Ecosystem
Consequences of Lake Harvesting. Proceedings of Conference at Madison, Wisconsin,
Feb. 14- 16, 1979. Madison: University of Wisconsin. 367 pp.
Bagnall, L. O., R. L. Shirley, and J. F. Hentges. 1973. Processing, chemical composition
and nutritive value of aquatic weeds. P. 40 in Water Resources Research Center Pub.
25. Gainesville: University of Florida.
Bagnall, L. O., T. de S. Furman, J. F. Hentges, Jr., W. J. Nolan, and R. L. Shirley.
1974. Feed and fiber from effluent-grown water hyacinth. Pp. 116- 141 in Wastewater
Use in the Production of Food and Fiber. EPA Paper No. 660/2-74-041. Washington,
D.C.: U.S. Government Printing Office.
Baldwin, J. A., J. F. Hentges, Jr., and L. O. Bagnall.' 1974. Preservation and cattle ac-
ceptability of water hyacinth silage. Hyacinth Control J. 12:79-81.
Baldwin, J. A., J. F. Hentges, Jr., L. O. Bagnall, and R: L. Shirley. 1975. Comparison
of pangolagrass and water hyacinth silages as diets for sheep. J. Anim. Sci. 40:968-
971.
Boyd, C. E. 1968. Fresh-water plants: A potential source of protein. Econ. Bot. 4:359.
Boyd, C. E. 1973a. Summer algal communities and primary productivity in fish ponds.
Hydrobiologia 41:357-390.
Boyd, C E. 1973b. Amino acid composition of freshwater algae. Arch. Hydrobiol. 72: 1-
9.
Bryant, C. B. 1973. Control of aquatic weeds by mechanical harvesting. Pestic. Art. News
Serv. 19:601 -606.
Chavez, M. I., R. L. Shirley, and J. F. Easley. 1976. Effects of feeding hyacinths to rats
for three generations. Soil Crop Sci. Soc. Fla., Proc. 35:74-76.
Chung, P., W. G. Pond, J. M. Kingsbury, E. F. Walker, Jr., and L. Krook. 1978. Pro-
duction and nutritive value of Arthrospira platensis, a spiral blue-green alga grown on
swine wastes. J. Anim. Sci. 47:319-330.
Clement, G., C. Giddey. and R. Menzi.1967. Amino acid composition and nutritive value
of the alga Spirulina maxima. Sci. Food Agric. 18:497-501.
Cook, B. B. 1962. The nutritive value of waste-grown algae. Am. J. Public Health. 52:243
251.
Culley, D. D., Jr., and E. A. Epps. 1973. Use of duckweed for waste treatment and animal
feed. J. Water Pollut. Control Fed. 45:337-347.
Dam, R., S. Lee, P. C. Fry, and H. Fox. 1965. Utilization of algae as a protein source
for humans. J. Nutr. 86:376-382.
Davis, I. F., M. J. Sharkey, and D. Williams. 1975. Utilization of sewage algae in as-
sociation with paper in diets of sheep. Agric. Environ. 2:333-338.
Desai, M. C., and P. C. Shukla. 1975. Effect of feeding seaweed to lactating cows on
body weights and milk production. Indian J. Anim. Sci. 45:823-827.
Golueke, C. G., and W. J. Oswald. 1965. Harvesting and processing sewage-grown plank-
tonic algae. J. Water Pollut. Control Fed. 37:471.
Grau, C. R., and N. W. Klein. 1957. Sewage-grown algae as a feedstuff for chicks. Poult.
Sci. 36: 1046- 1051.
Hart, M. R., D. de Fremery, C. K. Lyon, and G. O. Kohler. 1978. Dewatering kelp for
fuel, feed, and food uses: Process description and material balances. Trans. ASAE
21:186-189.
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Aquatic Plants 225
Heffron, C. L., J. T. Reid, W. M. Hascheck, A. K. Furr, T. F. Parkinson, C. A. Bache,
W. H. Gutenmann, L. E. St. John, Jr., and D. J. Lisk. 1977. Chemical composition
and acceptability of aquatic plants in diets of sheep and pregnant goats. J. Anim. Sci.
45:1166-1172.
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Representative terms from entire chapter:
water hyacinth
