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Joined: Apr 2007
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Duckweed is bad? It all depends......

It turns out the duckweed has a great potential as feed for livestock and in aquaculture. In aquaculture the duckweed is probably processed into a dry meal. It is also being used/tested as a means to process and reclaim nutrients in waste water.

This information may not directly benefit most pond owners, but it represents the type of technologies that can help make our society more efficient. If you raise livestock you might find that the duckweed you remove from your pond would be a treat for your animals. A wide variety of critters will eat duckweed including chickens, ducks, pigs, sheep, cattle. Oh, and I think Black Soldier Fly larvae will gladly eat it... \:\/


http://www.mobot.org/jwcross/duckweed/Fish.htm

http://www.mobot.org/jwcross/duckweed/feed-supplement.htm

http://www.geocities.com/RainForest/Canopy/3631/

http://www.cipav.org.co/lrrd/lrrd7/1/3.htm



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GW,

Duckweed is also used extensively by commercial Tilapia growers as fish food....in spite of some people suggesting I was wrong when I said Tilapia at high stocking rates will control duckweed and artificial feeding means you need more of them. You've probably read about closed-loop systems which rely on duckweed to feed Tilpia which are also artificially fed supplementally to produce food for the duckweed. I'm going to try it myself on a small scale.

Last edited by Bob Lusk; 09/15/07 08:39 AM. Reason: tone it down
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I would be very interested in anything you do with duckweed Meadowlark. At some point I'm going to test it as BSF feed and compare the conversion rate to the commercial hog feed that I'm trying now.



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GW, what do you put on DW? Thousand Island, or Ranch? \:D

No kidding, I always thought DW looked good to eat. I guess it reminds me of sprouts. I never had the nerve to taste it. Also no kidding, I get chills when I think about it. I've seen it all but ruin ponds and lakes.

Just a random thought, I bet goats could be trained to eat it along the banks.

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For Meadowlark, from this webpage - http://www.p2pays.org/ref/09/08875.htm :

"Duckweed-fed tilapia
Tilapia species are of African origin but have been introduced to most tropical and subtropical regions. (See figure 22). Tilapia are hardy, grow fast, and can tolerate low pond oxygen levels better than most fish. They are warm water fish which do not grow below 16 C and do not survive temperatures below 10 C. Unlike carp, they have no "floating" intramuscular bones, making it easier for the diner to separate bones from flesh.

Most species of tilapia tolerate brackish water well. Adult tilapia are primarily herbivorous, occasionally omnivorous, and some species are used to control aquatic weeds. Fry feed primarily on plankton. At least one species, Oreochromis niloticus, is reported to be extremely flexible in its feeding habits, readily consuming Lemna and Wolffia species along with phytoplankton and detritus.

Tilapia are well-equipped to feed on duckweed. They have grinding plates in their pharynx, a highly acidic stomach, and a long intestine to absorb digested nutrients. Duckweed supplies the high protein diet they need for rapid growth. The maceration and digestion of duckweed by macrophyte-feeding tilapia requires less energy expenditure than a diet of more fibrous plants.

Because the Nile tilapia appears to be able to harvest food from all of the space and food niches in a pond, it was tested in the Mirzapur experimental program as an alternative to the duckweed-fed carp polyculture. The single-species culture appears to benefit from duckweed as the single nutritional input in much the same way as the carp polyculture because the nutrients appear to be distributed similarly. Production at Mirzapur in a 0.6 hectare pond totaled 4.5 tons in one year of continuous operation. As management of the pond improved, and the stocking balance between recruits, juveniles, and mature fish became more efficient, productivity rates improved. Local pond managers now believe that they should be able to average at least 10 tons/ha/year for mixed (sizes) tilapia harvest.

Because of their fecundity, tilapia require special management to keep their population stable and to maintain even growth. They mature at about three months and breed prolifically in the pond at intervals of three to six weeks. The additional fish population, called recruits, leads quickly to extreme competition for food and, hence, a stunted population. There are three basic approaches to management of tilapia populations: monosex culture, intensive culling and inclusion of predators. Frequent, intensive harvesting to remove market-size fish and recruits is highly labor intensive and can stress the fish population. It is, however, a relatively simple technique available to the small farmer.

Predatory fish can be included with the tilapia culture to control recruits and allow the production of market-size fish. Predator species include the clarias catfish, notopterus, snakehead, and others, many of which have high market value. The principle constraints with this method are the difficulty of obtaining stocks of predator species and determining efficient stocking densities.

The tilapia culture strategy investigated at the Mirzapur experimental site is conceptually similar to duckweed cultivation. The concept is to determine an efficient "standing crop" and to maintain it with bi-weekly harvests. Tilapia are categorized either as recruits, adolescents, or adults. During harvests, estimates are made of the total amount of tilapia in the pond and their distribution among the three categories. For example, the standing crop today is 10 tons and, numerically, 60 percent of the fish are recruits, 30 percent are adolescents, and 10% are adults. To bring the standing crop back to the empirically derived "normative" size and balance, the harvesting heuristic should then specify a harvest profile by weight: harvest 400 kg - 50 kg of recruits, 150 kg of adolescents, and 200 kg of adults. Current harvest profiles will rely more on intuition than formula until efficient harvesting algorithms are developed.

Tilapia recruits, although very small, fetch a surprisingly high market price in rural markets in Bangladesh. They are purchased by people unable to afford fish in the size range prevalent in the market (0.5 - 1 kg). Where tilapia above 250 g can command up to $2.00 per kg in rural markets, mixed adolescents, and recruits can bring up to $1.00 per kilogram. This mechanism allows even the poorest people to include some fish in their diet. With production costs averaging between $0.40 - $0.50 per kg in Bangladesh, farming duckweed-fed tilapia is highly profitable."

Bobad, in Thailand watermeal is regularly eaten. It's name translates to "water eggs" because of it's caviar-like texture and nutty flavor.






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