Duckweed

[TCLynx]

Duckweed is a great plant and makes wonderful food for many kinds of fish and other water creatures, however, you need a huge surface area to grow enough duckweed to be the sold feed source for more than a few tilapia.  If you had a few ponds off in the woods behind your place where you could collect huge net fulls of duck wee every other day, you might supply enough duckweed to keep a tank full of tilapia in tucker but...

 

I had a duckweed tank for a while and it was about 30 inches wide by 16 feet long and I could keep the entire surface of that tank covered in duckweed as long as I fed the 12 tilapia in that tank a hand full of pellets each day.  As soon as I went away for a week and wasn't feeding them pellets every day, the entire surface of the tank was cleared of duckweed within that week and I had to go get more to re-start my duckweed culture.  So imagine that a thick cover of duckweed over that surface area doesn't equate to 7 hand fulls (and I have small hands) of 32% protein commercial feed.  For just 12 tilapia.

 

Now if you have the space to set up and fertilize several large shallow pools to grow duckweed to then dry for use as feed for the tialpia, you might manage but it takes a lot of space to grow enough duckweed to be anything more than just a supplement.

[Harold Sukhbir]

Hi TC,

Needed this one TC. Duckweed is far too important not to be adapted into AP as a cost effective high protein sole/supplement fish feed. For the discussions reading;   http://www.lrrd.org/lrrd7/1/3.htm

[TCLynx]

Just keep in mind that when people talk about duckweed being high protein to weight, they are usually talking about dried duckweed which is pretty light.  It takes a huge amount of wet duckweed (since it is mostly water) to equal much feed value.

 

It really is great stuff but it comes with some major logistical challenges (mostly space.)

[RupertofOZ]

Well even if duckweed can't totally feed your fish... it may turn out being able to feed you...

 

http://www.mailtribune.com/apps/pbcs.dll/article?AID=/20110314/NEWS...

[TCLynx]

or provide electricity

[RupertofOZ]

Or Both....

[SW]

Maintenance feeds are generally in the 34% protein range.  Fresh Duckweed is around 15% protein.  It's a great supplemental food source and is excellent at clearing/cleaning water your systems water. The rapidity with which it multiplies works for most people that have small backyard systems.  I grow mine in several plastic bins though I am on the lookout for a free kiddie wading pool that someone has abandoned.  Don't overlook feeding your tilapia the outer leaves from your vegetables too.  Kale, lettuces, etc are sure to get gobbled up!

Sam

[Kobus Jooste]

I have been looking at duckweed culture for a while now as a research project.  Here are some of my thoughts:

 

1) Lemna types typically used in wastewater treatment loves ammonia above nitrate.  In my research system, Nitrate continues to rise even when ammonia is almost gone, suggesting that algae will dominate grow beds if it is not high in Ammonia.  You therefore have to consider this in your system design.  Having Lemna positioned after nitrification structures may not give you the growth that you need.  In a large system though, it may reduce the plant carrying capacity of the set-up (if you are trying to grow enough to feed your fish daily).  I am therefore leaning towards stand-alone duckweed systems.

 

2) You can push the dry weight protein content of Lemna to above 40% if the waste water stream is high enough in ammonia.  It is not clear yet if AP quality water is concentrated enough for max protein yield though. 

 

3) Plant protein such as duckweed is more digestable to animals than animal proteins used in feed, thus even if you have a slightly lower protein content, you may have a more digestable one with a better FCR and thus well worth trying.

 

4) Duckweed have cyclical growth patterns, with vegetative growth dominating.  Many plants though have a limited life expectancy - such as number of divisions possible.  It is therefore possible to have large die-offs in the system.  Keep an eye on this if you are worried about fouling a system.

 

 

[steve]

The growth rates I've found range dramatically. Ballpark might be around .3 to 2 lbs. dried Duckweed per ft2 annually. Although studies claim very high output for ideal conditions. Need lots of space and extra nutrient water, great for anyone producing lots of fish.  Seems to have good feed potential. Seems a 50/50 pellets mix would be great to cut feed expense, and be more self  sufficient. Among duckweeds other aspects of cleaning waste water and potential for ethanol, probably methane. Would sure like to hear more experiences and comments, ideas.

[Kobus Jooste]

My system is currently in winter mode.  Temps range between 14 and 19 degrees Celcius and fish are not eating much.  Still, with ammonia levels down at 0.15 mg/L the duckweed (Lemna gibba) is still growing, although at about 50% of summer rates.  I now have over 50 fish and no filter in the system - just the duckweed.  I'll keep a keen eye on it to see how it copes when it warms up, as I think it will be overstocked for summer conditions.  At present, I'm getting around 1 kg wet mass duckweed out of 7m2 of water surface per week, but as said, it is winter.

[steve]

Thanks Kobus I know you are looking at waste treatment. Have you considered the ethanol production? Then still might be good for either feed or fertilizer after.       Does it seem worth the effort for fish feed supplement?

Kobus Jooste said:

My system is currently in winter mode.  Temps range between 14 and 19 degrees Celcius and fish are not eating much.  Still, with ammonia levels down at 0.15 mg/L the duckweed (Lemna gibba) is still growing, although at about 50% of summer rates.  I now have over 50 fish and no filter in the system - just the duckweed.  I'll keep a keen eye on it to see how it copes when it warms up, as I think it will be overstocked for summer conditions.  At present, I'm getting around 1 kg wet mass duckweed out of 7m2 of water surface per week, but as said, it is winter.

[Kobus Jooste]

I am currently only looking at fertilizer.  The project was set up to look at duckweed potential in stages, but as there are no (and I mean NO) bio-fuel distilleries here in my area, having some samples distilled will be very difficult.  You will only be taking the carbs out thus if you can culture it to max its carbohydrate production, you could well combine the two processes.  I will have to see if it is possible to find funding for such a follow on study.  What I'm doing now is to mince the wet duckweed with a hand blender to add to the mineralization process, but it could be easy to use the same pulp, dry it a bit more and put it through a mincer / extruder to make some trial pellets.  I will need a binding agent of some sort but in theory, the FCR of fish fed duckweed is far better than any commercial flake.  I think the 50/50 substitute is a good initial target (100% could be too ambitious now).  Another nice attribute of duckweed is that it picks up almost any trace element in the water, thus if you want to make a "better" fish food than straight duckweed, you could add trace ellemtns to your water and then test to see what % made it into your food.

 

I am hoping to find funding for such an experiment once we reached all the milestones on the current project (11 months to go).

 

Alternatively, once summer production kicks in, I can use some of the surplus duckweed to do initial feeding trials - that will take around 3 months from now to have the surplus.  Will struggle to get a lot of nutrient content analyses paid for though.

[Daniel Driscoll]

Hello,

   Ive been feeding my koi over a softball size clump of wet duckweed once a day. I also feed them some ornamental fish food once a day. Does anyone notice that it clogs up the filter fast? its like undigested fibers or something. I've got one of those laguna pumps with the shell, it clogs fast. And i have one of those classic round green Tetra bucket filters with the two filter pads and biomedia. The sprayer also clogs fast. I've gotta clean it like everyday. Is this something that I just have to deal with or maybe i should get a different pump that can handle larger solids and also get a larger filter?  Once my tilapia get bigger I'll be giving them most of the duckweed and I plan on using two Danner M18's and a DIY multi-stage 55gal drum filter, gravity fed. I was thinking about stuffing the first 55gal drum with bird net at the bottom and then sponge on top. 2nd drum will have hydroton from some indoor growbeds for bio. I'm hoping that I'll only have to clean it once a week.