Duckweed: growing it and feeding it to tilapia

[Michael Welber]

I plan to start growing duckweed to supplement my tilapia's diet. I'm going to grow it in a separate container, not in the fish tank. 

1. Do I need to have compost or other nutrient in the separate container? It's a plastic box.

2. Can I just harvest small amounts of the duckweed and toss it into the fish tank? Or does it need to be dried? 

I live in the Florida Keys and will add gambusia (a mosquito eating fish) to the duckweed tank so I don't also grow skeeters. 

If any of you have any experience with duckweed I'd love to hear about it. 

[TCLynx]

The duckweed will require nutrients to grow.

I've found it always seems to grow best when I'm not really trying to grow it.  When ever I try to grow it on purpose, it tends to fail.

It takes quite a bit of space to grow enough duckweed to make a big dent in your fish feed quantities.

You can feed duckweed fresh but make sure your system won't wind up getting clogged with it and a lot of splashing or water level fluctuation will tend to stick the duckweed to the walls of the tank where it will dry out and be useless.

Or you can dry the duckweed but then I'm not sure how you go about feeding it to them since I've never tried it myself.

Some people will warn you against duckweed.  Just make sure you don't have a hapa or net or cage which will hide dying duckweed from your view since dieing/rotting vegetation hidden in the system can cause a system crash if you don't catch it in time (much the same way a build up of uneaten fish feed in a tank can cause a nasty problem.)

[Jonathan Hall]

Make sure you feed it in small quantities. Learn how much your fish can eat when they are hungry without leaving any behind. Usually about five minutes worth, however really depends on the type of fish? If managed properly you can reap the benefits without disaster.

I personally grow mine in a bunch of plastic kiddie pools plumbed together. Hooked up to a fish tank which pumps the water to a header tank (small tote sitting on some bricks) which gravity feeds (Underwater) to one of the kiddie pools. which feeds to the next, and next and so on. The pipe used I put a 90 deg. elbow on to help direct the flow towards the bottom to help dissipate surface movement. (Which will stop duckweed from growing.

The water is aerated in the tanks, of course, but not in the duckweed pods.

1) Yes, I think so..

2) I try to harvest about half. It doubles in size every 36 hours approx. Dried works as well, but I prefer to freeze. Drying destroys more nutrients (i think...)

[Jon Parr]

Throw up a few wading pools, take a piss in each one, or add some compost or filter sludge or MG, that's about it. Harvest plenty, feeding plenty is fine too if it's living duckweed. It will just hang out and keep your FT water clean until your fish eat it. Personally, I feed them tons, and if there is not much left the next day, feed them more. I have my siphon return placed over my Redclaw hiding tubes. When the siphon drains it forces the duckweek down and much of it gets trapped inside the pipes, where the redclaws lay on the backs and eat fresh duckweed all day long. 

[Carey Ma]

We did some feed experiments this past year and duckweed was one of the of the ingredients along with algae in green-water aquaculture. This was sponsored as a possibility to bio-mitigate small dairy farm waste in an IBS (integrated bio system) to produce feed for secondary crop/s. The duckweed ran in a slow moving, high volume, one meter deep, bow shaped almost circular pond. This pond's surface area was calculated by the Beijing academy of agriculture, (I figure around a sixth of an acre)  and produced a fair amount of duckweed (sorry, not my info to give out) which was both freeze-dried and powderized and incorporated whole and live into a gel capsule for a super feed. These highly digestible, super potent, gel capsules were meant to represent the size of the fish's stomach for a one gulp and full concept.

This semi clean farm effluent flowed into a relatively wide and shallow, though surprisingly short trough which fed then into a large pond covering about half an acre or more. This rearing pond was mostly around two meters deep with a deep water whole at one end. In this pond were three types of carp, some talapia, soft shelled turtles, and freshwater prawns. During the growing season, the pond was tapped for blue-green algae to be freeze dried and powderized to make that super gel and dry winter feed. Water from the duckweed lagoon siphoned off onto an acre of apricot orchard which also held free range chicken and a hydroponic fodder shop.

So this farmer on three acres of land lived there and organically raised eight dairy cows, eight hundred chicken, tons of fruit and thousands of tail of fish plus turtles and shrimp, increasing his income by more than three fold and reducing his footprint close to zero instead of raising eight to twelve dairy cows. Note* Though this was originally a feed lot operation, with a constant pool of toxic urine waste, (unlike American feed lots with tall piles and expanding pools), most fecal material was quickly sold as a secondary income to local farmers, so there was little piling to begin with but the pool was a problem.

Cheers

[John Nicholson]

I have started growing duckweed in a separate growbed that contains only water with a protected overflow.  Growth is poor so far but I am adding more tilapia in a couple of weeks.  That should add more nutrients to the system which may help the duckweed.  I have been harvesting fish lately and they are somewhat depleted.

[Carey Ma]

Warm, highly potent, (almost toxic water) with no ripples (surface action) is best. Please let me know ow it goes.

[Michael Welber]

Thanks everyone. I'm going to give it a try. 

[Luis Arteaga]

Hi there Carey, what do you mean by highly potent almost toxic water?

Carey Ma said:

Warm, highly potent, (almost toxic water) with no ripples (surface action) is best. Please let me know ow it goes.