Backyard Aquaponics
A place to discuss aquaponics

Hello,

New to this forum, and loving reading a lot of the posts here already! I started asking and talking about something in another thread and wanted to bring the question here by itself instead, so here goes.

Can duckweed provide a complete source of nutrients for your fish, but mainly also for your vegetables and fruit that you grow? I am curious about the fish side, but my main curiosity is for the plants.

I do not yet, but I most definitely plan on building an aquaponics system. I'm not really a huge fan of fish as food myself, but my girlfriend is. I might or might not include an edible fish in the system, but at this point my main focus is the vegetables and fruit I will be growing.

I love vegetables and fruit, but I really want the ones I grow to be as nutrient dense as possible. I'm not just growing them for size, looks, or taste (although taste obviously is something I desire and am sure that will come along with nutrient density also) and I know that plants need so much more than NPK.

I want my system to be as organic/sustainable as possible, but I want to know that the veggies and fruit I'm growing is the best it can be. My #1. concern is nutrition.

So, will the poop that comes out of your fish after eating duckweed alone be enough for the plants in the system? Would adding worms help (not as fish food, but for further breaking down waste, and pooping it out) ? Or, does there absolutely need to be another source of food for the fish, and if so what?

Thank you!

This is a rather old study of duckweed. I'll do a more thorough search for studies on duckweed use in aquaculture/aquaponics when I have more time.

http://www.fao.org/ag/AGA/AGAP/FRG/lrrd/lrrd7/1/3.htm

you'll need more than duckweed as input for fish feed...
the best use imho, is as a supplement to a good quality aquaculture feed..
i supplement feed with rosy red minnows and crayfish..
remember the old adage, garbage in=garbage out
a good fish food will result in good plants

Another good (potentially free) supplemental food would be Black Soldier Fly Larva. Look it up.. there are several easy ways to set up a BSFL bin, and they can even self harvest!

edit:: another duckweed composition link http://www.mobot.org/jwcross/duckweed/n ... sition.htm

AquaPonicsFTW- very interesting study. It indicates that Duckweed would be an adequate source for input...providing you can grow enough of it. At the correct feed rates, conversion was about the same as commercial feed. The study also indicated substantial P & K available, as well as protein rates up to 40%. Pretty impressive!
Keith, we should all be so lucky as to have this garbage.lol I could see how tank solid could be added to shallow duckweed tanks and you could possibly be self sustaining in terms of feed. probably still a lot of work, but could appeal to some.

Thanks for the replies so far! Very interesting studies about the nutritional composition and etc of duckweed there. I'm going to have to see if I can hunt down anything more on those kinds of specifics, because that's exactly what I'm interested in.

I imagine it would also depend on where your growing your duckweed? It was sort of mentioned by way of water medium in those studies, but it seems that duckweed found in the wild vs being grown in an isolated tank might contain more nutrients. If you were growing them specifically for more nutrients, then that again might require more inputs?

We were talking on another thread about how the duckweed would compete with your plants for nutrients if you had them connected to your overall aquaponics system, so it might defeat the purpose. If your harvesting the plants then eventually some of the nutrition is leaving that system, so it must be put back in from somewhere else.

So then again the question might be how to grow duckweed to load it with optimal nutrition? I'm going to have to add that to my list of things to look up now!

There are also other things you can do to add nutrients to the system.

I've seen a few people use bug attracting lights in the FT at night. So the bugs come towards the light, and the fish zip up and get a free feed.

But I do agree that duckweed alone isn't enough, it can lower the amount you need to spend on the fish feed though.

i see there how you're trying to change what i said..
i use duckweed, and it has it's place, but you need more than that as as primary feed if you expect any kind of growth of both fish and plants..
i use it to consume excess nutrients
and "waste" more than i can use, it goes into my worm bin

No Duckweed expert here. But, based on the link to the study from inspiredhort : http://www.fao.org/ag/AGA/AGAP/FRG/lrrd/lrrd7/1/3.htm

It would appear that Duckweed does indeed have the nutrients required for both quality fish and plant growth. Again, this is based on that study showing N-P-K ratings. They did mention that minor elements where not analyzed. But, as you all know , you generally need to supplement Iron, Calcium, and Potash even when using a high quality commercial feed. According to that study, duckweed would provide similar results, and is actually higher in protein. I am referring to raising Tilapia, which are a vegetarian species(primarily). A conversion rate of 1.9/1 using duckweed is pretty darn impressive. Is anybody out there using duckweed as a stand alone food in their system?

I did a quick scan of the last link posted about the nutritional value of duckweed. I will assume the other links are similar.

While duckweed protein levels are reported at 43%, I saw no mention about its essential amino acid content.

Peanut meal is 44% protein but most mono-gastric vertebrates would die of malnutrition if this was their sole source of protein. That protein is classified as low biologic value. It is low in the essential amino acids lysine and methionine. Many plant proteins are.

Tilapia have specific essential amino acid requirements. They are listed somewhere but I can't put my hands on them at the moment. If the duckweed does not meet those essential amino acid requirements, it is an inadequate source of dietary protein.

As already stated previously, if placed in the same water source for growing the plant crop, duckweed will compete with crop plants for needed nutrients.

Also lets not forget the bit about duckweed being over 90% water, while the protein levels and mineral content are dry weight.. So take 1kg of duckweed, dry is out, then you have less than 100g, so at 40% protein, you really only have about 40 grams of protein in 1kg of duckweed.

Good job chappo is not here or we'd be moringa'd to death.

Hey what about moringa? ;-}

Just a thing I have noticed about my system (regarding wanting yr veggies to be as nutrient dense as possible) since I got my system up and running (around 18 months ago) I have had 2 minor respiratory issues. Only mild chesty colds but they lingered for around 4 weeks. I'm currently getting over the latest one. Both of those times I have had a nutrient deficiency in my system. Last time we pinpointed it to be potassium. When corrected, my plants did better and I recovered. This time I have no idea what the deficiency was but I corrected it with the addition of seaweed concentrate. I'm finally recovering.

I'm going to keep an eye out if it happens again but it makes sense because 90% of what I eat comes from my growbed.

Could also just be coincidence in that plants have a higher requirement for those elements during the colder months which is when colds and flu are prevalent.