Feeding Duckweed and Azolla growing it safely.

[Brian Graffius]

At a recent aquaculture seminar hosted by a local Georgia College, they said Azolla was a very good food plant for fish and was prefered to Duck Weed.   I have a sample of it and I have been experimenting with it.   I also noticed it floating in a local pond, so I have a local natural source. 

 

I wanted to see how fast it grows, so I put a few plants in a bucket that had about 1/2 gallon of water and a small piece of horse manuer (a manuer tea if you will).  I forgot about the plant for a week and when I went back it the population had exploded.  The surface of the water was completely covered in a thick blanket of the stuff.   Without the manuer, the growth is very slow. 

 

Manuer seems to present a host of problems an aquaponic system such as e coli and perhaps liver flukes among other really nasty hazards.  I thought this would be a great place to talk about the hazards of using manuer to those that are new to aquaponics.   Manuer is very commonly used in gardens and I can see someone not connecting the dots and do something like grow duck weed or azolla in manuer tea and then feed that to the fish.  What about getting these floating plants from local sources, are there other things to worry about with those.  How do you know when it comes to feed plants that they are safe and clean.

 

As for azolla, I wonder what other nutrient I can add to the water to get the same kind of growth, that will still allow me to feed it to tilapia.  Any ideas, I will experiment and post the results.  Azolla is used in several countries for green manuer in dirt gardening.  Growing azolla in manuer tea might just have an application for traditional gardening as a source for green manuer.   I am still researching, but it is also used as a water conditioner and purifier.  Will it kill e coli?  So far I have not been able to find that it does.

[TCLynx]

Add to that the fact that there are probably far more than just two species of duckweed and other similar plants and finding your answers may be really challenging.

[Michael Wood]

Joel, I appreciate your comment about adding fish solids as a duckweed fertilizer.  Could you tell me more about how to mineralize the solids before adding them to the duckweed ponds?  I've been putting my collected fish solids into a large tupperware tub, if I put an air-stone in there and bubbled in oxygen, would that mineralize it? How do you do it

Thanks,

Mike

Joel G said:

 

As for azolla, I wonder what other nutrient I can add to the water to get the same kind of growth, that will still allow me to feed it to tilapia.

 

Hi! You can gather all the solids (tilapia manure) from your tanks. This is all I feed to my duckweeds (which grows much faster than azolla). This way, you eliminate a potential (external) source of e. coli. It works even better if you mineralize the solids first.

While azolla is recommended as green fertilizer, it is duckweed that has been recommended as tilapia feed (up to 50% replacement of commercial feed is ok, according to studies).

 

 

 

[Joel G]

Hi, Michael!

I do just about the same thing. I normally feed the duckweed tank with water straight from the fish tanks (rich in ammonia) and just occasionally top up. I also have an airlift driven biofilter that sucks in the fish solids and aerate it in one go. Every week or so (when I clean the filter), I remove the solids from the filter and feed some of it to the duckweed tank and the rest to my garden plants.

Michael Wood said:

Joel, I appreciate your comment about adding fish solids as a duckweed fertilizer.  Could you tell me more about how to mineralize the solids before adding them to the duckweed ponds?  I've been putting my collected fish solids into a large tupperware tub, if I put an air-stone in there and bubbled in oxygen, would that mineralize it? How do you do it

Thanks,

Mike

Joel G said:

 

As for azolla, I wonder what other nutrient I can add to the water to get the same kind of growth, that will still allow me to feed it to tilapia.

 

Hi! You can gather all the solids (tilapia manure) from your tanks. This is all I feed to my duckweeds (which grows much faster than azolla). This way, you eliminate a potential (external) source of e. coli. It works even better if you mineralize the solids first.

While azolla is recommended as green fertilizer, it is duckweed that has been recommended as tilapia feed (up to 50% replacement of commercial feed is ok, according to studies).