vegetarian fish culture in aquaponics

[Kobus Jooste]

I have been looking at the various basic multi cropping extensive aquaculture / agriculture world wide, especially those related to duckweed culture for a research project that I am busy with.  It got me wondering why people all over are not giving edible carp species a go.  In places like Bangladesh, waste water pits are used to grow duckweed, which is then fed to fish  (in fertilized ponds, but that is not crucial) like carp, which is then harvested.  They also add a small amount of salt to the ponds - not more than what is often recommended for adding to koi systems.  In Australia, Jade Perch is also an excellent option.  Duckweed likes ammonia more than nitrates, thus if you set up a system that has a fish tank, some duckweed tanks, and then grow beds, (could the combined trace elements from minor sea salt addition and the proceeds from a worm bin or two) you could potentially be closing the loop a bit on your inputs - only the sea salt at this point. 

 

Are there any examples of systems such as these in operation already? 

[Wesley B]

I am going to grow enough duckweed to be the sole source of feed for 800 pounds of tilapia per year.

I have a space in the yard available for the project that is approximately 120 by 72 feet.

So I am considering a pond 120 feet long by 12 wide which would be 1440 square feet of duckweed

I am basing this on a statement in the Farming Manual put out by IPED.
Here is the link to the study.

http://www.ipedgy.com/publications/IPED_Integrated_Farming_Manual.pdf
 
According the Integrated Farming Manual it took 1 acre or 43560 square feet of duckweed to grow 12000 tilapia in one year
Pg.49

I can only guess to what exactly they meant by this statement because they didn't explain in terms of pounds of tilapia. But i think it would be a conservative estimate to say they meant from spawn to at least 2 pound fish or at least 24000 pounds of tilapia in one year.

I am aiming for more like 800 ponds of tilapia in one year which would be 1/30 of their example.

Perhaps scaling it down this much is too inaccurate. 

But if it is accurate enough then I would need 1/30 of 43560 square feet to grow 800 pounds of tilapia in one year or in other words 1452 square feet.

So one pond 120 feet long by 12 feet wide would be 1440 square feet of duckweed.
Pretty close match and it leaves me with plenty of space.
What do you think?
Will it work?
I will keep you posted.
By the way I live in central Florida and I have all the fresh cow manure I need in case your wondering about a nutrient source.
 



steve said:

Does anyone have an idea how many square feet of duckweed to feed 100 lbs. Tilapia, for example. I'm thinking 1/2 feed pellets supplement 1/2 duckweed.

[TCLynx]

If you are using cow manure to provide nutrient for the duckweed, will you be drying the duckweed before using it as feed for the fish but reduce pathogen introduction into your tilapia system?

Now I'm not sure I would assume the grow out of the tilapia is to two pounds.  They may mean what they said, a certain number of fish harvested at whatever weight they were.  I'm in central Florida too and I only had a few tilapia get close to two pounds, most of mine were harvested at a pound or less and I had many of them for two years.

Duckweed makes a fine feed source but don't expect it to grow tilapia as big as fast as a high protein commercial feed.  Also, if you are not heating your water, you may have difficulty growing tilapia out that big that fast on only duckweed.

It will be interesting to see the results of your experiment.

[Wesley B]

THanks for response. I am setting up a solar water heating system for the tilapia ponds. I was not planning on drying the duckweed before using it. The tilapia ponds will have a great deal of fresh water almost constantly coming in. I will be pumping out the water in the tilapia ponds to into an irrigation system watering fruit trees and vegetables and banana trees etc... So all of the water is constantly getting replaced with fresh water on a daily bases. Hopefully this will help keep the pathogens down. I am already doing this basic open system on a smaller scale and it seems to be working great. I have no filters in my tilapia tank. I barely use any electrical heating even during December thanks toa very simple and cheap solar water heating system and according to a lot of research the duckweed is at 30 to 40% protein. Also it is free when i grow it myself and self-sufficient witch is a major plus. They really seem to love it. I will keep you posted on growth rates and info. I really appreciate comments, suggestions and even critizimes. Thanks

[TCLynx]

Well if you are simply running to waste and constantly adding fresh water then It isn't really like aquaponics but more like aquacutlure.

And if you are not growing veggies to eat in the system and you always cook your fish well, then maybe adding the manure isn't such a big deal but don't assume that by flushing lots of fresh water through that you are eliminating the e. coli threat.  Contaminated rinse water is where some of the food borne pathogen outbreaks have come from in the past decade and others have come from fields that were spread with manure too close to harvest time.  (I believe 4 months is the appropriate waiting time from field application of mature to harvest for veggies, however that doesn't really work in a water system.)

[Rebecca B]

My understanding is the 30-40% protein figure for duckweed is in relation to the dry weight. Since duckweed is 98% water, the protein percentage of wet duckweed is very small.

[TCLynx]

Yep, Rebecca, you are right.

And it takes a huge amount of duckweed to make a pound of dry duckweed with that high % of protein.

[Raychel A Watkins]

It took me almost 2 years to get a tilapia up to 2 lbs most were 1.5 lbs.  This was on commercial feed plus lettuce and things but mostly feed,  My plan is to feed the duckweed, lettuce, BSF larvae and wean off the pellets.  I have started my young ones off this way,  I think 1 lb is big enough,  I will eat them as I want them and add young all the time ,  It doesn't matter how old they are ,  We may not be able top raise them as fast as we can with pellets but is that the important thing.  I trullu want to be able to be self sustaining as we were on the farm I grew up on.

[TCLynx]

And that is a very valid point, you do not have to raise them up so big (we used to eat bluegill at 1/3rd of a pound all the time)

You can eat your tilapia smaller than 1 or 2 lb.

And I think the fast grow out is mostly important to those people who are attempting to grow out tilapia in an outdoor system in a temperate climate before they freeze to death when the water drops to 50 F.  Those people might not have the luxury of being as sustainable since they probably require heating at each end of the season just to fit the grow out in and probably need high protein feed at the start and commercial feed through out just to manage it.

Anyone in a climate that doesn't have to worry about finishing their grow out before cold sets in, and doesn't mind slower food.  The natural foods are probably healthier anyway.

[Wesley B]

Thanks for the clearifiction on harvest size. Perhaps I need to dig 2 pond 12 by 120. I will try one first. Currently I have a few tubs of duckweed and it is still growing even in December! All be it this has been a crazy warm december for Florida.
As far as protein levels go duckweed is very high in protein compared to almost all alternatives crops I could grow for my cattle, chickens and tilapia. For instance alfalfa is generally 15 to 18% protein dry weight of course feed is always talked about in terms of dry wieight when discussing protein levels and I have read estimated that per acres one can produce 10 to 50 times the about of bio mass annually as compared to other traditional crops.
We also have a nursery from gainsville rooting 50 cassava plants to be delivered in April.
We hope to use the cassava and duckweed in combinationk to help feed all of our livestock.
There is a lot of information available online describing the utilization of these crops especially in veitnam.

And thanks, for the clarification this is aquaculture not aquaponics sorry if I am off topic for this site.

http://www.fao.org/ag/againfo/resources/documents/DW/Dw2.htm

[Sahib Punjabi]

Hello David.

Hope all is well. Thought you may by interested in this recent article that I can across recently (posted in Media Posts):

http://aquaponicscommunity.com/group/aquaponicsmediaposts/forum/top...

God bless

David Waite said:

I know the only thing Dept of fish and game hate worse than tilapia are asian carp species. They are banned in most southern and western states. Not sure about up north but Im sure its the same. Very invasive due to can survive the cold. I have tried carp and honestly it tasted like s\\\. Not quite sure how the asian culture eats that boney thing but they do by the millions of tons.

[marty lininger]

have you had any success so far?   i want to make an AP system that has duckweed as the main crop, and that going to the tilapia.  have lots of other stuff to figure out, but want to get moving ASAP.

i think the typical tilapia grow out size is 1.25 - 1.5 pounds for commercial, after that, they eat a lot still but grow much slower than before, so not economical if commercial considerations are important.

Wesley B said:

I am going to grow enough duckweed to be the sole source of feed for 800 pounds of tilapia per year.

[Wesley B]

We are going to start digging the ponds near the end of this month. We are building a large raised bed about 300 feet long with the dirt removed to create to ponds flanking either side of the raised beds, one for the tilapia and one for the duckweed. We are planting 150 dwarf plantains, 75 dwarf papayas and 75 fig trees into the raised beds. the water for the plants will be pumped out of the fish pond delivering a large supply of fresh water for the fish.

marty lininger said:

have you had any success so far?   i want to make an AP system that has duckweed as the main crop, and that going to the tilapia.  have lots of other stuff to figure out, but want to get moving ASAP.

i think the typical tilapia grow out size is 1.25 - 1.5 pounds for commercial, after that, they eat a lot still but grow much slower than before, so not economical if commercial considerations are important.

Wesley B said:

I am going to grow enough duckweed to be the sole source of feed for 800 pounds of tilapia per year.