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? 

[Chi Ma]

Here you go :)

http://www.youtube.com/watch?v=FwMEulvJ2Ps

[Kobus Jooste]

Neat, but I would like to see total dependence on the duckweed, and the duckweed cultured in the same system prior to the water getting to any media.

Chi Ma said:

Here you go

http://www.youtube.com/watch?v=FwMEulvJ2Ps

[TCLynx]

Hum, I don't know how much veggies one would be able to remove from a system that only gets a little sea salt and is growing carp and duckweed.  Needs to be a bit more addition of what ever minerals tend to be removed from the system in the form of veggies.

 

I expect it could work but probably wouldn't be very high production for the space. (12 tilapia were very quick to eat up all my duckweed and a large surface area would be needed to keep lots of fish fed.)

[Kobus Jooste]

Lemna grown in nutrient rich water has a very good trace element constituent - I'm willing to bet better than what most people expect.  Combined with the nutrients from a worm bin, I say it is a go for trying.  The duckweed can also suck a massive amount of nutrients out of water.  Currently, I have 20 small koi sustaining 7 square meters of duckweed.  Duckweed is not growing like wildfire, but they are growing, not receeding.  The advantage of duckweed as your first line of filtration is that it will whack ammonia better than most bacteria.  In waste water systems, they can clear a gram of Ammonia per square meter per day.  I'm not sure what the scaling will look like, but give me a grant and I will make it work :)!

TCLynx said:

Hum, I don't know how much veggies one would be able to remove from a system that only gets a little sea salt and is growing carp and duckweed.  Needs to be a bit more addition of what ever minerals tend to be removed from the system in the form of veggies.

 

I expect it could work but probably wouldn't be very high production for the space. (12 tilapia were very quick to eat up all my duckweed and a large surface area would be needed to keep lots of fish fed.)

[TCLynx]

Duckweed is a perfect thing for over a large settling tank and yes it is a great ammonia sink.  Main thing I am wondering is if you manage to grow enough duckweed to feed the fish, will there be any nutrients left over to feed veggies in the plant beds without adding more than a little salt?

 

Will be interesting to see how you get it to work, I hope you get the grant :)

[Kobus Jooste]

that is the real crunch question and my gut feel is perhsaps not enough, but if you look at the amount of tomato growth Dan got out of an aquarium with a few tropicals in them, I think the system may surprise us.  I do think the extra nutrients from the worm bin would be vital, but as it will be re-cycling plant clippings and vegetable wastes generated on site, I will try to sneak it in as part of the closed loop, if the loop can be considered the property that the unit is on.

TCLynx said:

Duckweed is a perfect thing for over a large settling tank and yes it is a great ammonia sink.  Main thing I am wondering is if you manage to grow enough duckweed to feed the fish, will there be any nutrients left over to feed veggies in the plant beds without adding more than a little salt?

 

Will be interesting to see how you get it to work, I hope you get the grant

[TCLynx]

There you go, if the aquaponics is thought of more as an integrated part of the larger "farm" yes, I expect it would be far more reasonable.

[steve]

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]

Hum.

Well it only took about 5 days for a dozen tilapia to eat up 40 square feet of duckweed to the point that I needed a fresh batch to replace it.  So I suppose if you were to be feeding duckweed early in the day and the give pellets later in the day (my tilapia wouldn't eat the duckweed if I was feeding pellets) I suppose you would probably need about 400 square feet of duckweed grow space to supplement for 100 lbs of fish for ten days.  Now if the fish are not in the duckweed grow space and you are simply netting out a % each day to feed the fish, you may get enough re-growth to keep it going.  The duckweed growing system would need a good amount of fertilization to provide a good nutrient balance for the fish but that is a topic that Kobus can probably answer better than I.

 

My numbers above are only my guess based on my old duckweed pee ponics system that I later put a dozen tilapia in and they consumed the duckweed quickly.

[steve]

Thanks TC, Seems like you've been experimenting Ya I was thinking of a separate tank and net it out every day. I understand they can optimally double their mass in a couple days. Realize more labor and start up costs, less space for other plants and complication would be involved. Wonder what other negative aspects. Seems like a such good thing, to reduce feed expense. I think it might even be good for chickens and pigs. Now if I could only get the dogs to eat it.

[TCLynx]

my chickens were not very interested in it without additional processing.

[David Waite]

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.