No external fish food?

[Eric T]

Is it possible to have a completely internal system, where all the fish food is generated by the aquaponic system itself?  I know that sounds like a "perpetual energy machine", but the sun is ultimately the engine for everything.  Could algae be grown in the tilapia pond, and duckweed in one of the grow beds, and then all vegetable waste (stems, leaves, etc) could be fodder for the BSF?  Would that be enough, or is some external fish food necessary?  Thanks for your help on this.

[Eric Warwick]

Yes, and of course you alluded to the perpetual motion machine. Unfortunately I think your system would have to be very large to get any tilapia out to harvest size. Also, going through BSFL is vastly inefficient. Check if Tilapia can digest Cellulose. If not then a bacteria should do the job of breaking it down. 

[RupertofOZ]

It might be possible for a fish such as Tilapia... which can survive/thrive on an almost totally vegetarian diet....

 

But most fish aren't/can't/wont....

[Eric T]

Thanks for the opinions.  I'm interested in creating a true ecosystem, and closing the loop as regards the fish.  Working with tilapia is fine.  I'm just wondering if anyone has attempted this, and what they have determined is necessary to do, or maybe they found it just can't be done.  If I need to grow some plant in some nearby soil, that would be okay, too.

[Eric Warwick]

I heard of some people converting a swimming pool to a green water culture tank. I think I heard about it from http://www.ecofilms.com.au/ . I don't see it on the front page, it was a while back. Shouldn't be too much of a search.

Eric T said:

Thanks for the opinions.  I'm interested in creating a true ecosystem, and closing the loop as regards the fish.  Working with tilapia is fine.  I'm just wondering if anyone has attempted this, and what they have determined is necessary to do, or maybe they found it just can't be done.  If I need to grow some plant in some nearby soil, that would be okay, too.

[Carey Ma]

Action equals reaction. What ever input you have, you can expect an equal output. If sunlight is the only energy put in, you can only harvest that amount of energy, minus inefficiency.

As Eric said, it would take quite an operation to scale in productive amounts of human usable crops.

@ Eric; even green-water culture requires nutrient input (most commonly~ chemical fertilizers and/ or manure).

[TCLynx]

If you want to harvest anything out of the system, then you are part of the system and your waste needs to somehow be returned to the system.  I don't think you will manage any "small scale" system that is just AP that can provide food for the fish while also providing food for the plants that lets you harvest much at all since most of the fertilizer from the fish will have to go back to growing more food for the fish and not veggies for you.

The sun provides the energy for the plants to grow and convert matter to energy and energy to more plant.  The sun does not create the nutrients (nitrogen, phosphorus, potassium, and all the lesser trace elements) if you keep removing those nutrients from the system by harvesting fish and plants but not putting any in, your system will starve.  It's kinda like how we have been mining our soils by harvesting and only replacing the big 3 with chemical fertilizers so our food becomes less and less nutritious. 

In other words, if you are not going to add external fish food, you will have to add some other form of external fertilizer to be able to grow the fish food as well as veggies and still be able to remove produce/fish from the system.

[Ellen Roelofs]

The sun is your power and you have air and water as inputs, as well, right?  You could also grow some fish food in available soil for added inputs.  My tilapia have done well on (cooked) sweet potatoes.  Also, they have eaten many different kinds of leaves steamed.  The challenge with feeding them scrap plant material, for me, has been securing the food so the fish can tear bite-size pieces off.  It's apparently hard to eat tough food without your hands... or teeth.   But I like that it gives them something to work on and that they can graze throughout the day.

[Eric T]

Thanks for all of your replies.  In Sylvia's book, she references GardenPool.org, a family in Arizona that converted a swimming pool to an aquaponic system, and they claim not to use any external fish food, which is surprising (for all above-mentioned reasons), but this is why I wanted to see if others have successfully done this, with maybe some side-growing of a crop or using humanure.  Permaculture advocates the development of "forest gardens", in which a complete ecosystem exists, where all nutrients do eventually end up back into the soil (through animal and bacterial action).  The sun is the only engine, ultimately.

[TCLynx]

In permaculture you are getting nutrients from the soil and from composting animal wastes back into that soil.

Are you going to poo and pee in your aquaponics system, In order that you can eat the salads from it?  I do not advocate this use of warm blooded animal manure in aquaponics.

Garden pool has chickens they keep caged above the pool and their waste goes into the water to feed the algae bloom to feed the fish.  I also do not advocate this unless you make a point of cooking all your veggies well before eating them.  do you really like cooked lettuce?

If you really want a NO input system and you want to eat something from that system, then you have to be part of it and your waste has to go back into it.  Since I don't advocate using warm blooded animal manure directly in an aquaponic system, I'm going to say no you don't get to have a NO input Aquaponics system, you would have to expand your scope of the eco-system to include something a bit more like permaculture so you can compost your waste to grow perhaps some fodder crops to use to feed the fish and so on.

[Eric T]

Thanks, I didn't know that about their chickens, that means they need to get chicken feed from somewhere external.  It would be interesting to take a full accounting of all the energy/resources that go into an AP system, to get the "true footprint" (beyond my abilities).  My guess though is if one is vegan, then it is probably more sustainable to just grow vegetables in soil, rather than use an AP system providing fish fertilizer.  If one eats fish, then AP seems a pretty good way to go, even though the true footprint may be quite a bit larger than one's set-up.

[Eric Warwick]

Hechem, the sun provides energy. The soil and air provides matter. The nutrient requirements are so small that taking external inputs from the ecosystem and recycling human waste is feasible. I actually think tha,t since soil N is finite (yes there was a study saying much of the available N in rocks, not from the air) a local source of chemical fertilizer is more sustainable, if used sparingly and wisely. Now if you were to grow a high cellulose-containing-plant (ex. tree) to be composted and otherwise get nutrients from it you'd have your NPK inputs. Now, off my soapbox and cue the arguing about my 3rd sentence.

[TCLynx]

Eric W, so why would chemical nitrogen fertilizer be more sustainable than an immediately available local nitrogen source like say (pee)?

Eric T,

The really big benefit to growing with aquaponics is the water savings.  If you don't want to eat the fish, you could do some other form of bio-ponics.  (Pee ponics for instance.)