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Dear Sylvia,

I do hope, reef fish excrete similar quantities of the different nutrients and metals. Please see the attachment.


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I'm curious how reef fish relate to aquaponics though? Has anyone figured out how to manage salt water aquaponics?
it's not the salt water fish, it's the excretion of them. Could be similar to freshwater fish.

TCLynx said:
I'm curious how reef fish relate to aquaponics though? Has anyone figured out how to manage salt water aquaponics?
Thanks, Werner! I'm not smart enough to completely digest what this report is saying, but I think the bottom line is there is a lot of great plant nutrients in fish feces. Makes sense, doesn't it? I'm a big believer in getting all that great stuff into your grow beds and letting the worms and bacteria make them available to the plants. I never have to add anything extra to my systems - it's all just uber happy ;-)
I believe the concept would the same. Salt water aquariums use biological filters (live rock and others) and protein skimmers, along with water changes as needed. My immediate question is which edible plants will grow in salt water?
That's a good question. There are only a few, most genetically modified crops able to grow in brackish or even in salt water.

George J. Thurmon said:
I believe the concept would the same. Salt water aquariums use biological filters (live rock and others) and protein skimmers, along with water changes as needed. My immediate question is which edible plants will grow in salt water?
Kobus, if you run across one of those papers that analyzes the sludge from tilapia in RAS again would you shoot the link to me? Are you saying "sans Molybdenum and Boron" because they aren't present? These are in the 16 elements required by plants, as you obviously seem to already know, but they are only required in trace amounts and I've never heard talk of these being a problem in aquaponics. Also, are you saying that solids are excreted in some way other than what you would normally think? I thought ammonia was through the gills and solids through the anus, so I'd be very interested in hearing more. Thanks!

Kobus Jooste said:
In my research I have come across a number of papers related to the chemical constituants of alquaculture sludge. These mostly entailed studies of tilapia RAS systems, and if you want to be more specific, only remains applicable if you use the same fish food. In general what it did show was that all basic growth elements required by plants, sans Molybdenum and Boron were present in the sludge, and that most of the elements were in a range suitable for plants, some a bit on the low side, some a bit on the high side. People also often forget that with fish, there are excretory pathways - solids and dissolved materials excreted through permeable membranes directly into the water. You therefore have to balance both sources of nutrients when looking at the usefulness of aquaponic solution for plants.
2) removing any waste from the system should not be considered. Systems should be geared towards being a perfect loop of fish and plants. Why toss food into the system and then toss the solids out again?

So if we harvest fish, fillet them and eat the fillets, most of the fish (approximately 65%, depending on species) is unconsumed by us and could be returned to the system but how could we do it? Some biopod users feed fish/fish carcasses to black soldier fly larvae. The larvae eat most of the fish but not scales and bone. The larvae could then be fed to the fish. The fish and bones (or entire carcasses) could be composted and perhaps the compost could be used to grow some type of fish food in a dirt garden. What could be grown that would then be fed to fish and how? Possibly something could be grown, mixed with dried carcasses (or not) and then fed back to the fish in pellet form. Likewise vegetable waste from the system could either be fed to BSFL or composted. That is an interesting idea, closing the loop to retain nutrients.
Hay guys, I just want to make note of something here, Saying "closed loop" when talking about any system where you actually harvest and sell something from it is really not a "closed loop". If you add feed, it is not closed and if you remove anything from the system (plants/fish) it isn't closed loop. Lets face it, a closed loop system is only productive for those creatures living inside the loop.

However, I do understand what you are getting at though. For instance, not removing solids is essentially patching the leak that would otherwise be draining away nutrients. And if you are happy to go a bit slower click on the fish (either not as many or not as fast a grow out) you can actually get much more efficient on the plant growth.

I expect it would be possible to greatly reduce the purchased ingredients for fish food by utilizing "wastes" as feed stocks for BSF larva and the sludge from BSF larva bins definitely could use some further processing by worms which can also be feed for fish as well as the castings making very good seed starting medium and by recycling that back into the system the complex compounds available from the worm castings are great for plants. Add to it the duck weed and perhaps some other bug catching feed for the fish and the loop becomes far less OPEN as long as the people eating food from the system return their scraps back to the BSF and worm bins.

Now here is a component that hasn't gotten much talk that I've seen. Natural live feed for the fish. When raising larval fish I know it's common for people to hatch brine shrimp or work up a bloom of zoo plankton and stuff like that but I haven't seen much talk of carrying this further (other than green water culture for tilapia) except a few comments of growing guppies as live feed for really carnivorous fish. So, for example, catfish are called omnivores (not quite sure why because I've never seen mine eat a plant, I have seen them grab plant matter in their mouths but they are probably just checking it out and spit it out) perhaps because they seem to do well on even lower protein feed than the tilapia. Anyway, their natural food in the wild is largely small crustations and small invertebrates along with insects and perhaps small slow fish/frogs etc when they get a chance. So what I'm wondering is, what detritus eating crustations could we add to our systems to provide feed for our fish?
And a admirable Goal to work towards too.
Defining what you mean by "closed" and sharing that info I think is really helpful too. Gives more of the framework for meeting the goals.

Thank you Kobus
We can also breed our own stock.

Can you recommend species for ease of breeding, other than tilapia?
I'm not sure about ease of breeding but one person I know said his blue gill did breed in his swimming pool system.
Kobus, your comments have been incredibly enlightening, and improved fish feed is a critical path to widespread aquaponics. You are clearly someone who is/will have a big impact on aquaponics. How are you doing solar/wind? With a battery running at night? What is a "Lemna"? Have you found that Molybdenum and Boron aren't present in fish poo? And finally, yes, if you can find those PDFs I would be eternally grateful. Thanks!

Kobus Jooste said:
Eish! Seems like I have to clarify my stance a bit.

The ecosystems we create contains the following:
1) recycling pathways - VERY important. All the microbes in our system.
2) Primary producers - the plants. The problem is that typically, the consumers of this system is not "resident" but migratory - US.
3) consumers - the fish, and us. We are part of the system (but don't feel obliged to go live in the tank)
4) population dynamics - we sow seeds, transplant them, introduce fingerlings, grow them out, eat them, stick in new fingerlings. We can also breed our own stock. This is a modification of mortality and natality. We ensure that nothing important dies out in this system. If we do not go and buy them elsewhere, the loop remains closed.
5) Imports - the buffers, micro nutrients and fish food we add
6) Exports - everything we remove.

I was not referring to some form of biopod when I was talking about a closed loop, but the following scenario that, as far as I am concerned, provides a closed loop in production philosophy. See yourself as predation or consumption, because that is what you are. Mr bear or fish eagle does not fillet his fish and dump the wastes back into the river. It is a predation export, which we then balance out with the import of a fingerling in its place. Now, if you were responsible for the production of said fingerling, you are still operating in a closed loop. If you take the wastes from your system, and produce BSFL for your system, then you are still keeping the loop closed. If your greenhouse has gutters, and all the water you use drops from the sky, then the loop is still closed - no municipal input. If you grow duckweed as part of your system, and use it as food for the fish, the loop is still closed.

Thus, to get back to what I said before, my closed system:

I have a greenhouse with gutters that catches water. The water keeps my tank levels right. Solar and winds supplies the power. I harvest some seeds from production, and use them the next year (if possible). I grow my own fish, and produce their food (if possible) from components of the system. What you take, you take as the apex predator. I do not use clarifiers, and I do not pull solids from the system. I do not clean my gravel - the bits that stays behind after I pull the plant out breaks down again. In other words. If you have no municipal services, and do not buy anything from a store, can you keep your system functioning. THAT is the question I am working towards.

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