The author glosses over the true source of the magical, "free" fertilizer: "some fish food." You have to feed the fish. I have never seen an aquaponics zealot do the math on the cost per unit of fish food versus the cost per unit of fertilizer. Intuitively, complexity and costs could be reduced greatly by removing the fish component, i.e. hydroponics.
I raise channel catfish in my own home aquaponics system. If you don't plan on eating the fish or enjoying them as pets, it's not worth it at all.
Feed is indeed the big pain point. All good feeds have fish meal and GMO soybeans etc, and the only way to get a reasonable price point is by buying a 50lb bag from a farm supply store. With a 3 month shelf life, you need a lot of fish and a lot of time dedicated to feeding to not have spoilage.
Theoretically a true closed home system could be achieved by routing household urine to a green tank growing algae, solid waste and food waste to a black soldier fly larvae bin, and feeding the algae and larvae to the fish. The BSFL harvest themselves, and the green tank could be periodically pumped into the fish tank on a timer.
None of it would be terribly complicated to build into a new home, but there's no will to do so as most people would find it gross, preferring to eat artificially cheap fossil fuel fertilized products and have their waste magically disappear.
I've been wondering about this for a long time. Many articles on the net gloss over the fact that conservation of energy also holds for "closed" aquaponics systems, and that in the end, we eat biologically processed fish food that needs to be bought in the first place. Fish food is probably produced with less stringent rules than food for humans, e.g. regarding heavy metal content \m/ and other contaminations.
I've been thinking about BSFL for aquaponics and there is one problem: warm blooded animal feces should never get into the water. If it could then you wouldn't need fish btw.
I don't know how many E. coli bacteria would survive the BSFLs. I guess this could work for your home, but I would not risk that. Of course you can test the water, but no one did that yet as far as I know.
Healthfulness of foods by comparative farming practices is not something I have been able to find any solid information about. Hopefully our taste buds know what's good for us when they're not confused by sugar and fat.
Life - Dan Barber said on "Chef's Table" that he felt his produce tasted better and better as he put more life into the soil. The hydro growing medium is relatively sanitized.
Freshness/Ripeness - We had an organic CSA farm box last summer, and in head to head comparisons, the stuff we grew at home (both soil and aqua) tasted way better. I think this is because we picked it when it was ripe and ate it immediately.
I do have some worries about using plastics. unless you are doing a large-scale operation with concrete and / or glass, hydro and aqua both involve water making a lot of contact with plastics. I have to assume that food grade plastics are safe, but no one really knows for sure.
My gut feeling is that as long as you're meeting all the needs of the plant, freshness/ripeness matters more than the presence of other life in the growing medium.
Permaculture practitioners have borrowed heavily from provably long-term sustainable aquaponics systems, though these tend to be larger scale (field-sized) and seasonal (wet season you have ponds, dry season you don't).
I haven't seen numbers on effectiveness, but similar to the article you linked, there's fly traps (easy to enter, hard to find their way out) that float on a pond - you put a stinky bit of old meat, cow pat, etc in there, flies lay eggs, fish either eat the larvae that drop through slats, or the flies when they touch the water. Similarly, small solar lights at night near the water's surface to attract more free food.
small error - Geoff's pond is 800 m^2, not 80(per his linked site). But thank you - this is my first time seeing his material. I've been doing forest gardening for ~12 years on my site, and am thinking about developing a nearby natural depression as a pond - Geoff seems like exactly the kind of person I need to study.
Glad you like Geoff - he's a legend in permy circles, and for good reason. Check David Holmgren, Bill Mollison (the two co-founders of permaculture)... and you'll doubtless find lots of other people's work to investigate from there.
Permaculture pushes the idea of building systems that don't need a constant input of external resources... more difficult to design, but maintenance is naturally cheaper / easier, and more resilient.
Azolla = free fish food. It obtains both nitrogen and carbon from the air and can double in mass every 2-3 days. Protein content is 17%. Needs only a few inches of water, sunlight and trace minerals.
I've done the math, and while Azolla can't provide 100% of fish nutrition, it can easily provide the majority of it. It can also provide human food and chickens love it. So do pretty much any domesticated animal: many papers have been written about studies on azolla raised hogs, ducks and cows.
BMAA is the neurotoxin (implicated in Alzheimers and Parkinsons). It also bioaccumulates over time, and potentially up trophic levels. So definitely not fish wonder food until there's some serious testing done.
Thank you. I will definitely look into this. At the very least, it still makes an effective and fairly high nitrogen organic fertilizer, while drawing down atmospheric CO2. It's so effective at harvesting CO2, ancient azolla sequestered sufficient CO2 (from 3500 ppm down to 650 ppm) to create a global ice age: https://en.wikipedia.org/wiki/Azolla_event
Edit: researchers are still studying the issue, but it seems some plants may be capable of concentrating BMAA, which is highly water soluble. Wheat seems to capture it in proteins of the shoots. I haven't found any further specifics other than cycads, which have a cyanobacteria symbiosis and concentrate it in their seed coatings.
Been there, done that and have read dozens of research papers on azolla as livestock feed, but there hadn't been any human research when I delved into the subject. That was quite a few years ago, however. I'll dig back into the stacks and see what I find. My chickens prefer azolla over just about anything, I need to grow more of it.
Agreed, this is why IMO it's much better to set up a tank with fish you can eat (Tilapia was mentioned in the article, but I've seen rainbow trout setups as well).
Makes paying for fish food a little better, because you get a delicious form of protein as well.
I'm far from an expert but I've seen some interesting things where people replace the fish tank with worm bins and/or black soldier fly bins and they just use compostable material and kitchen scraps as the feed. The flies especially will eat pretty much anything but the worms are easier to keep alive. The plants are fed hydroponically by pumping water through the feed bins, so it soaks up the nutrients in the compost. It's an interesting concept.
Well this site : https://lakewaytilapia.com/Tilapia-Feeding-Guide.php seems to have all of the information you need to understand how much food it takes to generate useful amounts of Tilapia. Could be combined with an aquaponics set up to do the TCO calculation.
Duckweed is a good tilapia feed, but requires a nitrogen source. Use it to supplement azola, it has around 4% more protein.
The problem with tilapia is they reach breeding size long before they reach useful eating size. Upon reaching breeding size, they pretty much quit growing and put all their energy into offspring. They are nearly impossible to separate by sex. Commercial tilipia is treated with large doses of hormones to hermaphrodize the fish to a single sex and grow those nice sized fillets.
Something I've wondered is what sort of distribution can you maintain in a Tilapia population. In some fish populations once you get to a certain size those fish can cannibalize the fry such that you get no additional fish regardless of breeding until they are removed. Any thoughts on that?
That doesn't happen in nature because the small fish can fit into hiding spots the large ones can't. That's why people who own ponds toss in things like pallets and felled trees. That'd be easy to replicate.
Fry are typically separated from the larger fish with netting. Sure, you could keep them all together, but a huge amount of system resources will be consumed by the endless cycle of breeding and cannibalizing and you will won't get fish to a useful size.
Sounds like it's free for him because he was going to keep fish anyway. The fish aren't a means to an end in his case; instead, the vegetables are a bonus.
As the author, yes I didn't really discuss that. But on the other hand, I would argue I wasn't trying to gloss over it either!
In my case, I took my fish tank which previously existed and turned it into something more -- at the same time, I also dramatically reduced my upkeep time because of the lack of water changes.
Except fertilisers are bad for the environment, especially Nitrogen which is mined.
I have a friend who is building a commercial aquaponic setup and he claims that not only is it better for the environment but it is price competitive now and will be cheaper than hydroponics as the prices of fertilizer keep increasing.
A substantial fraction of the world's natural gas is burned to produce nitrogen fertilizer. This is largely obtained through fracking. Fertilizers, as they are used on the large scale, are pretty bad for the environment.
You seem to be arguing that the current production of fertilizers is bad - but that doesn't implicate fertilizers in general(unless it is impossible to do otherwise for some reason).
Fertilizers in general aren't necessarily bad. It is important for us to actively recycle our phosphorous and potassium, because there is no short term replenishment of these vital elements in the soil. For more information, I highly recommend "The Humanure Handbook": http://humanurehandbook.com/downloads/Humanure_Handbook_all....
Fertilizers do increase the growth rate of plants. However, there is mounting evidence that nutritional content is inversely proportional with growth rate.
If they're meat plants. According to this article (http://animal-world.com/encyclo/fresh/Knifefish/BlackGhostKn...), they're carnivores who can eat pellets. Reading this entire page, it looks like Black Ghost Knifefish are not trivial to keep happy and healthy, and will eventually need 100 gallons of water. While I would argue that it's irresponsible to treat any fish as a mere fertilizer producer, this fish may be especially miserable for its limited life.
Hmm, is there some other kind of fish better suited to this type of system? Some kind of fish that could naturally survive on the plant waste? Maybe not even the waste in the water but some other form of biomass from the rest of the system?
e: Sibling comments seem to suggest Tilapia or Rainbow Trout.
Not sure what you're proposing, but something has to go into the system (fish food or fertilizer) if you're going to be taking things out (food). If the fish are living off of the plants, then you need to feed the plants. If the plants are living off of the fish, then you need to feed the fish. Something something Law of Conservation of Mass and Energy something something.
Sunlight and air are inputs though. Most of what you take our of the system comes from changing H2O and CO2 from the air into a different form using energy from the sun.
There is the potential various micro nutrients, and minerals. However the vast majority of what the system needs is air and sunlight.
Right, but nutrients and minerals are still being regularly removed from the system--they need to be put back in order for the system to function. Their mass relative to the mass of other inputs doesn't change the calculus.
Yeah conservation of matter, you need minerals other than carbon, oxygen and sunlight to make food therefore if human in the loop is introduced you need to take the human byproducts into the system as well
Why do you feel that using a fish for fertiliser production is irresponsible? It seems to be an effective way of using something that the majority of people who keep fish treat simply as a waste product.
I use the water from my tank's water change to water all my plants in the house. I can fill almost three watering cans which is enough for two waterings of the various decorative plants and herbs I have (I don't have any vegatables or this surely wouldn't be enough). And that's just a measly 10 gallon aquarium.
