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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 d
by asciimo 9y ago
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.
- mulmen 9y agoIs it possible to feed the fish using waste from the plants?
- asciimo 9y agoIf they're meat plants. According to this article (http://animal-world.com/encyclo/fresh/Knifefish/BlackGhostKnifefish.php#Foods%20and%20Feeding 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.
- mulmen 9y agoHmm, 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.
- weberc2 9y agoNot 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.
- mulmen 9y agoYeah good point, that must be why all ecosystems fail without human intervention. /s
- jfoucher 9y agoIn a natural ecosystem, nothing is taken out, whereas in this one, food is supposed to be removed from the system, making inputs necessary.
- bluGill 9y agoSunlight 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.
- weberc2 9y agoRight, 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.
- weberc2 9y agoRight. Just ecosystems wherein humans regularly remove a considerable portion of the overall biomass. Like a garden.
- nomadiccoder 9y agoYeah 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
- itsameta4 9y agoHis Black Ghosts are in a 150-gallon tank. They'll be quite happy.
- jordanwallwork 9y agoWhy 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.
- MadcapJake 9y agoI 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.
- JeffreyKaine 9y agoAgreed, 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.
- peterwwillis 9y agoAnd if you compost, the fertilizer is free.
- ryanmarsh 9y agoI too would like to know the cost per calorie.
- dundercoder 9y agoI haven’t done the math but I have read that growing duckweed to feed tilapia is a very economical alternative to commercial fish food.
- adrianmonk 9y agoSounds 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.
- ChuckMcM 9y agoWell this site : https://lakewaytilapia.com/Tilapia-Feeding-Guide.php 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.
- IdeaHamstir 9y agoDuckweed 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.
- ChuckMcM 9y agoSomething 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?
- mattmaroon 9y agoThat 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.
- IdeaHamstir 9y agoFry 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.
- disordinary 9y agoExcept 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.
- bluGill 9y agoFertilizers are not bad for the environment. They are bad for our water supply, but fertilizer that doesn't get to the water supply is helpful.
- disordinary 9y agoYou try and tell that to the people of Nauru.
- IdeaHamstir 9y agoA 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.
- oh_sigh 9y agoYou 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).
- IdeaHamstir 9y agoFertilizers 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.pdf 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.
- Qworg 9y agoYou don't have to feed the fish - you can also grow black soldier fly larvae and have them automatically feed the fish for you. https://www.theaquaponicsource.com/blog/black-soldier-fly-larvae-for-fish-food/ https://www.theaquaponicsource.com/blog/black-soldier-fly-la...
- Jedd 9y agoIndeed. 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. Geoff Lawton's 80 square metre aquaponics pond here: https://permaculturenews.org/2014/01/25/perfect-permaculture-fish-pond/ https://permaculturenews.org/2014/01/25/perfect-permaculture...
- oh_sigh 9y agosmall 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.
- freeflight 9y agoIf you need additional input you might also want to check out Sepp Holzer [0]. [0] https://www.youtube.com/watch?v=DFQUKQVwRXU https://www.youtube.com/watch?v=DFQUKQVwRXU
- Jedd 9y agoAh, fat finger mistake. 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.
- nkingsy 9y agoI 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. http://www.backyardaquaponics.com/forum http://www.backyardaquaponics.com/forum is a tremendous resource.
- mistermann 9y agoDo you have an opinion on the "healthiness" of a pure hydroponic system?
- nkingsy 9y agoHealthfulness 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.
- IdeaHamstir 9y agoAzolla = 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.
- JoeAltmaier 9y agoMaybe not human food - it may contain a neurotoxin. So not good for long-term consumption. Let the fish/chickens digest it first!
- IdeaHamstir 9y agoGood to know about the possible neurotoxin. Any suggestions for further information on the topic?
- JoeAltmaier 9y agoWikipedia?
- IdeaHamstir 9y agoBeen 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.
- tsjackson 9y agoBMAA 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.
- spiraldancing 9y agoI ran a small home/experimental aquaponics system for over a year, fed the fish, primarily, free worms out of my vermicomposters.
- edaemon 9y agoI'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.
- johncogg 9y agoAs 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.