Backyard Aquaponics
A place to discuss aquaponics

This is interesting, how did you correct the potassium deficiency? 90% is impressive, you must have quite the system! I'll have to read a bit more about seaweed concentrate, because I know seaweed is great stuff for plants in general.

Hmm, yea. Basically it's an INCOMPLETE protein. Complete proteins require specific ratios of amino acids, and if any of them are less than needed you'll only get as much protein as the limiting amino acid is capable of providing. So there might still be protein, but just at much lower amounts than listed.

I guess for a full on vegetarian fish this could be an issue, but now I'm wondering if a combination of duckweed and black soldier fly larvae might be enough? I just began looking into black soldier fly larvae, and they appear to have a good spread of nutrients.

I just found this in one of the pages that was linked previously, which is part of what I was wondering. This makes complete sense.





So grown on your own in a grow bed or what not would require some additional input of nutrients to maximize their nutritional value. I do think that the interesting thing about this is that you could add the nutrients to the grow bed where your duckweed is growing, without having to worry about adding it to the water that your fish are in.

If you look at this page http://www.mobot.org/jwcross/duckweed/n ... sition.htm you'll see a list of the potential mineral composition for duckweed. There is Iron (Fe) and Potassium (K) included.

I admit I don't really know yet how much of these nutrients need to be cycling around an aquaponic system, but if you think about it there just might be a possibility of growing duckweed optimally so that it already contains a lot of the nutrients that must be supplemented into a system. Again, this way you wouldn't have to add the supplements directly to your fish water and worry about adding too much, or any of the other issues that come up with supplementing from an outside source other than the fish food.

I'm completely speculating at this point, but what do you all think about that? Definitely interesting right? You might need some more protein as talked about before, but maybe you could get that from black soldier fly larvae? I mean, for fish that aren't solely vegetarian.

For a backyard system, I think it's possible. Not sure about commercial. I'm not buying the complete/incomplete protein in terms of tilapia after they reach a few inches. In the wild, I believe they are omnivores early in life, and then herbivores as they mature. If they needed a complete protein to mature and grow, I'm not sure what they would be eating in the wild to get it. There are plenty of fish and other species that convert plants matter to muscle, and don't require a complete or in some cases any protein.

Yea, all of our physiologies are different (ours and every other animal). According to most of our science (and I know there is debate about this, especially among vegans, vegetarians etc) our human body requires a specific amount of each necessary amino acid to construct a complete protein chain. Vegans and/or vegetarians can get this by combining foods that complement each others amino acid profile.

Too boot, if you simply eat a boat load of let's say Broccoli for example, eventually you would get enough of the limiting amino acid to start building complete protein chains. You would just have leftover amino acids in your system, and science is starting to believe that these leftover amino acids hang around for a bit so that if you ate something else within a period of time that complemented them, viola you get more protein! This is related to humans.

I've done a load of research into this, so you wont get an argument from me when it comes to many other animals getting all of their protein from a veggie source. I mean look at horses and cows for example. Their biology is either A. different from ours (which it is) and/or B. they eat so much grass or whatever else their fed that it is enough to complete the protein they need.

Obviously, the biology of a fish is different from ours, and in fact each fish has different needs from each other kind of fish. I guess you would have to know more specifically what each fish required, and yea there are no "commercial" or "human made" fish feeds out in the wild, so what are they eating out there?

Good point for sure Chris...

On a commercial level you would probably need a boat load of duckweed and/or something else to keep your fish healthy and your plants happy right? I would be curious if it would still be possible, or like you said at least possible at the backyard level. Protein is just one factor to consider, but if you could figure that out, as well as your other nutrients needed for both fish and plant, then there could be a way.

What I'm really interested in is not just giving the plants enough to get by, but to thrive. I think at minimum it looks like you would need to be growing your own duckweed in it's own bed and feeding it some nutrition. Unless you had a lagoon or something on your property where it grew naturally, and you could harvest it from.

Yeah, like someone mentioned earlier, the studies compare dry weight for duckweed. Yes, it would require a large amount of surface area. I don't know exact details of growing conditions, but think it's shallow, nutrient rich waters. In this area, the best duckweed I've seen is in agricultural areas. In areas where livestock are feeding and in the water. There are some YouTube videos of a few guys who grow it and use it in their systems, but not sure to what extent it supplies their fish diet. It's certainly possible, just not sure how practical it is. Time and expense setting up duckweed tanks/ponds vs. cost of buying bags of fish feed. Of course then there's the personal satisfaction of knowing that you don't HAVE to buy anything to have fresh fish and veggies. Although, i would still stock up on some Fe, K, and Ca. That and a solar system, and you could be self sufficient in terms of your AP set up. A lot of the preppers are more into this then I am, but it's an interesting concept.

Hello. So some time ago i made some research regarding this topic. i found a great page that provides infos and scientific papers about duckweed.

http://www.mobot.org/jwcross/duckweed/duckweed.htm

Fish:

Duckweeds can be grown separately and then provided to the fish, or produced in the same pond. Production of Lemna in the same pond is not likely to work efficiently, however. Vigorous aeration of the water, as is practiced in catfish-culture, will disturb the growth of the plant. The photosynthetic activities of the plant do not oxygenate the water, in fact the covering plants reduce gas-exchange with the atmosphere (Landolt and Kandeler, 1987, p 387).

Grass carp seem particularly adapted to feeding on Lemna, and there is a large literature devoted to this application (summarized by Landolt and Kandeler, 1987, pp. 387-388.). As reviewed by Landolt and Kandeler, channel catfish have been successfully raised on duckweeds, but no commercial application of these findings seems to have been developed.

The growth of hybrid carp were studied by Cassani and Caton (1983) to determine feeding preference and feed consumption. The hybrid was grass carp, Ctenopharyngodon idella (Val.) X bighead carp, Hypophthalmichthys (Aristichthys) nobilis Rich, 12 to 18 months old. Their conclusion was, "The most preferred plant was Lemna gibba when in combination with six other species." Moreover, at the same order of preference was exhibited at two different growth temperatures (12-15 C vs. 25-28 C). This preference was the same, based either on the time to complete consumption or the relative quantity consumed. Mean daily consumption (g) fish at 25-31 C for Lemna gibba tested separately was 178.

Gaigher, et al. (1984) compared the growth of hybrid tilapia fish (Oreochromis niloticus X O. aureus) on commercial pellets vs. duckweed. The fish were cultured at high densities in an experimental recirculating unit for 89 days with duckweed (Lemna gibba) or a combination of duckweed and commercial pellets. They conclude that a combination of pellets and Lemna gave the best performance:

When fed on duckweed alone, intake rate was low, feed conversion ratio good (1:1) and relative growth rate poor (0.67% of bodyweight daily). Sixty-five percent of the duckweed consumed was assimilated and 26% converted to fish. When the fish were fed on pellets in addition to duckweed the rate of duckweed consumption decreased and growth rate of the fish doubled with feed conversion ratios between 1.2 and 1.8. Seventy percent of the mixed diet was assimilated but only 21% converted. Fish grown on the mixed diet performed similarly to fish grown on pellets but had a better feed conversion ratio.

Porath, et al. (1985) attempted to recycle the solid wastes of these fish as a fertilizer for Lemna. The duckweed (Lemna gibba) was grown in shallow ponds containing mineral nutrients. However, the tilapia waste was poor in free NH3 and ammonium compounds. When separated and incubated at 38 C to allow anaerobic digestion to release mineral nutrients, prolonged digestion was necessary before it supported growth of the plant.

Tilapia were given duckweed as food as young fish from the larval to the fingerling stages (Moreau, et al., 1986). A comparison was made of three types of food: Lemna minor (duckweed, produced in shallow ponds or year-round in greenhouses), Chlorella (phytoplankton) and Daphnia (zooplankton). These authors studied both the nutritional value of these foods and the resulting growth rates of the fish.

Crayfish are often released in irrigated rice fields in rice- growth areas of the United States to control weeds (often duckweeds), according to Landolt and Kandeler. It is not known if the deliberate growth of Lemnaceae would be an efficient means of production of these crustaceans.

Conclusion:
Numerous demonstration projects prove the usefulness of duckweeds as the primary food source for production of fish and livestock. These studies show that duckweeds are highly productive and economical to grow, and that the plants provide nutritious and palatable food for meat animals. Based on this farming system, and with no additional basic research, highly profitable agricultural ventures can be developed.

"When fed on duckweed alone, intake rate was low, feed conversion ratio good (1:1) and relative growth rate poor (0.67% of bodyweight daily). Sixty-five percent of the duckweed consumed was assimilated and 26% converted to fish. When the fish were fed on pellets in addition to duckweed the rate of duckweed consumption decreased and growth rate of the fish doubled with feed conversion ratios between 1.2 and 1.8. Seventy percent of the mixed diet was assimilated but only 21% converted. Fish grown on the mixed diet performed similarly to fish grown on pellets but had a better feed conversion ratio."

Nutrional value:
http://www.mobot.org/jwcross/duckweed/nutritional-composition.htm

Seems like a great way to recycle nutrients in the system

Hello. So some time ago i made some research regarding this topic. i found a great page that provides infos and scientific papers about duckweed.

http://www.mobot.org/jwcross/duckweed/duckweed.htm

Fish:

Duckweeds can be grown separately and then provided to the fish, or produced in the same pond. Production of Lemna in the same pond is not likely to work efficiently, however. Vigorous aeration of the water, as is practiced in catfish-culture, will disturb the growth of the plant. The photosynthetic activities of the plant do not oxygenate the water, in fact the covering plants reduce gas-exchange with the atmosphere (Landolt and Kandeler, 1987, p 387).

Grass carp seem particularly adapted to feeding on Lemna, and there is a large literature devoted to this application (summarized by Landolt and Kandeler, 1987, pp. 387-388.). As reviewed by Landolt and Kandeler, channel catfish have been successfully raised on duckweeds, but no commercial application of these findings seems to have been developed.

The growth of hybrid carp were studied by Cassani and Caton (1983) to determine feeding preference and feed consumption. The hybrid was grass carp, Ctenopharyngodon idella (Val.) X bighead carp, Hypophthalmichthys (Aristichthys) nobilis Rich, 12 to 18 months old. Their conclusion was, "The most preferred plant was Lemna gibba when in combination with six other species." Moreover, at the same order of preference was exhibited at two different growth temperatures (12-15 C vs. 25-28 C). This preference was the same, based either on the time to complete consumption or the relative quantity consumed. Mean daily consumption (g) fish at 25-31 C for Lemna gibba tested separately was 178.

Gaigher, et al. (1984) compared the growth of hybrid tilapia fish (Oreochromis niloticus X O. aureus) on commercial pellets vs. duckweed. The fish were cultured at high densities in an experimental recirculating unit for 89 days with duckweed (Lemna gibba) or a combination of duckweed and commercial pellets. They conclude that a combination of pellets and Lemna gave the best performance:

When fed on duckweed alone, intake rate was low, feed conversion ratio good (1:1) and relative growth rate poor (0.67% of bodyweight daily). Sixty-five percent of the duckweed consumed was assimilated and 26% converted to fish. When the fish were fed on pellets in addition to duckweed the rate of duckweed consumption decreased and growth rate of the fish doubled with feed conversion ratios between 1.2 and 1.8. Seventy percent of the mixed diet was assimilated but only 21% converted. Fish grown on the mixed diet performed similarly to fish grown on pellets but had a better feed conversion ratio.

Porath, et al. (1985) attempted to recycle the solid wastes of these fish as a fertilizer for Lemna. The duckweed (Lemna gibba) was grown in shallow ponds containing mineral nutrients. However, the tilapia waste was poor in free NH3 and ammonium compounds. When separated and incubated at 38 C to allow anaerobic digestion to release mineral nutrients, prolonged digestion was necessary before it supported growth of the plant.

Tilapia were given duckweed as food as young fish from the larval to the fingerling stages (Moreau, et al., 1986). A comparison was made of three types of food: Lemna minor (duckweed, produced in shallow ponds or year-round in greenhouses), Chlorella (phytoplankton) and Daphnia (zooplankton). These authors studied both the nutritional value of these foods and the resulting growth rates of the fish.

Crayfish are often released in irrigated rice fields in rice- growth areas of the United States to control weeds (often duckweeds), according to Landolt and Kandeler. It is not known if the deliberate growth of Lemnaceae would be an efficient means of production of these crustaceans.

Conclusion:
Numerous demonstration projects prove the usefulness of duckweeds as the primary food source for production of fish and livestock. These studies show that duckweeds are highly productive and economical to grow, and that the plants provide nutritious and palatable food for meat animals. Based on this farming system, and with no additional basic research, highly profitable agricultural ventures can be developed.

"When fed on duckweed alone, intake rate was low, feed conversion ratio good (1:1) and relative growth rate poor (0.67% of bodyweight daily). Sixty-five percent of the duckweed consumed was assimilated and 26% converted to fish. When the fish were fed on pellets in addition to duckweed the rate of duckweed consumption decreased and growth rate of the fish doubled with feed conversion ratios between 1.2 and 1.8. Seventy percent of the mixed diet was assimilated but only 21% converted. Fish grown on the mixed diet performed similarly to fish grown on pellets but had a better feed conversion ratio."

Nutrional value:
http://www.mobot.org/jwcross/duckweed/nutritional-composition.htm

Seems like a great way to recycle nutrients in the system

First the cow comment. Cows are ruminants and they have bacterial colonies that can break down cellulose into sugar. If I am not mistaken, they get most of their protein from the breakdown of these bacteria. They constantly die and divide in the gut.

Gizzard shad are specialized at digesting veggie matter because they have a gizzard that crushes vegetation.

I believe if duckweed protein and carbs were made more bioavailable to tilapia etc, this may work. If the fish spends less energy breaking it down, it will get fat.

Maybe an industrial grinder might help the fish gain better?

..
and talking about Duck Weed... will Silver Perch eat the stuff..?

I was hoping to run a special bed, just growing DW, and hoped the SP's would take to it..
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I have duckweed growing wild in every tank (I originally put it in one tank only) and even in the inlets to GB's (I have teapots as a feature) including in new DWC tanks except the SP tank, and I even put some in there, so yep, can confirm they eat it!

Thanks for the confirmation/observations..

Duck Weed... I call it PITA weed - Pain-In-The-Arse weed.. because is makes such a mess of ornamental ponds..

I did throw some in the darkened FT and, indeed it seemed to disappear, so I have now committed to a DW tank, sitting atop the rain water tank.. Most inconvenient for access, as awkward place to grow anything else..

I had an IBC bladder "SIDE" that the bride was at me to "DO SOMETHING" with... ie.. get it out of the yard...

So it will now grow DW as a supplement for the SP's...

Found an interesting and different way of strengthening, avoiding external framing..
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