Tropical Fish Keeping - Aquarium fish care and resources

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Keyspoet 06-13-2013 10:38 AM

Some Advantages To Growing Duckweed
I have read a number of posts about the best ways of "getting rid" of duckweed in an aquarium. While I realize these threads are mostly from quite a while ago, and even though the suggestion to throw it on the compost pile was a step in the right direction, it seems to me that most are going about this all wrong.

Instead of looking at the duckweed as a problem, why not look at it as a blessing in disguise?

Duckweed is essentially a form of water lettuce in miniature, so providing you aren't using noxious chemicals in your aquariums - which you shouldn't be anyway for the sake of your fish and invertebrates - why not simply strain it out and throw it on your salad? Okay, you can rinse it first. Microgreens are currently in fashion, they are highly nutritious, much more so than their full-sized counterparts, and you can't get a whole lot more micro than duckweed. It is also a lot less work then other microgreens since you eat it roots and all.

By some estimates, duckweed is as much as 50% protein by dry weight, and it is tasty too. Since true lettuces stop producing completely in hot weather, duckweed can be a godsend during the hot summer months when the only fresh lettuce available has to be trucked in from thousands of miles away, especially since lettuces are one of the most highly sprayed crops grown. If you are doing it right, your aquarium should be pretty much organic, which is to say maintained without the need for chemical amendments, so your duckweed will be safer to eat than lettuces from the grocery store - and it's free!

And, being so tiny, it is easy to put just the right amount on a sandwich, in a wrap, sprinkled over soups or stews, in a smoothie, on a salad or wherever else your imagination and creativity take you, no tearing or chopping required, while getting some of the delicious leafy green vegetables that so many of us are lacking in our diets. Because duckweed is so prolific, it can be a real boon to the family diet, saving money and increasing nutrition at the same time. And even kids that don't usually like vegetables generally like duckweed, so that's another win.

Or you can start raising fish that are plant eaters, such as tilapia, for food or as pets. Tilapia and other vegetarian fish LOVE duckweed, as do chickens and other birds, so if you're growing a fair amount of duckweed you can cut down substantially on your feed bill while increasing their nutrition overall. Win/win.

You can even dehydrate duckweed in a food dehydrater, or on a window screen in the shade on a nice day, and powder the dried duckweed to feed to fish fry. It is a protein rich food suitable even for carnivorous fry. I know several people who keep tanks of duckweed growing specifically to stage their vegetarian fingerlings for a month or two, once they are past the fry stage, while growing them to a larger size. Many species can grow very quickly on duckweed alone.

The main caution with duckweed, as you have already discovered, is never to introduce it into a tank where you do not want it, which is even more reason to always keep a staging tank for any new fish or plants, before moving them to your primary aquarium.

Never introduce duckweed, or any other non-native plants or animals into a waterway, as they can out-compete native species and cause them to decline.

Byron 06-13-2013 10:53 AM

Never eat any plant from an aquarium with fish. There are various diseases you can easily pick up.

Some aquarists have become extremely sick just from swallowing a tiny bit of water when trying to start a suction. And many will advise you to wear protective rubber gloves when you are working in the tank, then washing your hands well with hot water and soap after.

I admit I don't go quite as far as wearing gloves, but I do wash my hands well after tank maintenance. But I would never eat any plant from a fish tank.


P.S. Welcome to TFK forum.:-D

rexpepper651 06-13-2013 10:58 AM

thats gross dude. never eat any thing coming from an aquarium with fish. maybe have a plant only tank but still you run the risk of having snails and snail eggs on your duckweed. i will add tho my dwarf water lettuce does look kinda tasty lol

Keyspoet 06-13-2013 02:25 PM

Clearly neither of you are familiar with aquaponics, in which fish (often tilapia, bass or carp) and plants (often vegetables, including lettuces) are grown together in a closed-loop environment, so that the fish waste is broken down by bacteria into a form that feeds the fish, while the plants clean the water and add oxygen for the fish. Both the fish and the plants do far better grown together than either does grown separately. Small scale and commercial aquaponic systems are currently feeding people and animals all over the world.

To clarify: yes, you want to thoroughly rinse the duckweed before eating it, but as long as you are keeping your aquariums without the use of chemicals, then the duckweed is perfectly safe to eat.

As far as people getting sick from ingesting a minute amount of aquarium water, unless you are using chemicals in the water, I'm inclined to think that that is more hypochondria than biological; in other words, they expect to be sick, so they are, but there is no biological basis for it. If the bacterial levels in the water are high enough to make you sick, they are clearly unhealthy for the fish, and you are doing something wrong; or something has happened to your system that needs to be addressed - urgently.

As for the erroneous belief that e coli can be transmitted by fish, it cannot. A cold-blooded fish cannot act as host to e coli, which can ONLY be carried by warm-blooded animals. It is biologically impossible, at least so far without genetic engineering, but you never know WHAT those idiots will try next.

People have been growing with aquaponics for literally thousands of years, including ancient China, Egypt and Israel, and eating vegetables from water in which fish have been growing hasn't killed anyone yet. It is, in fact, a much healthier and far more environmentally friendly way to grow food than conventional farming as practiced for the past hundred years or so. It also uses only around 10% of the water used in conventional farming.

I have two certificates in aquaponics and I majored in marine biology.

jennesque 06-13-2013 03:44 PM

I would think you'd only want to use fish that you know for a fact are disease free.. Which in the aquarium trade, I don't think is very easy. It's hard to tell if the fish ever, while being caught, shipped, stored, or sold was ever exposed to some sort of a disease and is a carrier for it. Sounds too dangerous to play with.

For instance, fish TB is nothing to play with, and also not something you can fake.
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ao 06-13-2013 07:53 PM

im pretty sure aquaphobics only brings tank water to the root system of edible crops... duckweed on the other hand grows best in water >.< I dunno wheter I'd want to risk that. Additionally, it's a pain as it sticks to everything and become a real headache to clean off. really isn't worht the wffort for me. lol~
The reason I hate duckweed in my tank is because it gets tangled in my moss and other floater, shading my light hungry plants and getting caught in the filter. lol

I mean it's certainly an interesting theory, but I wouldn't advocate it for human consumption here until studies have been done and paper published on this issue. After all this is a public forum and we dont want an amateur to try it without knowing the risks :)

jennesque 06-13-2013 08:03 PM

^ so true!

Also, duck weed doesn't have an expansive root system, just one little piece sticking out. Unless the fish are actually eating the duckweed, these don't provide the same sort of benefit as other floaters. Many fish that really need floaters like rummaging around their root systems.
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Keyspoet 06-13-2013 09:44 PM

There are many forms of aquaponics; bringing the water to the plant roots is one of them.

I agree that in a decorative aquarium duckweed is a major pain and generally to be avoided. I was merely suggesting an alternative to throwing it out with the garbage, which to me is wasteful and not recommended.

Personally, I grow my duckweed in a kiddie pool in a greenhouse, and the fish I am feeding with it don't leave enough behind to multiply, so the tanks with my fish are duckweed-free except at feeding time.

As for harboring disease, that is easy enough to mitigate. Consider the duckweed in the aquarium as a starter culture and remove it from the tank, soak for fifteen minutes in 1 litre of water in which you have added a full dropper of 35% food grade hydrogen peroxide, and then transfer it into a pristine tank or pool, without fish. It should already be disease free at this point, but give it good light, preferably full sunlight, and by the time it has multiplied enough to harvest, there will be no trace of fish diseases, as plants themselves are not carriers.

Addler 06-15-2013 10:17 AM

Having been involved in many aquaponics endeavors in the past, and still in contact with several people who have fairly large established tanks, I felt I might be able to put some input in.

Virtually all hydroponics systems nowadays comprise of a tank with water being pumped to a large bin above it filled with substrate, in which the plants reside.The substrate has been inert, charcoal, and/or mesh bags of sand. The fish are always Tilapia-- it's cheap to buy, sells well, and does well in low light. The plants vary from grasses all the way to vegetables like beans, lettus, and tomatoes.

The issue with consuming plants in general is the risk of bioaccumulation of metals, ammonia, nitrite, and other chemical compounds that may result from the setup (plastic leaching, as these are almost always done with large, cheap plastic tubs, comes to mind). These will likely not hospitalize you, but could easily be harmful to you all the same. I'd also question the nutrient content of the plants in mind, especially compared to hydroponically and soil-grown versions. I have not found any empirical testing done of these parameters that fulfills my wishes.

The other part, that applies directly to portions of the plants that have had -direct- contact with water, is bacteria. Viruses are minimal in these systems, though possible. Bacteria, on the other hand, is not only possible, but necessary for the systems to work. While the chance of directly pathogenic bacteria is very low, most bacteria that is otherwise harmless will gladly be an opportunistic pathogen. Given they're in the right location on or inside the body-- such as with eating a plant with the bacterial on them-- they will gladly find a way to make you sick. Bacteria have huge chemical and temperature tolerances, and many of them will tolerate hot water baths, freezing, and any detergent you throw at them. There is a very real risk with this, and I can't personally advise it for anyone. I will say that I've seen onions grown, which had direct contact with water, that ended up not harming the grower. His wife, however, ate the same onions and ended up vomiting for a few days.

JDM 06-16-2013 09:40 AM

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I see that it is used for fodder but would have never really considered it a product for human consumption... especially not out of an aquarium. Purpose grown in appropriate setups, sure. Seeing as it is a great sink for ammonia, nitrates and metals I would be hesitant to use it from anywhere that it is exposed to uncontrolled source water or an overstocked aquarium.... I think that has already been mentioned though.

I have a jug going that is plants only, and duckweed is the largest portion making up close to 99% of the plant material.

Ever the one to experiment, I took out some, rinsed it well and had a taste. I made sure that it was the smaller leafed that were green on both sides, some turn red or brown.

I expected it to have that "green" flavour, something like bean sprouts (which I hate BTW) or perhaps a little metallic flavour similar to a seaweed, without all the saltiness, so I was surprised to find that it was mostly tasteless and didn't remind me of any plant I have ever eaten. I wasn't quite as tough as I expected either, almost a brittle crunchiness.

Experiment over and not to be repeated. Our salads include things like kale, romaine lettuce, lots of fresh vegetables, seeds, seaweeds and fresh herbs... duckweed is certainly not needed.


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