Elise Chalcraft

Duckweed taste testing 2.0

Using duckweed as an alternative food source to feed our fish

Let me tell you about an aquatic plant I have come to love...

Duckweed is a floating aquatic plant commonly found in ponds, lakes, and other still-moving bodies of water. Duckweed is commonly seen as a weed as it grows quickly and expands across the top of the water by producing new offshoots. But these opinions are shifting somewhat as a new era of the "useful" duckweed begins.

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Duckweed close up shot - Elise Chalcraft

With:
Abhay Villa

Duckweed can be used for bioremediation of waterways, meaning it can take up and absorb high amounts of water pollutants such as excess phosphorus and nitrogen, commonly discharged from agriculture runoff (Fertig, 2021).

It is very rich in nutrients and has been shown to be rather successful as an alternative feedstock for aquaculture, up to 30% can be substituted (Fasakin et al., 1999; in Olasunkanmi et al., 2021) instead of the over-exploited and ever increasingly expensive fishmeal.  

Previous experiments have been done in the aquaponics greenhouse that can be seen here. They found that the duckweed used a lot of nutrients and that the bucket of choice might have been too small to properly start a good growth of duckweed. Hence our updated method seen below!

We added common duckweed found in the surrounding Amsterdam ponds to a large bucket with approximately 30L of aquaponics system water pumped from the sub-tank. We also set up a small pump stuck on the bottom of the bucket and hose that can be plugged in to aerate the still-water. 

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Duckweed growth in 1 week - Using duckweed as an alternative food source to feed our fish Here you can see how fast duckweed grows with our aquaponics system water. From left to right, the pictures are taken daily from Monday - Wednesday. Elise Chalcraft

As you can see, the far left picture was on Monday (day 1), followed by Tuesday (day 2) and Wednesday (day 3). In only 3 days there has been a significant amount of growth!

Next steps are to feed parts to the fish and judge their reaction towards their new supplemented diet.

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Fresh duckweed harvested ready to be feed to the fish - Here you can see the long thin stems of the duckweed wrapped around my fingers creating a green interwoven mass of aquatic plants! Duckweed grows very quickly so a few handfulls like this to be fed to the fish still allows the duckweed to keep growing.  Elise Chalcraft

References:

Fertig, W. (2021). Common duckweed (Lemma minor). U.S. Forest Service & United States Department of Agriculture. [online] Available at: www.fs.fed.us.‌

Olasunkanmi, J.B., Julius, O.T., Babalola, T.O., Jimoh, J.O. and Ariyomo, T.O. (2021). Alternative Feed Resources in Aquaculture: The Role of Underutilized Plants–A Review. In IOP Conference Series: Earth and Environmental Science (Vol. 655, No. 1, p. 012008). IOP Publishing.