Wednesday, December 21, 2016

What do fish and horses have in common?

Over the past few years, I have occasionally toyed with the idea of getting an aquarium.  Admittedly, I enjoy the fuzzy, hairy mammals the best, but there is something really fascinating about fish.  We had a small aquarium when I was growing up and I mostly remember the annoyance of cleaning the tank, which was always a family event.  My mom and dad were less than thrilled with one more chore to do around the house and I don't think my brother and I were too enthralled with the fish after awhile, so eventually the whole thing was shut down and I don't think I missed it much.  I did have a female Betta when I was in college, but it wasn't long before I remembered how much I'm not fond of cleaning and when she passed on, I was relieved.

But I'm always looking for ways to expose my daughter to new experiences and lately, she's been having a love affair with the fish in the pet store.  This love is probably due in part to the movie, "Finding Nemo," but also because she genuinely seems to love other species (except crickets and flies - they are banned from the house).  And I've been reading more and more about fish social lives and their fascinating physiology.

So, I started educating myself about aquariums, and I was thankful to learn that there are now lots of great gadgets that can make an aquarium owner's life much easier than it used to be.  And then I stumbled across this book:  Ecology of the Planted Aquarium by Diana Walstad, and things got a whole lot more interesting.  According to Walstad, there is a method that can be used to maintain an aquarium with fish and plants that doesn't require any fancy gadgets besides a tank heater and mechanical filter and that yields a fairly self-sustaining ecosystem.  I have to admit that I was hooked.

And then I read that something called duckweed is a great plant for aquariums because it floats on the surface, which allows it to utilize carbon dioxide much better than submerged plants.  Why is that important, you ask?  Well, it turns out that in many cases, access to carbon is the limiting factor for growth in aquatic plants.  Photosynthesis slows way down if CO2 levels fall significantly (which happens a lot under water because water isn't a good conductor for CO2) and even if there are plenty of other nutrients, the plant can't grow, which means it doesn't take any nutrients out of the water which means the fish start dying due to ammonia overload or you need some serious filtration, a whole bunch of new water, and a prayer to save your fish.  (Aquatic plants have a great affinity for ammonia, so they help keep levels under control in fish tanks.)

Duckweed:  Not just for ducks!  Source:
Anyway, duckweed is a plant that I started researching at least a couple of years ago as a possible horse feed because I was looking for something that could offer high quality protein wasn't from a GMO source and was readily available.  I first learned about duckweed through my job when we started getting grant applications from farmers who wanted to use it to manufacture biodiesel.  Duckweed is considered pond scum by most people and therefore a useless and sometimes even harmful vegetation that can suffocate ponds if it isn't kept under control.

As it turns out, however, duckweek is an amazing food source for livestock.  This article reports that duckweed can have a crude protein level of up to 43% and that it works well as a source of nutrition for fish, poultry, and pigs.  It also points out that the plant has little to no indigestible material for monogastric species (like horses).  Duckweed can even be eaten by people (check out this article and this one).

I have yet to find any research on feeding it to horses, though.  Which is why I wanted to run a little experiment involving a baby swimming pool in my backyard.  Duckweed basically needs stagnant ponds in warm weather with lots of nutrients in them to grow.  Which is basically every pond and puddle in Virginia during the summer, except our yard is on the side of a steep hill, so no ponds.  I thought I could create my own stagnant pond with a little pool and try growing duckweed on a small scale to see if I could and to see if Nimo would eat it.  As it turns out, both my dog and my daughter are crazy about water in the summer time and won't leave even a bucket of water alone, so it just wasn't possible to run my experiment.

UNTIL NOW.  Because as of this afternoon, I have a 65 gallon aquarium (seriously, it was the best deal I have ever seen and I could not pass it up!) in my family room.  The expression on my husband's face when he helped me unload it was definitely one of the better ones I've gotten from my crazy ideas - he's going to warm up to the idea of the fish very soon, I can tell:)  And after many, many weeks of getting the tank up and running and stocking it with plants and fish and testing the water to make sure everything is OK, I should be able to grow a very tiny crop of duckweed.

And then I can test my theory that it is edible for horses (or at least one horse) and see if it might make sense to grow it on a larger scale.  One big issue with duckweed is that it is mostly water (you know, because it grows in water), so you can end up harvesting a whole lot just to get one pound of dried duckweed, which would be easier to transport and feed - probably - assuming you knew how to dehydrate it, which I don't yet, but I'm sure I'll figure it out.  Although, I don't think a horse would need a whole lot because it is so nutrient dense.  On the other hand, imagine if horses really loved it and it provided good nutrition and you could bring a wet bucket of it to an endurance ride for your horse to use for hydration and nourishment at vet checks and after the ride...

Seriously, the possibilities for using what I used to think of as invasive pond scum are endless.  So stay tuned for the results!:)


  1. If you ever want to talk aquariums, let me know! I've been keeping Walstad-type planted tanks for years now, although I've just finally gotten rid of the last of the duckweed in the last tank that had it. :D

    The nice thing for your purposes is that duckweed doesn't need the same sort of high light that substrate planted aquatics do or things like my food plants I grow hydroponically out of the top of my tropical aquariums, and you don't need to keep it particularly warm.

    1. That's great to know! I may take you up on your offer once I get my tank up and running:)

  2. Love this of course as I work as a fish biologist! As a side note: you will probably be producing a whole bunch of mosquitoes in your stagnant pool duckweed farm...

    1. I don't think I knew you worked specifically with fish, Jo. So cool! And yes, mosquito breeding is a potential issue if I take my production process outside, but I may be able to keep it small enough that I can do something to mitigate the mosquito issue.

  3. Love this of course as I work as a fish biologist! As a side note: you will probably be producing a whole bunch of mosquitoes in your stagnant pool duckweed farm...