Duckweed and Taro for Commercial Aquaponics?

[Marc Casseres]

Hello Everybody,

I just joined this forum and found lots of useful information. In July we will be starting construction of two 10,000 square feet aquaponic units (based on the designs and drawings of Mr. Doug Burdette). We will be expanding to a total of ten units within two years (assuming all goes well of course).

In our small scale pilot project we have a tank with duck weed which is used about every other day for the Tilapia as an afternoon snack. They love it!

There's no natural body of water anywhere near the facility that we will be building. So the question is this; does it make commercial sense to grow duck weed in tanks on a large scale to replace a part of the commercial fish food? 

In the pilot project we also have a lot of Taro growing to enormous sizes. The Tilapia also love the leaves and strip it to the stem within minutes.

The follow up question then is; can these two plants be fed to Tilapia on a commercial scale? Has anyone done this successfully? Also, are they good for the Tilapia? Online I find conflicting reports on the duck weed.

I am planning a trip to Florida in the beginning of July, right before we start construction, and will be visiting several aquaponic locations in the Orlando area. If you have any suggestions on who to visit I'd like to hear it.

Anyway, I appreciate your input and I will be visiting this forum often in the future. 

Thanks

Marc

[TCLynx]

Hi Marc, I suppose the answers to some of your questions will depend on the goals of your commercial systems.

What is your primary product?  How much space you have for duckweed beds?  What will you feed the duckweed?

See if your primary goal is to grow veggies, then the duckweed shouldn't be grown within your AP system since it would steel the nutrients you want for the commercial veggies.  To grow good duckweed to feed your fish which in turn feed your veggies you will need to fertilize the duckweed growing system some how so take that into account.  Also growing a huge amount of duckweed requires lots of space, is turning that space over to growing duckweed going to be your most cost effective use of the space?

As to feeding duckweed to tilapia, my understanding is that you can replace maybe up to 50% of the commercial feed pellets with duckweed without seeing a substantial reduction in fish growth.  If you try to feed 100% duckweed, your fish are not going to grow as well.

If you are trying to grow lots of fish and are not as concerned with the veggies, you might be better off researching green water aquaculture to feed the fish algae but that is a really different method.

[Marc Casseres]

Thanks for your reply TCLynx. Really appreciate you taking the time to answer this.

Our primary products are the veggies and the fish (in that order). Space is not a real issue, but obviously taking nutrients from the system to feed the duck weed is not logical.

But would it make sense (financially) to construct troughs or beds separate from the AP system and maintain these to grow duck weed? Would the savings in Tilapia feed offset the cost of building such an installation? I doubt it myself, but I would like to hear your opinion. 

I know it's a bit difficult to answer without specific details. But I appreciate your thoughts on this.

Also, while I have your attention; The wells in this location have brackish water. Is reverse osmosis an acceptable way of generating clean water for the AP system? And if so, what nutrients have to be added? Will these be added on a continuous basis or just during initial fill? For the pilot project we have been using rainwater, but we simply do not have enough rainfall here for the large system for initial fill or for topping off (10 tanks each with 3500 gallons).

Thanks again

Marc

[TCLynx]

I don't have enough experience with the particular situation to answer the question about RO filters and brackish water.  Hopefully others who do know about that can chime in here.

Would it be cost effective to build a duckweed system?  Really hard to say from here.  I suppose it will depend on how costly the good commercial feed is to get in your location and how you would build the duckweed system and how much the fertilizer and electricity for that would cost.

I expect you would need to perhaps set up a duckweed system (likely a small one to run trials with one unit of your commercial operation) and see how you do with production of duckweed and maybe do some side by side trials with a couple of your systems to see how growth rates (both plants and fish) compare on different feed regimens.  Then you will have some real numbers to help you decide if adding a full scale duckweed feed production unit would be appropriate for your operation.  Duckweed does seem to grow differently in different situations.

Hum, I wonder if there is any sort of plant you could use (even duckweed maybe) to perhaps remove some of the salt from your well water?  Just how brackish is it?

[RupertofOZ]

Whether or not it's viable as a feed in comparison to pellet feeds.. is difficult to quantify, as TCL notes...

 

But the question may ultimately resolve to how much area, effort, and cost is involved to maintain the growth of duckweed... to feed the number of fish you have...

 

Be aware though... that duckweed is a supplementary feed... not a complete feed for fish... even for basically "vegetarian" fish such as Tilapia....

[Marc Casseres]

Yeah, I figured that it would be difficult to answer without complete information. I don't even have that information myself. I think that the best way to find out is to simply try it on a small scale on one of the units as TCL suggests or even on two mini systems for comparisons' sake. That would give me an indication of cost vs benefit. I'll post an update when I have more info on this.

Regarding the brackish water; I'm taking a sample to have it tested tomorrow. The land owner claims that it's pretty bad (salty). But a real test will give me a definitive answer. TCLynx, you make an interesting point on 'desalinatizion'. Hmmmm.... We have a lot of problems on the island with brackish well water. If there's a cheap, eco-friendly way to clean this up, this place would be a whole lot happier. Hmmmmm.....

Thanks for the info guys. I will start posting pictures of our progress once construction is under way. We should be starting in the middle of july.

Marc

[TCLynx]

Unfortunately, I fear that using more well water on the island is probably only going to make the salt intrusion into the aquifer even worse so I'm not sure what your best course of action really should be.

That said, it may be possible to use duckweed to remove salt from water that isn't too salty, but you would definitely need to use fertilizers that don't add to the saltiness of the water.  However, using that duckweed to feed the system might simply add the salt back in.  Now if you are growing tilapia, they don't have a big problem with brackish water (I believe we have Tilapia living in Tampa bay now and that is salt water.)  It is your veggies that might struggle with the brackish water.  However, depending on your plants, some things can survive a certain amount of salt.  That said, constantly topping up the system from a salty water source probably won't work since the salt levels will likely continue to rise so some means to limit the salt additions to the system will be necessary.  I would say collect all rain water you possibly can to reduce the amount of desalinization that is necessary.

[Marc Casseres]

@ TCLynx: I will be in Florida from friday to monday. Is there any way I can meet you, pick your brain, and maybe see your site? I am going to see a couple of AP farms in Florida and would really appreciate if we could meet. I could really use an expert's opinion before we start construction. 

Thanks

Marc

[TCLynx]

Sure Marc, I do tours by appointment.  I'll send you a private message with contact info so you can find out where I am in relation to the other places you are visiting so we can work out a schedule.

I sent a friend request since I can't send you a private message unless we are "friends" on here.

[Richard Kreher]

Marc,

Was the Doug Burdette system good for you?

I found his information online several years ago and have had email contact with him a few times.

Rich