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Friendly Aquaponics Newsletter
Number 45
July 26th,  2011
Images from our farmily aquaponics farm
Aloha Friend,
 
I had an unpleasant surprise this afternoon when I checked the water in our system #1 sump tank and found aquatic snails on the insides of the tank! How did the aquatic snails get there? They must have come over from our two tiny tabletop systems, which had had the snails in them for about a year, because there aren't any other systems with snails in them on the farm anywhere.

This surprise is somewhat mitigated by the fact that the snails in question are not parasites on plant roots, as some species are. They are just carriers for a deadly family of diseases that we luckily don't have in Hawaii called filariasis (does elephantiasis ring any bells? THAT is filariasis!). But if that disease somehow showed up and we already had aquaponics systems with these snails in them, they would be ready-made for transferring the disease to workers on the farm.

Now, we have been VERY careful with those two systems. We wrote a biosecurity article in our newsletter #4 which covered this kind of stuff, but we evidently hadn't learned our lesson. I thought just having the snails in the two tiny systems would be OK because we were SO careful to never transfer anything from one of those systems to any of our commercial systems. But somehow they got into a system that was 150 feet away and upwind. So, first thing tomorrow those two tiny systems are going to get all their plants dumped into the compost, the water dumped onto the ground FAR away from any aquaponics system, and the rafts, pots, and troughs will be sterilized with hydrogen peroxide.

After we're certain they are sterilized, we run the airstones until we're sure the hydrogen peroxide is gone, then refill with clean water from another aquaponics system or the faucet, put the rafts back in, and replant. That's all there is to getting rid of a biosecurity breach. That is, if you get it the first time. We had to do this to our Micro System twice because it wasn't a total cleanse the first time around.

How did these snails get into our Micro System and onto the farm in the first place? Well, an ex-intern of ours (who shall remain nameless), bought an aquatic plant at Petco because it cost $5. He saw this little plant that seemed expensive, so he thought it would be a good thing for us to grow and make money on. So he brought it back to the farm to try, and put it into the Micro System overnight to keep it alive. He did all this without asking us or telling us, so we didn't have any chance to block this introduction of a biohazard onto our farm. Yes, the intern's long gone, but we still have the snails! Hopefully we get rid of them with a single sterilization process in each of the systems that has them!

If you're interested in commercial scale aquaponics, please take a look at our Commercial Aquaponics Trainings (Special Offer in right sidebar of this email), where you will learn more about real-life operation of a commercial aquaponics system than you can anywhere else in the world. For smaller home backyard and apartment systems, please read on:
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Our Apartment/Condo System package includes new and easy-to-understand building instructions and complete operating information for 4 different sizes of small aquaponic systems based on our years of experience operating a commercial aquaponics farm. Anyone can build a system out of plastic barrels, but operating one successfully without good and easily-understood information can be frustrating. You simply use the "Daily Operations Checklist" in the manual and follow the step-by-step instructions on your way to success.

We spent hundreds of thousands of dollars, hundreds of hours, and built our first commercial aquaponics systems with FAR less information than this manual contains. We included all the information learned from that experience in this manual so you don't need to make any of the same mistakes we did.


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Aquaponics Nugget #45:
Raising Prawns in Aquaponic Systems


As everyone knows, prawns are sexy (ooooh). Prawns are expensive! Everyone loves prawns! Everyone immediately jumps to the conclusion that raising prawns will make them the most money of any aquacultured species. The only problem with this conclusion is that it ignores all the natural behavior, breeding habits, and other facts about prawns that one MUST know about to be able to raise them successfully. If you read on, you will at least know about the major issues involved in raising prawns, and have some idea of where to go next if you insist on doing so.

I know a prawn farmer in Honduras, and she makes money raising prawns. But she has 600 acres of ponds, expert labor that costs her $6/day, an $8/pound price for her prawns (she ships them to Europe), and says if her operation was any smaller, she couldn’t make a go of it.

There are several things you need to know to successfully raise prawns in an aquaponic system. Tilapia (or any other fish you try to keep them with) will eat the prawns, so you need to keep the prawns separated from the fish in different tanks or troughs. Everyone likes to eat prawns, even other prawns. To raise prawns commercially, breeders stock PL's (post larvae, or juvenile prawns) at 3 to 4 PER SQUARE YARD of pond space, and harvest at 1 to 2 per square yard of pond space.

The reason they only harvest half of the prawns they stock is that the prawns are territorial and fight with and eat each other. Apparently a lot of the mortalities come from large prawns being eaten by smaller prawns when the larger ones are molting and unable to protect themselves because their shells are quite soft for a long time during the molting process. The only way to successfully raise prawns commercially is to have tens or even hundreds of ACRES of pond space, and even then success is in question because the prawns are VERY susceptible to disease, and predation by fence-hoppers (human thieves).

The reason prawns work in an aquaponics system is that they are detrivores. This means they eat organic garbage: anything that falls to the bottom of the troughs; a dead mosquito fish, some roots that fell off a plant, another prawn that just died or was drygulched by a group of prawns while molting. As a result of this feeding behavior, we don't need to feed them anything, and having prawns in the system does not increase the amount of feed we need to purchase. Our opinion is that in the process of eating the detritus of dead roots and other organic refuse that falls to the bottom of the troughs, they further break up this stuff and liberate nutrients that the plants thrive on, as well as add their own excreta to the system, which then turns into nutrients for the plants in the system.

As mentioned, the prawns are raised in the hydroponic troughs under the vegetables to keep the tilapia from eating them. We have never seen any damage to vegetable roots caused by prawns, or any decrease in system vegetable production after we introduced prawns to one of our systems. We have noticed that the smaller ones will shelter in particularly large root groups, and come zooming out when you lift a raft to inspect the roots.

We stocked 300 +- PL's into a total of 864 square feet of hydroponics troughs in a commercial system (a stocking density of 3 per square yard), and 4 months later harvested 30-40 lbs of prawns from that system. These prawns can be sold off the back of the truck for $10/lb in Hawaii. So this would total 90 to 120 lbs of prawns a year from a system that produces 8,700 lbs of organic lettuce and 600 lbs of tilapia a year. You can see it is not the largest or even the second largest system output.

(Next week: Part 2 of "Raising Prawns In Aquaponics Systems")

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Aquaponics tour at the Friendly farm!

We hold a free workshop on our farm the FIRST Saturday of every month,  focused on growing food with aquaponics and permaculture.  Click here for information. See you there!

If you are a school, a non-profit organization, an organization working with the poor, Native Hawaiians, or ex-inmates, or if you are a church, we will hold a free farm tour for you anytime. You DO need to email us first to schedule, or we might be out on errands!


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3-1/2 pound kalo (taro root) grown in a 2" net pot (little bump at bottom)



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4-month old prawn (macrobrachium rosenbergii) grown in hydroponics troughs of our aquaponics systems


Special Offer! Sign up for our October 2011 Hawaii Commercial Aquaponics Training OR our September 2011 Florida Commercial Aquaponics Training now, and we will email you our Micro System package so you can begin studying aquaponics! ($99.95 value)

Sign up for Hawaii and Florida Commercial Aquaponics Training

In The Farmily
Jack's Micro System is back on track, in fact it is full of 2-foot tall vegetables that are overdue for harvesting. We've been eating off it a lot lately.

Lately, we've been looking at how much food we purchase, and are setting out this year to grow as much of the food we eat on the farm as possible. We've started experimenting with ebb-and-flow gravel bed technology because it has shown some promise with peppers and other vegetables that haven't seemed to grow well (or at all!), in the standard rafts in the aquaponics.

We're hoping to try it on eggplants and some other fairly woody-stemmed plants that didn't do well For example, we planted an eggplant and a tomato plant at the same time in the same system in our original growing test in 2007-08.

After three months, the eggplant was about 18 inches tall and had a single fruit about 2 inches in diameter; during the same three months the tomato had a STEM 2 inches in diameter, was six feet tall, and had given 200 pounds of tomatoes. So what gives?

We were baffled by it back then, but when one of our students tried scotch bonnet peppers in an ebb and flow bed just this year and got fantastic growth, we decided it was worth another try. We really only know ten percent now of what we'll know in another ten years about aquaponics, and trying new things such as this to quantify the knowledge is how we'll get there!
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Honoka'a, Hawaii 96727
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