Slime and Scuds and Giant River Prawn…Oh My!

What is making our garden grow?


Slime has been covering everything in the system…the bottom of the rafts, the bottom and sides of the grow bed, and the inside of the fish tank.  This slime is actually the nitrifying bacteria the system needs to convert the toxic ammonia from the fish to nitrites, and the nitrites to nitrates.  Then the plants use the nitrates to grow delicious fruits and vegetables.  This process is called the Nitrogen Cycle, which occurs in water and soil.

There is also a buildup of decaying material on the bottom of the grow bed and fish tank.  The brilliant white liner is now a brownish grayish yucky color.

This material is a combination of leaves and other plant material from our yard and from plants in the system, dead insects, fish excrement and uneaten fish food.  As all of these solids decay, they release excessive amounts of ammonia that could injure and kill the fish if it’s not removed or converted to something the plants can use.  We could add filters to the system to remove these solid wastes, but we’ve decided to use natural waste removers instead.

Gammarus, also known as scuds, are a freshwater, shrimp-like, amphipod crustacean that eat decaying organic matter.  Here’s a YouTube video (not ours) that shows what they look like and how they swim.  This video makes them appear to be giants, but they are actually less than an inch (14 to 21 mm) long.

We first bought two orders of live Gammarus from Carolina Biological Supply, but there were very few Gammarus in the order and most of those died before we could put them in the grow bed.  At first we were a little disappointed, but then we realized it was just a $41.29 learning experience.

So we placed another order with an Ebay seller and received about 150 Gammarus, including mating pairs and newborns.  These scuds seem to be doing very well so far, and they only cost $19.99 including shipping.  If we ever need any more, we now have a source.

Before transferring them to the grow bed, we’re letting them reproduce for a month or so and then we’ll place about half of the larger population in the system.  That way we still have some available if the first group dies after the transfer.  But first we had to make them a home.

Actually, it was an easy process.  We just cut off the top of a 2-liter plastic bottle and poured them in.  Then we partially filled the rest of the bottle with water from the grow bed.  The scuds came with a small plant (Hornwort, I believe) that they like to hide in during the day.  We added an air line so they have plenty of oxygen and we’ve been feeding them a couple of pellets of fish food every other day.  That’s it.  They’re as happy as a bug in a rug, and they look like one too.

The Gammarus are very small and have been difficult to photograph with our camera.  Here’s a photo with a mating pair near the bottom left.

Our other sanitation engineers are Macrobrachium Rosenbergii, also known as Giant River Prawn.  Here’s a short YouTube video of one of these “beautiful” creatures (not ours).

We bought them for a number of reasons.  First, they can grow up to 12″ (about 30 cm) in length and they will taste great with some Tilapia tacos and salad.  Second, they’ll help keep the bottom of the grow bed clean, because they eat almost anything that will fit in their mouth, including dead mosquito fish and pieces of plants that sink to the bottom of the grow bed.

Here are some of the juvenile Prawn that we bought from Craig Upstrom at Aquaculture of Texas.

Before we released them, we let the bag float in the water so the temperature inside the bag equalized with the water in the grow bed.

The system now has Tilapia, Mosquito Fish, Scuds, Prawn, and Nitrifying Bacteria working to create the most delicious and nutritious vegetables and fruits for our family and friends.

Now we can just sit back and watch nature go to work…or can we?

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30 Responses to Slime and Scuds and Giant River Prawn…Oh My!

  1. Geordon says:

    I’m so glad that you visited me originally. I had heard about aquaculture systems, but never knew what they entailed. While I’m not going to build one in my climate (Northern Illinois, it gets REAL cold here), I am learning a lot about the system and am vicariously living the lifestyle. (also, I’m the only one in my house who will eat fish, so it would be kind of pointless for me)

    Thanks for letting me come along for the ride!

  2. What an awesome and detailed post. Love the little prawn, so small though, even smaller than the Canadian shrimp we get in a can.

    Very interesting on the slime, perhaps you could make a monster movie on the side in youtube and make some bucks then sell it to Hollywood! They can use all the help they can get creating movies.

  3. Kellyann says:

    Gross but so, so cool! I’m taking notes . . .

  4. Thanks for such a detailed post. It’s great seeing folks like you using natural solutions for natural problems. How perfect to create an ecosystem to grow your food in! Love it!

  5. everysensory says:

    Love this! Love watching this grow into a ecosystem in miniature, just awesome. I have envy 😀 Thanks for the information, photos, and post – look forward to reading more!

  6. AmySue says:

    Great Post! Its all very interesting. Thanks for sharing.

  7. NEOKIE says:

    Reblogged this on Zone Seven Gardening and commented:
    From time to time you come across a garden on the web, that is just plain cool. Over at Aquaponic Family they’re using an impressive Aquaponic setup to grow all sorts of things. I noticed that their fastest growing plants are Nitrogen-fixing beans, which could cause Algae blooms and oxygen depletion. Personally, I’m not the biggest fan of fish–except for Rainbow Trout (They’re delicious when grilled).

    • Thanks for reblogging!

      That’s interesting. Hopefully the lack of sunlight will minimize algae blooms and the Tilapia will eat the rest. They LOVE algae.

      I’ve never been a big vegetable or fish eater either, but there is something special about eating something I’ve grown. It tastes so much better than store bought. Uh, well, the slime may be an exception to this rule.

  8. narf77 says:

    You forgot to put a warning on this post…Gammarus porn! I am shocked! I saw a video somewhere on youtube about someone who was using worms in the growbed/raft to keep it clean.

    I am probably preaching to the converted here but it made a lot of sense. Have a great day and cheers for another excellent informative post 🙂

    • Hilarious! You’re right. I should have warned everyone before posting that photo. 🙂

      When we add a grow bed filled with Hydroton or Shale, we will definitely add some worms. In fact, I already have worms. Hmmm, that didn’t come out right. I mean we have red-wiggler worms in our vermicomposter that’s right next to the grow bed.

  9. That’s really great – thanks for the detailed post!

  10. The plants are really growing and filling in. This is still one of the coolest things I’ve seen!

  11. theozarker says:

    I’m just fascinated with your project. Thanks so much for sharing it in such detail so people can follow along or develop their own system. You folks are great.

  12. Amazing job! Love watching your garden grow. Thanks for taking the time to document your journey of discovery. Do you think the prawn might eat the scuds?

    • Hmmm, I don’t think so. The scuds are pretty fast, but they reproduce so fast it shouldn’t matter too much if the prawn catch a few every once in a while. I’ve even thought of catching some scuds and feeding them to the Tilapia as a treat a couple times a week. I’ll post a scud update in a few weeks if the prawn or tilapia are eating them.

  13. Laal says:

    Great post! Thanks. I love learning about these methods!

  14. I wonder if bacteria is why my chicken water buckets get slimy too? I never had thought of it that way.

    • It could be. The nitrifying bacteria are photophobic, so they cover themselves in slime and other stuff to protect themselves from light. I’ve heard that you can add some Apple Cider Vinegar to the water to prevent the slime, as long as there is nothing in your buckets that can corrode.

  15. urzaeb says:

    Prawn need brackish water to multiply. Is it your plan to constantly restock?

  16. Hello,
    I just wanted to say hi, I am very interested in self sustainment, aquaponics is amazing im glad you have a chance to mess with it. I realize that Police and Military are not the same thing but after completing 4 years Marine Corps I feel like we have more in common than the love of self-reliance. I am watching with good will and tons of interest.

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