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?