Thursday, August 25, 2011

Aquatic Systems of Life

Ever since I was a kid, my hobby has been creating terrestrial systems of life. The trick with creating good ones is to balance the cycling of nutrients through the system such that the beneficial organisms out compete the disease-causing organisms. In terrestrial systems, you have a plant to cycle water and oxygen and provide a centerpiece. In larger systems it can also provide food. You have a fungus to decompose decaying plant material. I prefer mushrooms because they also provide food, even in small systems. Earthworms till the soil and decompose vegetative and fungal matter. Beneficial bacteria take up most of the rest of the niches. In order to keep the system healthy, a regular infusion of organic matter is about all that is required. Without the mushrooms and earthworms, disease and pest organisms, such as gnats and disease-causing bacteria and fungus can get in and dominate the system, reducing the health.

After my big idea of creating a stock tank with tilapia in it a few months ago, I am considering a foray into the creation of aquatic systems of life. First of all, let me say that I don't know a lot about it. Yet. I do need to find two good books. The first needs to be on aquaculture. The second will need to be on how to create and balance aquatic systems of life. If any of you have any good suggestions, I would certainly appreciate them.

The basic need of aquatic systems is going to be the same as in terrestrial systems. The flow of nutrients through the system is going to be crucial. However, in aquatic systems, the balancing of this system is much more important than it is in terrestrial systems. Water is a much more robust system for life to flourish in, so algal or bacterial blooms that could potentially be harmful can happen in a matter of  days rather than weeks like they would in soil. First of all, fungal allies are out of the picture, so other players need to be introduced to do a lot of the decomposition quick enough that the harmful bacteria don't get to it.

Right now, I am thinking that the first step to creating the pond at the bottom of the greenhouse will be to create a robust system with players that are either really tough or pretty easily disposable. For the first year or so, I will be actively building soil in the garden beds above the pond. This will involve the addition of lots of organic matter that will need to decompose into healthy soil. As the grey water from the house filters through the decomposing organic matter and down into the pond, it will carry a lot of nutrients with it. I need organisms in there that will filter out those nutrients in a way that is healthy for the aquatic ecosystem.

Those organisms can balance the system until the tilapia arrive, with many of them providing food for the tilapia once they get there. I am sure that the cast of players will change as I do further research and give it more thought, but here is the cast of characters I am currently considering:

1) Water from a real pond - I will find a healthy pond and collect a gallon or so of the water from it. Ideally, it will be a clear pond without obvious signs of pollution or algae blooms or the like. I think I have just the source. This water will carry with it the necessary bacteria, algae, and other microorganisms for treating my water and making it healthy. It will also form the base level of the aquatic food chain, the food chain that will feed off of the nutrients in the water and feed my larger forms of life.

2) Snails - I need to be careful about this one, but I am thinking that aquatic snails will serve as grand decomposers, helping to fill the niche that earthworms take up in soil. They will burrow through and consume the layer of muck that ends up on the bottom of the pond. I just need to make sure that I find a species that is aquatic only and won’t climb the walls at night and eat my plants.

3) Duckweed. From what I understand, duckweed will meet two major needs. It will filter nutrients from the water, cleaning the water. It will also serve as an eventual food source for the tilapia. It reproduces rapidly, so a solid colony of duckweed in place when the tilapia arrive would be a very good thing. There are probably other aquatic plants that I could put in to serve a similar purpose.

4) Crawdads (crayfish) - They are not native to my area, but are very common in the lakes and streams around here. As such, local wildlife managers want rid of them as much as possible, so I have a nearly endless supply. Crawdads will also help consume dead and dying matter, especially animal matter, like dead fish. I am hoping that they will also act as a food source for the tilapia. I’ll have to look into that one. The one note of caution is that crawdads eat fish eggs. Too many, and my tilapia won’t be able to reproduce. That is, unless they can eat the crawdads. It might be a self-balancing system.

5) Guppies - One of my wife’s worries about the tank is mosquitoes. There is a little fish called a mosquito fish that lives almost exclusively on mosquito larvae. Guppies are a close relative and are readily available and inexpensive. They also consume mosquito larvae. Additionally, they are prolific breeders and stay small. There is a good chance that if I got a really healthy population going, they would serve as a good initial food source for the tilapia.

6) Catfish -. This is probably more of a hope than a reality. My real hope is that I can get a system in place such that I don’t have to buy food for the fish. I suspect that if I include catfish in the pond, I’ll probably have to buy food to keep them going. But I know that tilapia eat catfish waste and I know that catfish are bottom feeders, consuming organic matter on the bottom of the pond. So there is hope. Again, research.

7) Plecostomus - I figure one of these will be enough, especially if I can find a big one. He will definitely have to be big enough to not get eaten once the tilapia are introduced. But this guy, along with a little help from the snails, would have the job of keeping the algae down on the sides of the tank and keeping everything clean.

I am sure that there are plenty of other players needed. I will probably need something that will act as an intermediate step between the plankton and the guppies. The food web needs to be complete for the system to function as a whole. I think that even after the soil is complete, there will be enough nutrients washing through the soil to keep the system fed and active.

Once the tilapia are introduced, they should have enough food in the tank to begin reproducing rapidly and producing more fish. Ideally, the tank ecosystem will provide most to all of the food they need. As they get more numerous, I will supplement with black soldier flies, but that is another post.

As a first test of how well such systems might work, I introduced 8 guppies, 4 feeder goldfish, about a dozen tiny snails, and about 4 cone snails to a 55 gallon rain barrel I have on the side of the house. 2 of the feeder goldfish and 1 of the guppies died within the first 48 hours of being introduced to the system. However, the rest of them seem to be thriving despite the fact that I don't feed them. Actually, I do occasionally drop bugs in there to see what the guppies eat. They particularly liked the weed covered in aphids. But I definitely haven’t given them enough to eat that they would survive if they weren’t finding something in the water to eat. The guppies have even reproduced already. I know the tiny snails have as well, because they are already all over the place in there. So I will watch that system for a while and see what I can learn.


  1. Might be worth talking to someone with experience of decorative fish-ponds - they're going to be closer to your scale. I kept goldfish for years, but goldfish are notoriously hardy and often survived despite me rather than because of me.

    Some observations: snails aren't nearly as useful as you might think. They're inefficient cleaners and breed like crazy. Once they're in there, you'll never get them out - many hobbyists will pick over incoming plants looking for eggs to destroy.

    Without active filtration, the density of fish you can support will be surprisingly low - google "goldfish stocking levels" for examples.

    Crayfish are complete pyschos. They'll take full-grown guppies, and anything smaller, out of the water. With them in there, I don't think you'll be seeing many young fish.

    Personally I'd consider skipping the fish and making the crayfish the top predators. They're pretty edible.

  2. Thanks for the info, David! It gives me more to look for. As for the filtration, I think I'll have a pretty good filtration system, even if it is a little unconventional. I am going to pump the water up to the soil and let the plants and soil filter it. That's part of why I want to start with tough stuff like crawdads and guppies the pioneer species. If I get it wrong and everything dies, it isn't too big of a deal. I just want to get it balanced before I put in the tilapia.

    As for the crayfish, I certainly plan on eating some of them. If they will eat the guppies, that is SO much more awesome. With a water depth of 2', the guppies should be able to escape often enough to breed and proliferate. If they eat the little stuff in the water and the crayfish eat them and the decaying stuff, that would be a pretty cool ecosystem right there.

  3. I have always been fascinated by the Farm Fountain installation

    The main installation is wonderful, and they have a nice how-to page.


  4. I'm not an expert, and I'll be watching with interest - I hope it works out. But I think you're underestimating the amount of waste fish put out. Here's an interesting link:

  5. How did your system do? Ive got guppies in my pond outside i havent fed them in a few years. They eat algie and mosquito larva. Nowdays people are into aquaponics.. keeping a stytem where the tilapia waste is fed to plants and they in turn purify the water.. just wondering what happened in your experiment

  6. How did your system do? Ive got guppies in my pond outside i havent fed them in a few years. They eat algie and mosquito larva. Nowdays people are into aquaponics.. keeping a stytem where the tilapia waste is fed to plants and they in turn purify the water.. just wondering what happened in your experiment

    1. Boy, I actually don't remember. Honestly, I don't even remember doing this experiment. I moved away from that house less than a year after writing this. I will say that the experiments have continued. I moved towards aquaponics and then quickly beyond. My prototype system of aquaponics with soil is 3 years old and I am working on expanding it. I took the posts I wrote on it down because I am considering patents. But I will put them back up when it is safe to do so. Thanks for asking!