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.