“Give a man a fish; you have fed him for today. Teach a man to fish, and he will sit in the boat and drink beer all day.” (Mahatma Gandhi)
As I begin to write this article, at this very moment, actually, I feel obligated to inform my loyal readers that I am not in my usual abnormal state of mind. Well, not the same abnormal state of mind, anyway. I have been water fasting for 92 hours. That’s right, no food, only water, for just about 4 days now. And since I’ve sort of just started, and this article could take days to write, I may at times sound a little less delusional than usual.
Allow me to digress a little. Some of you may wonder why I’m interested in aquaponics and why on earth I want to do it on the Bolaven Plateau. Well, the truth is, I’ve wanted to play with aquaponics for ages. I just want to do it. So, indulge me a little. The Bolaven Plateau simply bumped into my train of thought at the right time. Then, having seen some villages there where they still practice slash and burn agriculture, and knowing that much of the more rural population, especially the children, suffer from malnutrition, I realized that I might be able to help by setting up a model. If it doesn’t serve to reduce rural poverty one day, at least I’ll be able to have my fun and say I tried.
One thing that must be understood about the Bolaven Plateau is that it’s far from being the ideal place to raise Nile tilapia. It can get downright cold there at 1,200m. That’s why the whole system needs to be in a greenhouse. However, the greenhouse design has to allow for a lot of ventilation during the day as daytime temperatures can get pretty high. The average mean temperature is 19.5 C, and tilapia thrive in a water temperature of 28 C. Can a fairly constant air and water temperature of 25 to 28 C be maintained year round without the use of sophisticated heating equipment? Only time will tell, but I think so.
What are the advantages of raising an immensely popular yet tropically inclined fish, not to mention a myriad of tropical vegetables, in the cold climate on top of an extinct volcano? Well, there’s a fancy marketing term for it, I’m sure. Something to do with the fact that the same stuff has to be brought up by truck from the city of Pakse which is roughly 1,000m in elevation away.
This is the system I envision (without the greenhouse enclosure). It is almost exactly 1/4 the size of the University of the Virgin Islands’ commercial scale system but with a number of modifications (not necessarily improvements). Those familiar with the system at the University of the Virgin Islands (UVI) will first note that the fish rearing tank I’ve incorporated is not very circular. In fact, it’s undeniably rectangular. This one will hold about the same amount of water as 1 of the 4 tanks utilized in the UVI system, about 8,000l. I’ll probably build it with bricks, a mortar render, and a coating of waterproof paint/sealant on the inside. It will face south and the exposed surfaces will be painted flat black in order to get some passive heating during the day. As an aside, the coldest season is also the sunniest. Whereas the UVI system stocks each tank with fingerlings and leaves them in the same tank until harvest, I’ve decided to have one tank that can be partitioned into four areas, the size of each partition being adjustable in accordance with the state of growth of the fish. This will give the little fish less room to frolic about than in the UVI system, but will allow the bigger fish a bit more room to stretch their fins.
Four more or less equally spaced drains in the bottom of the tank will take the fish poo and any uneaten food by gravity to a larger pipe which will in turn divide this waste water among 4 clarifiers, one for each hydroponic tank. Those are the bigger of the blue drums that you see in the sketch at 200l each. A number of DIY swirl filter designs are available on the internet. The solids will need to be removed from a bottom drain periodically, probably a few times a day. This is excellent worm food, or it can be applied directly to my coffee trees. From the clarifiers the water goes first into a smaller blue drum filled with bird netting then into a second blue drum for a bit of vigorous aeration. The first acts as a filter for smaller suspended solids and is also a biofilter of sorts, and the second is for degassing. My system’s solids removal, biofiltering, and degassing may not be up to par with the UVI system, but since it will use easily available materials it will be easy to expand it if necessary.
From the degassing drums the water flows by gravity into the hydroponic component of the system. Each hydraulic tank is 40cm deep and will be filled with water to a depth of 30cm. They are 1.2m wide and 12m long. The combined grow area is 57.6m2. This is also roughly 1/4 the size of the UVI system. The tanks, or troughs, will be lined with pond liner (plastic). They will be made by shallowly excavating the 1.2m by 12m area, filling polypropylene bags with the earth, and stacking the bags 3 courses high (30cm). This is called earthbag building. The bags will function as both the walls and the aisleways. They will be covered with burlap to protect them from UV light. As aisleways, at about 35cm wide, they are a bit precarious (especially the center aisleway which has wooden poles projecting upwards every 2.8m), but planting and harvesting are actually done from the ends (the plants will grow on floating Styrofoam boards, each 1.2m X 0.6m, so you just pull them off at the far end and load them again at the front end). Besides, a 35mm aisleway is enough room for a petite Lao girl to dance in circles without falling into a patch of lettuce. I, however, am sure to tumble in once or twice.
One thing I will be doing, which is a bit daring but has seen some success by others, is adding giant freshwater prawns (technically, they are shrimp, I read somewhere, but who cares), Macrobrachium rosenbergii, to the hydroponic component. It is claimed that they will only eat the dead roots of plants, not the healthy ones, and will vacuum up the fish poo and other suspended solids which make it past my homemade instruments of clarification and settle on the bottom. These same suspended solids often cause problems as they coat the roots of the plants, making it difficult for them to suck up nutrients. Supposedly the smaller prawns will take refuge in the roots of the plants to avoid cannibalism by their brethren.
As for the system’s capabilities, on an annual basis, let’s take an example in which the 4 hydroponic tanks were planted 1 each with basil, lettuce, okra, and pak bung (water spinach). The results, including Nile tilapia and freshwater prawns, are as follows:
- Basil – 312kg
- Lettuce – 2,100 heads
- okra – 181kg
- Pak bung – 2,000kg
- Nile tilapia – 1,000kg
- Freshwater prawns – 150kg
I’m trying to design a system that will run on 500W or less (water pump, aeration, lights). I’ll have plenty of power from my 14m high waterfall, but if it’s going to work in some remote village that’s not connected to the grid, running off of a small, inexpensive hydropower setup is a key to success. In the same strain, the use of easily available materials, including the earth beneath your feet, is essential. With that in mind, I came up with the greenhouse enclosure shown here. The file got too big so use your imagination for the front opening.
Without getting into too much detail in this article, I found that some innovative people in the West have set up tunnel greenhouses in their backyards using only PVC pipes. Some reinforce it by putting an equal length of rebar into the pipe and capping both ends. I like it, as both are flexible, cheap, and available everywhere. I plan on using 12mm pipe for wiring (the yellow stuff) with 9mm rebar shoved down it. I’ll have some 30cm lengths of 25mm steel piping with a 40 or 50cm piece of rebar firmly welded to the bottom and bang these into the ground until only the pipe is exposed. One end of the PVC/rebar poles will be planted in these, and they will arch over to the wooden structure running down the center, where they will be firmly attached. With as little waste as possible in mind, I’ve designed it such that the combination of a left-hand segment and right-hand segment is about 10m. This is the standard length of rebar. The segments are at a span of 1.4m, and the posts are at 2.8m. This is due to the fact that the greenhouse plastic comes in 3m wide rolls. Short pieces of slightly larger diameter PVC pipe will be cut vertically such that they will act as fasteners, or clips, holding the plastic sheeting to the framework.
Well, that’s it for now. I’m going to join one or two aquaponics forums that I often lurk on and warn them that there is another amateur out there with delusions of grandeur. Readers! I’m actually going to start building this next month, so any constructive criticism will be much appreciated. By the way, writing this was fun, as only one who has, at this very moment, subsisted on water and air for 116 hours and lost 6.5kg.