Yes! by popular demand!
The list of backyard Aquaculturists is growing, and so is the demand for more advanced information! Be aware! "industrial strength" Aquaculture terminology is in use here!
Don't let it intimidate you, though, you can always do it by using the old tried and true "handfull" of this and a "bunch" of that methods!
In this page, we'll explore the little details that are needed in order to maximize the efficiency of your backyard Tilapia farm.
By now, we can take care of the inside work very well. We can manipulate the colony and have oodles of fry survive until they are ready to go outside, so:
As we discussed earlier, there are simple methods, like kiddie pools, that we can use to raise our Tilapia to eating size and more elaborate ones like ponds, large tanks, above ground pools, etc.
In either situation the parameters we need to maximize are: Density, aeration, and food. Remember, these parameters are not absolute requirements. You can go at your own pace and achieve the same results in a little longer period of time.
Here is the magic formula: in order to raise a Tilapia fingerling to 1 pound, we need to provide it with 1 pound of oxygen and 1 pound of food. What could be simpler!
Here's the trick, though. We need to provide these materials in just the right amounts over the desired length of "grow-out" time - generally anywhere from 8 1/2 months to a year.
The first question that arises is density: How many can I place in the tank?
Several hundred fingerlings in a 500 gallon pool.
This is where the first "industrial strength" term comes in:
The tank's "carrying capacity"
Having too few fingerlings in a tank wastes resources, but having too many will cause them to grow slower because of overcrowding.
My rule of thumb is to allow for a carrying capacity of 2 pounds of biomass (Tilapia) per cubic foot of water.
Lets picture a 500 gallon kiddie pool. It has a volume of 66.85 cubic feet. At a density of 2 pounds per cubic foot we could have in this pool 66 two pound Tilapia, OR 132 one pound Tilapia, OR 264 half pound Tilapia, etc.
This density can be achieved with standard pond filtering and aeration equipment.
Densities of 5 pounds per cubic foot or higher can be accomplished with more sophisticated equipment like pure oxygen systems, sand or bead filters, etc.
The next big question is aeration:
Pond fountains transfer large amounts of oxygen into the water!
A tank without aeration can only support a couple of ounces of biomass per cubic foot, at best.
Aeration is basically adding oxygen to the water. It is measured in "parts per million." (PPM)
Aeration is required when we keep a large number of Tilapia in a small body of water.
Besides breathing, Tilapia use up oxygen in order to metabolize the food they eat in order to grow, and the food itself uses up oxygen as it decomposes if it is not eaten.
We introduce oxygen into the water by causing friction between the water and the air. Bubbles, fountains, waves, even a showerhead raining water over a tank are methods to cause friction between air and water. In advanced systems, pure oxygen is dissolved into the water with "oxygen saturators".
In order to grow our 66 Tilapia to 2 pounds (908 grams), we will need to dissolve in the water 6.8 grams of oxygen per hour for 12 months. If we were to increase the dissolved oxygen to 10.4 grams per hour and provide better waste disposal and water changes, we could do it in 240 days (8 1/2 months)!
How did I arrive at that? well, 908 grams times 66 is 59928 grams (total biomass). We need to dissolve that amount of oxygen into the water over say, 365 days. That's 164.19 grams per day or 6.84 grams per hour.
All we have to do now is either shop for an air pump and diffuser (air stone) set-up that can do the job or just go for overkill and get a nice pond fountain for our pool that will aerate the heck out of the water. No such thing as "too much oxygen" in my opinion.
Of course, in more advanced set-ups, aeration becomes more critical. No need to come to the farm one morning and find 50.000 Tilapia all belly up floating on the surface just because you forgot to flip a switch!
Food! Food! Food!
Duckweed! It's a great supplement and, in enough quantities, could be all that's necessary!
That's all they want! How much? 1.76% of body weight per day to be exact!
What that means is that we need to weigh a few Tilapia in the tank every week and figure out what their average weight is. Then we proceed to feed them at a rate of 1.76% of average body weight for that week.
You can also do it "by the numbers" and use the weigh- ins as a back-up.
For example: Say our 66 Tilapia are in the tank for their first week and they each weigh 10 grams. We have a biomass of 660 grams. 1.76% of that is 11.6 grams. That's the amount of food they get the first day.
The next day their weight should be 660 grams plus the previous day's growth, which should have been 11.6 grams for a total of 671.6 grams. 1.76% of that is 11.8 grams. That's the amount of food they should get the second day.
And so on and so forth until they reach the desired weight.
It works like compound interest!
The bigger they get, the more they eat, the faster they grow!