In my never-ending quest to build the ultimate incubator for Tilapia eggs, I have built at least 5 prototypes, none of which worked exactly the way I planned. Summarised below are some of the problems that I have encountered in my experiments.
- The eggs were not “tumbled” sufficiently and they settled in dead spots and fungus killed them.
- The eggs were “tumbled” too vigorously breaking the egg wall.
- The eggs were washed out of the incubator before hatching and eaten by fry in the receiving tank.
- The power failed and the eggs died because they were not “tumbled” at all.
- Newly hatched fry were washed out the incubator before they were free swimming and eaten.
I discussed incubators previously here;
Enter the “Airlift Tilapia Incubator”
I have always been intrigued by airlift pumps. Using only air pressure, it is possible to pump water up without any moving parts whatsoever. You can read more about the subject here.
This got me thinking. What if I used air from my existing blowers to pump water up to and into an incubator creating a welling and oxygenation effect? So I got building. First came some experimenting.
How much air was needed to pump water?
I took an existing airline and pumped air into a 65mm PVC pipe submerged in the water.
The water rose…………………. 0 mm and all that I could see in the pipe were bubbles.
Oops, what have I done wrong?
Even increasing the air flow had zero effect. The water just didn’t rise.
After much head scratching I decided to decrease the pipe diameter.
I tried 40mm, nothing.
I then went MUCH smaller to 15mm.
VOILA, water squirted out the top of the pipe.
After a bit of fiddling, I discovered that the water rose about 50% of the depth at which the suction line was submerged in the water. This meant that If I wanted to pump the water up 500mm, I’d need a suction line submerged 1M in the tank.
Here are some images.
This is the first airlift. The longer pipe goes down to the bottom of the tank from which water is being sucked. If you look carefully near the bottom of the long pipe you can see the air connection nipple. The shorter pipe goes into the bucket which acts as the incubator.
When it is mounted it looks like this.
I turned on the air and this is how it worked.
You will notice from this image the very vigorous bubbling. I popped some eggs into the incubator to test and they were bashed around to such an extent that I just knew from experience that although this airlift was working extremely well it just wouldn’t work as an incubator.
So I put the thinking cap back on and tried to analyse what the problem was.
It then dawned on me. The very big bubbles that were entering the suction line and sucking up the water were exploding into the bucket together with the lifted water. This is what would do the most harm to the eggs. In this design 100% of the air and 100% of the water was exiting the short pipe into the bucket thus causing all of the upheaval. But how could I moderate this effect?
I figured that if I could seperate the air from the water before it entered the bucket, I could increase the water flow (by adding more air) without harming the eggs. But how? What if I could get the air to go one way and the water the other. 3 hours and many pipes and tubes later, I had it. Allow the air to vent off at the highest point and the water run down into the bucket by gravity.
Here is the final result and it is working perfectly.
Note the volume of water existing the bucket and also note how still the water looks inside the bucket.
Update : 03/11/2009
I checked the incubator to see how it had performed over 24 hrs and I can declare this incubator my best ever!! About 100 Tilapia had hatched and where just hanging around midway up the incubator (they would probably be washed out after another day or two when the egg sacs were absorbed and they were free swimming) and the remaining eggs all looked fine with no signs of any fungus. Here is an image. Note the eggs at the top of the image as I tilt the bucket towards the camera. The lighter coloured eggs are dead/unfertilised and I try and remove them. The others are all fine and will probably hatch in the next 24 hrs. The hatched fry are in the foreground still with their eggs sacs attached. These I removed to the fry tank and put the incubator back into position.
Some valuable lessons have been learned here and I have at least 4 or 5 ideas for other products from my experimenting.
Enough for now.