Ok, first this is not for a commercial venture so I will not be counting pennies.
I have a 1/2 hp pump, I have close power, I have some pvc laying around. Could I set up a 600 gallon tank, freestanding with an inflow from the pump, let gravity feed the outflow, and just rely on the pond to be my filter? In other words, pump pond water into a tank, let it flow back into the pond, and grow fish out? Obviously using feed. I was thinking about tilapia, i have plenty in my pond. How long does it take to grow a fish out?
Maybe a little sophmoric but just thinking about a weekend project. If it failed I would not be out anything but elbow grease. Unless its doomed from the start by something I am not thinking about.
Toby
Toby,
A circular tank with a moderately conical bottom is optimum for growouts, flat bottoms are still more than adequate. The venturi withdrawl and a slow to moderate circular flow in the tank will keep waste at the very minimum possible. Oblong tanks are nearly identical in performance and can reduce the wasted space if multiple units are used.
Flow through systems provide the easiest water quality control, BUT, they cause a large amount of feed to get wasted since nearly continuous feeding will be needed to get the same growth rates as in the circular tanks.
Square "Tote" tanks pose many problems with stagnant areas that will accumulate waste without turbulant water movement. Too much water turbulance causes stress and requires much of the fish's energy to be consumed swimming instead of turning into flesh. These problems can be overcome in many ways, but require an imagination and a lot more actual work on your part. The easiest drin for a square tanl is using a variant of the venturi that has 4 small pipes fingered out to the corners to draw the waste from the dead flow areas. The bottom of the center stand pipe must have a greatly reduced open area. Biggest benefit is that you can get these tanks real cheap or often for free.
As for growth rates. Nliotica, Mozambicus, and Aureus(Blue), Are fairly close, with fillet sizes (1.5 lbs) coming in 6-10 months with GOOD water quality. Stocking density has little effect on growth rates as long as filtration is adequate.
Optimum water temp for all 3 species is 82-85, Optimum PH and salinity for any fish is 7.4 and 8g/L (matches the fish's blood levels) and a calcium hardness above 150. This isthe least stressful.
Maintain ammonia/nitrite/nitrate levels near zero with optimum temps and water parameters, and you can grow out over 500 pounds of fish in 100 gallons of water in under 9 months---NOT easy to do!!! Oxygen is of little concern with growing tilapia...They can live in as little as .03mg/L of dissolved oxygen...that ain't much air!!! Normal water movement will provide all the DO needed
