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

I'm really curious to see what someone with more experience has to say. I think it's a good and viable idea. You might have to control the amount of water pumped in, and might have to screen the outflow if you were worried about small fishes escaping. To keep pellets from floating out of the tank, a feeding ring may be needed. You'll probably want to monitor the temps, IIRC Tilapia do the best @ around 80* water temp.

What about just building some cages to raise them in your pond?

Toby, that is the very way most Tilapia are grown in southern Florida. Lack of a back-up heating source, it is also why most Tilapia died this January there.

I use even smaller 300 gal rubbermaid commercial stock tanks. Fish waste will accumulate at the bottom along with food not eaten. With careful monitoring that should be very little. The koi guys are experts at this, as growing them out is money. I learned some tricks from an actual koi master. One was to have a conical bottom with the drain at the bottom of the cone. In the morning he would open the drain for a minute, flush out all of the waist. He used everything from doughboy pools to produce haulers. Water temp is the key. He had a huge barn set up with dozens of tanks in it. It was well insulated and he heated the entire enclosure. Another tool I use on flat bottoms is a muck vac. Just a siphon with a vacuum type head and you run it along the bottom and it really does not bother the fish. I think grow out tanks are a proven concept.

Like everyone says it would most certainly work! Not much better of a biofilter than a pond and lots of surface area too!

Even if your tank bottom is not conical I would suggest a venturi drain as in the below illustration and make it so your inflow creates a circular flow to push uneaten feed and wastes to the center for flow out and easy removal by lifting one of the stand pipes.





Pictures and info from Principals of Aquaculture - Robert R. Stickney.

There is some good starting advice here. Both flow through tanks and cages have pros and cons. Consider your goals and needs, then choose what is best for your situation.
Length of time to grow out depends on at least 3 main things assuming water quality is good: 1. start size of fish, 2. quality and amount of food eaten, 3. start size of stocker fish. Should we assume you will harvest at the first size to produce an average fillet? Tilapia have standard growth rates for teh speices and those should be farly easy to locate. Rainman should know this info right away.

I really like that venturi set up. That works in tandem with the sloped bottom towards the drain. If you do not have some kind of easy sediment removal system it can become a chore. Plus the venturi works with the sloped or conical bottom adding circulation and water movement. And you could put them in series with one as a bio filter, no fish and not even need a pond.

I totally agree with the points, what size you start with. If you start with small fish they may double in size, but you end up with bigger small fish. You should have a starting point and more importantly a where you want to get to point. That will give you a timeline.

Water quality. Can't have fish loaded up in thier own waste, nitrates, nitrites and bad ph. They just don't grow well, tend to get sick and are disease prone depending on crowded conditions. You are artificially sticking a lot of biomass in a little area. You have to artifically keep it clean. Dead and diseased fish don't grow out, they float up.

Feed. Depends on what you are feeding, I've seen people feed thier trout dog chow. You really should get the right food for the right species and feed the right amounts. This is very important. Too much food is a waste and also will foul the water. Wrong kind of food and you don't get the desired growth for the amount invested. Not enough food and slow growth. Some species go everyday, some every other day.

Temperature. Especially tropicals like tilipia. They will die at cold temps. They will go off feed in cold water, almost dormant as thier metabolism slows to hiberanation like levels. Trout on the other hand will die if too warm. They also start getting weak and sick even in borderline water.

Just keep in mind it is not as easy as you would think. The smaller the capacity, and the larger the biomass of fish the higher the risk of problems. But once you get the formulas and the set up down the rewards are well worth it.

My only true goal would be to have a standing supply of tilapia that I could net, filet and eat, I imagine that I would occassionally have a 'pack the freezer' day. Also have a repository for smaller fish that the kids catch out of the pond and grow them out.
Flushing the waste appears to be the biggest concern. I cant really worry about temp. I live in SW florida, to much of an expense. If they float I will filet them
Toby

here is a DIY link to your project
http://www.koiphen.com/forums/showpost.php?p=1057432&postcount=22

They have a set up of that Rubbermaid commercial 300 gal stock tank up on cinder blocks. Best grow out or holding tank for the price I have ever seen. Close to bulletproof, nice drain fitting on bottom. Eventually I will have 10 of those. Very universal and fairly inexpensive. The black even gets my water temp up early in the Spring, actually now.

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

hey rainman,
if dissolved oxygen isnt much of an issue and your strain of tilapia survive temps of 45 degrees, can I dig my pond deeper to provide water temps that are more stable thru winter and improve survivability?
I live in mid louisiana...
Thanks
Bryan

The Blues can survive to temps as low as 45, but fungus and infections will begin easily around 52*. You rarely see the secondary problems that are stress related to the cold because they get eaten so easily before they occur.

Where you live, I wouldn't mention tilapia and ponds without fearing a visit from the state. Louisiana gets all ryled up when tilapia even fly over the state in cargo planes!

Ditto. I was reading either in one of my aquaculture books or an online comment from Dr. Timmons, one of the leading authorities on RAS culture, that a conical tank bottom is over rated. Additionally I'm not sure it would be the best thing for my fry sized bluegills (Although i could be wrong). They seem to prefer to lay on the bottom when not feeding in my tank, especially during the night. I can't see them being able to do that in a tank with a conical bottom.