The MAX rule of thumb is around 1 lb of full grown fish per about 5 gallons of grow bed media with a minimum of 2.5 gallons of fish tank (chances are most systems are going to have 5 gallons of water but some of it might be traveling through a sump tank.) THAT IS MAX!!!!!!!!!! If you go more fish than that you are gonna need to start bubbling with pure O2 and other very high end stuff.
Please keep in mind the above is for flood and drain media bed systems. I don't really know the rules for raft systems since the entire system tends to operate differently.
A better number to remember might be the Recommended stocking density that would say 1 fish (with a planned grown out weight of 1 lb) per cubic foot of grow bed media with 1 cubic foot of water to go with it (that cubic foot of water could be split between the actual fish tank and a sump tank if need be.)
(If you think in metric better, Recommended stocking would be 20-25 fish per 500 liter grow bed (that is with a planned grow out of about 500 grams for the fish.)
The thinking here is if you need to ask the rule of thumb, you probably shouldn't be stocking to the MAX. Also, a new system should never be stocked to the MAX.
Again these numbers are for flood and drain media based systems.
Now Nates towers will provide a whole new set of design numbers to play with.
Yes the rules of thumb generally are about the bio-filter and the dissolved oxygen able to support the amount of fish.
If you put more fish in a smaller amount of water, you eventually hit a point where you need major chemical intervention just to keep the fish alive until you can sell them (think bait shops.)
Thanks for the clarification. 1 *pound* of fish per 5 gallons of water. That's a much easier ratio to keep track of.
So I'm thinking about a 12'X4'X3' pond-- about 1000 gallons. Sounds like that should be able to hold 100-1lb tilapia, but in order to do that I need 100 cubic feet of grow bed? I really only have room for 3- 4'X4' growbeds which I was planning to fill with 8" of media, so that's only 32 cubic feet of media. Does this mean I can only safely do about 32 fish? Can I put some kind of supplemental filter between the end of the grow beds and the pond to make up for this or...?
Thanks! I was thinking the 100 fish because that's the quantity that's easiest for me to buy. Maybe I'll just sell half or so on CL. I was planning on the 8" because I read (I think on DIYaquaponics?) that if you go too deep you have problems with solids getting to the bottom of your grow beds and anerobic bacteria. How do you deal with that? I could probably go a foot deep or even 18", I'm just concerned with being able to clean it out. Also trying to figure out if I will need a sump or not. So much to learn!
Great bunch of information on stocking levels vs grow bed sizes, tank sizes, and fish per gallon. The next thing that would affect all this also would be how the water circulates, ie. pipe and pump sizes, and how much the various agitation points are adding oxygen to the water through sprays, jets, burblers, etc. - moving water and agitation adds more oxygen at all points. Seeing as how the emphasis is on arriving at a balanced system, there seems to be one item not being addressed; this is the question of consumption. It is one thing to use lbs. per gallon as a measure for ultimate grow out numbers, and stocking levels; 100, 200, or even 300 fry for early stocking levels may be alright in a tank at the early stages, but may be crowded as the fish get bigger - the question then would be at what point do they hit the soup pot or the dinner plates to help maintain that all important balance, meaning that being optimistic with the number of fry may not be a bad thing.