Backyard Aquaponics

How many fish can I put in my tank?
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Author:  aeldric [ Sep 11th, '06, 19:09 ]
Post subject:  How many fish can I put in my tank?

I have seen two really useful pieces of advice about stocking densities in aquaponics - and I think they were both from this forum.

The first: Allow 2-3 kg of fish per 100 liters of water.
The second: Allow 1 gallon (4.5 liters) of water for every half inch (roughly 12-13 mm) of fish.

Both these techniques work out about the same in terms of water/fish, but you use them at different times. If you have fingerlings or goldfish, then the second piece of advice works well for calculating the minimum tank you need. If you want to know how much water to allow for growing your fingerlings out to plate size, then the first piece of advice is perfect.

However, when starting up you need to get your system established. Aim to start smaller and grow up to these densities.

David C.

David, thanks for putting that together, i've "stickyed" your post.

Author:  Gary Donaldson [ Sep 12th, '06, 01:13 ]
Post subject:  Re: How many fish can I put in my tank?

The amount of fish that can be kept in a given volume of water is dependent upon the rate at which you can remove the ammonia from the system and your capacity to maintain oxygen levels.

The rate at which you can remove ammonia from a system is dependent upon the growing system or bio-filter capacity that is attached to the system. Maintenance of oxygen levels comes down to bio-filter and general system design.....and the use of air pumps, blowers and mechanical aerators.

Commercial recirculating aquaculture systems are capable of much more than 3kg of fish per 100 litres because they use bio-filters, faecal particle clarifiers, mechanical air blowers and high volume pumps.

Author:  nick [ Sep 12th, '06, 05:34 ]
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also some commercial producers utilise direct oxygen injectionto have fish at up to 10kg/100l. pretty impressive

Author:  creative1 [ Sep 12th, '06, 07:50 ]
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Not much fun for the fish though.

Author:  Donarto [ Sep 12th, '06, 08:04 ]
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I thought there was a problem with getting aquaponics organic certified because of the strocking densities, surely 3kg/100l is much better than 10kg/100l I wonder what the "humane" limit is.

Author:  creative1 [ Sep 12th, '06, 08:26 ]
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Donarto- I agree, whilst it maybe possible not very savoury.
1 failure and a mass murder would ocur.

Author:  nick [ Sep 12th, '06, 13:44 ]
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didn't say it was nice or ethically approved, just that the only dependant things is the dissolved oxygen levels,

Author:  Aquaddict [ Sep 12th, '06, 15:33 ]
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True. You'll need to filter solids at some point of stocking density.

I like the humane approach, up to 3 kg per 100 litre. Even less if I got a big enough tank. I like watching fish grow big...

One thing to consider is additional water in system using floating raft beds and DWC. If all of this is recirculating and being replenished with oxygen utilising the water flow it 'buffers' your stocking rate quite nicely.

ie my 600* litre pond. Add 200 litres (dwc sink above tank) 100 litres (5 x dwc buckets) and 250 litres (other dwc beds)

That comes to 1150 litres. Plus a fluctuating 150 litres in 3 ebb and flow filter beds, and the water in the pipes.

1300 litres, plus pipes.

This makes higher stocking in your actual tank a bit safer.

* My pond will actually take 800 litres as opposed to 600, the fluctuating beds and pipes will cover the extra 200. If the pump fails, and for some reason like never recalibrating the 3 ebb and flow beds and they all drain at once, still wont flood fingers crossed. 8)

Author:  Jaymie [ Sep 20th, '06, 13:42 ]
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so what would the stocking rate for redclaw be? For example in an IBC how many would you have?

Author:  creative1 [ Sep 20th, '06, 17:03 ]
Post subject: ... r_crayfish

Bit of reading again but worthy.

Author:  mevans [ Sep 22nd, '06, 01:13 ]
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This is a link to research published by Rhodes University in South Africa.

It is a very big site and unfortunately difficult to navigate. It deals with African catfish (we call tham barbel) aquaculture but has masses of material that would be of interest to anyone intersted in AP.

They were able to achieve stocking densities of 965 kg/m2 in an ultra high density aquaculture setup.

This is hard to imagine, with nearly a metric ton of fish in a cubic metre there can't be a lot of water left. Freakish and guaranteed to get you a bunch of bad karma if you give it a try.

Author:  michael_Ferrini [ Sep 22nd, '06, 03:14 ]
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AA I completely agree that a DWC tank helps buffer the system, which is the theory behind my large sump. I purposely keep the sump half full in the event I have to do an emergency dilution, so far never. But let's say I had infinite grow beds I could attach to one tank. The more the concentration of fish emulsion gets spread out, the closer to the threshold of plants suffering from malnutrition I get. If the ratio is not just right the other way, the fish can crash. Working from a large resevoir sump, I can float a raft and check water parameters daily, and if I get an awful spike, I can emergency dillute the system, temporarily suspending the spike to deal with the problem. I can always come back later and plant more or less veggies or clean out grow beds, but I can't rescue sick fish with the same method.

Author:  Rampant [ Aug 29th, '07, 00:07 ]
Post subject:  Re: How many fish can I put in my tank?

A good rule of thumb with home aquarium setups is 1 inch of fish, length wise, for every gallon of water that your tank holds. However, if your tank is tall and deep, instead of fat, then there is less surface area to be oxygenated for your fish. The aquaponics should add considerably to your tanks ability to hold fish though, because all of your grow beds create a massive biological filter, which also oxygenates the water. My experience with densly stocking fish is that, even though the fish may look like they are getting along, but they will actually kill each other to get more space :roll: Also, keep in mind, when stocking tanks, that all of your fish are going to grow, and as they get bigger, not only are they going to need more space, but they will eat much more food, and create much more waste, and you're going to have a harder time managing ph, and nitrates, and solid fish waste, and different kinds of algae infestations can be a nightmare. Also, if the grow beds are anything besides a constant flow, then it lessens the effectiveness of the biological growbed filter, because most of the water is staying in the tank, most of the time. I would just experiment with some cheap fish :twisted:

Author:  steve [ Aug 29th, '07, 03:16 ]
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read on, rampant ;)


Author:  janethesselberth [ Aug 29th, '07, 03:42 ]
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Hi Rampant, Welcome!

I have heard that rule of thumb about 1" per gallon, but it's really only any good at the smaller end of the scale. After fish get over about 4 inches long, the weight of the fish becomes a much more important factor. Visualize 4 1" (25mm) neon tetras, as compared to 1 4" (100mm) angelfish. And since a lot of us want plate-sized fish, rules based on length don't work well.

My limiting factor is the size of my growbeds, iow, my capacity to filter the ammonia/nitrite. If I had ginormous filters, then my limiting factor would become the volume of my fish tank. The important thing is to learn the specific limits of your own system.

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