Stocking Densities

[Murray]

There has been much discussion regarding this topic.
Often people will ask "How many fish can I have in my fish tank"
This has come up again just this morning by private email from 2 x students in Denmark who are setting up a small aquaponics system at their University.

It is difficult to give an all encompassing answer because the number of fish or the Kg of fish to a given volume of water depends on how closely you are prepared to manage your system.
Most private/home systems I have seen or read about tend to run to between 5 or 7 kg per M3 of water.
My own system currently has approx 350 fish in a 2300 ltr tank. The fish range in size from very small fingerlings to some fish that are 1.5 kg or more.

Some commercial high intensity aquaculture systems claim densities of as high as 400 Kg per M3. That kind of stocking level (If true) would be really out there on the edge, and require very sophisticated techniques like pure oxygen injection into the fish tank water and very elaborate filtration systems. That kind of stocking level is obviously way beyond normal and of little or no interest to the home or commercial aquaponics system.

The factor that comes into play with home systems is that the Silver perch fingerling's do not all grow at the same pace.
If you started in January with 100 fingerling's in a 1 M3 tank (1000 ltrs) you would only have about 500 to 750 grammes of total fish weight actually in the tank at that point.
As those fish grow out during the following months the total weight of fish in your tank obviously increases.
Just as humans all grow at different rates , so do fish. Some of your fish would reach "Plate size" while others would still be relatively small.
The "Plate size" fish would be harvested and the others would be left to grow on to "Plate size".

If you harvest regularly, it is most unlikely that the particular tank which started with 100 fingerling's would ever reach a density of 100 kg of live fish per 1000 ltr of water because the fish do not all grow at the same rate, and the fast growers will be harvested as soon as they are big enough.

A year on, the likely density in the above hypothetical fish tank would be around 50 to 70 kg per 1000 ltrs. Remember this is dependant on how often/quickly you choose to consume those "Plate size" fish as they become available. It also assumes that you have fed and managed the fish well.
If you did not harvest any of the fish then you would need to take a decision to get another tank and separate some of the fish, or be prepared to provide very close management of your system.
This is a very manageable/achievable level of stocking for the home grower.

This is the basis upon which I recommend purchasing 100 fingerling's per 1000 ltrs of fish tank volume.
This recommendation is given as a starting point, and at no time is it suggested that you should or would end up with 100 Kg of fish per 1000 ltrs of water. Remember, close management of the system is necessary at any level. Aquaponics is not a "set and forget" type of activity.

Based on this information you will need to decide just how much management you wish to put into your system and purchase your fingerling's accordingly.

Further on this subject I add this abstract by the listed authors. You will notice that the Max stocking density achieved was 21 Kg per 1000 ltrs of water and 200 fish per 1000 ltrs of water. It should be noted that this density was achieved using flow-through cages.

Stuart J. Rowlanda (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T4D-48WJRGF-1&_user=10&_coverDate=01%2F12%2F2004&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=0d7169c6889ccff7375b442b38f59b27#aff1),, Geoff L. Allanb (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T4D-48WJRGF-1&_user=10&_coverDate=01%2F12%2F2004&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=0d7169c6889ccff7375b442b38f59b27#aff2), Matthew Hollisa (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T4D-48WJRGF-1&_user=10&_coverDate=01%2F12%2F2004&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=0d7169c6889ccff7375b442b38f59b27#aff1) and Trevor Pontifexa (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T4D-48WJRGF-1&_user=10&_coverDate=01%2F12%2F2004&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=0d7169c6889ccff7375b442b38f59b27#aff1)
a NSW Fisheries, Grafton Aquaculture Centre, PMB 3, Grafton, NSW 2460, Australia
b NSW Fisheries, Port Stephens Fisheries Centre, Private Bag 1, Nelson Bay, NSW 2315, Australia
Received 12 November 2002; revised 22 April 2003; accepted 24 April 2003. ; Available online 20 June 2003.

Abstract.
Silver perch fry (mean weight 2.3 g) were stocked at densities of 50, 100 or 200 fish/m3 in replicated cages or tanks (both 1 m3) and cultured for 140 days. The cages were floated in an aerated, 0.32-ha earthen pond and the tanks were on a flow-through system at 5 l/min. Fish were fed a formulated diet containing 35% crude protein. Water temperatures ranged from 23.9 to 31.0 °C in the pond and 23.2 to 28.9 °C in the tanks. Mean survival ranged from 92.0% to 99.5%. Growth and condition were not affected by stocking density in either facility; however, fish stocked in cages grew significantly (P<0.01) faster (specific growth rate [SGR] 2.80%/day, absolute growth rate [AGR] 0.8 g/fish/day), to a larger size (mean weight 116.3 g) and were in better condition (K=2.0) than fish cultured in tanks (2.15%/day, 0.3 g/fish/day, 46.6 g, 1.8). Production of fingerlings was significantly (P<0.01) affected by stocking density and rearing facility, and the maximum production rate achieved was 21.0 kg/m3 in cages stocked with 200 fish/m3. An overall FCR of 2.0 of fish in cages was significantly (P<0.05) lower than an FCR of 2.5 in tanks. The results of this study suggest that cages are more suitable than tanks in a flow-through system, and are a viable alternative to ponds for the culture of silver perch

Muzza

[GaryD]

Hi Millie,

The weight of fish that can be kept in an Aquaponics tank will depend on the following factors:

The size of the tank
The size of the fish
The species of fish
The Dissolved Oxygen levels
The bio-filtration capacity of your system
The ability of your growing systems to remove nitrates from the water.
The level of risk that you wish to assume.Theoretically, the amount of fish that can be kept in any system is limited only by its ability to convert ammonia and nitrites to nitrates (bio-filtration) and to maintain appropriate levels of oxygen in the water.

For practical purposes, however, the level of risk is proportionate to the stocking rate. What this means is that, if you are just managing to stay ahead of the requirement for ammonia/nitrate removal and dissolved oxygen in the system, you will have very little margin for error or mishap.

The Department of Primary Industries in Victoria has reported stocking rates for Murray cod of 80 to 150kg per 1000 litres of water. This was in a recirculating aquaculture system (rather than an aquaponics unit) and involved the injection of pure oxygen at the higer stocking levels.

Would I use pure oxygen? Probably not, but the fact remains that higher stocking rates are possible if you do use it.

I'd recommend something closer to 30kg per 1000 litres for those who are new to Aquaponics.


Gary

[Murray]

I have had some PM's and emails about stocking densities.
It would appear that some folk want to be given a specific formula as to how many fingerling's will turn into how many KG of fish in a specific number of months.
It is just not possible to be that specific.
We are dealing with live creatures that are not entirely predictable in their growing habits. There are lot of variables that will decide the outcome.
It is all about BALANCE.
To repeat part of Gary's previous post,

The weight of fish that can be kept in an Aquaponics tank will depend on the following factors:
The size of the tank
The size of the fish
The species of fish
The Dissolved Oxygen levels
The bio-filtration capacity of your system
The ability of your growing systems to remove nitrates from the water.
The level of risk that you wish to assume.Theoretically, the amount of fish that can be kept in any system is limited only by its ability to convert ammonia and nitrites to nitrates (bio-filtration) and to maintain appropriate levels of oxygen in the water.

To any beginner, my specific recommendation is to purchase 100 fingerlings per 1000 ltr tank. (If you have some other size tank, do the math)
If you are able to purchase advanced fingerlings, then cut the number in half, at least.
When you gain experience by observation of your own specific system and circumstances you can then increase or decrease the stocking density if you so desire.
If you are unsure, then be conservative.
Cut the number in half. You can always add more fish later.

If you do a good job of managing your system you will soon be harvesting fish on a regular basis and enjoying the wonderful benefits of home food production.

[GaryD]

Hi,

Crusty's still at it. This time, he's commenting on my blog post Mythconception #1 - Stocking Density (http://www.microponics.net.au/?p=192).


I am not sure how suggesting that generalised advise on stocking densities is worthless and then offer generalised advise on stocking densities is helpful.

Further suggesting people start (cut their teeth) at 20 or even 30kg per 1000 liters without knowing what filtration they have is downright careless.
You're right......on both counts......and I have inserted a note into the post to that effect. In fact, premised on my latest reflections, I regard 20 - 30kg per 1000 litres as probably unsustainable in a system that is not fitted with adequate mechanical and biological filtration.


So, in part I agree that it is pointless to suggest stocking densities where no actual design has gone into the systems. This is a massive failure in duty of care by the folks selling systems without qualifying the design. It is not enough to calculate stocking densities based on the grow bed acting as a filter.
I agree.


Yes, you may know the (hydroton or aquaclay) surface area however this is only good for the first few months, if that. One thing that is unknown is the efficiency of the media because it is acting in 4 different functions. The grow beds are acting primarily as a fluidized static filter without any wash facility and there are some basic rules applied to these types of filters which are not used in aquaponics.
Your reading of my work will have revealed that I do not advocate the use of grow beds for what you describe as "fluidised static filters" (I think I used the term "outhouse") in place of appropriate mechanical and biological filtration.


Further, stating that you “might lose the odd fish so start out with 50 fish”, is not a qualified statement of mortality rates. What does one do if they all live? It will mean your calculation goes from 30kg/m3 to 37.5kg/m3 and that is pushing into levels that require a great deal more skill. The starting out enthusiast or even professional should calculate their stocking densities without a mortality rate and work on not losing any. If none die (which is the ideal) then their filtration is designed for the entire load. If some die, it only makes a difference to the bottom line not the bio load. Trying to predict mortality rates that you can not possibly know and include that as part of your stocking density calculations will leave you and your fish in a bad position.
I think you're reading a lot into the one sentence you've quoted. I don't recall trying to predict mortality rates.


As much as I enjoy people trying to make a difference, I prefer that the information being provided is pertinent and accurate. If not it simply contributes to the confusion and ignorance surrounding aquaponics.
I'm happy to cop it on the nose if my information is not as it should be (notwithstanding the lecturing manner in which it is being done)......even though it is conservative compared to what's being peddled elsewhere.

If you though my post was problematic, check out the one that precedes this one......particularly the bit about the 100 fish in 1000 litres.

Gary

[Crusty]

Crusty's still at it. This time, he's commenting on my blog post Mythconception #1 - Stocking Density (http://www.microponics.net.au/?p=192). Only because I have nothing better to do.


I think you're reading a lot into the one sentence you've quoted. I don't recall trying to predict mortality rates. Not really. You have suggested stocking with 40 fish then to get 50 in the event you lose a few. As I said the difference in the final weight is 7.5kg/m3. In short, mortality can not be considered before they happen or your filtration will be under size.



I'm happy to cop it on the nose if my information is not as it should be (notwithstanding the lecturing manner in which it is being done)......even though it is conservative compared to what's being peddled elsewhere. Indeed it is conservative compared to others but that does not make it right. I am doing my best not to be harsh, I apologize if you find my approach offensive.

I
f you though my post was problematic, check out the one that precedes this one......particularly the bit about the 100 fish in 1000 litres.
Fair enough, I will and dissect it....


I have had some PM's and emails about stocking densities.
It would appear that some folk want to be given a specific formula as to how many fingerling's will turn into how many KG of fish in a specific number of months.
It is just not possible to be that specific.
I find this to be somewhat hard to believe. Information on the specific growth rates and feed rates are readily available from the DPI for most aquaculture species in AU. Admittedly, some of the lesser known species data was worked out on Trout which leaves some some of the warmer species questionable. You can pick any species really. Take silver perch for example. Give the Grafton Aquatic research center a call and see if they can provide the expected growth.

Indeed, the formula for calculating the time it will take to grow a silver perch to an average 350grams are somewhat confusing for the average Joe or Jill. Are they available? Yes they are. I would expect someone of Murray's experience to know these and be able to provide a reasonably accurate guidelines for each species in a system designed by him.


We are dealing with live creatures that are not entirely predictable in their growing habits. There are lot of variables that will decide the outcome.
It is all about BALANCE.
The idea of culturing fish in a tank is that they become predictable in that environment. Sure there are variations to the length of an optimal growing season, but these too can be reasonably predicted. If I was asked the same questions about my systems and responded "its all about balance" I would be broke and laughed out of the industry in a heartbeat.





To any beginner, my specific recommendation is to purchase 100 fingerlings per 1000 ltr tank. (If you have some other size tank, do the math)
If you are able to purchase advanced fingerlings, then cut the number in half, at least.
When you gain experience by observation of your own specific system and circumstances you can then increase or decrease the stocking density if you so desire.
If you are unsure, then be conservative.
Cut the number in half. You can always add more fish later.


I have no way of making any sense out of the above aside from numbering them so I will correspond my comments by number also. Wow where to start...


Offering a stocking recommendation without knowing the species is a small concern as majority can be grown at the kind of densities you can achieve in a tank. But suggesting 100 fingerlings per 1000liters without also suggesting a harvest weight is just plain madness (eg 350grams = 35kg/m3 - 500grams = 50kg/m3). You can quickly see how that will lead to an issue down the road. Further and even more insane, is to suggest that if you have larger (other) size tank just work from there, so I have 2 grow beds and a 5000liter fish tank...
It makes no sense at all to suggest 100 fingerlings with advice number one then suggest to cut the number in half if you get advanced fingerlings (what size are they again) with advice number two. So the fish in advice number one will not grow to advanced fingerlings? When they do get there, should we cut them in half? The mind boggles.
Even with my experience in aquaculture, I can not increase the stocking density just because I desire it. The system is entirely restricted primarily by its ability to oxidize ammonia to nitrate.
If you are unsure one should seek advice proptly from someone else that knows what they are doing.
Do not be so keen to add younger fish to a single tank containing mature fish at a later date. You can suspend them in a basket but they can not live there forever. The larger will dominate the feed in a tank environment and the young ones will starve to death. If they are carnivores, such as barramundi, then forget that suggestion all together as the young will be eaten.

It was one of Murrays larger systems I had to fix. Pipe work is wrong, pump sizes wrong, fish tank wrong, aeration wrong to name a few. 8 grand simply bought some big buckets to hold water. Personally or professionally, I would not be asking this chap any advice on anything.

I hope that candid assessment does not offend anyone.
cheers
Paul V

[GaryD]

Hi Paul,


It was one of Murrays larger systems I had to fix. Pipe work is wrong, pump sizes wrong, fish tank wrong, aeration wrong to name a few. 8 grand simply bought some big buckets to hold water. Personally or professionally, I would not be asking this chap any advice on anything.
Since I wasn't involved in the project, I have to take your word for all of the things that you allege were wrong......and therein lies a problem.

When I'm not scratching around in my backyard, I lead a technical training unit of nine people. I've managed to instil in them that I'm always to willing to listen to their problems but that I'm particularly willing if the problems also come with some prospective solutions.

In this situation, it would be more useful to me (and our members) if we knew exactly what was wrong and what you did to resolve the problems.....and what effect that had.


I hope that candid assessment does not offend anyone.
I'm calm about it.........not too sure how Murray would cope with it though.

Gary