Backyard Aquaponics
A place to discuss aquaponics

Swanberg made a request for a discussion on the pros and cons of high density versus low density off fish in comercial systems. So.....

If it is possible to make money from fish in a RAS system then why not make money from fish in an AP system?

The capital costs for a high density system are much lower per head of fish in a high density system than in a low density system. Similarly the $/m2 of growing area can also be lower in high density system. Along the same lines the embodied energy per kg of production is less in a high density system.

There is a certain amount of work that has to be done for any size/level of density of a system. In a high density system this cost in man hours is divided amongst more kgs of production.

Those are some of the pros.

The ability of running high density RAS ie around or over 10kg's per 100 litres of water is enabled by the addition of UV sterilisation, Oxygen injection , extreme filtration of solids and extreme biological filtration plus constant monitoring etc. In order to truly run AP at high density all these expensive and complicated additions would have to be incorporated.

First you need to define High Density vs Low density.

Personally, I would consider high density anything over 1/4lb per gal....

Thats when you really need to start considering pure O2 and other extensive filtration components.

Id agree with all that except the uv sterilisation bit but there needs to be some sort of sterilisation. There are other options other than uv including "granular media sterilisation" ie gravel beds. The level of control and monitoring that we would have needed to run at ~35kg/m3 is almost as much as we are planning for running higher densities. The biggest extra capital expense is the O2 concentrator.

I was going to say that anything that requires O2 injection would qualify but having thought more about it it is not that simple. Id consider a system running trout at 35kg/m3 without O2 injection to be a high density system. While a simple definition woild be nice I think it is better to assess the pros and cons if you view it as a continium.

Is this what you have in mind for the backyard Stuart.

http://www.youtube.com/watch?v=EGlIS-8Q ... re=related

Anything over 30kg/m3 is considered medium-high density in RAS.... and that's the max stocking density that has been suggested for AP .... although some have suggested double that...

Sadly many opt for double that.... while halving their filtration....

Anything above 30kg/m3... means constant monitoring, and filtration Stuart.... and with a lot of eggs in one basket.... you can end up with an omelette pretty quickly...

I guess the question ultimately... is where will the bulk of your revenue come from... the plants or the fish....

You really don't need a very high density of fish to produce copious amounts of veges.... I reckon 10-15kg/m3 is enough....

The second point Stuart... is just how do you intend to market the fish.... and do you have a market available...

Thirdly.... given a complete harvest, or partial harvest and hold of "mature" stock.... you're going to need multiple tanks, probably 10-12... to garuantee continuity of supply...

Well it depends. Tom Sp had a density of over 60kg/m3 without even supplementary aeration. Thats why I was suggesting that it s better to view things as a continuim. The need for monitoring at 30kg/m3 is not a lot less than for 80kg/m3 hence our decision to go for higher densities.

I disagree. For us it is a question of how much profit can we get from a given amount of capital relative to production costs. Once over heads are covered any little bit of extra revenue can add a significant % increase in profit, as long as production costs are not increased too much. In our modeling increasing the density significantly increased the rate of return and justified the extra capital, production costs and slight increase in risk.

As for not needing many fish for many vegies that is true but consider this....

In a multispan greenhouse one span may be dedicated to fish tanks and be covered with an opaque cover rather than gh film while other spans are covered in gh film for the plants. In a low density system you may have two spans for plants per span for fts, in a high density system you may have four spans of plants per span per span of fts. That would mean that the gh for the low density system of equal capacity would have 6 spans versus 5 and twice as many tanks as compared to the high density system. Now there is more risk but as the densities increase so do the savings.

I'm assuming you mean the Speranos system.... perhaps... but they were using a notoriuosly low oxygen demand fish species.... Tilapia.... which are also known to survive appalling water conditions....

And sorry... but the need for monitoring and maintenance between 30kg/m3, and 80kg/m3.... is almost exponential.... as is the cost...

Probably true Stuart... but you wont be getting a return of the fish for 15-18 months at best...

And lose a tank... and you could be either in short supply... or non-supply for a year...

As a curiousity, and because I've looked at a very similar sized operation.... could you PM or email me some more detail and proposed costings????

P.S .... I hope you realise that this venture will require two people... full time, 7 days a week...

And that's without packaging, transporting and marketing the produce....

This topic looked to be good until it became a pissing contest of who knows more with out actually giving any real information.

I know no one wants to or can release sensitive information but can we stop the mine is bigger/better than yours and actually have a discussion about the actual topic: "the pros and cons of high density versus low density off fish in commercial systems".

The Pros and Cons I can see:
PRO: More product (fish) to sell.
CON: More filtration required.
PRO: More filtration means more area to grow fruit and veg -> to increase revenue.
CON: More labour required

I am sure there are many more.....

Don't think there's any "pissing contest" going on Arbe...

The discussion is about high stocking rates, compared to whatever might be considered medium... and requirements for monitoring etc...

I tall ties back to Stuart's proposal for commercialisation....

I'm merely trying to point out some of the risks attached to high stocking densities, and whether they can be justified from a "commercial" point of view... and revenue stream....

Many of the figures quoted so far, for the high end... are more applicable to Tilapia RAS operations in the US....

I'm not sure that they're sustainable here in OZ with our fish species...

Then layout the figures you believe can be achieved with our local fish species. Lets not worry about justification too much - just the pros and cons.