Backyard Aquaponics
A place to discuss aquaponics

Sorry if this is a dumb question, but it the target is 50-80 fish per week and OBO doesn't feed at the suggested rate (from memory 10kg per day), why would it take more fish?

If it takes longer to get them from fingerling to plate size, but once the time to do this is established, wouldn't you just be replenishing what has been removed from the system?

Ie if you are removing 50 fish per week and replenishing every quarter, then you would need to add 600 fingerlings per quarter (plus some for contingency)?

yeh thats what i thought too

True enough if they grow uniformly with a lower feed rate... but they probably wont...

So to meet the numbers... you'd probably need more...

because the fish will take longer to grow out at a reduced rate of feeding. So if you're aiming for X fish per week, but your feeding at a low rate you will have to have more fish in there growing slower rather than fewer growing quicker..? Now I'm confusing myself.

yep so if you have more growing slower, once you start harvesting surely it owuld tick over, i.e. 80/week out, 80/week in (or top up whenever). i guess having more fish means less trips to the fish farm, as apposed to less fish with more feed

I have to agree with Freoboy at the moment, but I am no expert. Let me put this out there to continue the discussion (so I can get an understanding):

Month...In....Out...Total
1..........600..0......600
2..........0.....0......600
3..........0.....0......600
4..........600..0......600
5..........0.....0......600
6..........0.....0......600
7..........600..200..1400
8..........0.....200..1200
9..........0.....200..1000
10........600..200..1400
11........0.....200..1200
12........0.....200..1000
13........600..200..1400
14........0.....200..1200
15........0.....200..1000
16........600..200..1400
17........0.....200..1200
18........0.....200..1000

Even if you put in a contingency of 600 fish the system would never have more than 2000 fish in it at a time. Is this achievable/maintainable?

Ah nope... by your figures... you forgot to add the next 600 in...


Month...In....Out...Total
1..........600..0......600
2..........0.....0......600
3..........0.....0......600
4..........600..0.....1200
5..........0.....0......1200
6..........0.....0......1200
7..........600..200..1600
8..........0.....200..1400
9..........0.....200..1200
10........600..200..1600
11........0.....200..1400
12........0.....200..1200
13........600..200..1600
14........0.....200..1400
15........0.....200..1200
16........600..200..1600
17........0.....200..1400
18........0.....200..1200

And that assumes a 6 month grow out... at uniform rates... to supply 200+ fish a month

OBO wants closer to 250 a month... every month... even with trout... I don't think you could gaurantee 250 fish a month... with anything less than 6000 fish....

You'll need at least 6 x 10000L tanks on the figures above.... more IMO...

And you will lose some fish... and probably somewhere along the line at least a complete tank...

To garantee supply... you'd need at least 2 other 10000L tanks... then theres holding/purging tanks, and/or hospital tanks....

Yeah 6 month grow out is rather hopeful... If only....

How about this then:

Month...In....Out...Total
1..........750..0......750
2..........0.....0......750
3..........0.....0......750
4..........750..0......1500
5..........0.....0......1500
6..........0.....0......1500
7..........750..0......2250
8..........0.....0......2250
9..........0.....0......2250
10........750..0......3000
11........0.....0......3000
12........0.....0......3000
13........750..250..3500
14........0.....250..3250
15........0.....250..3000
16........750..250..3500
17........0.....250..3250
18........0.....250..3000

So a 12 month grow out and harvesting 250 per month. Does this satisfy growth rate and supply numbers? Or am I banging my head against a wall trying to discuss this with you Rupe and EB?

Either way, once you start harvesting fish you reach a level which does not get exceeded (in this example 3500.

Note this is not a discussion about what size or how many tanks you need.

Arbe, I see where you're coming from... and in a perfect world... they might be perfect numbers...

But... Ok... maybe you could do it with trout.... not sure you could do that in OBO's location though...

Maybe, if you can source Silvers at 100mm min at the start of one summer.. then maybe you might have them to 4-500 gm in 12 months, more likely 15+ months IMO.... And Silvers wont grow uniformly....

So... if you can't do trout all year... and have to stock a mix of fish... then you'll have cross over periods between harvest fish and grow out fish... to cover... you'll need more fish...

Then there will be losses... and there will be...

If OBO stocks Silvers only... the growout is longer, the size less uniform.... the number of tanks and/or stock to garantee a level of sales greater....

And the bottom line.... no return from the fish for at least 12 - 15 months, probably closer to 18...

I still think you'd need to stock to around 6000.... even if (perfectly) your levels were higher than expected... you'd then just might drop out/delay a restock...

I guess in the end... it comes back down to "what is the focus"... the fish or the veges...

If it's the fish... then at the levels suggested... pure RAS might be a more viable option... beyond that, pond based aquaculture...

If it's the veges, or a desire to stay with aquaponics... then IMO... it requires a UVI style model with lettuce, herbs, perhaps asian greens....

I'm really not trying to put the "knockers" on things... I'm just not sure that the returns are there in the form of the proposal...

And I get the sense that OBO's market, and margin... is probably more directed toward the fish...

Going RAS would probably be just as cost effective... and probably more easily managed... but still just as at risk of unforeseen disaster that interuppts supply...

Chillie... did you do a RAS module in your course... with planning projections for stocking...

I've got notes somewhere.. but not sure where at the moment...

My two cents

I would definitely try for the 6000 fish, at least.
If nothing else the photo's of what happens will make for interesting reading.
Really happy for you OBO that the council gave you permission.
I wonder if mature systems gradually stressed have a change in biomass within the bacteria in the growbeds to deal with the new nutrient/fish/fish poo loads. I actually wonder that with time and slow changes in the environments that they could handle nearly any fish load.

You're a bit early Rupe - I'm doing it next semester