Backyard Aquaponics
A place to discuss aquaponics

Hey all,

First of many posts here I hope

I have been investigating and exploring the wonderful world of aquaponics for a while now and there is a question that I have that has been bugging me since day one: the ratio of fish production to plant production seems to be much higher on the fish side then plant side? I would imagine one can only eat so much fish in a year and more plant support would be beneficial.

For instance, I read about one setup where they had 300 total gallons, with 100 adult tilapia supporting five 10sqft 12" deep grow beds. 50 sqft is a pretty small grow area and would not nearly produce the same amount as food as the tilapia.

So do people eat all the tilapia? Are some just killed and used for fertilizer? How does the imbalance, balance itself out?

I would love to know!

Welcome to the forum

not really sure what you are asking here. Veg and fish are not really linked so you eat your fish if you like as they reach plate size and you eat your veg all season as it grows. Some like more fish and some like more veg. Some use goldfish and don't eat the fish at all.

>> I would imagine one can only eat so much fish in a year and more plant support would be beneficial.
basically you don't get a lot of fish meals as fish take some time to grow (Tilapia = 6-7 months in ideal warm conditions). Depending on your climate and water temperatures you would probably only be eating fish for 3 months at most unless you freeze them (as some do with trout). 100 Tilapia probably only make 20-30 meals.

All systems are different but as a rule from most well run systems you get **a lot** of veg from 100 fish..
To start off with the fish tank component would have to be 1500+ Litres to hold that many fish.
and veg grows much quicker (more harvests = many meals) than fish which are one 'meal' per season.

[edits here] Details of your quoted system are limited - they may be more interested in fish and using filters etc.
50 sqft is at the lower end (4-5m2) but not impractical. And 300 Gallons is a bit on the small side for a FT for that many fish. So maybe not an ideal example.

A normal balanced system would have around 25L of wet media per fish.
(actually to fish weight but 25L to one 500g fish is a starting point, Tilapia are 300-600g as a rule)
so 25L x 100 = 2500 L. You would ideally have around 1500-2000L of fish tank at least for that many fish.
So this gives a media-fish tank ratio of 1:1 which is easily achieved.

at 12" (300mm) deep surface area is 8m2 of beds (8 IBC halves for instance).
If you look around this forum that is a lot of vegies.
In most cases you can grow even more veg using DWC in conjunction with media.
You get lots of harvests of veg for each period of fish raising.
Ratios of 1:2 (FT:GB) can even be achieved for those that just want veg primarily.

So re: your question "much higher on the fish side then plant side"
growing veg is not the issue - mostly it is the slow rate the fish grow (so the opposite).

someone who wants fish over veg would use filters or some form of RAS approach.
And just eat the fish and veg as it arrives.

the one area where Tilapia might be an exception is in breeding and higher stocking capacity.
Because Tilapia breed easily a system may become overstocked.
But that would apply mostly to people who live in warm areas where water temperatures remain optimal all year round.
In those cases fish numbers would have to be managed to avoid overstocking and fish deaths.
But that generally doesn't present an issue for most AP'ers who basically get one harvest per year and have trouble carrying fish over the cold/hot season without effort or special planning.

most fish do not breed at all since they do not reach sexual maturity in a growing season.
Even goldfish apply here - if they do have eggs/babies most would be eaten by the adults.

p.s. when I said 20-30 meals I was thinking of a family - and allowing for fact that you will get a mix of sizes and not many will get to full size. So assumes you will use 2-3 fish per meal. From a small 300-400 Gallon system you would be unlikely to get 100 serves from 100 fish particularly if you over-stock. So maybe 30-50 meals tops.

One dinner party (or odd visit from relatives/friends) would dent your stocks.... and there is always the family cat who is less fussy about undersized fish (and you offset the odd tuna in the process so get an environmental credit).
so it is not really that hard to consume that many fish if you really did get high success.

..
I've got about fully grown Silver Perch in one system with 3000L of water and 300L of clay and NO PLANTS..
and
In another system (AP) about 160 Silver Perch, in 3000L of water and about 900L of clay and lots of plants
..
The secret is bags of Zeolite.. :-)
..
.

Thanks for your indepth reply perth!

I guess what I am thinking is comparing that 50sqft of growing space compared to my conventional 192sqft garden plot and how much food comes out of that. We can supplement a decent portion of our veggies we need (maybe a little over 50% during the summer months) but even then there is a lot that we have to buy. I don't have any hands on experience with aquaponics and I guess I can't wrap my mind around how much food can be grow in 50sqft using this system versus 192sqft conventionally.

I think I need to start a system in the near future, keep it small, and get a grasp on how fast the veg grows and what harvest times are like.

All the info you gave was amazing by the way What a great first experience on here!

I guess what I am thinking is comparing that 50sqft of growing space compared to my conventional 192sqft garden plot and how much food comes out of that.

basically its the hydroponics thing - some things can be grown more intensively than they can in the ground.
For AP that is mainly leafy greens - lettuce, herbs etc in particular. But also the various kale, silver beet etc type veg.
With right conditions you can push out tomatoes and other fruiting veg.

Other things wont go as well as a good dirt garden.

Lots of examples around here.
Fayes Garden is one to look at - she produced quite a lot.
viewtopic.php?f=18&t=1622

Like most things (particularly in Canada) you will be limited by your temperatures and limited growing seasons.
Those of us in most parts of Australia pretty much go for 9-10 months at a time, some get full 12 months.
Same for Florida and many parts of California.

You probably wont get all your meals but if you like lettuce or spinach they are very easy ones to have lots of.
Particularly if you go with a DWC (Deep Water Culture = baskets over tub of just water, no media)

Tomatoes and fruiting plants vary a lot - some have good production others don't.
Green houses and glass houses make a huge difference.

A lot of us here also run with wicking beds - these are great for things that prefer dirt (various threads here).
For us Australians water & moisture sucking heat are major issues - so all these things (wicking beds and AP) simply help deal with the fact that we are very restricted on garden wateringa nd sprinklers. In Perth, West Australia we are limited to only 2 or 3 days per week for not more than 1 hour. Then we have very poor sandy soils and gravelly soils that cost a lot of money to get up to vegetable garden requirements. So the BYAP type approaches provide solutions to some quite major issues - and thus there are quite a few of us around here.

The other side (me included) are faced with smaller near-city blocks that are increasingly getting smaller and are often very inconvenient for light and over-run by concrete. Many SE Asian people fall into this category and we even have roof top systems around the forum.
So there is no longer space for a fish pond and conventional vegie patch - and thus intensive methods allow opportunities to still grow vegetables and raise fish (even if just goldfish or koi) etc.

In terms of DWC versus growing in media beds, assuming the plant grows just as well in either format, do you know if you can get more dense planting in a DWC versus growing media? Whenever I see growing media pics they always seem so sparse for some reason. I don't know if it's just me but I always think they look entirely inefficient.

I think you could probably plant either way and just as packed in. Most of the media grow beds you see are mixed plantings and backyard systems. Usually with DWC it's one crop where they've measured out the plant size to determine the optimum hole spacing so it's a bit more planned out and it's also sometimes small scale commercial operations. Along with that the plants are often harvested at the same size and time while that's less common in media beds so they may use the space less efficiently.

Some pics from the BYAP trials thread on this page that give you more of an idea with the media beds - http://www.backyardaquaponics.com/forum/viewtopic.php?f=51&t=8621&start=360

The ratio has an inverse relation. If you want to give fish better quality, grow more plants. If you want more plants growth or have chosen the type which needs more nutrients, Your fish may need to eat more, produce more waste and tolerate some bad water.

>> If you want more plants growth or have chosen the type which needs more nutrients, Your fish may need to eat more, produce more waste and tolerate some bad water.

not actually true, you can easily run a lower fish stock and simply supplement direct to grow beds or foliar..
(and it is generally much cheaper than equivalent amount of fish food).

and at end of day you get a lot more veg per week/month/year than fish because fish take much longer to grow.
A lot of fish will grow a lot more veg....

there is no excuse for fish having to suffer "some bad water".. as there are lots of alternatives.