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Just Don

How many fish?

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Okay... I've seen various "rules of thumb" out there for designing an aquaponics system (i.e. 1:1 ratio of volume of grow beds to volume of fish tank). However, I'm struggling with how I can know how many fish my system can support. How can I calculate the "carrying capacity" of my system knowing that I have built it to a 1:1 ratio.

Obviously the chemistry is different between systems that have the right volume ratio if one system has a single fingerling and a grow bed full of plants, and the other has 100 full sized fish and one little seedling. (I suspect in the first case you'd have scrawny "weakling" plants, and in the second case you would soon have much fewer than 100 fish.)

Any suggestions? (My intent is to have a grow bed full of seedlings planted at 6-8" intervals, and to stock the FT with tilapia fingerlings.)

Thanks,

Don

6. Stocking density: a complex issue

Stocking density is a pivotal factor affecting fish welfare in the aquaculture industry,

especially where high densities in confined environments are aimed at high productivity.

Although rarely defined, stocking density is the term normally used to refer to the weight of fish

per unit volume or per unit volume in unit time of water flow through the holding environment

(Ellis, 2001). The stocking density at any point in time will increase as fish grow or decrease

following grading. Stocking density is, therefore, hard to measure in the field. The concept of

minimum space for a fish is more complex than for terrestrial species as fish utilise a threedimensional

medium (Ellis, 2001; FSBI, 2002; Conte, 2004). Because fish are dependent on this

medium for both physiological and behavioural needs the welfare concerns associated with

stocking density should address both the carrying capacity of the holding environment and the

spatial and behavioural needs of the species. Carrying capacity refers to the maximum number of

fish that an environment can support through oxygen supply and removal of metabolic waste and

will be determined by, amongst other things, the oxygen consumption rate of the fish and their

response to metabolic waste products such as CO2 and ammonia (Ellis, 2001). Beyond providing

for the physiological needs, the FAWCrecommends that fish ‘‘need sufficient space to show most

normal behaviour with minimal pain, stress and fear’’ (FAWC, 1996). Stocking density is,

therefore, an area that illustrates both the significance of species differences and the existence of a

complex web of interacting factors that effect fish welfare.

For species that live naturally in large shoals, low rather than high densities may be harmful,

whereas for territorial species the opposite may be the case. Reductions in stocking density may

P.J. Ashley / Applied Animal Behaviour Science xxx (2006) xxx–xxx 13

+ Models

APPLAN-2652; No of Pages 37

Please cite this article as: Paul J. Ashley, Fish welfare: Current issues in aquaculture, Applied Animal

Behaviour Science (2006), doi:10.1016/j.applanim.2006.09.001

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If Aquaponics is that technical, Shoot someone will need a BS in Aquaponics to even build a system.. A few simple calculations and a little rule of thumb works will for me. We are not launching the space shuttle for Gods sake, it just a few tomato plants and what have you along with some fish...:)

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If Aquaponics is that technical, Shoot someone will need a BS in Aquaponics to even build a system.. A few simple calculations and a little rule of thumb works will for me. We are not launching the space shuttle for Gods sake, it just a few tomato plants and what have you along with some fish...:)

If that is a response to my answer/quote I think it's odd.

If it's a response to the "calculator" disscusion in the thread I might agree a bit?

AP is not complicated at all IMO.

But if you wan't to do a deep dive, in the science involved, there is a lot available, if you look beyond the AP comunitys, on all the differente aspects/matters/subjects my only motivation to post links, is to help, not to complicate.

cheers

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Definitively is was about the calculator as the thread was started about fish density and has become the calculator debate.. had nothing to do with your post. As when I started to write I had not seen your post yet. watching TV and writing created a delay with my posting. I apologize if it created any confusion. As much as I like the technical aspect of aquaponics there comes a point when it seems that it is becoming overly complicated for no viable reason.

And your post was right on topic. let alone it was more than accurate and totally above reproach..

Edited by Pugo (see edit history)

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Definitively is was about the calculator as the thread was started about fish density and has become the calculator debate..

As much as I like the technical aspect of aquaponics there comes a point when it seems that it is becoming overly complicated for no viable reason.

I appologise for the hijack, but the calculator was posted in response to the OP question in regards to "How man fish" and I am simply taking a closer look at the calculator which is very related to the thread.

I am simply trying to understand the calculator. Please carry on with your discussion.

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I appologise for the hijack, but the calculator was posted in response to the OP question in regards to "How man fish" and I am simply taking a closer look at the calculator which is very related to the thread.

I am simply trying to understand the calculator. Please carry on with your discussion.

I think the discussion is fine/good and agree that it(calculator) is very related.

Just remember the calculator is only a tool.

The calculator have its limits but is indeed a good helper/tool that goes beyond rule of thumb.

To me there is no hijack, just felt like adding another point, I enjoy and learn all the way so please keep the discussion rolling you to.

cheers

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Okay... I've seen various "rules of thumb" out there for designing an aquaponics system (i.e. 1:1 ratio of volume of grow beds to volume of fish tank). However, I'm struggling with how I can know how many fish my system can support. How can I calculate the "carrying capacity" of my system knowing that I have built it to a 1:1 ratio.

Obviously the chemistry is different between systems that have the right volume ratio if one system has a single fingerling and a grow bed full of plants, and the other has 100 full sized fish and one little seedling. (I suspect in the first case you'd have scrawny "weakling" plants, and in the second case you would soon have much fewer than 100 fish.)

Any suggestions? (My intent is to have a grow bed full of seedlings planted at 6-8" intervals, and to stock the FT with tilapia fingerlings.)

Thanks,

Don

Quote from page 9 in this http://www.ca.uky.edu/wkrec/454fs.PDF here

Component ratios

Aquaponic systems are generally

designed to meet the size requirements

for solids removal (for those

systems requiring solids removal)

and biofiltration (if a separate biofilter

is used) for the quantity of fish

being raised (see SRAC Publication

No. 453, “Recirculating Aquaculture

Tank Production Systems: A Review

of Component Optionsâ€). After the

size requirements are calculated, it is

prudent to add excess capacity as a

safety margin. However, if a separate

biofilter is used, the hydroponic

component is the safety factor

because a significant amount of

ammonia uptake and nitrification

will occur regardless of hydroponic

technique.

Another key design criterion is the

ratio between the fish-rearing and

hydroponic components. The key is

the ratio of daily feed input to plant

growing area. If the ratio of daily

feeding rate to plants is too high,

nutrient salts will accumulate rapidly

and may reach phytotoxic levels.

Higher water exchange rates will be

required to prevent excessive nutrient

buildup. If the ratio of daily

feeding rate to plants is too low,

plants will develop nutrient deficiencies

and need more nutrient supplementation.

Fortunately, hydroponic

plants grow well over a wide range

of nutrient concentrations.

The optimum ratio of daily fish

feed input to plant growing area

will maximize plant production

while maintaining relatively stable

levels of dissolved nutrients. A volume

ratio of 1 ft3 of fish-rearing

tank to 2 ft3 of pea gravel hydroponic

media (1⁄8 to 1⁄4 inch in diameter)

is recommended for reciprocating

(flood and drain) gravel

aquaponic systems. This ratio

requires that tilapia be raised to a

final density of 0.5 pound/gallon

and fed appropriately. With the

recommended ratio, no solids are

removed from the system. The

hydroponic beds should be cultivated

(stirred up) between crops

and inoculated with red worms to

help break down and assimilate

the organic matter. With this system,

nutrient supplementation

may not be necessary.

As a general guide for raft aquaponics,

a ratio in the range of 60 to 100

g of fish feed/m2 of plant growing

area per day should be used. Ratios

within this range have been used

successfully in the UVI system for

the production of tilapia, lettuce,

basil and several other plants. In the

UVI system all solids are removed,

with a residence time of <1 day for

settleable solids (>100 micrometers)

removed by a clarifier, and 3 to 7

days for suspended solids removed

by an orchard netting filter. The system

uses rainwater and requires

supplementation for potassium, calcium

and iron.

Another factor to consider in

determining the optimum feeding

rate ratio is the total water volume

of the system, which affects nutrient

concentrations. In raft hydroponics,

approximately 75 percent

of the system water volume is in

the hydroponic component,

whereas gravel beds and NFT

troughs contain minor amounts of

system water. Theoretically, in

systems producing the same quantity

of fish and plants, a daily

feeding rate of 100 g/m2 would

produce total nutrient concentrations

nearly four times higher in

gravel and NFT systems (e.g.,

1,600 mg/L) than in raft systems

(e.g., 400 mg/L), but total nutrient

mass in the systems would be the

same. Nutrient concentrations outside

acceptable ranges affect plant

growth. Therefore, the optimum

design ratio varies with the type

of hydroponic component. Gravel

and NFT systems should have a

feeding rate ratio that is approximately

25 percent of the recommended

ratio for raft hydroponics.

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I think I'm done for now. Busy with house work.

I do have some off topic questions for Earthan Group regarding NFT and mineralization in commercial AP systems. The response can be left in the lonely commercial sub section. I'll make a copy of this post there.

----off topic---

It's hard to find any good NFT how to guides that are not related to growing weed. Large commercial hydro growers don't get into operational details of systems online so there seems to be a void of info in this area.

Has Earthan Group done any aquaponics only NFT systems and if so is there any advice you'd like to offer for backyard systems trying NFT only besides keeping solids out of the NFT component?

Not sure what the best practices are in this area so here goes. When using rock wool cubes in NFT is the trend now to just place them directly on the nutrient film? If rock wool is not the trend now what are newer systems doing?

Is mineralization being done in commercial systems or are solids just being dumped? Are you guys using an activated sludge/aerobic digestion method?

Edited by jobney
Added link to post in Commercial section. (see edit history)

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Hi Just Don,

On the question of component ratios for basic flood and drain systems......see here for an explanation of why they are usually pure bunkum. The exception is where you are running tilapia in a warmer climate - and assuming that you are performing appropriate maintenance......as you can see explained here.

A 1:1 ratio (originally proposed by Murray Hallam et al) will be barely adequate for tilapia (of limited size). While such a ratio might get you going with some fingerlings, things will become increasingly risky as the weeks pass.

Gary

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"If Aquaponics is that technical, Shoot someone will need a BS in Aquaponics to even build a system.. A few simple calculations and a little rule of thumb works will for me. We are not launching the space shuttle for Gods sake, it just a few tomato plants and what have you along with some fish..."

Thank God....thought I was gonna have to dig my slide rule out.

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Okay... I've seen various "rules of thumb" out there for designing an aquaponics system (i.e. 1:1 ratio of volume of grow beds to volume of fish tank). However, I'm struggling with how I can know how many fish my system can support. How can I calculate the "carrying capacity" of my system knowing that I have built it to a 1:1 ratio.

Obviously the chemistry is different between systems that have the right volume ratio if one system has a single fingerling and a grow bed full of plants, and the other has 100 full sized fish and one little seedling. (I suspect in the first case you'd have scrawny "weakling" plants, and in the second case you would soon have much fewer than 100 fish.)

Any suggestions? (My intent is to have a grow bed full of seedlings planted at 6-8" intervals, and to stock the FT with tilapia fingerlings.)

Thanks,

Don

WOW, I'm surprised no one has come up with the right answer yet (but sort of because it becomes evident after 4 pages of posts). The answer is... /drumroll

IT DEPENDS!

You guys are touching on only a few of the factors that matter when determining the system's capacity for fish (or plants for that matter). You can sit down and try to calculate it all day long, but until you build YOUR system in YOUR geographic location using YOUR biota, well heck you won't really know will you?

Yes, surface area is important. So is the climate, weather, sunlight, season, plants used, stage of plant growth, pH, SO ON AND SO FORTH.

You can't calculate it all. You just can't. A rule of thumb is useful as as a starting point, and that's it! You have to get to the end point yourself by testing your system out. It will change from day to day, month to month, and even year to year.

But don't worry. You will figure it out, and you will enjoy it. You are armed with a handy API Master Test Kit or something like it; so, you have EVERYTHING you need to make figure it out (the test kit plus your senses). Go, build, have fun! :smile:

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There are many kinds of people involved with aquaponics some very technical other not so much. You will find different people, find different things enjoyable, a lively discourse on any topic could occur, but remember there are always little nuggets of information that can be gleamed for these debates at the least, at best a better understanding of a given topic.

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There are many kinds of people involved with aquaponics some very technical other not so much. You will find different people, find different things enjoyable, a lively discourse on any topic could occur, but remember there are always little nuggets of information that can be gleamed for these debates at the least, at best a better understanding of a given topic.

I couldn't agree more! :smile:

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