Production of salmon smolt in recirculation systems
The presentation of salmon has been divided into:
- Smolt
- Post Smolt
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Smolt
The general advantage of recirculation is that a recirculated smolt facility
in general is cheaper in investment and operation costs, as a smaller
system will produce the same amount of fish, and energy costs and labour
costs will be reduced.
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The main cost reducing elements are:
- The geographical position of the recirculation unit is independent of climate and water supply source. This means that the unit can be positioned where it is optimum solely from a logistical point of view, meaning that operational costs for transport can be minimized dramatically. This is a very important economical factor when considering to establish an aquaculture unit based upon recirculation technology
- Due to a controlled water chemistry, a smolt unit operated with recirculation technology can be operated with much higher fish density: Salmon 70-120 kg/m3, Trout 100-300 kg/m3 (Recommended 100-150 kg/m3). Less tank volume requires less capital costs
- Due to temperature control, up to three groups of smolt can be produced in the same facility during one year. This also gives less capital costs
- Higher productivity per tank means less labour costs, as labour is more related to number of tanks to be looked after, than density in tanks
- Reduced energy costs, as pumping head typical will be less in a recirculation system, compared to flow through, using state of art recirculation technology
- Disease control through water management, means reduced losses
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Recirculation system design and operation is in reality a matter of maintaining mass balances. Any input that enters the system, must come out at the end, and what comes out must be dealt with properly.
The principal waste outputs from fish production are organic matter in dissolved or particulate form from feed, carbon dioxide from fish respiration and ammonia excretion products.
The central water quality parameters of importance are as follows:
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Recommended Max levels of compounds/parameters
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| Ammonia (NH3) |
< 0.02 mg/l (0.04 mg/l)* |
| Nitrate (NO3- |
< 70 mg/l (NO3--N) |
| Nitrite (NO2-) |
< 1.0 mg/l (NO2--N) |
| Carbon dioxide (CO2) |
< 15 mg/l |
| Oxygen (O2) |
Between 60 and 120% saturation |
| Hydrogen Sulfide (H2S) |
< 0.001 mg/l |
| Chlorine residuals |
< 0.001 mg/l |
| pH (fresh water) |
Between 6.0 and 7.0 |
*Peak levels can be accepted up to twice as high levels, if levels are very stable.
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The job of the water treatment system, is simply to remove waste
products in a reliable way, so that the chemical composition of the water,
will remain optimal for fish growth.
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Waste products |
Removed in |
| Organic matter |
Mechanical filter, biological filter |
| Carbon dioxides |
CO2 stripper |
| Ammonia products |
Biological filter |
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The feed composition is obviously one of the parameters that has important
effect on the amount of waste products, and hence the water treatment system.
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Parameters |
Type of feed |
1 |
2 |
3 |
| Protein |
58 |
44 |
38 |
| Fat |
15 |
30 |
31 |
| Carbohydrates |
6 |
13 |
17 |
| Theoretical O2 use, total g./kg feed |
1164 |
1444 |
1423 |
| Theoretical CO2 production, total g./kg feed |
1289 |
1591 |
1588 |
| N content, total g./kg feed |
93 |
70 |
60 |
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| Notes: |
| The average N content in fish is 30g/kg fish. |
| The key factors that influence the water treatment system are,
feed conversion, characteristics of particulate waste and "gentle" handling of waste. |
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Multistep biofilter
In freshwater systems it is not necessary to have a multistep biofilter,
however it is often the best solution. Sometimes the multistep filter is more expensive
than a single step biofilter. UNI-Aqua offers both types of filters.
There are two major advantages of including the multistep biofilter.
Firstly, it will create a more stable level of ammonia (NH3),
which has a positive influence on fish growth, and secondly,
the multistep biofilter, efficiently removes pathogeneous bacteria. On the other hand - it is more expensive.
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CO2 Stripper
Carbon dioxode is removed in the CO2 stripper.
At the relatively low pH levels a higher fraction of the carbonate
system is present as CO2 instead of bicarbonate.
This fraction is stripped effectively off the water inside the
CO2 stripper as the water passes through.
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Production models
The growth is highly dependable on temperature and for a 16°C
level the growth looks like this:
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An example of a production model for the southern hemisphere
is shown here, based upon 3 annual intakes of eggs, all becoming
batches of 1.200.000 smolt within 1 year. The production is divided
into the following sections:
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The division into the 3 production units or phases, Hatchery, Nursery and
Smolt unit, is done because it is crucial to utilize the large unit for
smolt production as much as possible, because this is the most cost heavy
part of the production. The Hatchery and Nursery units can be operated in a
flexible manner, thereby enabling a very flexible production planning tool
by varying time of egg intakes and by adjusting growth by temperature
manipulation of the individual batches.
As it can be seen 3 annual batch outputs are possible giving a
potential of 3.600.000 smolt at around 100g per year. For the northern
hemisphere the strategy is different but still the system flexibility
will enable just as high productivity level.
An example of a system design including hatchery nursery and smolt unit
is shown in this illustration.
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As an alternative to immediately establishing a full production unit e.g.
as illustrated above, a first phase consisting of e.g. the hatchery and
nursery unit only could be used until full confidence in working with the
technology is in place.
As investment are closely related to biomass production per time unit,
the optimal investment will be small, and the "pilot" system will be fully integrated in the final system.
Hereafter decisions regarding expansion with the
smolt unit can be done on a safe basis without losses of investment.
It is important to stress that the illustration above is only a principle
drawing, as a solution is designed and adapted individually in close
collaboration with the client following the clients needs and specifications.
Recirculation units can of course also be added to existing farms where a transfer into recirculation
operations is desired.
In the system illustrated above, the individual water treatment systems are incorporated.
All with multistep filters on location, with little pathogen pressure.
It is a cheaper option to use multistep technology for hatchery and nursery,
and a single step filter for the smolt unit.
UNI-Aqua can provide both technologies, and give advise on which technologies to use.
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- Post Smolt
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