Trout in recirculation and flow through
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Production of trout is a well known species in recirculation, as well as in flow through systems.
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Trout in tank.
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With trout it is possible to operate with very high recirculation levels and very high fish densities.
In fact, the only water we need to renew, is the water bound to the sludge removed, and what leaves the
system through vaporization (the majority of the water consumption). The water consumption can be as
little as 10-20 ltr. of water per produced kg of fish.
This means a 1000 ton trout farm can be located in the middle of a city, and operated on tap water!
The sludge can be removed from the site in containers, with a dry matter content of up to 20%, ready to
be used as fertilisers in the agriculture industry.
Densities above 150-180kg/m3, which is the max density range recommended by UNI-Aqua, is clearly obtainable, giving a highly competable commercial production.
Even peak levels at +300kg/m3 have been seen, without causing disease problems.
Average densities of more than 300 kg is clearly a possibility, but above what we will normally recommend,
as it will cause some fin deformities etc. Within the staff group of UNI-aqua there exists full experience
from production of trout in recirculated systems from hatchery to harvest.
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In a classic outdoor flow through system for trout production in freshwater,
total dependence to weather conditions is a growth limiting factor,
compared to producing in an indoor, controllable environment.
Here is an example of the temperature variation throughout the year in a Danish river system.
In autumn-winter-spring the growth is limited by the lowered temperature, whereas in some places
the peak summer temperatures can also limit growth due to the fact that the temperature is too
high and oxygen available is limiting.
Ideally, a constant temperature regime throughout the year would be optimum for producing trout.
Optimum temperature for trout growth is around 17°C and this is obtainable only by creating a
closed environment recirculating the water and securing a high and constant water quality securing the
optimum growth conditions for the fish.
The growth curve shown here illustrates the potential growth curve from 2g to 300g at constant 17°C in
comparison to varying temperatures as indicated in the river temperature illustration. The growth
curves are theoretical and indicates growth under ideal conditions (sufficient oxygen, no disease etc.),
without interruptions (grading, treatment etc.) where the only difference thus is the direct effect upon
growth of different temperature regimes. In reality the pattern will of course differ to some extent.
The dramatic difference in growth performance indicates the potential of running constant high temperature
production in comparison to varying temperature regimes as the growth duration is almost half in recirculation production.
The temperature regimes used for modelling are as shown here.
Skilled flowthrough farmers will probably be able to perform better than indicated in the graph,
but the potential of recirculation production is clear.
Another factor is disease protection, where indoor production in a controlled recirculation
environment has proven to be stabilizing to an extent that eliminates the need for medical
treatment, prophylactic as well as curative, almost completely! This covers all phases from
reception of disinfected eyed eggs to sale of +300g fish.
This is another very important factor when considering to establish a recirculation system,
or turning a flow through production into recirculation, as the disease prevention and
treatment in traditional systems is a lot more problematic - unwanted, but necessary,
costly and limiting performance of production.
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Talking freshwater production of trout, the key problem is, that the sales price of trout is very low, below 2 EUR/kg, which is sufficient for covering the production costs in a recirculation system, but insufficient when considering the investments involved to build a new facility.
Still for trout juveniles/smolt where the produced biomass is low, and security and logistics have high priority,
a recirculation system, will most likely be the best option.
Working with freshwater production of trout, Uni-Aqua would then typically offer the following services:
- Technology supply, hatchery/juvenile production
- Upgrade of flow through systems with oxygenation system or recirculation
- Design of new flow through systems with advanced oxygenation technology
- Upgrade/modification of existing recirculated farms into trout farming
- Design new farm where the geographical location secures a higher local sales price
See further description below
1. Technology supply, hatchery/juvenile production
When building a new hatchery, juvenile production facility, using recirculation technology will
often be the best option.
The investment cost will be the same or even lower than for flow through, as the produced biomass
is relative small (small water treatment facility) - and the closed facility due to temperature control,
typically can produce several batches in the same system in a year. Further due to the improved water
quality control and disease control the closed system can operate with higher fish densities.
Thus the profit margin per kilo of fish produced will be higher.
The advantage of using a closed recirculation system, is that:
- The production cost per fry will be reduced
- The logistics can be improved
- The production is much more safe
- Diseases will not be transferred from a river system to the production site
- The hatchery can be located where it is most optimal considering the production facility
- The production becomes independent on local climate and water source
- Improved logistics can be a tool to obtain year around delivery of fish, also to processing industry
The technology/design is very similar to what is used for Salmon, so please look further under
salmon.
2. Upgrade of flow through systems with oxygenation system or recirculation
Many existing flow through systems for growout of trout in freshwater, operates very simple by simply
using the incoming water as it is. Here we can often supply a simple solution, which will increase the
production capacity massively. Simply by implementing a modern oxygenation system, as developed for
recirculation systems.
It is important for us, that we always supply the right solution for the right purpose and location.
Recirculation or flow through.
3. Design of new flow through systems with advanced oxygenation technology
With the right water source available it might be more beneficial to use a modern flow through system
with oxygenation, for grow out of freshwater trout. And even more likely, to combine the flow through system,
with a small recirculated system, which will add logistical control of juvenile supply, and hence
improve the utilisation of the water source, as temperature and amount of water available over the year
will typically fluctuate, without recirculation.
4. Upgrade/modification of existing recirculated farms into trout farming
Today, one can thus operate with fish densities of more than 150-180 kg of trout in recirculated fish farms -
and the fish are very healthy.
Our trout and salmon expert Stig Jensen (UNI-Aqua), was in charge of converting one of the bigger
recirculated eel farms in Denmark, into trout farming in 2002. This farm is now successfully producing above
500 ton of trout per year, according to expectations.
By using recirculation technology it is possible to operate with much higher densities than in normal flow through.
This is primarily possible, due to the reduced pathogen pressure, and secondarily due to the controlled water
environment/quality.
5. Design/construction of new farms where the geographical location or other factors secures a higher local
sales price
Even though that the sales price of trout is usually relative low, then a number of factors can secure a higher
sales price of the fish produced in the recirculation system.
- The recirculation technology makes it possible to establish a production system even in the middle of a city.
And fresh fish, potentially alive can be sold locally, with short logistical notice
- The fish from a recirculation system can be produced without use of chemicals and medication,
that would normally be mandatory in a flow through system
- There is a demand for fish to be released in to lakes for leisure fishery (angling).
At the same time in many countries, there are veterinarian restrictions when it comes to moving fish from
one river system to other lakes. A closed production system, might here well be the only option for a supply
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