Production of Halibut in recirculation systems
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Halibut (Hippoglossus hippoglossus) is a new species in Aquaculture.
It is a highly valuated specie, although only well known mainly in
Scandinavia, Britain, USA and Canada.
It is an interesting species, due to the high market value, and it
has been seen as a new big potential specie in aquaculture.
The problems in farming this specie, have though proven to be more
difficult to handle than first expected.
The problems are mainly related to fry production and farming the
halibut in cages.
The problems with fry production, have more or less been solved,
and there is today sufficient fry available on the market, although
not all of equal good quality.
The problems at this stage seems more related to the farming of
the halibut in the cages.
First of all halibut is a flat fish, and it requires bottom area,
and is not really suitable for farming in cages. Husbandry is difficult,
especially optimal feeing is difficult, and the low biomass per
cage volume, makes investments in installations relative expensive.
But apart from this, a major economical and risk problem with the
farming of halibut is, the long production period under natural
conditions, where it takes 5-7 years to grow the fish from fry to harvest.
By using UNI-aqua recirculation technology, the production time
can be reduced to only 2-3 years,
with a serious overall reduction in production costs and risk.
In a landbased recycled facility in Norway using UNI-Aqua technology.
The production time was drastically reduced after implementing recirculation technology.
With recirculation, the production time from 5 to 500 gram was 10 month.
500 gram is considered to be the size from when the fish potentially can
be farmed in cages.
With flow through technology, the fish would only reach a size of 50
gram in 10 month time, and only be less than half way through.
The valuable experience from this relative large facility is, that it
is now clear that production costs can be reduced seriously by doing
the entire production on land with recirculation technology.
The production time of a market size fish, will be reduced from 6
years to approx 2½ year. And the overall production costs, including
capital costs will be reduced with approx 30%.
The halibut farm in Norway with UNI-Aqua technology
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Halibut farm in Norway using recirculation technology.
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Multistep biofilter
In the biofilter removal of organic matter and ammonia products
takes place.
Due to the high pH a relative high proportion of total ammonia is
in the form of toxic un-ionised ammonia, NH3.
Therefore a traditional single chamber biofilter is not suitable, as
ammonia levels will fluctuate to much. A recycling system for freshwater
potentially only has a single flow loop, Whereas a recirculation system
for seawater has a multi loop system. The bio-filters would be to unstable,
if the necessary flow for removing CO2, also had to pass through the biofilter.
The Uni-Aqua multi-step biofilter system secures a very stable water quality,
with minimal fluctuations of Ammonia. Further the multi-step biofilter
effectively adds control of the pathogen situation.
The multi-step filter is the only safe option when dealing with seawater.
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CO2 Stripper
Carbon dioxide is removed in the CO2 stripper.
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Production facility
The halibut farm for 500 gram halibut at Dønna Norway.
The facility has two units, each of 450 kg feed per day
capacity, and is equipped with automating grading facilities etc.
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Fish in circular tank with two layers
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The halibut are grown in two layers. Low layer at 1,3 meter,
up to 10 meter visibility at full feed capacity.
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Growth model
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Growth of halibut - based on experience with UNI-Aqua's technology.
Cage transfer takes place after 10 months growth.
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Using recirculation technology means that production time from 5
gram to harvest at 7 Kg will be reduced with more than 50%.
This means saving on capital costs/standing stock, and a
severe risk reduction in general.
UNI-Aqua recommends the following production conditions
- Ammonia (NH3) < 0.02 mg/l*
- Nitrate (NO3-) < 50 mg/l (NO3--N)
- Nitrite (NO2-) < 1 mg/l (NO2--N)**
- Carbon dioxide (CO2) < 15 mg/l
- Oxygen (O2) 100% ±5%, never < 60% or > 120% saturation
- Hydrogen Sulfide (H2S) < 0.001 mg/l
- Chlorine residuals < 0.001 mg/l
- pH 7.2
- Temperature 12 degree C.
- Salinity 28-34 ‰
- Artificial light regime to avoid early maturation especially on males.
*Peak levels can be accepted up to twice as high levels,
if levels are very stable.
**Not too critical in seawater. During start up of biofilter,
levels of more than 8 mg/l can be found.
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