Aquaculture Aeration In Scotland & Norway

Aquaerators have been tested by Marine
Harvest in their Lochleven fish farm in
Scotland and at Hjelmeland in Norway. .
Reports seen at the University of Stirling
indicate that improvements in DO levels at
6-12m helps the salmon to be less
lethargic, thus increasing their desire to
eat. Particularly as cooler water is brought
to the surface during the summer and 

warmer water during the winter, this 

should be an aid to growth.

OBJECTIVE

The overall objective of the Trials is to 

determine the advantages and

disadvantages of using the huge mixing

bility and bubble plume flow created by 

an AQUAEATOR to improve fish farm 

husbandry and enable the fish to grow 

faster in a more environmentally friendly atmosphere.


The main invention and research for the Aquaerator were based on producing the best possible rotating bubble plume using the least energy and no moving parts. The reason for the research was because the rotating plume constantly entrains water as it travels towards the surface. It is primarily a turbulent mixing device which decreases the density of the rising plume so that it stays on and flows over the surface.

SCOTTISH TESTS (on above video)

When discussed with Marine Harvest, the tests which they wanted to carry out were intended to reduce the salmon body fat by energetic swimming, followed by eating more and earlier harvesting. Other research was to include reducing sea lice, expelling jelly fish, also algae (oscillatoria) dispersion and reduction due to not being able to maintain its desired position.

Trials at Lochleven used a 130cfm compressor, at 80% capacity, enabling the bubble plume emitted by an Aquaerator at 20m depth to explode outwards as it rises to a surface diameter of 9.8m. Each plume surfaces under the central walkway at the junction of the nets of four pens, giving outward corner flows through each cage propelled by 13.4 tons of water per second rising from each Aquaerator. This resulted in increased salmon activity, leaping into opposing flows as shown in the accompanying film.

The flow of the Aquaerator creates a strong current within the fish farm simulating their natural up river instinct. When the system was turned on the fish started jumping out of the water, getting much more exercise, becoming less lethargic, healthier and therefore a more muscular fish which would increase the profit margins of the farm.

This reaction was also recorded with carp in Barcelona and rainbow trout in Bristol, where the Aquaeration System is switched off during fishing competitions. It has also been suggested that the flow of the Aquaerator will make sea fleas less able to pass so easily among the population.

NORWEGIAN TESTS

The aim of the Aquaerator was to minimise the temperature fluctuations in the farm. The Aquaerator is able to reduce the surface water temperature in summer and increase the surface water temperature in winter. This prevents the surface water from freezing in winter.
It is important to appreciate that the bubble plume is three dimensional and constantly changing in shape at each depth, as shown in the photographs, due to the huge entrainment of water, plus horizontal movement caused by any tide or current. The present temperature readings were taken along the line of the fish farm walkway over a short time cycle.


The chart below is based on temperature readings taken on the 4th and 5th of August and allows for 1-2 m of fresh water at the surface. This is important as it is difficult for the plume to break through to the surface, thus the maximum plume diameter is often well below it.


TEMPERATURE REDUCTION ACHIEVED BY AN AQUAERATOR AT 36m USING 40 L/s OF AIR

Depth

Temp ReductionPlume Max DiameterWater Discharged

1mm

6mm

10mm

12mm

15mm

20mm

30mm

-1.4c

-3.2c

1.5c

13.0 m

-1.6c

-0.6c

-0.0c


11.0 m


20 tons/sec





15 tons/sec







When the plume is at its maximum diameter for a certain depth, as detailed above, salinity will cause it to spread outwards and discharge water horizontally which using the recorded temperatures appears in the two listed positions. This table illustrates that with 40 L/s the main discharges are 15+20=35 tons/sec (3.0 million tons a day)T

ests in Norway proved the Aquaerator can reduce surface water in a fjord from 18ºC to 15ºC which is preferable for salmon in summer and melt the ice in winter using bedwater.

CONCLUSIONS

Aquaerator efficiency should be considered in terms of:-

  • Improvement at Fish Grading
  • Quantity of food consumed
  • Overall time in pens to achieve final weight
  • Observations of Sea Lice infestation
  • Quality of Salmon, less fat, more lean and muscular
  • Number of Mortalities
  • Dispersion of concentrated medical therapy administered within the fish food.

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