Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02612379 2007-12-14
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Device and method for aquaculture facilies for exposing
marine organisms to light
The present invention relates to a device in connection with aquaculture
facilities for
exposing marine organisms to light.
Today, light fixtures exist for placement under water for the purpose of
exposing marine
organisms to a light which corresponds as far as possible to the incoming
daylight from
the surface. The object is partly to affect the sexual maturation process and
partly to
increase growth rate and feed utilisation in the farming of salmon, cod and
other marine
io species.
It is known to use submersible metal halogen vapour lamps having a colour
spectrum
which mimics daylight, i.e., 5500 - 6000 K. Light sources of this type also
have
relatively low efficiency, i.e., they must be supplied with a great deal of
energy in order
to produce sufficient light quantity. The portion of the energy that does not
become
light is converted into heat and is lost (approx. 80 - 90%). In consequence of
the need
for a substantial energy supply, there will be a need for large cable cross-
sections and
sizeable power supply systems. Also, light sources of this type cannot be
intensity-
regulated.
Furthermore, light sources of this type do not allow for the fact that the
light has
different penetration power in water depending on its wavelength, and that the
pineal
gland of fish reacts differently to different wavelengths of light.
The light sources, metal halogen vapour lamps, which are used also have a
shorter
lifetime and poorly withstand the movement they are subjected to during
installation
under water in fish farming facilities. Metal halogen vapour lamps require AC
voltage
in the range of 230/240 V which may be a risk if the equipment is not handled
in a
prudent and safe manner.
According to the invention, there is therefore provided a device and a method
in
connection with aquaculture facilities for exposing marine organisms to light
as
disclosed in the independent claims, 1 and 6 respectively. The device is
characterised in
that it comprises a plurality of light-emitting diodes. Advantageous features
of the
device according to the invention are set forth in dependent claims 2, 3, 4
and 5.
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The method is characterised in that it comprises exposing marine organisms to
light
emitted from light-emitting diodes. Advantageous features of the method
according to
the invention are set forth in dependent claims 7, 8 and 9.
One advantage of the device according to the invention is that a far higher
proportion of
the input power is transformed into light. This results in cost savings
compared with the
prior art.
The device comprises encapsulated light-emitting diodes having a higher
efficiency than
io metal halogen light sources. These light diodes emit light in a narrower
part of the
visible spectrum, preferably from 380 - 600 nm wavelength range. This light
has greater
penetration power in water than wavelengths in lower and higher parts of the
spectrum.
In this wavelength range, the light has a greater capacity to suppress
melatonin
production in light-sensitive marine organisms such as salmon and cod.
Manipulation
of melatonin production is advantageous since it has an effect on the sexual
maturation
process. Furthermore, such effect results in increased growth rate and better
feed
utilisation.
2o Light-emitting diodes can be dimmed, i.e., light intensity can be adjusted
in relation to
the natural incoming light in the same part of the spectrum. This contributes
to a
reduction in energy consumption. By gradually dampening the light in relation
to the
incoming light from the surroundings, it will be possible to reduce energy
consumption
by fading out artificial light when daylight arrives.
The invention contributes to a substantial reduction in energy costs in
connection with
light control of marine organisms, e.g., fish.
The invention will now be described in more detail by means of examples, and
3o reference is made to the appended drawings, wherein:
Figure 1 shows plasma melatonin level in salmon post-smolt exposed to
different types
of light from light-emitting diodes.
Figure 2 shows the penetration power in seawater for different wavelengths of
light.
Figure 3 is a perspective view of the device according to the invention.
Figure 4 shows a longitudinal section of the device in Fig. 3.
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Figure 1 shows the plasma melatonin level (pg/ml) at different times ( 30
min) in
salmon post-smolt in saltwater tanks exposed to different types of light from
light-
emitting diodes. The figure shows the melatonin level on exposure to either
dark or light
blue, green, yellow or red light at night from a light diode-based underwater
light. The
figure shows that blue and green light are most efficient at suppressing the
production
of melatonin. Values were also measured at 10.00 hours which show the same
level in
all groups as at 16.30 hours, i.e., no differences between the groups (data
not shown in
the figure).
io Figure 2 shows the penetration power in seawater for different wavelengths
of
electromagnetic radiation from the sun, including visible light. The figure
shows that
the relative reduction in the penetration power on increasing water depth is
least for
light in the blue-green range with wavelengths from about 450 nm to about 540
nm
(blue and green light).
This shows that blue and green light emitted from light-emitting diodes have
two
advantages compared with light in the other parts of the spectrum. First,
these
wavelengths of light better suppress the production of the hormone melatonin.
Secondly, light of these wavelengths has better penetration power in seawater.
Figure 3 is a perspective view of the device 1 according to the invention. The
device 1
comprises a housing 2 with connector 3 for power supply and sinker 4. The
device 1
further comprises an element 5 on which light-emitting diodes 6 are mounted.
The
element 5 and the diodes 6 are enclosed by a glass housing 7 which is filled
with
silicone oil 8. The element 5 surrounds a transformer (not shown).
The glass housing 7 may be made of glass, but it is also possible to use other
materials.
It is important that the material is clear and lets light through in an amount
as close to
100% as possible. An advantageous material for the glass housing 7 is acrylic,
as this
3o also has the advantage of greater mechanical strength.
The glass housing 7 encapsulates the element 5 and the light-emitting diodes
6. The
glass housing 7 is filled with silicone oil to ensure that the light-emitting
diodes operate
in the correct temperature range, i.e., below 65 - 70 C. Silicone oil has a
high thermal
capacity and ensures that the temperature does not become too high.
Furthermore, the
silicone oil acts as leak-proofing as water can barely penetrate it. It is
also an advantage
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that silicone oil is not toxic. Since silicone oil is environment-friendly, an
accident
resulting in a leakage of silicone oil will not be harmful to the marine
organisms.
Figure 4 shows a longitudinal section of the device 1.
The element 5 may advantageously be configured as a cylinder with an octagonal
cross-
section. However, many other configurations may be possible. For example, the
element
5 may be spherical or be configured as a flat element. The housing 2 may be
made of
materials having a high specific gravity, thereby rendering a separate sinker
io unnecessary.
EXAMPLE
Results from a full-scale experiment in commercial offshore salmon farming
show the
following effects of illumination using the device 1 according to the
invention
compared with traditional metal halogen lighting and with a control group:
The control group had natural light from January until June, and in this group
13%
sexually mature fish were registered.
In the group exposed to light from metal halogen lighting (6 x 400W) from
January to
June, 2-3% sexually mature fish were registered.
In the group exposed to light from light-emitting diodes (6 x 50W, with a
wavelength of
485 nm) from January until June, 0% sexually mature fish were registered.
Sexually mature salmon is of such poor quality that it must be discarded or
sold at a
lower price. The experiment shows that a better effect, i.e., a smaller
proportion of
sexually mature fish, can be obtained by using just 13% of input power when
the device
with diodes according to the invention is used than when traditional metal
halogen
lighting is used.
In one advantageous embodiment of the invention, the device 1 also comprises a
sensor
which measures light in the desired spectrum and which, via feedback,
regulates the
light intensity from the light-emitting diodes by means of voltage regulation.
The light
intensity from the diodes is regulated automatically in relation to the
incoming light
from the surroundings. Thus, energy consumption is further reduced.
The sensor may be arranged on the device 1. It is also possible to mount the
sensor
above the water surface or at another point on the pen or cage.
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Tests have shown that biomass consisting of salmon in a bounded volume of
water such
as in aquaculture pens follow the light in the water. By using several devices
and a
means for controlling the position of the devices in the water and the
intensity of the
emitted light, it is possible to reduce the biomass density in the pen. This
will result in
5 better oxygen availability and thus better well-being of the fish.
In some tests it has been found that sea lice remain in the upper water
layers. By using
lighting devices in deeper water, it has been seen that it is possible to have
a lower
build-up of sea lice than if light is used above the water or high up in the
water mass.
