Background of the Invention

Field of the Invention

The invention relates to aquaculture in general and more specifically a method and apparatus for controlling and preventing sea lice from attaching to fish in aquaculture facilities.

Background Art

From prior art one should refer to US20170094950 and the corresponding

WO2017044985 regarding ultrasonic eradication of sea lice on farmed fish. A method and device are disclosed for removing sea lice from salmon with use of a salmon herding passage tube, with ultrasound transducers on the periphery thereof, in a number sufficient to provide ultrasound treatment of the salmon being herded therethrough at a normal herding rate and at a sufficiently high enough frequency to kill the sea lice. This, however, is a treatment for when the fish is already infested with lice.

One should also refer to W01994017657 regarding removal of parasites from fish. Parasites are removed from fish by subjecting them to sound waves, preferably in a pipe interconnecting two floating netting containers. Again this is a treatment for when parasites already are attached to the fish.

In addition one should refer to GB2309621 regarding reducing parasite infestation in aquatic creatures. A method is disclosed for reducing parasite infestation or damage to aquatic creatures includes means for generating transitional cavitational events in the medium surrounding the creatures so as to produce biological changes which affect their development cycle and life expectancy. Also this is a treatment for infested fish with the added stress that cavitation causes.

Furthermore one should refer to W09417657 regarding removal of parasites from fish. An apparatus is disclosed for the removal of parasites from fish comprising a chamber for containing water in which fish to be treated are swimming and means within the chamber for generation of sound waves to be transmitted through the water. Also disclosed is a method of removing parasites from fish, the method comprising subjecting parasitized fish swimming in a chamber to sound waves having characteristics to cause dislodgement of parasites from the host fish for a time sufficient to dislodge the parasites, and removing the parasite-free fish from the chamber. Again this this is a treatment for when parasites already are attached to the fish. Also disclosed is the use of sound waves for creation of micro-vortices and/or turbulence in the water in which the fish are swimming, in order to cause shear damage to the parasites, particularly when they are soft due to ecdysis. While this is directed to eliminating free swimming parasites not yet attached to fish, it is a different way of killing parasites than the present invention.

Accordingly, a method and a system to overcome the problems mentioned above is needed.

Summary of the Invention

Problems to be Solved by the Invention

Therefore, a main objective of the present invention is to provide a method and apparatus for controlling and preventing sea lice from attaching to fish in aquaculture facilities.

Means for Solving the Problems

The objective is achieved according to the invention by a method for preventing and controlling sea lice in aquaculture facilities as defined in the preamble of claim 1 , having the features of the characterising portion of claim 1 , and a system for preventing and controlling sea lice in aquaculture facilities as defined in the preamble of claim 6, having the features of the characterising portion of claim 6.

A number of non-exhaustive embodiments, variants or alternatives of the invention are defined by the dependent claims.

In a first aspect a method for controlling and preventing sea lice from attaching to fish in aquaculture facilities, the facility comprising a volume of water comprising sea lice in various stages of development that are not yet attached to fish. The facility further comprises a system which comprises a control unit and at least one transducer positioned within the volume of water. The method comprises steps for operating the control unit to generate a signal applied to the transducer so that the transducer emits ultrasonic energy into the volume of water, wherein the ultrasonic energy has a frequency selected to match the self-resonant frequency of the sea lice causing stress.

By exposing sea lice to carefully designed ultrasonic waves that activate their self resonances, and maintaining intensity and duration adapted to exhaust their endogenous energy reserves - the sea lice lifecycle is broken by preventing the sea lice from seeking out hosts and attaching to a fish. Designed ultrasonic waves in this context means the waveform taking into account the properties and positioning of the transducer.

In a preferred embodiment the frequency is in frequency range 500 kHz - 10 MHz.

In a more preferred embodiment the frequency is in frequency range 1 - 5 MHz.

In a further embodiment the control unit generates a wideband (multi-frequency) signal in the frequency range 500 kHz - 10 MHz.

In another preferred embodiment the control unit generates a sweeping signal in the frequency range 500 kHz - 10 MHz.

In a second aspect a system for controlling and preventing sea lice from attaching to fish in aquaculture facilities is provided, the facility comprising a volume of water comprising sea lice in various stages of development that are not yet attached to fish. The system comprises a control unit and at least one transducer positioned within the volume of water, wherein the control unit is provided to generate a signal that is applied to the transducer so that the transducer emits ultrasonic energy into the volume of water, wherein the ultrasonic energy has a frequency selected to match the self-resonant frequency of the sea lice, causing stress..

In a preferred embodiment the at least one transducer is positioned at a periphery of a fish farming cage. In another preferred embodiment the at least one transducer is positioned inside a fish farming cage.

In yet another preferred embodiment the at least one transducer is positioned outside a fish farming cage.

The present invention attains the above-described objective by a method and a system for emitting ultrasonic energy having a frequency selected to match the self resonant frequency of the targeted parasites.

Effects of the Invention

The present invention comprises a technological advantage over known systems and methods by use of ultrasonic energy having a frequency selected to match the self-resonant frequency of the targeted parasites. The effect is that the ultrasonic energy prevents the parasites from attaching to the fish, rather than attacking parasites that already have attached themselves to the fish.

These effects provide in turn several further advantageous effects:

it makes it possible to avoid treating the fish with the chemical/mechanical stress this involves, and

it makes it possible to avoid the use of medicine with the environmental side effects and ultimately immunities this involves.

Brief Description of the Drawings

The above and further features of the invention are set forth with particularity in the appended claims and together with advantages thereof will become clearer from consideration of the following detailed description of an [exemplary] embodiment of the invention given with reference to the accompanying drawings.

The invention will be further described below in connection with exemplary embodiments which are schematically shown in the drawings, wherein:

Fig. 1 shows a volume of water comprising fish, parasites, and a system for preventing parasites from attaching to fish.

Description of the Reference Signs

The following reference numbers and signs refer to the drawings:

Detailed Description of the Invention

Various aspects of the disclosure are described more fully hereinafter with reference to the accompanying drawing. This disclosure may, however, be embodied in many different forms and should not be construed as limited to any specific structure or function presented throughout this disclosure. Rather, these aspects are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Based on the teachings herein one skilled in the art should appreciate that the scope of the disclosure is intended to cover any aspect of the disclosure disclosed herein, whether implemented independently of or combined with any other aspect of the disclosure. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, the scope of the disclosure is intended to cover such an apparatus or method which is practiced using other structure, functionality, or structure and functionality in addition to or other than the various aspects of the disclosure set forth herein. It should be understood that any aspect of the disclosure disclosed herein may be embodied by one or more elements of a claim.

The invention will be further described in connection with exemplary embodiments which are schematically shown in the drawings, wherein Fig. 1 shows a volume of water comprising fish, parasites, and a system for preventing parasites from attaching to fish.

Principles forming the basis of the invention

The following reference numbers and signs refer to the drawings:

Infection with sea lice remains a key environmental constraint to the continued growth of salmonid aquaculture industries worldwide, and it is becoming apparent that the existing combating methods are insufficient to prevent their increasingly irreversible damage.

Successful preventive measures have the potential to significantly reduce the abundance of lice and the number of delousing operations, and thus the resource intensive physical fish treatment - which also deteriorates the fish welfare

unacceptably. Development of new and efficient mitigating methods is therefore highly prioritized.

The current invention represents a novel, innovative and resource-saving technology in fighting sea lice, offering the following benefits:

• Environmentally friendly; safe for both fish and the environment

• No chemicals, and hence preventing the sea lice from developing resistance to this method

• Non-contacting, which reduces physical fish treatment and increases fish welfare

• Undemanding installation, use and maintenance

• Economically advantageous, both in acquisition and operation

• Preventive and sustainable

The sea louse Lepeophtheirus salmonis (L salomonis) has a direct life-cycle comprising eight morphologically distinct stages, with ecdysis in between each stage. The adult female sea louse extrudes a pair of tubular egg-strings, each normally between 5 and 20 mm long and 0.5 - 1 mm in width (-‘diameter’), which are filled with embryos. These remain attached to the female as they develop. A pre- infective planktonic naupliar stage hatches from the egg and leaves the string as a planktonic larva, directly into the water column. It moults to the second nauplius stage, from which the infective copepodid stage is reached. The duration of the egg phase varies from about 18 days at 5°C to about 6 days at 15°C of seawater temperature. Furthermore:

(1) Nauplius 1 stage lasts about 2 days at 5°C, and about 9 hours at 15°C of seawater temperature. The length of individuals in this stage is about 0.5-0.6 mm, and the width about 0.2 mm.

(2) Nauplius 2 stage lasts about 7 days and 1.5 days at these temperatures, respectively. The size is about the same as for nauplius 1.

The planktonic nauplii cannot swim directionally against the water current, but drift almost passively, although having the ability to adjust their vertical depth in the water column.

(3) The third stage is the infective copepodid stage, in which the length of the individuals is about 0.7 - 0.8 mm and the width about 0.2 mm. They could last about 15 - 20 days and 8 days at the respective seawater temperatures, before seeking out a host and attach to the fish.

(4 - 8) The remaining five stages comprise two chalimus stages, two pre-adult stages and one adult stage, all of which being parasitic with the sea lice attached to the fish.

Nauplii and copepodids are positively phototaxic and exhibit a daily vertical migration, normally rising during the day and sinking at night. They are responsive to light and salinity, and low salinities appear to have a greater effect on the planktonic stages than on the parasitic stages.

The copepodids actively seek out hosts over short distances to parasitize, and they respond to a variety of signals, such as shadows, movements and semiochemicals that could indicate host presence. Over larger scales copepodids are also mostly passive, but they can maintain their depth more effectively than the nauplii, and they can swim over several centimeters to find hosts. They have been shown to be particularly responsive to low frequency water accelerations, such as those produced by a swimming fish. The time, and hence the distance, over which larval lice are transported depends on maturation and mortality rates.

These three planktonic larval stages of the sea lice are entirely lecithotrophic (‘yolk feeding’), relying for energy upon maternally derived lipid reserves stored in the cells of the developing gut of the nauplii, and ultimately in lipid vesicles within the gut epithelium, until the infective copepodids find and attach to a host, where they moult to the parasitic chalimus 1 stage.

It has been revealed that the mean endogenous lipid content decreases by approximately 95% in copepodids between 7 and 20 days post hatch. Thus, the viability and longevity of infectivity among free-swimming copepodids depend closely on the rate of consumption of their endogenous lipids.

A decline in their finite energy reserves has been associated with reduced infectivity among copepodids aged 3 to 7 days old. Settlement experiments with aged copepodids, at both summer and winter sea water temperatures, have shown a statistically significant difference in settlement ability between the older (7 days) and the younger (1 - 3 days) age groups. However, once attached and settled on the host, the rate of development and initial survival has been found not to be statistically different from that of the other age groups being examined.

Hence copepodid durability, as a free-swimming stage, and its ability to infect the host in appreciable numbers one week after moulting to the infective stage will have important implications for the aquaculture industry. The current invention is primarily targeting the larvae in these vulnerable stages to exhaust their endogenous energy reserves before the copepodids are able to attach to the fish, and consequently rendering them harmless as infectious carriers. The plan of attack is also energy-based, relying on the power of high frequency vibrations as the method of approach.

The Universal Law of Vibration states that "Nothing in the Universe rests; everything moves and vibrates at one speed or another" (Ref. e.g. Albert Einstein: "Everything in Life is Vibration").

Accordingly, everything on the Earth vibrates, featuring resonance frequencies which can be activated by sonic waves, and each living organism on the Earth has a 'critical' resonance frequency, at which a particular sonic wave can do crucial damage to it by releasing its stored vibrational energy. This 'critical' frequency is being referred to as the object's natural frequency, eigenfrequency or self-resonant frequency. Most objects have multiple self-resonant frequencies.

As an example, a capable singer can break a crystal glass by singing notes at (one of) its self-resonance frequencies (like e.g. a famous commercial from the 1970s showed Ella Fitzgerald do), and the sonic wave intensity required to obtain such effects is normally not very high, particularly for small objects.

Accordingly, such self-resonance phenomena also apply to sea lice, where individuals at various stages of their lifecycle have different self-resonant

frequencies, depending on their morphology; size, shape and biological

characteristics.

The current invention relates to self-resonance activation methodologies and technologies primarily targeting individuals in the most vulnerable of the sea lice lifecycle stages, i.e. the free-swimming nauplii (1&2) and the copepodids (3), by exposing them to carefully designed ultrasonic waves that activate their self resonances, and maintaining intensity and duration adapted to exhaust their endogenous energy reserves - thus breaking the sea lice lifecycle by preventing the copepodids from seeking out hosts and attaching to a fish.

Various other sea lice of the Lepeophtheirus and Caligus genera are marine ectoparasites that feed on the mucus, epidermal tissue, and blood of host marine fish. Any and all of these species having similar planktonic development stages as the L salmonis are targeted by the present invention.

Moreover, the adult female sea louse egg-strings are also targeted by this invention, as the ovisacs’ width (-‘diameter’) is comparable to the size of the nauplii.

Additionally, the current invention is capable of mitigating biofouling on aquaculture facilities. As a justification of the latter feature, it should be noted that the blue-green algae (cyanobacteria) have gas vesicles that can be shattered by the vibrational self resonance activated by ultrasonic waves. Green algae do not have such vesicles, but their contractual vacuoles (connected with the function of the plasmalemma) can be damaged when subjected to ultrasonic waves at their self-resonance frequencies. This would prevent the algae from obtaining fluids and nutrients, and from controlling their internal pressure. Without these functions, single-celled algae die.

The inventor has realised that the volume of an adult louse is typically several thousand times larger than the volume of the planktonic stage. Thus 21 - 54 kHz ultrasonic waves disclosed in references 1 , 2, and 3 will not be affect the planktonic stage though this band will be effective against attached parasites. Extensive research has shown that much higher frequencies such as 500 kHz - 10 MHz will have an effect and that 1 - 5 MHz is preferred. The research also confirms that this stage can be killed by exhaustion at lower power levels or expend their energy reserves attempting to evade the ultrasonic waves, as opposed to killed instantly by higher power levels which could be negative for the fish one seeks to protect.

Best Modes of Carrying Out the Invention

The embodiment of the apparatus according to the invention shown in Fig. 1 comprises a volume of water 100 comprising fish 102 and parasites 104 such as sea lice in various stages of development that are not yet attached to fish. Also shown is a system 200 for preventing parasites from attaching to fish. The system 200 further comprises a control unit 210 and at least one transducer 220 positioned within the volume of water 100.

The control unit 210 generates a signal that is applied to the transducer 220 so that the transducer emits ultrasonic energy into the volume of water 100.

The frequency is determined by the eigenfrequency or self-resonant frequency of the targeted parasites 104, causing stress. This stress in turn prevents the parasites from attaching to the fish, and given sufficient time the parasites in their free- swimming stages will exhaust their endogenous energy reserves and die before being able to attach to a fish. The frequency is preferably in the 500 kHz - 10 MHz range, and most preferably in the 1 - 5 MHz range. The signal frequencies and power levels are carefully designed not to harm the fish or any other significant marine organism in the sea lice environments. Accordingly, the power output from a transducer is but a few watts, nominally 1 - 5 W, and thus being far below the limits for creating any form of cavitation effects whatsoever.

It is beneficial to position transducers over an extended area in order to maintain a high stress level in the parasites.

The transducers are preferably attached to a submerged section of a buoy assembly or another similar platform structure, which can be located in any area assumed to comprise parasites, both within, at the rim of, or on the outside of fish-farming cages, without any intentional physical contact with the fish, and without requiring any auxiliary equipment such as pipes or similar facilities that the fish need to move through for delousing treatment.

The transducers are preferably positioned in an array configuration at the peripheral of the submerged section to provide approximate omnidirectional coverage of the pertinent surrounding water volume.

Alternative Embodiments

A number of variations on the above can be envisaged. For instance the control unit 210 can generate a wide band (multi-frequency) signal rather than a single frequency signal. The bandwidth can then extend from preferably 500 kHz to 10 MHz, more preferably 1 MHz to 5 MHz.

In yet another alternative for instance the control unit 210 can generate a sweeping signal rather than a constant frequency signal. The sweep can then extend from preferably 500 kHz to 10 MHz, more preferably 1 MHz to 5 MHz.

In another variation the system can be adapted to impair the adult female sea lice egg-strings and/or the embryos they are enclosing.

In yet another variation the system can be used also to mitigate biofouling on aquaculture facilities by attacking algae and similar marine organisms.

Verification In experiments about 500 lice larvae are placed in a 150 mL PET container filled with seawater that has been boiled and saturated with oxygen. During testing the dissolved oxygen (DO) is measured while applying ultrasonic waves. For comparison a similar test is performed without the use of ultrasonic waves. After about 10 hours there is insignificant change in DO and microscopic analysis shows that the larvae are destroyed using ultrasonic waves. Time to reduce the population by half is about 1 - 2 hours. Power levels around 1 mW/m ² were used, a significantly lower power level than for a sonar at an depth of 50 m.

Industrial Applicability

The invention according to the application finds use in the aquaculture industry, and particularly in fish farming.

References

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Veterinaerinstituttets rapport-serie 5--2016

2 Nofimia Rapport 63/2016:“Effekt av uitraiyd pa Iakseius”, desember 2016

3- Solvang-Garten, T., Hagemann, A , Svendsen, E.:“Uitraiyd mot lakselus:

Kontrollert testing av effekt dlrekte pa Iakselus”, SINTEF Rapport A28013, 22 desember 2016

4. Lavery, A.C., Stanton, T.K., Duncan E., McGehee, D.E. and Chu, D.:“Three- dimensional modeling of acoustic backscattering from fluid-like zooplankton”, J. Acoust. Soc. Am. 111 (3), March 2002

5. Lavery, A.C., Wiebe, P.H., Stanton, T.K., Lawson, G.L., Benfield, M.C. and

Copley, N.:“Determining dominant scatterers of sound in mixed zooplankton populations”, J. Acoust. Soc. Am. 122 (6), December 2007