WO2017123096A1

WO2017123096A1 - Method and device for removing parasites and microorganisms from anadromous fish

Info

Publication number: WO2017123096A1
Application number: PCT/NO2017/050009
Authority: WO
Inventors: Bjørn Erik JOHNSEN
Original assignee: Akvo As
Priority date: 2016-01-11
Filing date: 2017-01-11
Publication date: 2017-07-20
Also published as: NO20160044A1

Abstract

Method and device for removing parasites and microorganisms from anadromous fish (host) in a farming environment. At least one first container is provided with freshwater, whereas at least one second container is provided with brine having salinity higher than sea water. The fish is guided from net cage to the first container with freshwater and is kept there for a first period of time. Then, the fish is transferred from the first container to the second container having brine, and is kept there for a second period of time. Then the fish is returned to the net cage or the process may be repeated in that the fish is returned back to the first container. This stepwise exposure of parasites and microorganism disturbs their osmotic balance in a way that they drop off the host.

Description

Method and device for removing parasites and microorganisms from anadromous fish

The invention concerns a method and device for removing parasites and microorganisms from anadromous fish, according to the preamble of claim 1 and 10, respectively.

Background Salmon louse is a crustacean living as a marine parasite on salmon. The salmon louse is living of the mucosa, the skin and the blood of the fish and hence extract nutrition from the fish. Moreover, it causes sores that can cause infections and problems with the salt balance.

Salmon louse occurs on fish in fish raising farms and on wild fish and sea trout. When the fish enters the fjords to spawn in rivers, the lice follow along, but fall off when contacting fresh water in the rivers.

Norway has a large fish farming industry with an increasing number of fish in the sea, which again increase the number of hosts for salmon lice. Accordingly, it is an aim to keep the level of salmon lice in the fish farms as low as possible. The same applies for the fish farming industry in Chile, Scotland, The Faroe islands and Ireland, among others. Numerous attempts have been made to keep the level of salmon lice at a bay. One alternative is addition of chemicals to restrain the synthesis of chitin in the salmon lice and hence stop the ecdysis. Another alternative is preventive medication, but this has resulted in increasing resistance in the salmon lice, and spill of medicaments and chemicals to the environments. This typically applies to hydrogen peroxide (H₂0₂). Yet another approach has been use of wrasse that eats the salmon lice on the farmed fish.

It is known that fish farms located in fjords having large fresh water run-off, traditionally have had a low level of salmon louse, and that these in periods with reduced supply of fresh water caused by drought have experienced increased salmon louse levels. Experiments have also been conducted with use of fish carrier where fish was transferred from cage to fresh water in the fish carrier to expose fish for a period of time to remove the salmon lice. However, in commercial se this approach requires use of fish carrier in addition to a freshwater source.

NO 333846 Bl describes a treatment container for treatment of fish in fish farms. The container is provided with water from a reverse osmosis plant. Use of a tarpaulin has also been described, which wraps the upper part of the net cage thus creating an upper water layer having lower salinity. It should be mentioned that there are other parasites and microorganisms that also are relevant in context of the present invention, such as Neoparamoeba perurans. This parasite is the cause of amoebic gill sickness (AGD) in marine fish, which can result in decreased vitality and high mortality. Also this parasite is removable by treating the fish with fresh water. However, the fish farming industry still has failed to find sustainable effective methods to combat parasites.

Object

The object of the invention is to provide a method and device for releasing parasites and microorganisms like this from anadromous fish in open fish farming cages in sea, thus reducing mortality and reducing costs in combating salmon louse and AGD.

The invention

This object is achieved with a method according to claim 1 and a device according to claim 10. Additional advantageous features and embodiments appear from the respective dependent claims. Definitions

The terms "natural water environment" and "original water environment" as used in this context in connection with fish, are meant to refer to the water environment where the fish normally resides. A fish farming cage floating in sea is comprised by a definition like this, but is not limited to that. The definition also comprises other water environments where fish is kept for a longer period of time.

The term "fresh water" is in this context meant to refer to water having low salinity compared to sea water, such as fresh water produced by reverse osmosis.

The term "permeate" refers to water with low salinity produced by reverse osmosis, such as water of potable water quality. The term "sea water" or "salt water" refers to water having a salinity corresponding to natural sea water.

The term "salt solution", "brine" or "burbot" refer to water having salinity higher than natural sea water, such as brine produced from reverse osmosis, or by mixing sea salt and water or sea water. The term "concentrate" is here meant to include water having high salinity produced by reverse osmosis.

The term "salt content" as used here, refers to water having content of cations and anions in the form of, e.g., Ca²⁺, Mg²⁺, C0₃, CI and F . General description

The invention is based on the task to remove parasites and microorganisms from anadromous fish, wherein the fish is transferred from its natural water environment to a water environment with freshwater and exposed to the freshwater for a certain period of time.

In accordance with the present invention, a method is provided that comprises the steps of: a) guiding the fish from its natural water environment to a first container containing freshwater having a first salinity, and keeping the fish in the first container for a first period of time in a magnitude of hours, b) transferring the fish from the first container to a second container with brine having a second salinity higher than sea water, and keeping the fish in the second container for a second period of time in a magnitude of hours, c) optionally repeating step b) above one or more times, and d) guiding the fish back to its natural water environment.

The manner how the brine has been produced is not important. In one embodiment the brine is produced from sea salt and water. In another embodiment the first container is supplied with freshwater (permeate) from a plant for production of freshwater from sea water by reverse osmosis (RO plant), whereas the second container is supplied with brine (concentrate) from the RO plant.

In yet another embodiment, the first container is supplied with the concentrate from the RO plant, whereas the second container is supplied with permeate from the RO plant. The fish is transferred between the natural water environment, such as a net cage onshore or in the sea, and the first container and/or the second container, and between the containers, by means of a fish pump. The retention time of the fish (first and/or second period of time) in the respective containers may vary with numerous factors, and desired degree of removal of parasites and microorganisms, and vary in a magnitude of hours, particularly at least about 1 hour.

The invention also provides a device for removal of parasites and microorganisms sensitive to freshwater, from anadromous fish.

According to the invention, the device comprises:

• at least one first container for water having a first salinity different from sea water,

• at least one second container for water having a second salinity different from the first salinity and different from sea water,

· means for transporting fish between the water environment natural to the fish and the first container, between the first container and the second container, and between the second container and the water environment natural to the fish, and

• an apparatus for production of brine, said apparatus comprising

o means for guiding freshwater from a freshwater source to the first container and the brine to the second container, or

o means for guiding freshwater from a freshwater source to the second container and the brine to the first container.

The device can be arranged on a fish carrier, on a floating stage or on another vessel, where pumps and pipes forward the fish from its natural water environment, e.g. a net cage, to one of the containers and between the containers with different salinity. The device comprises at least two containers, but can if desired exhibit three or more containers to accommodate water having varying salinity. For example, a first container can contain freshwater, a second container contain brine, a third container freshwater etc. Alternatively, e.g. a third container can contain sea water, a fourth container contain freshwater etc. A central aspect of the invention is that fish is kept in one container with water having a first salinity and transferred and kept in a subsequent container with water having a different salinity different from the first salinity to challenged and stress the osmotic balance in parasites and microorganisms to make them drop off the fish.

The means for transporting fish between the water environment natural to the fish and the containers, and between the containers, can be performed by pipes and pumps known per se for transporting fish. This transport will also contribute to parasites and microorganisms drop off from fish being transported. The fish can also be subjected to a mechanical treatment known from the prior art, such as water flushing, to remove parasites and microorganisms prior to, during, or after residency in the water containers with mutually different salinity.

In yet another embodiment, at least one of said first and second containers are arranged at least partially submerged in the sea and provided with permeate and concentrate, respectively, from an RO plant. These components can for example be arranged at a floating stage or a vessel, where the RO plant is arranged aboard whereas the containers are arranged fully or partially submerged adjacent to the vessel or floating stage

The device according to the invention can also be arranged at plants onshore for storage or raising fish. Detailed description

The invention is based on the basic idea that anadromous fish (host) infected by parasites and microorganisms sensible to freshwater, are exposed to water having a varying salinity in several steps, thus stressing the osmotic balance in the parasites and microorganisms further and make them drop off the host. Whereas the industry until now has been using methods by exposing the fish to freshwater for a certain period of time, typically in the magnitude of several hours, combined with mechanical affection from pumps and pipe transport, among other things, to remove parasites and microorganisms, the present invention provides a method and device where anadromous fish is further exposed to water having varying salinity in several steps before the fish is returned back to its original water environment, e.g. in the net cage. These steps of water treatment result in an increased number of changes in osmotic pressure which stress the microorganisms to a higher degree than the prior art.

In one embodiment, the treatment is performed by first exposing the fish to freshwater for a certain period of time (retention time), such as from 1 to 10 hours, and then exposing to brine for a certain period of time, such as from 1 to 10 hours, whereupon the fish is returned back to its original water environment, such as sea water in a net cage. This is in context of the present description denoted as a "treatment sequence".

The treatment sequence can if desired be repeated one or more times in that the fish again is exposed to freshwater for a certain period of time and then exposed to brine for a certain period of time, whereupon the fish is returned back to its original water environment. However, in a second embodiment the treatment sequence described above can be reversed in that the fish firstly is exposed to brine for a certain period of time and then exposed to freshwater for a certain period of time. As with the embodiment above, also this reversed treatment sequence can optionally be repeated one or more times before the fish is returned back to it original water environment.

The retention time for the fish may vary with numerous factors, such as difference in salinity between sea water and the salinity in the separate steps in the treatment sequences, or to what extent the fish is infected by parasites and microorganisms.

It shall in this connection be emphasized that the term "treatment" which is used here, does not refer to any form of therapy or diagnosis. However, treatment refers to an operation or activity which at least partly removes parasites and microorganisms from anadromous fish.

The exact salinity of the water environment is not limiting: an important aspect of the invention is that the difference in salinity between the respective water environments in the method according to the invention is sufficient to subject the parasites ant microorganisms to osmotic disturbance in several treatment steps.

In a second aspect according to the invention, a device is provided, for removal of parasites and microorganisms sensitive to fish, comprising at least one first container for water with a first salinity different from natural sea water, at least one second container for water with a second salinity different from the first salinity and different from sea water, means for transporting fish between the natural water environment for the fish, such as a sea pen, and the first container, between the first container and the second container, and between the second container and the original water environment, and an apparatus for production of freshwater and brine from seawater by reverse osmosis, to the first container, and the second container, respectively, or to the second container and the first container, respectively.

In accordance with the invention, the brine from production of fresh water by reverse osmosis is therefore used in the treatment of anadromous fish to remove parasites and microorganisms from the fish, contrary to prior art which disposes of this brine to the sea without making further use of it.

In production of water from a plant based on reverse osmosis ("Reverse Osmosis" - RO), one will, depending on numerous factors, such as membrane quality, be able to produce a permeate (freshwater), for example with a salinity of about 0.16 g/L, a concentrate (brine), for example with a salinity of about 74 g/L, from sea water with a salinity of about 37 g/L. These figures indicate that the plant exemplified above has a yield of about 50 % and can produce for example 1 m³ freshwater and 1 m³ brine from 2 m³ sea water.

This difference in salinity in the permeate and the concentrate, respectively, will be more than sufficient to infer the osmotic balance in parasites and microorganisms so that they become stressed and drop off the host (the fish). On the other hand, anadromous fish will also be able to withstand these variations and levels in salinity as stated above.

It can be interesting to note that whereas permeate from a RO plant has lower pH than the sea water, e.g. about pH 6.5, and hence would require buffering to obtain a sufficient water quality with respect to animal welfare, the concentrate will exhibit about the same pH level as the sea water. Hence, the concentrate in the principle can be used in the present method without additional pH adjustment. If the permeate and concentrate are used for a longer period of time, the pH of the water could be reduced because of for example C0₂ from the fish respiration.

The device of the present invention can be arranged onboard a floating stage/raft or a fish carrier, or another vessel. It can also be arranged stationary at net cages or arranged floating in or outside a net cage.

For example, a fish carrier already having two tanks and an RO plant for production of freshwater, can be modified in that one of the tanks is supplied with concentrate from the RO plant instead of permeate, and that means are established to transport fish between those two tanks. With a floating stage or similar, the device can be realized by arranging at least two containers on, or adjacent to, the floating stage, and arranging means to transfer fish between the sea and the containers, and means to transfer fish between the respective containers. The containers can be arranged upon the deck of the floating stage, or it can be fully or partly submerged in the sea. 'Example

Experiments were performed at a Norwegian aquaculture station to demonstrate the effect of the present method. The experiments were performed in two phases:

Phase 1: Salmon lice without host were exposed to freshwater (FW) and sea water added with salt (SW+) in numerous combinations.

Phase 2: Salmon lice on host (salmon) were exposed to freshwater and sea water added with salt in numerous combinations as in Phase 1.

Water quality

Brine having a salinity of 62 - 66% was produced by dissolving sea salt in natural sea water (SW). The salt was sea salt of nutrition quality and contained 99.223% NaCI, 0.125% Ca, 0.049% Mg, 0.381% S0₄, 3.5 ppm FE and 0.007 ppm Cu. A master batch for subsequent dilution was prepared the day before. On the test day brine with salinity in the range of 62 - 68% was prepared by diluting the master batch with freshwater. In comparison the sea water in the in the test range had a salinity of about 34%o. The salinity was measured with ATAGO hand-held refractometer, calibrated against pure freshwater and an accuracy of ±l%o. During the tests, oxygen saturation and temperature was measured with an YSI ProODO hand-held oxygen meter.

Test Phase 1

In Phase 1, tests were conducted where salmon lice without host was exposed to different combinations of freshwater and brine as described above. After the different treatments, the lice were returned to normal sea water.

The test was conducted in 2 liter plastic containers filled to 1800 mL. Salmon (about 500 g large individuals) infected by louse were killed by an overdose of benzocaine, and the lice were picked from the fish with a pincher and deposed directly into the plastic container. The lice that were used in the test were mature male and female lice. The egg strings were picked away from the female lice for further use in Phase 2 of the project. According to experience louse is affected to a small degree by benzocaine, and the sedation is therefore considered to be suitable for use in this experiment.

The ability of the salmon lice to self-motion and survival was registered in six different combinations of freshwater and brine. After the treatment, all lice which were included in the test were brought back to normal sea water, and number of surviving individuals was registered. All tests were conducted in duplicate, and natural sea water was used as control

The results from the tests in Phase 1 are summarized in Table 1 below:

Table 1

Result from louse without host to exposure of freshwater and brine

Treatment lh SW+ 0,5h FW + 0,5h lh FW + lh 2h FW + lh 4h FW 6h FW Control

SW+ SW+ SW+ SW

Replica 1 II 1 II 1 II 1 II 1 II 1 II 1 II

Number of motive louse start 18 18 20 18 18 18 18 18 17 18 18 18 18 18

Number of motive louse end 10 14 3 2 0 1 0 0 0 0 0 0 18 18

Number of motive louse without self- 8 4 17 16 18 17 18 18 17 18 18 18 0 0 motion

% louse without self-motion 44 22 85 89 100 94 100 100 100 100 100 100 0 0

Survivals after 24 hours 18 18 18 16 1 5 0 0 0 0 0 0 18 17

% survival after 24 hours 100 100 90 89 6 28 0 0 0 0 0 0 100 94

Test Phase 2

Salmon was infected with lice in a bath, and the lice were allowed to develop naturally on the salmon. The salmon used in the experiment had an average weight of 217 grams and were launched 6 months prior to infection. The fish was infected by a known amount of louse and kept in natural sea water with a salinity of about 34 %o and at 13-14°C in 20 days prior to exposure to freshwater/brine according to the present invention.

The tests with exposure to freshwater/brine were performed in containers with a capacity of 500 L, filled with 250 L. In the fresh water treatment, the water replacement was adjusted to 10 L per minute, which gave an oxygen saturation of about 90%. The exposure to freshwater/brine (sea water added with salt in the range of 63-66%o) was performed in 500 liters containers with stagnant water (250 liters), which was supplied with oxygen if needed.

The results from the tests in Phase 2 are summarized in Table 2 below.

Table 2

Result from exposure of louse on host (salmon) to freshwater and brine

Treatment lh SW+, 2 rounds lh FW, lh SW+ 2h FW, lh SW+, 2 rounds 4h FW, lh SW+, 2 rounds 6h FW, lh SW+

Number of fish 20 20 21 20 19 20 20 20

Number of louse start 23 22 23 20 19 21 23 23

Number of louse end 6 2 1 3 0 0 0 2

Number of louse lost 17 20 22 17 19 21 23 21

% reduction 74 91 96 85 100 100 100 91

% reduction total 82 96 92 100 91

Summary

The results of the experiments above show that substantially all louse can be removed from the fish by exposing the louse to freshwater for about 1 hour and then to brine for about 1 hour. This is a substantial improvement compared to the known de-lousing methods by exposure of louse on host in a fish carrier, for example, which require about 7 hours.

However, the values registered should not be interpreted as exact, and the delousing effect is expected to vary with other factors such as water temperature and mechanical influence from pumping of fish for example.

Claims

1. Method for removing parasites and microorganisms from anadromous fish, wherein the fish is transferred from its natural water environment in sea water to a water environment with fresh water and exposed to the fresh water for a specified period of time, characterized in a) guiding the fish from its natural water environment in se water to a first container containing freshwater having a first salinity, and keeping the fish in the first container for a first period of time of a magnitude of hours, b) transferring the fish from the first container to a second container with brine having a second salinity higher than sea water, and keeping the fish in the second container for a second period of time of a magnitude of hours, c) optionally repeating step b) above one or more times, and d) guiding the fish back to its natural water environment in sea water.

2. The method of claim 1, characterized in that the first container is supplied with freshwater (permeate) from a plant for production of freshwater from sea water by reverse osmosis (RO plant) and that the second container is supplied with brine (concentrate) from said RO plant.

3. The method of claim 1, characterized in that the first container is supplied with freshwater from a source of freshwater, particularly onshore, and that the second container is supplied with brine produced from sea salt mixed with freshwater or sea water.

4. The method of claim 1, characterized in that the fish is exposed to freshwater in the first container for a first period of time of about at least one hour, particularly about 1-2 hours.

5. The method of claim 3, characterized in that the fish is exposed to brine in the second container for a second period of time of about at least one hour, particularly about 1-2 hours.

6. The method of any one of the claims above, characterized in using brine with a salinity within the range of about 60 - 75%o, particularly 62 - 68%o.

7. The method of claim 1, characterized in that the fish is transferred between the natural water environment and the first container and/or the second container, and between the containers, by means of a fish pump.

8. The method of any one of the claims 1 to 7, characterized in that the steps a) and b) are reversed, whereby the fish firstly is guided to the second container with brine and then further to the first container with fresh water.

9. The method of claim 8, characterized in that step b) is repeated several times.

10. A device for removing parasites and microorganisms, sensitive to freshwater, from anadromous fish, characterized in that the device comprises

- at least one first container for water having a first salinity different from sea water,

- at least one second container for water having a second salinity different from the first salinity and different from sea water, - means for transporting fish between the natural water environment of the fish and the first container, between the first container and the second container, and between the second container and the natural water environment for the fish, and

- an apparatus for production of brine, said apparatus exhibiting o means to guide freshwater from a source of freshwater to the first container, and the brine to the second container, or o means to guide freshwater from a source of freshwater to the second container and the brine to the first container.

11. The device of claim 10, characterized in that the device is prepared to be arranged on a fish carrier.

12. The device of claim 10, characterized in that the device is prepared to be arranged at a floating stage or a similar vessel.

13. The device of claim 10, characterized in that the device is prepared to be arranged at a fish farm onshore.