WO2024123189A1 - Frost cleaning of fishes - Google Patents

Abstract

The present invention relates to a new method of removing sea lice from aquacultured fish by frost cleaning. The method comprises exposing the fish to ultra-cold temperatures for a very short time and subsequently exposing the fish to mechanical treatment by flushing with seawater. Experiments have shown that the method very efficiently removes sea lice from the fish without adversely affecting the welfare of the fish.

Description

Title: FROST CLEANING OF FISHES

Field of the invention

The present invention relates to a new method for removal of sea lice.

Background of the invention

Sea lice are one of the main challenges in fish farming. Some methods have been developed to remove sea lice, but due to resistance (e.g. to hydrogen peroxide treatment), welfare and environmental challenges, the industry is looking for new alternatives.

Mechanical removal of sea lice by flushing with seawater has been under development in recent years to provide alternatives to medicinal lice removal. However, the effect of mechanical treatment is limited.

Thermal treatment in the form of heat has been tested with some success, but negative biological response from the fish to high temperatures makes such methods difficult from a welfare perspective.

In report no. 2019-8 from Institute of Marine Research of Frode Oppedal et al., «Avlusing med kaldt vann? - effektivitet og laksens velferd» (25.02.2019), methods using chilled seawater down to -1°C are described, but the effect is limited and the treatment time is long (from a few minutes to hours), which can affect fish welfare.

In report no. 9/2022 from Nofima of Svein Kristian Stormo et al., «Bedovelse ved ultra- lav temperatur», (31.03.2022), using ultra-cold temperature, -18°C, (supercold brine) to stun fish prior to slaughter is described. Experiments carried out with live fish (salmon) showed that a 30-second treatment immobilizes the fish (stunning effect), but the fish woke up after approx. 15 seconds in normal seawater - apparently unharmed. Removal of sea lice is not mentioned in this report.

Now, the present inventor has surprisingly found that by exposing fish to ultra-cold temperatures for a very short time, the lice's ability to grip the fish is weakened.

On this basis, the present invention has been provided. Summary of the invention

It is a main object of the present invention to provide a method of removing sea lice without the drawbacks of the prior art as discussed above.

These and other objects are obtained by the subject-matter as defined in the accompanying claims.

Definitions

It is to be understood that the herein disclosed invention is not limited to the particular component parts of the material described or steps of the methods described since such material and method may vary. It is also to be understood that the terminology used herein is for purpose of describing particular embodiments only and is not intended to be limiting.

It should be noted that, as used in the description and the appended claim, the articles "a", "an", "the", and "said" are intended to mean that there are one or more of the elements unless the context explicitly dictates otherwise. Thus, for example, reference to "a unit" or "the unit" may include several means, and the like. Furthermore, the words "comprising", "including", "containing" and similar wordings does not exclude other elements or steps.

The terms “sea lice” and “lice” as used herein have the same meaning and are used interchangeably in the present disclosure.

The term “fish” as used herein means aquacultured fish, including salmonid fish and other fish species.

The terms “mechanical treatment” and “mechanical washing” as used herein have the same meaning (i.e., flushing with seawater), and are used interchangeably in the present disclosure.

The term “frost treatment” as used herein means treatment at ultra-cold temperatures (i.e., temperatures in the range of from -5°C to -50°C) for a very short time (i.e., time periods in the range of 0.5 second to 5 seconds).

The term “frost cleaning” as used herein means frost treatment and subsequent mechanical washing.

The term “supercold” as used herein in the context of aqueous solutions such as brine, means that the temperature of the solution is below the freezing point of water without becoming solid (i.e., the solution remains in liquid form) and sufficiently low to form ice crystals in parasitic organisms living in seawater.

Figure 1 : Shows the number of pre-adult lice on one individual salmon before and after frost treatment for 1 second and subsequent mechanical washing according to the invention.

Figure 2: Shows the number of pre-adult lice on one individual salmon before and after frost treatment for 4 seconds and subsequent mechanical washing according to the invention.

Figure 3: Shows the number of lice on one individual salmon before and after mechanical washing only (control).

Figure 4: Summary of reduction of lice on salmon for three different groups (n=5 each):

1. Frost treatment for 1 second and subsequent mechanical washing,

2. Frost treatment for 4 seconds and subsequent mechanical washing, and

3. Control (mechanical washing with no prior frost treatment).

Figure 5: Summary of reduction of lice on salmon, a repeat experiment with a higher number of fish in the groups (n=10):

1. Frost treatment for 1 second and subsequent mechanical washing, and

2. Control (mechanical no prior frost treatment).

Detailed description of the invention

In a first aspect, the present invention provides a method of removing sea lice from aquacultured fish, comprising exposing the fish to ultra-cold temperatures for a very short time and subsequently exposing the fish to mechanical treatment by flushing with seawater.

In a preferred embodiment of the invention, the method is for removing sea lice from aquacultured salmonid fish species, such as salmon and trout. The method is also applicable to all other aquacultured fish species, such as cod.

In an embodiment of the invention, the ultra-cold temperatures are in the range from -5°C to -50°C, preferably from -10°C to -25°C, and more preferably from -17°C to In another embodiment of the invention, the very short time is from 0.5 second to 5 seconds, preferably from 0.5 second to 2 seconds, and more preferably from 0.5 second to 1 second.

In an embodiment, the fish is exposed to ultra-cold temperatures by passing through a supercold aqueous solution not containing components harmful to the fish.

The supercold aqueous solution is typically a supercold brine. Examples of brines applicable in the present invention are aqueous solutions of NaCl, MgCh, and CaCh. NaCl brine is capable of theoretically withstanding freezing to -21 °C, MgCh brine may withstand freezing to -33°C, and CaCh brine may withstand freezing to -50°C.

In a preferred embodiment of the invention, the supercold aqueous solutions is a saturated NaCl brine.

In one embodiment of the method, the fish are exposed to ultra-cold temperatures by passing through a supercold aqueous solution for a very short time. This can be done by transferring the fish from the seawater and dipping it manually in the supercold aqueous solution before relocating it back to seawater. The fish then undergo standard mechanical washing for removal of lice. For this embodiment, sea lice can be removed by water curtains or jets of water, such as a shower. This is taken advantage of by moving fish through a system with water curtains or jets to flush off lice. The fish are briefly passed through the flusher and detached lice are collected and then the fish are returned into the seawater.

Alternatively, in another embodiment of the method, the fish can be exposed to ultracold temperatures by passing through a device that sprays a supercold aqueous solution over the fish for a very short period of time. If the fish is guided through the device in one direction, the spray of supercold aqueous solution can be directed toward the fish in the opposite direction, so that the gills are less exposed to the supercold aqueous brine solution. The distance and speed at which the fish travel through the device can be adjusted to the appropriate treatment period. Like the manual method discussed above, the fish subsequently undergo standard mechanical washing for removal of lice.

The method according to the invention, causes ice crystals to form in the lice, which weakens the lice without affecting the fish. Thereby, removal of lice is scientifically improved by the subsequent mechanical treatment.

The invention is explained in more detail in the examples below. The examples are only meant to be illustrative and shall not be considered as limiting. Examples

Two different experiments on salmon smolt illustrate the effect of frost cleaning. Both experiments were carried out on heavily infected fish immediately after the fish was euthanized. The experiments suggest that the method according to the invention (frost cleaning) very efficiently removes sea lice from the fish.

Example 1

Three different groups of sea lice infected salmon smolt (n=5 in each group) were tested. Photographs of individual fish before and after sea lice removal was used to determine removal percentage. The fish in Group 1 was immersed in supercold NaCl brine (-18°C) for 1 second, while the fish in Group 2 was immersed for 4 seconds. Group 3 was not immersed in supercold brine (control). All groups underwent mechanical washing.

The results showed that both frost treatments (1 s. and 4 s.) have a very clear effect. The results showed that a very short (1 s.) treatment is as effective as the longer (4 s.) treatment. It is likely that formation of ice crystals within the sea lice influence its ability to stay attached to the fish. These results indicate that such ice crystal formation occur in less than a second at a temperature as low as -18°C.

Examples of individual fish before and after treatment are shown in Figures 1-3 for the three groups. Results for all the fish is summarized in Figure 4.

Example 2

In another experiment two different groups were compared; Group 1 : 1 second frost treatment, (-18°C) and Group 2: no frost treatment (control). In this experiment larger groups were used (n=10 in each group), and the frost treatment and subsequent mechanical washing were carried out as a randomized blinded trial. Here the results showed that frost treatment prior to mechanical washing increased removal percentage from 26.5+20.3% (control) to 86.1+7.9% (1 s. frost cleaning treatment). Results for all the fish are summarized in Figure 5.

The experiments show that the method of the invention very efficiently removes sea lice from the fish without affecting its welfare.

The person skilled in the art realizes that the present invention is not limited to the preferred embodiments described above. The person skilled in the art further realizes that modifications and variations are possible within the scope of the appended claims. Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the disclosure, and the appended claims.

Claims

C l a i m s

1.

A method of removing sea lice from aquacultured fish, comprising exposing the fish to ultra-cold temperatures for a very short time and subsequently exposing the fish to mechanical treatment by flushing with seawater.

2.

The method according to claim 1, wherein the ultra-cold temperatures are from -5°C to -50°C, preferably from -10°C to -25°C, and more preferably from -17°C to -20°C.

3.

The method according to claim 1 or 2, wherein the very short time is from 0.5 second to

5 seconds, preferably from 0.5 second to 2 seconds, and more preferably from 0.5 second to 1 second.

4.

The method according to any one of claims 1 to 3, wherein fish is exposed to ultra-cold temperatures by passing through a supercold aqueous solution.

5.

The method according to claim 4, wherein the supercold aqueous solution is a supercold brine.

6.

The method according to claim 5, wherein the supercold brine is selected from the group consisting of an aqueous solution of NaCl, MgCb or CaCh.

7.

The method according to claim 6, wherein the supercold brine is a saturated NaCl brine.

8.

The method according to any one of the preceding claims, wherein the fish is exposed to ultra-cold temperatures by transferring the fish from seawater and dipping it manually in a supercold aqueous solution.

9.

The method according to any one of claims 1-7, wherein the fish is exposed to ultracold temperatures by passing through a device that sprays a supercold aqueous solution over the fish. The method according to any one of the preceding claims, wherein the mechanical treatment is carried out by moving the fish trough a system of water curtains or water jets.

11.

The method according to any one of the preceding claims, wherein the fish is aquacultured salmonid fish.

12.

The method according to claim 11, wherein the fish is salmon or trout.

13.

The method according to any one of claims 1-10, wherein the fish is aquacultured cod.