NO347811B1

NO347811B1 - Fish feed for treatment of ectoparasite infections

Info

Publication number: NO347811B1
Application number: NO20201004A
Authority: NO
Inventors: Bjørn-Inge Rikhardsen; Berit Anne Aas Rikhardsen
Original assignee: Norvet As
Priority date: 2020-09-11
Filing date: 2020-09-11
Publication date: 2024-04-08
Also published as: NO20230256A1; NO20201004A1; WO2022055360A1

Description

FISH FEED FOR TREATMENT OF ECTOPARASITE INFECTIONS

Field of the invention

The present invention relates to a floating feed comprising a chitin synthesis inhibitor, an avermectin, or a neonicotinoid as active ingredient for treatment of ectoparasitic infections in fish, especially of infections of salmonids by the ectoparasitic lice Lepeophtheirus salmonis.

Background of the invention

For the time being, Atlantic Salmon, Salmo salar, in the on-grown and postsmolt stages are mainly cultivated in open net-pens/cages, which are submerged in the sea. These net-pens are dependent on a free-water exchange with their surroundings through the net to guarantee a sufficient supply with fresh and oxygenrich water at any time. The water exchange in and out of the cage will be affected by local currents, waves, wind, and tides. Open sea cages have the draw back that they are not isolated from the environment. Thus, small particles and planktonic stages including poisonous microalgae, or the infectious stages of salmon lice, virus, and bacteria can pass with the water through the net meshes. On the other side, excrements, non-eaten feed residues, chemicals, and agents used in farming processes and for treatment of fish and any other small particulate waste may be transported with the water current out of the cage and will be spread to the surroundings. Discharges from aquaculture production are recognized as a major problem due to potential negative impact and effects on the environment such as the water quality, sediments and wildlife in vicinity to the aquaculture site.

Parasitic infections in intensive farming of fish such as the Atlantic salmon, Salmo salar, are one of the main problems in salmon aquaculture. In particular infections by ectoparasitic copepods Lepeophtheirus spp. and Caligus spp.

Especially the Salmon lice Lepeophtheirus salmonis, as well as the sea lice Caligus elongatus are a major challenge for the industrial production. They are affecting fish welfare and health and as a consequence cause considerable economic losses in the production.

Salmon lice, Lepeophtheirus salmonis, is an ectoparasite, which belongs to the family Caligidae. Salmon lice have eight different stages in their life cycle with ecdysis in between. Adult salmon lice have eggs strings comprising developing embryos, which after hatching pass through a pelagic phase with two nauplii stages and one copepodite stage. These three stages are free-living planktonic stages. They are passively transported and spread by the water current and cause the spreading of the disease between fish and locations. The copepodite stage, lasting about 10 days at 12 ̊C, is the stage that finally infects the fish by attaching to its skin.

After attachment, the louse develops further and harms the fish by damaging/feeding on the skin and sucking its blood. Resulting skin lesions can additionally be infected by bacteria causing even more harm to the fish. Lice may also act as vectors for certain bacterial and virus infections such as the ISA-virus (Infectious Salmon Anemia virus).

Treatment of infected fish is important to keep control of the pest and there is a strong focus on the development of effective and environmentally sustainable methods for prevention and treatment of the ectoparasite infections. Pest management of lice infections has become a major focus area in salmon farming.

Salmon lice infections have previously mainly been treated using chemical drugs and agents for delousing, by bath treatment of infected fish. However, in the later years, lice have increasingly developed resistances against most of the commonly known agents used to combat lice infections. Moreover, many of the known agents represent a danger for the environment also affecting the ecosystem in vicinity to aquaculture sites.

Use of cleaning fish such as the wrasse are considered environmentally friendly and have proven to be effective in keeping down the infectious rates with salmon lice. The drawback of cleaner fish is their availability, high costs in their cultivation as well as a problematic fish welfare of these fish during use and handling.

Nowadays, also mechanical and physical methods for removal of lice are increasingly used as an alternative in the treatment of lice such as laser treatment, brushing, treatment with water nozzles, freshwater, warm water etc. A drawback of many of these mechanical and physical methods is the risk to harm the fish and the caused stress during the treatment and handling as they require a physical interaction with the fish in order to remove the attached lice.

Effective agents for prevention and treatment of lice infection may also be supplied as orally administered drugs. The least stressful and most effective method is to simply administer a drug comprised in a fish feed such as in form of a medicated feed pellet. Medicated feed pellets comprising an effective agent are thereby distributed in a suitable amount in the cage with the farmed fish to be treated and the feed pellets are consumed by the fish.

One problem with the oral administration of drugs in intensive salmon farming are feed losses. Feed pellets not readily consumed by fish sink and may also disintegrate. Feed pellets and smaller particles from the feed pellets may be passively transported out of the cage by currents. Thereby, the active agents will be spread to the surrounding water with all the negative consequences this may have on the food chain, wildlife and ecosystem. Moreover, they may accumulate in sediments and pollute the water over time. Floating nutritional fish feed offers improved digestion rate of shrimp and crab and further contributes to reducing feed waste to the surroundings (Effects Of Floating Fish Feed On Aquaculture, Fusmar, 2019).

An exact control of the amount of ingested medicated feed is very important not only to reduce losses, but also to obtain and ensure the desired therapeutic dose and thus also effect. Loss of medicated feed which sinks makes it very difficult to assess whether the fish have ingested the correct and effective amount of the therapeutic agent.

Insufficient therapeutic treatment with an agent is also problematic for the development of reduced sensitivity and resistances of parasites against a drug.

Many of the effective agents used today in treatment of salmon lice infections are belonging to the group of chitin synthesis inhibitors (CSIs, also called Chitinase inhibitors) which act by interfering with chitin formation and molting of the copepod. Known CSIs are diflubenzuron and teflubenzuron. Another effective agent used is the avermectin emamectin benzoate. Emamectin benzoate acts by inhibiting muscle contraction by causing a continuous flow of chlorine ions in the GABA and H-Glutamate receptor sites. These are highly effective in the treatment of salmon lice infections. For example, administration of SLICE containing 0.2% emamektin benzoate via feed at a dosage of 50 μg/kg bodyweight daily for 7 days demonstrated high efficacy in the treatment of L. salmonis compared to EKTOBANN containing 2g/kg of teflubenzuron (Ramstad et al., 2002). US 2017135956 discloses a method of eliminating, reducing, or preventing parasites in a fish population, such as sea lice, comprising feeding emamectin or a salt thereof to said fish population at a daily dose of 25 μg to 400μg/ kg fish biomass per day for a period of 3-14 days. The emamektin benzoate and fish oil are coated onto pellets. A disadvantage of these agents is that they are unspecific in their mode of action, which means that they not only affect the ectoparasitic lice infested to the fish, but also any other crustacean in case they were to be exposed to the drugs.

Another very effective drug for treatment of salmon lice infection is imidacloprid which is a systemic insecticide belonging to the class of neonicotinoids acting as a neurotoxin. JP2019055923 discloses parasite control agent comprising a synergistically effective amount of at least two active compounds selected from a number of compositions including imidacloprid and ivermectin. Like the CSIs this agent is not specific for only copepods, but will affect other organisms such as other crustaceans if these were to be exposed to the agent. US20150272931 discloses the use of another neonicotinoid, clothianidin, in feed for controlling sea lice in a fish population. A preferred in-feed treatment comprises a daily dose of 0.5 to 30 mg clothianidin per kg fish biomass for a period of time.

WO2015/198247 (US2017135956) discloses a fish feed comprising neonicotinoid, especially imidacloprid, for preventing and treating of parasite infections in fish such as salmon lice. Neonicotinoids are added to a premix, which is applied to feed granules or pellets consumed by the fish. The concentration of imidacloprid is preferably about 40 wt%, based on the total weight of the composition. One of the main problems addressed in WO2015/198247 is to provide a suitable mode of oral administration of the drug in fish feed, where the feed is accepted by the fish and consumed/ingested with reduced feed losses.

Chemicals such as delousing agents which are toxic to the targeted species may also be toxic to non-target species if they are released into the environment. Studies have shown that there is a risk of negative environmental effects when delousing agents enter the surrounding water. Many studies have addressed effects of neonicotinoids on terrestrial non-target species. There are also data available for aquatic systems, indicating that this is both, a problem in freshwater and marine aquatic systems. Many studies have been performed on aquatic crustaceans in particular in fresh water, which show that imidacloprid induces toxic effects at minimal levels in several aquatic organisms indicating a high sensitivity. This further supports the need for solutions where discharge of this type of unspecific drugs is minimized or excluded as much as possible.

Objects of the present invention

There is a need to provide improved methods for therapeutic treatments with neonicotinoids, avermectins and CSIs used in treatment of ectoparasitic copepod infection of fish, especially of salmon lice infection of salmon. The present invention aims at providing an environmentally friendly method for salmon lice treatment by oral administration of neonicotinoids, especially imidacloprid, avermectins and CSIs whereby discharges of active ingredients to the environment are minimised or substantially excluded. In particular, the present invention aims at a better control and reduction of feed loss and discharge of drug to the environment when orally administering named drugs to fish. There is a need to improve the control of feed intake when orally administered medicated feed is fed to fish to obtain the desired therapeutic effect. There is also a need to provide improved methods for oral administration of feed in order to reduce the risk for development of resistances and reduced sensitivity.

Summary of the invention

The present invention solves one or more of the above mention problems. The scope of the present invention is defined by the independent claims. Preferred embodiments are defined in the dependent claims.

Thus, the present invention relates in a first aspect to a medicated fish feed for use in preventing and treating of ectoparasite infections in fish. The medicated fish feed comprises as active agent a drug selected from chitin synthesis inhibitors, avermectins and neonicotinoids. The fish feed is a floating pellet having a positive buoyancy. The fish feed pellet is coated with a composition comprising said active agent and the fish feed pellet is additionally coated with a fish oil as a second coating.

Preferably, the active agent is selected from imidacloprid, emamectin benzoate, diflubenzuron, and teflubenzuron.

The floating feed pellet is preferably coated with a composition comprising said active agent and is additionally coated with a fish oil as a second coating. The fish oil serves as an attractant and serves as a barrier for leakage of the active ingredient. Preferably, the medicated feed is used for prevention and treatment of lice infections of salmonids, more preferred for Atlantic salmon Salmo salar.

Preferably, the ectoparasite is a species selected from Lepeophtherius spp. and Caligus spp., more preferably Lepeophtheirus salmonis.

A preferred daily dose administered to the fish is

0.5-4 mg per kg fish per day for 7-21 days for imidacloprid;

25-400 µg per kg fish per day for 7-21 days for emamectin benzoate;

1-100 mg per kg fish pr. day for 7-21 days for teflubenzuron; or

1-100 mg per kg fish per day for 7-21 days for diflubenzuron.

The medicated feed is particularly useful in the treatment of fish kept in an open net pen.

In a further aspect, the present invention relates to a medicated fish feed comprising as active agent a drug selected from Chitin synthesis inhibitors, avermectins and neonicotinoids, characterized in that the fish feed is a floating pellet with positive buoyancy.

Preferably, the active agent is selected from imidacloprid, emamectin benzoate, diflubenzuron, and teflubenzuron, most preferably imidacloprid.

Using a floating pellet has the great advantage that the pellet is not sinking down when not readily consumed by the fish. Feed pellets commonly used in salmon production, as well as the pellets disclosed in WO2015/198247, have the disadvantage of a negative buoyancy. Uneaten pellets may sink to the bottom or they may be taken by the water current and become unavailable for the fish in the pens. In the best case, unconsumed pellets are stable and will not disintegrate and can eventually be collected together with other waste in the bottom area of the cage.

However, on their way down they may also be transported by the water current out of the net cage and may be spread into the water surrounding the cage and environment. If the pellets are not stable, they may also disintegrate into smaller particles and/or the drug may leak out and is thereby spread into the environment. This can have a negative environmental impact on the wildlife where the drug is spread to. As these drugs are unspecific in their mode of action, they may affect other crustaceans and planktonic species which are likewise sensitive to the drugs.

Floating pellets have the advantages that they allow observation of the feeding behavior of the fish, improving the control of feed intake and that correct overall dosage is achieved. The use of floating pellets thus provides an improved control of administered amount of therapeutic agent. This is not only crucial to achieve an effective treatment, but it contributes to avoid reduced sensitivity and resistance over time for a defined drug.

Unconsumed feed floating at the surface can be easily collected and can be quantified or optionally even refed. Moreover, since medical feed is expensive considerable costs can be saved having a better control and reducing losses.

This is thus a new and more effective way and method to administer these unspecific orally administrated drugs to fish in intensive production and solves the above-mentioned problems occurring in particular in open net pens used today. Due to the large volumes and high number of fishes in the cages in today’s intensive production, discharges from medical treatment represent a threat to the ecosystem and environment.

Description of the diagrams

Embodiments of the present invention will be described below. The following diagrams are referred to in the detailed description, wherein:

Figure 1 shows time series of the maximum concentration of imidacloprid per kilogram sediments over time when including feed waste of 2 % (sinking feed pellets);

Figure 2 shows time series of the maximum concentration of imidacloprid per kilogram sediments over time when excluding feed waste (floating feed pellets).

Detailed description of the invention and of preferred embodiments The present invention will be further explained using the ectoparasitic copepod salmon lice Lepeophtheirus salmonis and the Atlantic salmon as an example. However, the skilled person will understand that the described medical feed and methods of treatment can also be used for other salmonids or fish species infected with these ectoparasites or other parasites which can be treated by medicated feed according to the invention. The invention will, however, be limited to the use in species which ingest feed at the water surface/upper water layers since feed particles according to the invention are floating.

Preferred ectoparasite infections to be treated by the medicated feed according to the present invention are ectoparasites belonging to Lepeophtheirus spp. and Caligus spp.

Preferred drugs comprised in the medicated feed are all belonging to the group of chitin synthesis inhibitors (CSIs), avermectins or neonicotinoids (i.e. imidacloprid). Preferred active ingredients for treating infections according to the present invention are imidacloprid, emamectin benzoate and di- and teflubenzurone. Emamectin benzoate is an avermectin, while di- and teflubenzurone are belonging to the group of benzoylurea. Particularly preferred is imidacloprid as active agent in the disclosed medicated feed according to the invention.

Features and production of the medicated feed

There are different methods for production of a medicated feed that meet the properties of the feed according to the present invention. In common for all methods and an essential feature of the present invention, is that the feed pellet comprising the drug for treating ectoparasite infections is a floating pellet i.e. a feed pellet or particle which has at least a neutral buoyancy and more preferably a positive buoyancy.

Production of floating feed and medicated feed

Use of floating feed for feeding fish or aquatic organisms is well known as well as different methods to produce feed particles with a neutral or positive buoyancy. Floating characteristics of feed pellets are most commonly adjusted by regulation of the expansion rate of the pellet during its production. The expansion rate of the pellet both depends on ingredients used in the feed formulation, in particular the amount and source of starch, as well as the temperature or the steam pressure in front of the die. High temperature in the process result in more expansion, a low bulk weight and a floating pellet. Typical standard methods used to produce floating fish feed pellets are described in teaching books in the field and are thus well known to the skilled person in the field.

A feed mash formulation of dry (without or with liquid ingredients) can be extruded into a highly expanded floating aquatic feed (320-500 g/l) or a sinking pellet (5550-700 g/l) by adjusting temperature and steam pressure during the extrusion process. One description of the procedure for production of highly expanded floating aquatic feeds describe that it requires 200-250 square millimeters of die open area per metric ton of throughput. Expansion of the extrudate after it passes through the die results in a product with a bulk density of 320-400 grams per liter and 21-24 % moisture (Feed manufacturing Technology IV, 4<th >edition, American Feed Industry Association 1994; manufacturing of floating pellets disclosed on p.514). An example, how a suitable floating feed can be produced is also disclosed in a recent publication by Welker et al.2018 (Welker, T.L., Overturf, K., Snyder, S., Liu, K., Abernathy, J., Frost, J., Barrows, F.T., 2018. Effects of feed processing method (extrusion and expansion-compression pelleting) on water quality and growth of rainbow trout in a commercial setting. Journal of Applied Aquaculture). The described method for the production of floating and sinking feed uses an extruder with five barrel sections. The floating feed was produced at 119<o>C with the last section heated up to 131<o>C. The retention time was 18 s and screw speed was 544 rpm. The same receipt was produced into a sinking feed by processing the mash at 116<o>C in the barrel but cooling the last section to 17<o>C. The retention time in the extruder was 18 s and the screw speed was reduced to 509 rpm.

The fish feed has otherwise standard compositions known in the art and will be adapted to be suitable for feeding of salmon or any other fish species to be treated. The same applies to the chosen size of the pellet which will be adjusted to be suitable for oral administration to fish.

There are different methods how the medication according to the present invention can be added to the floating feed pellet (also called feed carrier).

In a preferred method the drug can be added to a feed carrier which is a defined fish feed used to produce the medicated feed pellet. The pellet will thereafter be coated by a fish oil. Typical steps are:

The feed pellet/carrier is controlled, weighed, and added to a mixer.

The active pharmaceutical ingredient (API) is controlled, weighed, added and mixed together with the medicated feed carrier in the mixer.

Final step is the spraying (coating) of fish oil through nozzles in the mixer. Suitable mixing times are defined for each step. Before the batch leaves the mixer, samples for analyzes are taken out by a separate sample collector. Each batch has to be analyzed for its API content confirming that the medicated feed is within the specifications.

Vacuum coating of feed pellets

Vacuum coating is a standard process in the production of high energy aquatic feeds and is also used in the production of medicated feeds. This is a method which is well known to the skilled person. Heat sensitive nutrients can also be applied in post extrusion coating operations.

Extruders are used to produce the pellets in order to get the right physical properties of an expanded pellet. The expanded pellets contain pores which can be filled with oil during the vacuum coating process. The dried pellet, containing about 8-10% moisture is transferred to the vacuum coater. The vacuum coater is an air tight mixer e.g. ribbon or paddle type mixer. Rotating drums or devices inside the drum, will make sure that all pellet surfaces are exposed to a mist of oil sprayed into the drum through nozzles. A negative air pressure is generated inside the drum using a vacuum pump removing the air. When vacuum is gradually applied to the airtight closed drum, the pressure drops and the air bubbles are leaving the pellets, ascending through the layer of oil to the top. The constant mixing of

pellets distributes the oil on all pellet surfaces. By slowly opening the air inlet the negative pressure will gradually disappear until the pressure in the drum equals to the surrounding air pressure. Oil is gradually sucked into the pellet as vacuum is released.

The vacuum coating principle can also be used for application of additives or to produce medicated feed. Different components can be applied in layers to the pellet by use of double coating.

Preferred dosage regimes (daily dose) comprised in the medical feed according to the invention

Imidacloprid:

Dosage of 0.5-4 mg per kg fish per day for 7-21 days.

Emamectin benzoate:

Dosage 25-400 µg per kg fish per day for 7-21 days.

Teflubenzuron:

Dosage 1-100 mg per kg fish pr. day for 7-21 days.

Diflubenzuron:

Dosage 1-100 mg per kg fish per day for 7-21 days.

The above given dosages are given per kg body wet weight of fish.

Feeding to the fish in a fish cage

The floating pellets can be distributed to the fish by suitable known feeding distributors either at the water surface or under the water surface. Unconsumed pellets will float up. If not consumed over longer periods, pellets can be collected and quantified.

The medicated feed can be feed out continuously or batchwise. Preferably the feed is supplied continuously to the fish during the whole day.

Experimental section

In an Environmental Risk Assessment (ERA) for imidacloprid, it was simulated a scenario where 2% of the medicated non-floating feed with imidacloprid as active agent sank down to the sediment as feed loss and a scenario where medicated floating feed pellets according to the present invention with imidacloprid as active agent where used without any feed losses. The feed was administered for 7 days (March 2 to March 9) and the concentrations in the sediments under the net cage was assessed until April 20.

Even with this low amount of feed loss of only 2 %, differences in the accumulation rate of imidacloprid in the sediments were found over time for the different feed types (see figure 1 for scenario with 2 % feed loss and figure 2 without feed loss). Since feed losses in open-net aquaculture are typically about 10-15 % for sinking feed pellets, the accumulation of the agent in sediments will in reality be much higher as well as the potential negative impact on the ecosystem.

Claims

1. A medicated fish feed for use in preventing and treating of ectoparasite infections in fish, where the medicated fish feed comprises as active agent a drug selected from chitin synthesis inhibitors, avermectins, and neonicotinoids, wherein the fish feed is a pellet with a positive buoyancy.

2. A medicated fish feed according to claim 1, wherein active agent is selected from imidacloprid, emamectin benzoate, diflubenzuron, and teflubenzuron.

3. A medicated fish feed according to claim 1, wherein the feed pellet is coated with a composition comprising said active agent and is additionally coated with a fish oil as a second coating.

4. A medicated fish feed according to any of the preceding claims for use in prevention and treatment of lice infections of salmonids.

5. A medicated fish feed according to claim 4 where the fish is an Atlantic salmon Salmo salar.

6. A medicated fish feed according to any of the preceding claims, where the ectoparasite is a species selected from Lepeophtheirus spp. and Caligus spp., preferably Lepeophtheirus salmonis.

7. A medicated fish feed according to claim 2 wherein the daily dose administered to the fish is

0.5-4 mg per kg fish per day for 7-21 days for imidacloprid;

25-400 µg per kg fish per day for 7-21 days for emamectin benzoate;

1-100 mg per kg fish pr. day for 7-21 days for teflubenzuron; or

1-100 mg per kg fish per day for 7-21 days for diflubenzuron.

8. A medicated fish feed according to any of the preceding claims for use in the treatment of fish in a net pen.

9. A medicated fish feed comprising as active agent a drug selected from Chitin synthesis inhibitors, avermectins and neonicotinoids, characterized in that the fish feed is a floating pellet with positive buoyancy.

10. A medicated fish feed according to claim 9, wherein active agent is selected from imidacloprid, emamectin benzoate, diflubenzuron and teflubenzuron, most preferably imidacloprid.