GB2360432A

GB2360432A - Method and apparatus for controlling fish lice populations

Info

Publication number: GB2360432A
Application number: GB0102596A
Authority: GB
Inventors: Norman Gault
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-02-02
Filing date: 2001-02-01
Publication date: 2001-09-26
Also published as: GB0002280D0; GB0102596D0

Abstract

A method for controlling fish lice populations consists of providing a body for fish lice to lay their eggs upon and removing the body once the eggs have been laid. The body may either be cleaned and replaced, or replaced by a new one. Successive rounds of treatment lower the lice population. The body is opaque and has at least one hydrophobic surface. In a preferred embodiment the body is a planar piece of darkly coloured plastic (polyethylene or polypropylene), has a degree of flexibility and is buoyant in water. It may be anchored within a fish tank in various configurations and may include open ended channels which fill with water to provide ballast.

Description

2360432 AND APPARATUS FOR CONTROLLING FISH LICE POPULATIONS The present

invention concerns a method and apparatus for controlling fish lice populations in a body of water.

The fish lice Argulus are a common parasite of fresh water fish, and are becoming increasingly prevalent in fresh water fisheries in the United Kingdom.

There are several known methods of controlling or eliminating these parasites from any given body of water. Various chemical treatments may be used, but are often harmful to the fish population and the surrounding environment. Another such method involves draining the lake, having removed the fish, and leaving the lake fallow for a prolonged period in order to kill all of the parasites present. However, these forms of control are quite drastic and are not a practical or desirable solution to the problem, since the parasite eggs themselves may be capable of surviving the winter/fallow period and hatching in the spring.

Research associated with the present invention indicates that the eggs of this parasite are laid on hard surfaces within a body of water, such as concrete or wooden piers, rocks such as those forming the shore line, or the like. The eggs are laid by the female, generally during the warmer months of the year, and preferentially at a depth of less than 1 metre. It has been found in particular that the lice prefer dark nonturbulent regions in which to lay their eggs, which 2 then take between 10 to 50 days to hatch, depending on the water temperature.

Accordingly, a first aspect of the present invention provides a fish lice population controlling apparatus comprising a body that is predominantly opaque and has at least one surface that is hydrophobic. Preferably, the body is made from hydrophobic and predominantly opaque material.

When the body is wholly or partly immersed in a quantity of water containing fish lice, the gravid female fish lice are attracted to the body and lay their eggs thereon. The body, and therefore the eggs, can then be removed from the water.

Preferably, the body is substantLilly planar in form.

Preferably, the body is arranged to be buoyant in water. More preferably, the body is formed from material having a specific gravity less than that of water in which the apparatus is, in use, located.

Preferably, the body is flexible to allow complia nt movement of the body with water in which the apparatus is, in use, located.

Preferably, the apparatus further includes at least one ballast chamber. More preferably, the at least one ballast chamber is included in the body. Further preferably, said at least one ballast chamber comprises a channel having at least one open end arranged so that, in use, water substantially fills the channel.

3 Preferably still, the channel is open at both ends so that, in use, water may enter the channel by either end.

Preferably, the body comprises a plurality of channels.

Preferably, at least one surface of the body is formed from plastics material. More preferably, the body is formed from a plastics material. More preferably, the body comprises polypropylene. Alternatively, the body comprises polyethylene.

Preferably, the apparatus further includes an anchor coupled to the body and arranged to maintain the body at a desired location. More preferably, the anchor is coupled to the body by means of a - tether, the length of the tether being selectable to d(Aermine the disposition of the body relative to the surface of the water in which the body is, in use, located. Further preferably, the tether is selected to allow the body to be substantially parallel with, and adjacent, the surface of the water.

Preferably still, the length of the tether is selected to allow the body to be substantially perpendicularly disposed with the surface of the water. Preferably, the length of the tether is further selectable to determine the depth of the body below the surface of the water.

Preferably, at least one surface of the body is formed from a predominantly dark material. More preferably, the body is formed from a predominantly darkly coloured material 4 Preferably, the apparatus is arranged for controlling Argulus fish lice including Argulus coregoni, Argulus foliaceus or Argulus japonicus.

A second aspect of the invention provides a method of controlling fish lice populations, the method comprising: introducing a body into water containing fish lice; waiting until at least some fish lice have laid at least some eggs on the body; and removing the body from the water, wherein the body is predominantly opaque and has at least-one surface that is hydrophobic, the at least one hydrophobic surface being wholly or party immersed in the water during use.

Preferably, L-he body is introduced into the water such that all or part of the at least---one hydrophobic surface is in shade.

Preferably, the body is included in an apparatus according to the first aspect of the invention.

The invention further provides for the use of a body, that is predominantly opaque and has at least one surface that is hydrophobic, in the control of fish lice populations. In use, the at least one surface is wholly or partly immersed in water containing fish lice, the fish lice being attracted to lay their eggs on the immersed hydrophobic surface or part-surface Preferably, the body is as described according to the first aspect of the invention.

A specific embodiment of the invention is now described by way of example and with reference to the accompanying drawings, in which:

Figure 1 illustrates a perspective view of the apparatus; Figure 2 illustrates the apparatus of Figure 1 suspended substantially horizontally below the surface of a body of water; and Figure 3 illustrates the apparatus of Figure 1 suspended substantially vertically below the surface of the body of water, adjacent to a solid boundary.

Referring now to Figure 1, there-is illustrated an apparatus, generally indicated as 10, for controlling the fish lice populations present in any given body of water. The apparatus 10 comprises a body 11, or substrate, on which, during use, gravid female fish lice (not shown) lay their eggs. The illustrated body 11 is substantially planar and rectangular in form, although other regular or irregular shapes may alternatively be used. It is preferred for the body 11 to be substantially planar, or sheet-like, in form as this provides the body 11 with a relatively high surface area-to-volume ratio and reduces the degree to which the body 11 is disturbed by turbulence in the surrounding water. It will further be appreciated that any sized body 11 may be used to suit the particular application. The body 11 is formed from a water repellent, or hydrophobic, material. As is described in more detail below, the body 11 may alternatively have 6 at least one surface painted, coated or layered with a hydrophobic material. It is found that lice prefer to lay their eggs on hydrophobic material. Plastics, for example thermoplastics such as polypropylene, polyethylene, polybutylene, ethylene vinyl acetate, or polymethylpentene are particularly preferred for this purpose. Such material is generally light and easily handled, as well as being easily cleaned. Thermosets including Glass Reinforced Plastic (GRP) and epoxides are also suitable. It will be understood that other thermoplastics, thermosets or other predominantly hydrophobic materials may be used to form, coat or layer the body.

The body 11 is preferably arranged to be buoyant in water, for example fresh water of-the type normally found in fresh water fisheries, 1-dkes, rivers or reservoirs, or salt water (particularly brackish water). To this end, it is preferred to form the body 11 from a material having a specific gravity equal to or, more preferably, lower than the water into which the apparatus 10 is placed during use. Polypropylene, which normally has a specific gravity of between 0.9 and 0. 91, is particularly suitable for this purpose but other plastics such as polyethylene, which normally has a specific gravity of between 0.92 and 0.97; polybutylene, which normally has a specific gravity of 0.91; ethylene vinyl acetate, which normally has a specific gravity of between 0.92 and 0.95, or polymethylpentene, which normally has a specific gravity of 0.83, are also suitable. Polyvinylchloride, Polystyrene, or other plastics substances such as styrene acrylonitrile. polyamides, acrylics, 7 cellulosics, polycarbonates, polyesters, polyacetals, polyphenylene sulphide, and the like, with specific gravities of greater than 1.0, that have been aerated to confer buoyancy may alternatively be used. It is desirable to make the body 11 buoyant so that it does not sink should it become detached from its float (see Figures 2 and 3) - a sunken apparatus is difficult to locate and, if not retrieved, would provide a permanent egg-laying substrate for fish lice. Materials with a specific gravity of greater than water, for example polyvinylchloride (PVC)) may also be used but a float is required to prevent such a body from sinking. Alternatively, the apparatus may be suspended in the water by conventional means from, for example, a pier.

In an alternative embodiment (not illustrated) where the body is made from material hA-v-ing a specific gravity of grater than water, buoyancy may be conferred to the apparatus by means of one or more buoyancy chambers (not shown) which may, or may not, be integrally formed with the body. For example, if the body were formed from PVC, then the body may be formed with one or more sealed air chambers.

Preferably, the body 11 is sufficiently flexible to allow it, in use, to bend with the waves and any additional turbulence in the water i.e. sufficiently flexible to allow compliant movement of the body with a body of water around it. This helps to keep the body 11 in its, in use, allocated location and reduces the disturbance effects of turbulence in the water. However, the body 11 should not be so flexible that it folds, crumples or collapses in the water.

8 In the case where the body 11 is to be formed from a solid sheet of material, this may be achieved by appropriate selection of sheet thickness, the actual thickneSs selected depending on the material used to form the body. In the preferred embodiment illustrated in Figure 1, however, the body 11 comprises a fluted sheet of material in which a plurality of hollow, or tube-like, channels 12, or flutes, are formed between two plate-like surfaces 13, 15, (only surface 13 visible). The channels 12 may be formed by providing spaced-apart dividing walls 17 between the two surfaces 13, 15 (as shown in Figure 1) or by any other suitable means, for example, by corrugation. The channels 12 are open-ended so that, in use, they fill with water. The channels serve a s ballast chambers and provide ballast to stabilise the body 11 in the water by reducing the disturbance effects of turbulenc,.- By way of example only, a fluted polypropylene sheet of approximately 5mm in thickness is suitable for use as the body 11.

Referring now to Figure 2, in one mode of operation, the apparatus 10 is suspended substantially horizontally (i.e. substantially parallel with the surface 30 of the water) at, or just below, the surface 30 of the water, and maintained in this position by means of an anchor 16 connected by means of a tether 18 to an edge 24 of the body 11. A float 14 is preferably connected to the edge 24 of the body 11 and serves as a positional marker to allow the apparatus 10 to be easily located and retrieved. As the body 11 is preferably formed from a material having a specific gravity less than that of the water, for example polypropylene, the body 11, in this mode of operation, 9 remains substantially horizontally disposed adjacent the surface of the water. In this mode, the hollow channels 12 (seen in Figure 1) fill with water which acts as ballast to help maintain the apparatus 10 in 5 position.

Although in this embodiment the channels 12 are open at both ends, it will be appreciated that this need not be the case. For example, the channels 12 may be open at one end only and still be open to the surrounding water so that they fill, or substantially fill, with water when immersed. Further, the channels need not necessarily extend along the entire length of the body 11. Alternatively sbill, the channels may be closed at both ends and filled, or partly filled,(prior to use) with a suitable ballast material, for example water or sand. In general, the apparatus 10 preferably comprises one or more ballast chambers which may, or may not, be integrally formed with the body 11 and may, or may not, be open to the water in which the apparatus is, in use, immersed.

The channels 12 also confer a degree of flexibility to the body 11, allowing the body 11 to deform slightly under the influence of any turbulence present in water. This reduces the turbulence at the in use underside 20 of the body 11, making it more attractive for the fish lice to lay their eggs on.

The body 11 is predominantly opaque, thereby preventing the penetration of light to the underside 20, making the underside of the body 11 dark and therefore more attractive for the fish lice to lay their eggs on. This has the additional advantage that, when the body 11 floats adjacent to the surface of the water, the surrounding area will be illuminated, allowing the fish lice to more easily home in on the shaded underside 20 of the body 11. For similar reasons it is preferred that the body 11, or at least one surface of the body 11, is made from (or coated with) a darkly coloured material.

Referring now to Figure 3, in another mode of operation, the apparatus 10 is suspended substantially vertically below the surface of the water. Again the anchor 16 serves to maintain the body 11 in place while the float 14 acts as a marker to the location of the apparatus 10. This mode of operation is advantageously, but not exclusively, used when placing the apparatus 10 adjacent existing objects in the water, such as a man made bank 22, or similarly water towers (not shown) or piers (not shown).' The bank 22, or similar surfaces offering shade, are favoured sites on which the lice lay their eggs. It is therefore advantageous to place the apparatus 10 on the leeward side of such sites (where there is less turbulence), thereby attracting the lice to lay their eggs on the body 11 as opposed to the existing site.

In the mode of Figure 3, the body 11 is pivoted in a vane-like manner by the movement of water around it. In this way, a leading narrow edge of the body 11 is caused to face the direction of water flow and the body 11 is therefore not unduly disturbed by the passage of water around it. It is preferred to connect the float 14 and the anchor 16 to opposite corners of the body 11 11, although the float 14 and anchor 16 may alternatively be connected to opposing sides or edges of the body 11.

Other arrangements (not illustrated) of the float and anchor are also possible. For example, a single length of tether may be used to connect the anchor, the body and the float. In such an arrangement, the tether may run through two holes at opposite ends of one edge of the body (like a flag flying) with the tether fixed in position at the, in use, top end (to stop the body %\running up" the tether to the surface and thence to the float above). Hence the vertically floating (sunk/pulled down) body would hang in the water like a flag in a strong wind.

Equally, the tether, with a relatively short end section attached to the anchor, may be attached and fixed at one edge or corner of the body only, with the free top section of the tether then running to the float at the surface. In this mode, the body is pulled down into the water by the anchor tethered to the connecting edge. The free opposite edge or corner of the body would then, because of its buoyancy, rise up from its fixed position towards the surface to the float.

It will further be understood that the apparatus 10 need not necessarily adopt the horizontal or vertical positions illustrated in Figures 2 and 3. Using the Figure 3 arrangement by way of example, the disposition of the body 11 with respect to the surface 30 of the 12 water may be altered by adjusting the length of the tether 18.

Also, the body 11 may be placed at differing depths below the water surface. It is found that in cooler weather, fish lice tend to lay their eggs near the water surface where the water pressure is lower. In these circumstances, the mode illustrated in Figure 2 may be preferred. In warmer weather when the surface layer of water is warmer, fish lice tend to lay their eggs in deeper (and therefore cooler) water and so the mode of Figure 3 may be preferred. Clearly, in Figure 3 mode, the depth of the body 11 below the water surface 30 is determined by the respective lengths of the tether 18 to the anchor 16 and the tether to the float 14.

In Figures 2 and 3, the anchor 16 is shown anchoring the body 11 to the bed 32 of the body of water into which it is placed. It will be understood that the apparatus may equally be anchored to a bank (not shown) or to any suitable natural or made object located in, or adjacent, the water.

It will be appreciated that many different arrangements of one or more anchors are possible. For example, one or more anchors (not shown) may be connected to the corners and/or edges of the body 11. If, for example, it is desired to hold the body 11 under the water away from the surface 30 and in a substantially horizontal disposition, then a respective anchor may be placed at each corner of the body. The disposition of the body 11 with respect to the surface 30 then depends on the 13 relative lengths of the respective tethers. As before, one or more floats may be used as markers to the location of the apparatus 10.

In cases where the body 11 is formed from a material having a specific gravity greater than water and which is not aerated, or otherwise adapted, to be buoyant, one or more floats may be used to prevent the body 11 from sinking.

In an alternative embodiment (not illustrated), one end of the body is weighted to cause the body to be substantially vertically disposed in the water (i.e. substantially perpendicularly disposed with respect to the water surface). Such weighting may be achieved in any suitable manner. For examp 1 e, one or more weights, such as studs, pipe leads or leadline, may be fixed to one edge or corner of the body. In the case where the body comprises one or more hollow channels (Fig. 2), the or each weight, e.g. pipe leads or leadline, may alternatively be incorporated into one or more of the channels. Alternatively still, in the case where the body is associated with one or more ballast chambers, by partly filling the ballast chambers the same weighting effect is achieved. Such modifications advantageously cause the body to be substantially vertically disposed in the water column without the need to use the pull of the anchor on a short tether. This weighted arrangement is therefore particularly useful in cases where an anchor is not used and the body is suspended in the water by rope, wire, or the like. Since it is advantageous that the body is buoyant, it is preferred that the weighting is such 14 that the body does not lose its inherent buoyancy, or the buoyancy conferred on it by one or more buoyancy chambers (as applicable).

In use, the apparatus 10 is placed at any number of sites, preferably (but not necessarily) in close proximiLy to known egg laying sites, prior to the time at which the lice lay their eggs. The arrangement is such that at least one hydrophobic surface of the body 11 is wholly or partly immersed in the water. The lice are attracted to the body 11 and lay their eggs thereon. In particular, the lice are attracted to lay their eggs on an immersed hydrophobic surface (or part surface if the body is not wholly immersed) of the body, particularly a surface that is darkly coloured and/or in shade. Preferably, t he apparatus 10 is regularly removed (approximately every 10 to 14 days) and optionally cleaned to remove any lice eggs or additional organic matter that is adhered thereto. The use of a plastics material for the formation of the body 11 facilitates the cleaning of the apparatus 10 once it is removed from the water. Alternatively, a used apparatus 10 may be discarded and replaced by a fresh one. The apparatus 10 is used throughout the egg laying season to aim to eliminate the next generation of fish lice.

Although both Figure 2 and Figure 3 illustrate a single apparatus 10 suspended in the water, it will be apparent that a plurality of the apparatus 10 may be arranged in series, or in any alternative array, in order to effectively attract the fish lice to lay their eggs thereon.

In an alternative embodiment, the entire body need not necessarily be formed from the same material. For example, the body may be formed from a mixture, or admixture, of plastics. Alternatively, the body may comprise a two or more layers of material laminated or fixed together in conventional fashion such that at least one surface of the resultant body is hydrophobic. Alternatively still, at least one surface of the body may be rendered hydrophobic by painting, or otherwise coating, the surface with a suitable substance, such as water-repellent paint or Glass Reinforced Plastic (GRP). It will also be noted that the body (or the layers thereof, if applicable) need not necessarily be formed from plastics. Other materials such as wood or metals, for example aluminium, may alternatively be used although, as described above, for non-buoyant materials it is preferred to provide at least one buoyancy chamber to lend buoyancy to the apparatus.

In general, if the body of the apparatus is formed predominantly from an inherently non-buoyant material, it is preferred to confer buoyancy to the body by means of aeration or one or more buoyancy chambers. If the body of the apparatus is formed predominantly from an inherently non- hydrophobic material, then at least one surface, or part-surface, of the body is layered or coated with a hydrophobic material.

It is preferred to form the body 11 from polypropylene or polyethylene because these materials are naturally buoyant, naturally hydrophobic and readily provide the desired degree of flexibility described above.

16 The body need not necessarily be formed entirely from opaque material. Eor example, an otherwise transparent or translucent material may be rendered opaque for the purpose of the present invention by, for example, dyeing, painting, coating or otherwise colouring at least one surface (or at least a part thereof) of the body with an opaque substance, or by fixing a layer of opaque material to at least one surface of the body. It will be noted that a surface which is rendered opaque as described above need not necessarily be the same surface that is hydrophobic. It is preferred that any dye, paint, coating or other surface layer is darkly coloured.

The present invention is not limited to the embodiments described herein which may be amended or modified without departing from the scope of the invention.

Claims

CLAIMS:

1. A fish lice population controlling apparatus comprising a body that is predominantly opaque and has 5 at least one surface that is hydrophobic.

2. An apparatus according to Claim 1, wherein the body is made from hydrophobic and predominantly opaque material. 10

3. An apparatus according to Claim 1 or 2, wherein the body is substantially planar in form.

4. An apparatus according to Claim 1, 2 or 3, wherein 15 the body is arranged to be buoyant in water.

5. An apparatus according to Clairr 4, wherein the body is formed from material having a specific gravity less than that of water in which the apparatus is, in use, 20 located.

6. An apparatus as claimed in any preceding claim, wherein the body is flexible to allow compliant movement of the body with water in which the apparatus 25 is, in use, located.

7. An apparatus as claimed in any preceding claim, in which the apparatus further includes at least one ballast chand-,er. 30

8. An apparatus as claimed in Claim 7, in which the at least one ballast chamber is included in the body.

18

9. An apparatus as claimed in Claim 8, in which said at least one ballast chamber comprises a channel having at least one open end arranged so that, in use, water substantially fills the channel. 5

10. An apparatus as claimed in Claim 9, wherein the channel is open at both ends so that, in use, water may enter the channel by either end.

11. An apparatus as claimed in Claim 9 or 10, wherein the body comprises a plurality of channels.

12. An apparatus as claimed in any preceding claim, wherein at least one surface of the body is formed from 15 a plastics material.

13. An apparatus as claimed in Claim 12, wherein the body is formed from a plastics material.

14. An apparatus as claimed in Claim 12 or 13, wherein the body comprises polypropylene.

15. An apparatus as claimed in Claim 12 or 13, wherein the body comprises polyethylene. 25

16. An apparatus as claimed in any preceding claim, wherein the apparatus further includes an anchor coupled to the body and arranged to maintain the body at a desired location. 30

17. An apparatus as claimed in Claim 16, wherein the anchor is coupled to the body by means of a tether, the length of the tether being selectable to determine the 19 disposition of the body relative to the surface of the water in which the body is, in use, located.

18. An apparatus as claimed in Claim 17, wherein the length of the tether is selected to allow the body to be substantially parallel with, and adjacent, the surface of the water.

19. An apparatus as claimed'in Claim 17, wherein the length of the tether is selected to allow the body to be substantially perpendicularly disposed with the surface of the water.

20. An apparatus as claimed in Claim 17,.iherein the length of the tether is further selectable to determine the depth of the body below the surface of the water.

21. An apparatus as claimed in any preceding claim, wherein at least one surface of the body is formed from a predominantly dark material.

22. An apparatus as claimed in any preceding claim, wherein the body is formed from a predominantly darkly coloured material.

23. An apparatus as claimed in any preceding claim, arranged for controlling Argulus fish 1JLce including Argulus coregoni, Argulus foliaceus or Argulus japonicus.

24. A method of controlling fish lice populations, the method comprising: introducing a body into water containing fish lice; waiting until at least some fish lice have laid at least some eggs on the body; and removing the body from the water, wherein the body is predominantly opaque and includes at least one surface that is hydrophobic, the at least one hydrophobic surface being wholly or party immersed in the water during use.

25. A method as claimed in Claim 24, wherein the body is introduced into the water such that all or part of 10 the at least one hydrophobic surface is in shade.

26. A method as claimed in claim 24 or 25, wherein the body is included in an apparatus as claimed in any of claims 1 to 23. 15

27. Use of a body, that is predominantly opaque and has at least one surface that is hydrophobic, in the control of fish lice populations, wherein the at least one surface is wholly or partly immersed, in use, in 20 water containing fish lice.

28. A fish lice population controlling apparatus substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings. 25

29. A method of controlling fish lice populations substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.