WO2003043414A1

WO2003043414A1 - A method of treating a target species of fish within a general fish population

Info

Publication number: WO2003043414A1
Application number: PCT/AU2002/001558
Authority: WO
Inventors: Gray Stephen Barr Jamieson; James Fajt
Original assignee: Australian Water Management Pty Ltd
Priority date: 2001-11-16
Filing date: 2002-11-15
Publication date: 2003-05-30

Abstract

A method of delivering an active component to a target species of fish within a local fish population is disclosed. The method comprises delivering a trainer bait comprising pellets into a treatment zone of the water way for a plurality of days. The purpose of the trainer bait is to condition the target species to take the bait and also to ascertain the level of non target species that are showing a tendency to take the bait. The pellets are designed to float on the surface of the water so that an operator can easily visually observe the fish and their behaviour towards the bait. Typically the trainer bait is delivered to the treatment zone for a time period of 14 to 21 days. Applicant has found that this period achieves a maximum conditioning of the fish. After this management bait is delivered to the fish. The management bait has an active component that has a specific and desired effect on the target species of fish when they consume the bait. In a preferred form the active component is toxic to the fish and is designed to kill the fish. Thus the target fish die when they take the management bait and are removed from the water way. The method will be particularly useful for removing exotic and introduced fish species from natural water ways when they are damaging the fauna and flora. A system for carrying out the method is also disclosed.

Description

A METHOD OF TREATING A TARGET SPECIES OF FISH WITHIN A GENERAL

FISH POPULATION

FIELD OF THE INVENTION

This invention relates to a method of treating a target species of fish within a general population of fish in a waterway by delivering an active component to the fish to achieve a desired management effect. This invention also relates to a system for use in carrying out this method of treating a target species of fish. The invention relates particularly but not exclusively to a method of killing a target species of fish within a waterway containing a general population of fish comprising more than one species. The purpose of the method is to reduce the number of the target species within the fish population with a view to possibly eradicating that target species from the waterway. For example the invention may find particular application in the control of introduced or exotic species of fish such as carp, eg the common carp and grass carp. It will therefore be convenient to hereinafter describe the invention with reference to this example application. However it is to be clearly understood that the invention has broader application. For example it must be understood that the invention extends to the delivery of active components that have an effect other than killing the target species of fish. For example the active component may affect the growth or reproduction of the target species of fish or the nutrition of the target species.

In the specification the term "pellet" shall be interpreted broadly and shall cover all discrete elements of food matter that are fed to fish irrespective of the shape and size of the element.

BACKGROUND TO THE INVENTION

There are a number of exotic or introduced species of fish inhabiting the natural waterways of Australia, eg rivers, lakes, dams and billabongs. One type of fish, namely the carp, has caused severe problems in these waterways. The carp is an exotic fish that was originally introduced into natural waterways such as rivers when a private dam containing the fish flooded over into a natural waterway. The carp has survived and prospered in these natural waterways and the numbers of the fish in natural waterways has steadily increased and is now at high level. These exotic fish compete with the native fish for food and restrict the numbers of native fish in the waterways. Further the carp cause damage to the flora and fauna. For example they are known to eat away at the roots of eucalyptus trees near the banks of rivers causing erosion of the banks and runoff of top soil into the waterways.

The threat posed by exotic introduced species and particularly the carp has been recognised by the public and water management authorities. There have been efforts to keep the numbers of carp from increasing but these have generally not been successful. In any event a program merely designed to limit the numbers of carp would have limited utility. The only long term solution to this problem is to remove carp from natural waterways.

Active components that are toxic to fish and that reliably kill fish when they enter into the physiological systems of fish are known. Such components include Rotenone, Antimycin A, and pyrethrum. However the real challenge is to effectively deliver the active component to the fish with little wastage and to effectively target the species of fish to be controlled in terms of numbers. For example if the active component was simply dispersed in the treatment zone most of it would be wasted because it would be uniformly dispersed through the volume of water. Further there would be a real likelihood that it would not be taken up consistently and reliably by the target fish.

Clearly therefore it would be advantageous if a technology could be devised that made it possible to remove carp from natural waterways and rivers. In fact such a technology would represent a quantum and significant breakthrough in managing this difficult problem. Up to now a solution to this problem has been considered an unreachable dream.

SUMMARY OF THE INVENTION

According to one aspect of this invention there is provided a method of delivering a substance to a target species within a population of fish in a water way, the method comprising the following steps: delivering a trainer bait comprising pellets that float generally in or on water into the waterway at least once a day for at least once a day; measuring the relative propensity of the various species of fish within the fish population to consume the trainer bait when the trainer bait is delivered and then observing changes in said propensity of the target species of fish over succeeding days of said plurality of days; and then delivering a management bait into the water that contains an active component capable of exerting a desired physiological effect on the target species of fish to achieve a desired management outcome, wherein the management bait floats in or on water like the trainer bait and is perceived by the target species to be the same as the trainer bait that has previously been delivered to it.

Typically the trainer bait is delivered for a plurality of days.

The challenge in designing a technology or method to manage a fish population is to efficiently deliver the active component into the physiological system of the target species of fish. It is also to preferentially deliver the active component to the target species with little or no take up by the non target species of fish.

Generally the population of fish will have more than one species of fish, eg the target species, and at least one other species but this is not essential. Very often the target species will be an introduced species and the population will also include more than 5 other species of native fish.

Generally the active component will exert its effect equally on all species of fish once it is consumed by the fish but this need not be the case.

Many fish species, eg carp, are bottom feeders and move around a body of water near the bottom looking for food and generally feeding off the bottom. However if they were fed a bait that dropped to the bottom of the body of water an operator practising the method above would not be able to see the extent to which the target species of fish were taking the bait. The operator also would not be able to see the extent to which, if any, non target species of fish were taking the bait. Thus the Applicant in this invention has appreciated the importance of using the floating bait to be able to see the fish taking the bait. The Applicant has also established that it is generally possible to train fish that by nature are bottom feeders to take bait floating at or around the surface of the water. This was an important breakthrough in the successful innovation of this invention. Where the term "day" is used in this specification it means a day in the sense of a twenty four hour time period from midnight on one night to midnight the following night. It is therefore not limited to daylight hours from about 6am in the morning to about 6 pm in the evening. This is important to recognise as some fish are nocturnal feeders and the bait may be delivered into the water during the night on each so called day. Examples of nocturnal feeders are eels and gobies. Examples of day feeders are goldfish, carp and trout.

Conveniently the trainer bait may comprise pellets that include grain matter, vegetable matter or animal matter, eg fish meal. The matter may include proteins and fats and optionally also carbohydrates. The pellets may also include agents to firmly hold and adhere the pellets together, eg emulsifying agents and gelatin. The actual composition of the pellets of a particular trainer bait is chosen based on knowledge of that particular fishes likes and dislikes in terms of food. It will be readily appreciated that this will differ from fish to fish and that it would be inappropriate to specify any such preferred composition in this specification.

The pellets are manufactured such that they do not dissolve or dissociate or break up in water. Further the pellets may have a specific gravity of less than 1.0 to enable them to float on the water. The pellets may also be encapsulated within a capsule, eg made of a transparent material that can be broken down in the gut of the fish to release the active component.

The trainer bait is introduced into a specific treatment zone of the water way which remains the same for the duration of the method. That is the bait is introduced into the same geographical area of the water way each day.

The method may further include placing barrier means that float on the surface in the water to mark out the defined treatment zone and also retain the trainer bait and management bait within the treatment zone. The barrier will generally be designed to float on water but will have a skirt that depends down below the water level so as to act as an effective barrier to pellets that are floating near the surface but below the surface. The barrier may also include anchor means or tether means for holding it in a fixed position relative to the water way.

In one particular form the barrier may be in the form of a floating ring or the like. Clearly however it is not limited to a circle and many other configurations could also be used that can be anchored in a specific position in the water way. Preferably the trainer bait is delivered into the water at least once a day for a training period of a plurality of days. More preferably the trainer bait is delivered at least once a day into the water for a training period of 1 to 25 days, most preferably 10 to 21 days. As a general principle the training or conditioning of the fish is continued until they show a satisfactory uptake of the trainer bait on the surface of the water. Applicant has found that the conditioning of the fish generally improves up to 15 to 21 days after the commencement of the method at which point it reaches a threshold and after this it does not improve. Clearly there is no point in continuing the conditioning of the fish with the trainer bait once this threshold has been achieved. Thus the training period may be terminated when the target species of fish shows no day to day improvement in their propensity to take the trainer bait and this will typically be after 10 to 21 days.

While the trainer bait must be delivered at least once a day to the fish Applicant has established that it may be preferable to deliver the trainer bait twice a day, eg in the morning and the evening. Applicant has found that for some species of fish this improves conditioning of the fish.

It is highly preferable that the trainer bait be delivered to the fish at the same time/s on each day of the treatment period to get the best results. This applies when the trainer bait is delivered once a day and also when the trainer bait is delivered two or more times a day. Generally the bait may be administered at times when the target species are known to feed, eg in the early morning and in the evening. However it will be appreciated that this will generally vary from fish to fish. Some fish are nocturnal and feed at night. Other fish feed during the day. Without being bound by theory Applicant believes that this is may be due to circadian rhythms that exist in the fish physiology. Further the feeding of the fish at the same time on each day enhances training or conditioning of the fish as in the Pavlovian conditioning of animals generally.

The step of measuring the propensity of the various species of fish to take the bait may further include the step of visually inspecting the behaviour of the different species of fish in the treatment zone when the trainer bait is introduced to the water each day, and calculating the fraction of the target species of fish that are readily taking the trainer bait, and also calculating the fraction of non target species of fish are taking the trainer bait.

Optionally the method may include the further step of modifying the composition of the trainer bait by adding further components to the trainer bait to change its composition whereby to reduce the fraction of non target species of fish that are taking the bait.

For example this may include adding components to the trainer bait that are highly desirable to the target species of fish and thereby encourage the target species to compete aggressively for the bait in preference to the non target species of fish. Alternatively this may include adding components to the trainer bait that are generally not consumed by the non-target species of fish but are consumed by the target species of fish so as to discourage or dissuade the non target species of fish from taking the bait.

In one specific application of the invention that is envisaged, the active component of the management bait is selected for its ability to kill the target species of fish, eg the active component is toxic to the fish and blocks an essential physiological pathway within the fish.

In one embodiment the active component is antimycin A. Particular success has been achieved with this embodiment. In another embodiment the active component is rotenone and in yet another embodiment the active component is pyrethrum.

An important consideration in choosing an active component is to choose something that will not be sensed or detected by the fish, eg by their sense of smell, sight or taste when they approach the bait and consume the bait. The management bait must be perceived by the fish as being the same as the trainer bait so that it is taken in by them without hesitation. This is important for the successful implementation of the invention. All of the active components above have this property and if they are incorporated in the pellets of the management bait correctly, they will not be noticed by the fish. The method may include the yet further step of estimating the number of fish in the treatment zone.

The bait may be manually delivered into the water in the treatment zone. This may be done by throwing the pellets into the water from a boat or platform. Alternatively the pellets may be delivered into the water by a mechanical feeding means such as a chute, hopper or the like.

In other applications of the invention the objective may be not to kill the fish but instead to have some other effect on the fish. For example the active component may enhance the health and growth of the fish within the target population. Typically this would occur within an aquaculture environment where the target species of fish is being cultivated to be sold off as meat for human consumption. In this application the target species may be tuna, salmon or trout. In this application the active component may be a vitamin or mineral supplement. For example the active component may contain a mixture of vitamins and minerals designed to promote good condition within the fish and/or promote vigorous growth of the fish.

In yet another application of the invention the active component may promote sterilisation of the target species of fish such that they cannot propagate further generations and thereby indirectly control numbers of the fish into the future.

In yet another application the active component is a pharmacologically and/or pharmaceutically active compound that is taken in parenterally by the fish and is then absorbed into the blood of the fish. This may be used to deliver a compound to a target species of fish, eg that is suffering from a disease, within a general fish population.

Further the applicant also contemplates that the method might be used to introduce a particular gene, eg conferring a specific genetic trait on the target species, into the fish. In other examples the active component may be selected to have one or more of the following effects on the target species of fish: alter the rate of growth of the fish, alter the propensity of the fish to reproduce, alter the resistance or susceptibility of the fish to disease, or treating a parasite, virus or bacteria into the fish.

According to another aspect of the invention there is provided a method of controlling a population of a target species of exotic fish within a wild population of fish in a waterway, the method comprising: delivering a trainer bait comprising pellets that float generally in or on water to a population of fish within a treatment zone at least once a day for at least one day; observing the relative propensity of the various species of fish including the target species to consume the trainer bait when the trainer bait is delivered and then observing changes in this propensity over succeeding days; and then delivering a management bait into the water that is the same as the trainer bait with the exception that it contains a toxic compound that kills the fish when they consume it thereby reducing the numbers of the target species of fish in the waterway.

Typically the trainer bait is delivered into the water for a plurality of days. Thus this method is directed specifically at killing off numbers of a particular species of fish with a view to reducing the numbers of the fish within a wild population of native fish.

The target species of fish will generally be an introduced species of fish and the water way may be a natural water way, eg a river or the like. Specifically the river system may be the Murray Darling basin. In one particularly envisaged application the target species is a species of carp, eg the common carp or the grass carp.

It is preferred that the active component is rotenone, pyrethrum or antimycin A and more preferably antimycin A. However at the same time other particularly suitable active components may be found at a later time and these are to be covered by the invention. The key is that the active component kills the fish when it takes the bait into its body and that the active component does not affect the taste, smell or appearance of the bait.

The method may include the yet further step of physically removing the dead fish from the water way after they have died. The dead fish tend to float and can generally be gathered up using a gathering tool such as a gaff from a boat. They can be dumped on the edge of the water way and then be removed to a solid waste site. The dead fish could also be processed to provide products for sale. At the same time it should be clearly understood that it is not necessary to remove the fish from the water way. From an ecological point of view it would be better to leave the fish in the water way to rot and decompose as this would return the nutrients and compounds in the body of the fish to the water way environment rather than this being lost. However applicant believes that there may be adverse public perceptions of such a step which will result in it not being used. According to yet another aspect of this invention there is provided a treatment program for reducing numbers of a target species of fish from a water way including carrying out the method defined in the aspect of the invention described above in a first treatment zone and then repeating said method described above in a plurality of other treatment zones in the water way until the numbers of the target species of fish are reduced within desired ranges.

The treatment program may include carrying out the method at discrete spaced intervals along the water way, eg at approximately equal distances along the water way. The program may further include re-treating certain treatment zones after a certain time has elapsed, eg several weeks or months.

In a most preferred form the method comprises treating the waterway until the target species of fish, eg grass carp or common carp, has been removed from the water way. Further the method may also be used to achieve an adjustment of the numbers of different species of fish in a water way. For example an ecological imbalance of numbers of fish can occur in a water way and water management authorities or wildlife authorise may determine that they need to embark on a culling program in relation to one or more species to restore a more viable balance of numbers of the various species. This happens from time to time in animal game reserves where the inevitable disturbance of natural ecosystems and food chains has wrought some disturbance of normal population numbers found in nature.

According to yet another aspect of the invention there is provided a system for delivering a substance to a target species within a population of fish in a water way, the system comprising: a trainer bait for training the target species of fish to take a bait and quantifying the non target species of fish that take the bait; and a management bait containing an active component that exerts a desired physiological effect on the fish to achieve a desired effect.

The system may further include a barrier that encloses an area and defines a treatment zone when placed in water, the barrier being designed to float on water and also extend a short distance down into the water so as to block the movement of bait out of the treatment zone. The barrier may comprise a flotation member in the form of a closed circle so as to enclose a said treatment zone and a skirt depending down below the flotation member so as block the movement of bait suspended in the water below the surface of the water out of the treatment zone.

The barrier may conveniently be in the form of a floating circle although clearly other shapes are also contemplated.

The system may further include mechanical means for delivering the bait into the water from above the water, eg in the form of a chute or hopper mounted on a support.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A method of treating a target species of fish within a general fish population, eg to control numbers of the fish, may manifest itself in a variety of forms. It will be convenient to hereinafter describe in detail several preferred embodiments of the invention with reference to the accompanying drawings. The purpose of providing this detailed description is to instruct persons having an interest in the subject matter of the invention how to carry the invention into practical effect. It is to be clearly understood however that the specific nature of this detailed description does not supersede the generality of the preceding broad description. In the drawings:

Fig 1 is a schematic view of a water way containing fish of more than one species in a treatment zone;

Fig 2 is a schematic view of the treatment zone showing the initial application of a trainer bait to the treatment zone and the initial behaviour of the fish within the treatment zone to the bait;

Fig 3 is a schematic view of the treatment zone after conditioning of the fish with the trainer bait for several days;

Fig 4 is a schematic view of the treatment zone after training of the fish in the treatment zone has been completed; Fig 5 is a schematic view showing the fish within the treatment zone after the management bait has been administered; and

Fig 6 is a three dimensional view showing a barrier defining the treatment zone and for retaining the bait within the treatment zone. The description below will describe the use of the method for controlling the numbers of common carp in a natural waterway by delivering an active component to the carp that kills the carp. Common carp are a problem in natural water ways and the object will be to kill the carp. The method for treating the carp requires two types of bait namely a trainer bait and a management bait.

The trainer bait is used initially to condition the fish to take the bait. It comprises pellets that are made of grain matter, vegetable matter and/or animal matter that are stable in water in the sense that they do not break up or dissolve in water. Thus they retain their form and size when introduced to the water. Further the bait is made to float on the top of the water. To achieve this it has a specific gravity of close to 1 or slightly less than 1. The size of the pellets will generally vary according to the size of the fish being treated. When treating carp the pellets are cylindrical and have a diameter of 10mm and a length of 10mm. Naturally it is important that the trainer bait is made attractive to the carp. To do this an appropriate mixture of fats, proteins and carbohydrates from plant and animal matter is used.

The management bait is the same as the trainer bait with the exception that it contains an active component. It looks and feels the same as the trainer bait and the pellets are the same size, shape and consistency as the trainer bait. The active component is distributed throughout the bait as granules, microcapsules or the like. The active component is deliberately chosen because it is not sensed or perceived by the fish in the water when it is delivered. To the fish it is alike in all respects to the trainer bait. In this application the active component is chosen for its ability to kill the fish and particularly the target species of fish. One preferred active component is antimycin A. Other preferred active components are pyrethrum and rotenone.

Antimycin A is a natural antibiotic that is derived from fungi and mould in the soil. It was discovered by the University of Wisconsin in 1945 and is sold under the trade mark FINTROL by the company Aquabiotics Corp based in 10750 Arrow Point Drive, Bainbridge Island, in the state of Washington in the USA. The antibiotic kills the fish by interfering with a biochemical pathway in the cell like other antibiotics. Specifically it interferes with an enzyme system needed for oxygen consumption. It is not detected by fish and acts in many ways like carbon monoxide poisoning in humans. The sensitivity of different fish species to Antimycin A may vary from species to species. The antibiotic may be neutralised by 1 ppm of potassium permanganate. It does not affect water quality and importantly fauna and flora are not harmed by it.

Pyrethrum is a well known natural compound that is used widely as an insecticide. It exerts a similar effect on fish and kills the fish. As its composition would be well known to persons skilled in the art it will not be necessary to describe it in greater detail in this specification. Rotenone is a naturally occurring plant extract that has been used to kill fish since the 1930's. Rotenone is obtained as an extract from the tissue of several different plant species known by the names of Derris, Timbo and Barbasco. The general chemistry of Rotenone is given on the table below. In addition it is highly toxic to fish but is not toxic to other animals. It is therefore well suited to use in this invention.

General Chemistry of Rotenone

Classification: organic, odorless, yellow crystal or

Structure: five ring structure

Reactivity: binds to acids

Degradation: oxidation, hydrolysis, UV light does not bio-accumulate

Solubility: lipid soluble (non-water soluble) Rotenoids: active forms: Deguiline, Sumatrol, Rotenolone I, Rotennol (2,0)inactive forms: Munduserone, Dehydroroteonoe, EpirotenoneDesoxydehydrorotenone

Source: plant extract

Rotenone passes across the lining of the Gl tract into the capillaries of the blood stream by diffusion. The rotenone is then transferred by the blood throughout the systemic blood circulation vessels. Rotenone is lipid soluble and therefore diffuses out of the blood capillaries into the interstitial fluid of the tissues. Rotenone causes changes in the binding of the oxygen to haemoglobin. The blood of the fish is saturated with haemoglobin but cannot release it to diffuse into the tissues. As a result the cells are starved of oxygen and the fish die.

A major advantage of these active agents is that they are all biodegradable and therefore do not accumulate in the environment avoiding any further possible adverse effects to non target fish species populations.

Generally the active component would be contained in small microcapsules which are homogenously dispersed throughout the food matter making up the pellet. The microcapsules are insoluble in water.

In use the method is commenced by choosing a treatment zone in the water way. Generally this might be an area of the water where the flow is reduced or quiet and it is accessible from the bank. The treatment area is marked out by placing a barrier in the water enclosing and defining the treatment area. The barrier will generally have a flotation member that floats on the water and projects up a short distance above the water. The barrier will also have a skirt that depends down below the surface of the water a short distance to retain the bait within the treatment zone.

Fig 6 shows a barrier that defines a circular treatment area although clearly other shapes could equally be used. The treatment area covers a surface area of about P/S m2.

Fig 1 shows a treatment zone containing two species of fish before the trainer bait is delivered into the water. It is to be understood that the illustrations are provided purely for illustrating the purpose of the invention and are not indicative of the numbers of fish expected to be found in the treatment zone. Generally there would be at least several hundred fish in the treatment zone and often 1000 to 2000 fish. As is illustrated the fish mainly graze on the bottom of the water way which is their natural feeding habit and are not close to the surface of the water. The carp is indicated by the designation X and the other species which might typically be a native species is indicated by the designation O.

In carrying out the method a trainer bait is delivered into the water in the treatment zone once or twice a day for about 21 days. Initially the response to the bait by the fish in the treatment zone is muted. This is because the carp are bottom feeders and are not used to consuming food towards the top of the water. This state is illustrated in Fig 2 which contains two species of fish in the treatment zone. The trainer bait may be delivered manually into the water, eg by throwing handfuls of pellets into the treatment zone from a boat. Applicant has found this to be a convenient and easy way of doing this job. Alternatively a mechanical dispensing means in the form of a chute of hopper suspended above the water may be used to perform this task. Such a mechanical dispenser may be more useful where the treatment zone that is treated is greater and the numbers of fish in the treatment zone are much greater than those illustrated.

After several days of the treatment period the behaviour of the carp changes and they start taking the trainer bait on the surface of the water. Similarly other fish within the treatment zone may also start taking the trainer bait. This is shown in Fig

3. Most of the carp are shown in the upper reaches of the water and there is some non target species of fish expressing an interest in the trainer bait.

If a significant percentage of non target fish are taking the bait it may be desirable to vary the composition of the bait so that it is more selectively taken by the target species. This may involve adding a component that is known to be disliked or avoided by the non target fish. It may also involve adding a component that is highly desired by the target species the carp such that they compete aggressively and successfully for this bait. Generally these changes to the bait are devised by the operator on site using basic knowledge of what components of food are liked and disliked by the subject species of fish. The operator trials different components and observes the behaviour of the fish and arrives at a modified bait that as a result of routine trial.

At the completion of the training period the operator will know the fraction of target species of fish that are taking the bait. The operator will also know if a fraction of non target species of fish are taking the bait. The treatment zone at this time is illustrated in Fig 4. In the illustration no non target fish are taking the bait. This is obviously the most preferred situation.

If there are no non target species of fish taking the bait the operator proceeds with the application of the management bait without giving the matter any further consideration. Obviously this is the preferred scenario but it does not always occur.

If however a fraction of non target species of fish are taking the bait then the operator has to establish whether or not he can proceed with the management bait.

This may involve consulting with water management authorities who decide whether or not the level of non target kill is acceptable in the light of the benefits being obtained by the process. If not then the method is terminated without the application of the management bait.

If however it is acceptable then the operator proceeds with the delivery of the management bait on the very next day. The management bait is delivered at the same time of the day as the trainer bait was delivered and the fish eat the bait and this causes them to die. The management baits described above will kill all fish that ingest the bait into their systems. Typically the fish will start to porpoise after 20 minutes when rotenone is used as the active component and after one hour they will typically be dead. This is shown schematically in Fig 5. The fish will usually be dead within 24 hours no matter what active component is used. The only fish that are killed are those that take the bait. Thus the non target species that do not take the bait are not harmed in any way. After the fish have died any uneaten management bait in the treatment zone is collected up and removed from the waterway. This is an important step to manage side effects of the method.

The management baits have been designed to have a flotation time of at least four hours. This enables any uneaten bait to be retrieved from the water after it has been administered and before it sinks.

Further the management bait is encapsulated on a capsule material so as to resist any leaching of active component from the pellet or capsule into the water way. The trainer bait may also be encapsulated to make it the same as the management bait.

Finally the dead fish are removed from the water way. To do this they are physically gaffed and lifted into a boat and then deposited on the bank. They can they be removed for processing or disposed of in a waste disposal facility.

In a natural waterway such as a river the method as described above could be practised at a number of locations at spaced intervals along the length of the river.

This will lower the carp population along the length of the river. Thereafter further treatments could be carried out at the original treatment locations again until target reductions in the numbers of fish for the target species of fish are achieved.

Applicant has found that the method described above with reference to the drawings is very effective at killing the grass carp. For example several thousand carp can be killed by one treatment regimen in one treatment zone. This enables very substantial inroads to be made in controlling numbers of exotic fish such as carp in the space of relatively few treatments. This is important as the cost benefit of any proposed management program will be rigorously analysed by water authorities before being implemented. Applicant believes that it may become possible with the method to completely remove carp from say a natural waterway or a dam.

A further advantage of the method described above is that it uses fish behaviour that occurs naturally and fish physiological processes to do the work of selectively treating a target species of fish. The process is extremely efficient in the way it uses the active component and there is very little wastage of the active component.

It will of course be realised that the above has been given only by way of illustrative example of the invention and that all such modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of the invention as is herein set forth.

Claims

CLAIMS:

1. A method of delivering an active component to a target species of fish within a local population of fish in a water way, the method comprising the following steps: delivering a trainer bait comprising pellets that float generally in or on water into the waterway at least once a day for at least one day; observing the relative propensity of the various species of fish within the fish population to consume the trainer bait; and then delivering a management bait into the water that contains an active component capable of exerting a desired physiological effect on the target species of fish to achieve a desired management outcome, wherein the management bait floats in or on water like the trainer bait and is perceived by the target species to be the same as the trainer bait that has previously been delivered to it.

2. A method according to claim 1 , wherein the trainer bait is delivered into the water way for two or more days.

3. A method according to claim 1 , wherein the relative propensity of the various species for the trainer bait is observed on the first day on which the bait is delivered and also on one or more succeeding days of delivery of the bait.

4. A method according to claim 1 , wherein the trainer bait is introduced into a treatment zone within the water way which remains the same for the duration of the method, and the method further includes placing barrier means that float on the surface in the water to mark out the treatment zone and also retain the trainer bait and management bait within the treatment zone.

5. A method according to claim 1 , wherein the trainer bait is delivered at least once a day into the water for a training period of seven to twenty five days.

6. A method according to claim 5, wherein the trainer bait is delivered into the water twice daily on each day of the training period and the trainer bait is delivered into the water at approximately the same time/s on each day of the training period.

7. A method according to claim 6, wherein said training period is terminated when the target species of fish show no day to day improvement in their propensity to take the trainer bait and maximum conditioning of the target species of fish has been achieved.

8. A method according to claim 1 , wherein the step of observing the relative propensity of the various species of fish includes visually inspecting the behaviour of the different species of fish in the treatment zone when the trainer bait is introduced to the water each day, whereby to measure the fraction of the target species of fish that are readily taking the trainer bait, and also to ascertain whether or not any non target species of fish are taking the trainer bait.

9. A method according to claim 8, further including the step of adding further components to the trainer bait to change its composition whereby to reduce the fraction of non target species of fish that are taking the bait.

10. A method according to claim 9, including adding components to the trainer bait that are highly desirable to the target species of fish and thereby encourage the target species to take the bait in preference to the non target species of fish.

11. A method according to claim 9, further including adding components to the trainer bait that are generally not consumed by the non-target species of fish but are consumed by the target species of fish so that the target species take the bait in preference to the non target species of fish.

12. A method according to claim 8, further including quantifying on a numerical basis the fraction of each non-target species of fish that is consuming the trainer bait when the trainer bait is introduced into the treatment zone.

13. A method according to claim 1 , wherein the active component of the management bait is selected for its ability to kill the target species of fish.

14. A method according to claim 13, wherein the active component is toxic to the fish and blocks an essential physiological pathway within the physiology of the fish.

15. A method according to claim 14, wherein the active component is Antimycin A, rotenone or pyrethrum.

16. A method according to claim 1 , wherein the pellets of the trainer bait include grain matter, vegetable matter or animal meat, and wherein the matter making up the pellets is adhered together so as not to dissolve or break up in water, and the pellets have a specific gravity of less than 1.0 to enable them to float on the water.

17. A method according to claim 1 , wherein the active component is selected to have one or more of the following effects on the target species of fish: alter the rate of growth of the fish, alter the propensity of the fish to reproduce, alter the resistance or susceptibility of the fish to disease, or treat a parasite, virus or bacteria that has entered the fish.

18. A method of controlling a population of a target species of fish within a wild population of fish in a waterway, the method comprising: delivering a trainer bait comprising pellets that float generally in or on water to a population of fish within a treatment zone at least once a day for at least one day; observing the relative propensity of the various species of fish including the target species to consume the trainer bait when the trainer bait is delivered; and then delivering a management bait into the water that is the same as the trainer bait with the exception that it contains a toxic compound that kills the fish when they consume it thereby reducing the numbers of the target species of fish in the waterway.

19. A method according to claim 18, wherein the target species of fish is an introduced species of fish and the water way is a natural waterway.

20. A method according to claim 19, wherein the trainer bait is delivered for two or more days, and wherein the relative propensity of the various species is observed on the first day that the bait is delivered and changes in this propensity are observed over one or more succeeding days.

21. A method according to claim 20, wherein the target species is one of the following species of fish: grass carp, common carp, tilapia, gambusia or gold fish and the trainer bait is delivered into the water for 2 to 25 days.

22. A method according to claim 18, wherein the active component is rotenone, pyrethrum or antimycin A.

23. A method according to claim 18, further including physically removing the dead fish from the water way after they have died.

24. A treatment program for reducing numbers of a target species of fish from a water way including carrying out the method defined in claim 19 in a first treatment zone and then repeating said method defined in claim 19 in a plurality of other treatment zones in the water way until the numbers of the target species of fish are within desired ranges.

25. A treatment program according to claim 24, further including re-treating certain treatment zones after a certain time has elapsed.

26. A treatment program according to claim 25 that comprises treating the waterway until the target species of fish has been eradicated from the waterway.

27. A system for delivering a substance to a target species within a population of fish in a water way, the system comprising: a trainer bait for training the target species of fish to take a said bait and quantifying the non target species of fish that take the bait; and a management bait containing an active component that exerts a desired physiological effect on the fish to achieve a desired effect.

28. A system according to claim 27, further including a barrier that encloses an area and defines a treatment zone when placed in water, the barrier being designed to float on water and extend a short distance down into the water so as to block the movement of bait out of the treatment zone.

29. A system according to claim 28, wherein the barrier is in the form of a floating circle.

30. A system according to claim 29, further including mechanical means for delivering the bait into the water from above the water.