Field

The present invention relates to methods and apparatus for reducing cannibalism in crustacean populations and in particular crustacean populations which are farmed in commercial scale aquaculture set ups.

Background

Cannibalism is one of the primary causes of mortality in spiny lobster culture and represents a key bottleneck to largescale aquaculture of this and other high-value crustacean species. Cannibalism generally occurs when animals are in the process of moulting, i.e., when they have begun to extricate themselves from their old exoskeleton. For a short period they are defenceless and can be attacked by conspecifics, even those much smaller than themselves. Over a farmed lifecycle there can be numerous moulting events occurring in intervals of weeks or months, depending on development stage and culture conditions. The present inventors have identified that approximately one quarter of juvenile tropical lobster (Panulirus ornalus) moulting events result in cannibalism regardless of other measures, such as hide structures being placed in a culture vessel to provide protection from attack. This is a common problem across many crustacean species that have considerable aquaculture potential. Currently the only way to culture some of these species, including, tropical lobsters - P. ornatus, Mitten crab - Eriocheir sinensis, Mud crab - Scylla serrata, Blue Swimmer crab - Portunus pelagicus, Giant Freshwater prawn - Macrobrachium rosenbergii, American lobster - Homarus americanus, European lobster - Homarus gammarus and other spiny lobster species such as the European spiny lobster Palinurus elephas is by either extensive or segregated culture, to prevent or limit cannibalistic attacks.

The aquaculture potential of many of these high value crustaceans have not been realised due to their aggressive nature and the prevalence for cannibalism during farming. Various strategies to rear these crustaceans have been explored from extensive culture where low stocking numbers are maintained and constant grading for size is undertaken, to individual culture in structures/systems such as individual cells. Both strategies work to a certain extent however in general they are not effective due to slowness of growth, high labour inputs, animal welfare concerns and ineffective use of facilities. Further, it has been shown that crustaceans often engage in cannibalistic behaviour even when provided adequate feed rations and/or when provided hide structures within the culture vessel.

There is a need in the art to further minimise cannibalistic behaviour within farmed crustacean populations.

Summary

The present invention is predicated on a physical separation technology to prevent cannibalism. In particular, the inventors have developed a prevention method and system that exploits specific behavioural traits of crustaceans to reduce the incidence of cannibalism. The present inventors have recognised that typically, crustaceans cease to feed prior to a moult (pre-moult phase), while during the inter-moult phase (the majority period between moulting) animals continue to feed. It is also recognised that there is a standardised period during a day when predominately all animals will moult, some crustaceans will feed and moult after dark (in a standardised day), and that this is when moulting animals are exposed and vulnerable to cannibalism. The timing of moulting can be species specific.

In one aspect of the present invention, there is provided an apparatus for restricting cannibalism in a population of crustaceans farmed in an aquaculture system, said apparatus being configured to hold feed and comprising a culture vessel and a barrier configured to define in the vessel to respective sides of the barrier a first zone, within which said crustaceans of the population can moult, and a second zone, for containing crustaceans of the population that have moulted (in a "post-moult phase") or are not about to moult (in an "inter-moult phase"), wherein the barrier is fluid -permeable and the apparatus is operable to flow fluid from the second zone to the first zone to effect fluid current such that the fluid current carries a scent of the feed through the barrier from the second zone to the first zone, the barrier being trafficable from the first zone whereby crustaceans in a post-moult or inter- moult phase in the first zone, can, under the attraction of said scent, transit to the second zone through the barrier, so as to be kept from cannibalising crustaceans in the first zone.

In some embodiments of the invention, the apparatus is operable to subject the first zone to light in a phase during which crustaceans in the first zone assume a pre-moult condition ("pre-moult phase"), and to darkness in a phase during which they moult so as to assume a post-moult condition ("moulting phase"). It may further be operable to subject at least one of the first or second zones to darkness to promote consumption of said feed by post- moult and inter-moult crustaceans.

In some embodiments of the invention, the including at least one or more lights are arranged to provide illumination in the first zone such that it is subjected to said light. The barrier may comprise a divider or partition. The barrier may be configured with at least one pathway via which post-moult and inter-moult crustaceans can move therethrough to the second zone. In some embodiments, the, each, or at least one said, pathway comprises an aperture through the barrier. The, each, or at least one said, pathway may further comprise a passageway extending though the barrier. The passageway may be defined by a conduit. The, each, or at least one said, conduit may comprise a conduit section projecting into the first zone. The, each, or at least one said, conduit may comprise a conduit section projecting into the second zone. The, each, or at least one said, passageway may also be inclined in a direction from the first zone to the second zone.

In some embodiments of the invention, the, each, or at least one said, passageway comprises an entrance large enough to facilitate ingress of crustaceans from the first zone into the pathway, and an exit sufficiently large to permit egress of crustaceans from the passageway into the second zone and small enough to obstruct ingress of crustaceans from the second zone into the passageway.

The passageway may be convergent and/or of reducing cross section in a direction from the entrance to the exit. The passageway may be tapered so as to be convergent and/or of reducing cross section in said direction.

In some embodiments of the invention, the apparatus includes at least one door associated with the, each, or at least one said, pathway, biased to a closed condition and urgeable to an open condition by crustaceans transiting from the first zone, to permit the crustaceans to leave the pathway so as to be contained in the second zone, the door(s) being unopenable by crustaceans contained in the second zone. The, each, or at least one said, pathway may be further configured to permit travel of said scent therealong to said first zone.

In some embodiments of the invention, the internal surface of each of, or at least one of, the barrier or pathway is rough. The roughness of the internal surface of each of, or at least one of, the barrier or pathway is provided by spaced extrusions of the internal surface. The spaced extrusions of the internal surface of each of, or at least one of, the barrier or pathway are spiral shaped extrusions.

The vessel may comprise a first region and a second region, the apparatus being configured such that the first and second zones are selectively definable in either the first and second regions, or the second and first regions, respectively. The apparatus may also include at least one barrier component arrangeable relative to the vessel in one position to define said barrier, said one position being such that the first and second zones are defined in said first and second regions respectively, and in another position to define said barrier, the other position being such that said first and second zones are defined in said second and first regions respectively.

In some embodiments, the apparatus comprises a further barrier, wherein the vessel and said further barrier are configured such that defined in the vessel to respective sides of the further barrier are said second zone and a third zone, the apparatus being configured such that said second zone can, once said crustaceans are contained therein, become a said first zone whereby said third zone becomes a said second zone. The apparatus may further comprise an additional barrier, wherein the vessel and said additional barrier are configured such that defined in the vessel to respective sides of the additional barrier are said third zone and said first zone, the apparatus being configured such that said third zone can, once said crustaceans are contained therein, become a said first zone whereby said first zone becomes a said second zone.

The apparatus may also be configured to hold said feed in said second zone. The apparatus may include at least one station configured to provide said feed in said second zone. The at least one said station may be operable to provide said feed in consecutive rations in said second zone, and may be configured to hold said feed upstream of said second zone.

In another aspect of the invention, there is provided a method of minimising cannibalism in a population of crustaceans which are farmed in an aquaculture system, said method including housing said population in an apparatus, said apparatus being configured to hold feed and comprising a culture vessel and a barrier configured to define in the vessel to respective sides of the barrier a first zone, within which said crustaceans of the population can moult, and a second zone, for containing crustaceans of the population that have moulted (in a "post-moult phase") or are not about to moult (in an "inter-moult phase"), wherein the barrier is fluid-permeable such that a scent of the feed can travel thereacross from the second zone to the first zone, the barrier being trafficable from the first zone whereby crustaceans in a post-moult or inter-moult phase in the first zone, can, under the attraction of said scent, transit to the second zone through the barrier, so as to be kept from cannibalising crustaceans in the first zone; and delivering feed to the second zone such that a scent of the feed can travel thereacross from the second zone to the first zone whereby non-moulting (actively feeding) individuals of said population migrate to the second zone leaving the moulting individuals of said population in non-feeding first zone away from potential feeding individuals and hence minimise cannibalism in said population.

This technology utilises the behavioural responses of crustaceans to achieve physical separation at the moult. Moulting animals don’t feed for the period prior to moulting while the rest of the population continues to feed and hence will move to, and remain in, a feeding zone prior to when moulting of non-feeding animals may occur. Moulting and feeding occurs in the dark phase for most lobsters; moulting generally occurs 3-5 hours after the onset of the dark phase, while feeding is encouraged upon the onset of dark. Up to 25% of all moulting events in some spiny lobsters (and other crustaceans) result in cannibalism, the above method could dramatically reduce this mortality.

In some embodiments of the invention the feed is delivered upstream from the second feed zone. The population of crustaceans may be a population of spiny lobster. The population of crustaceans may more specifically be a population of the spiny lobster of species Panulirus ornatus. In other embodiments, the method may be repeated on a 24 hour cycle.

Current technology for reducing cannibalism in crustaceans is to grow them very extensively (in a low density population) to reduce the opportunity for cannibalism, constantly grading out larger animals in some species and holding animals in separate containers so they are not exposed to other animals and hence remove the cannibalism factor - this method has some negative effects as without social interaction growth in isolation is much slower. Brief Description of Figures

The present invention will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Figure 1 shows a culture vessel configuration including a barrier, in accordance with an embodiment of the present invention;

Figure 2 shows an alternate embodiment of the present invention, in which the barrier defines two regions, and the barrier includes passageways that are tubular;

Figure 3 is a front and rear view of a culture vessel configuration, in which the barrier defines two regions, and the barrier includes passageways that are conical.

Figure 4 shows a further alternate embodiment of the present invention, in which a second region is disposed within a first region;

Figure 5 is yet another alternate embodiment of the present invention, wherein the zone corresponding to each region is cyclically altered; and

Figure 6 shows a perspective view of a barrier and conical passageway in which the passageway is provided with texture, in accordance with an alternate embodiment of the present invention.

Figure 7 shows a proportion of Panulirus ornatus juveniles present in either the Day 1 or Day 2 zones at the morning daily inspection, for three iterations (II, 12, 13) of Version 2 (A) and Version 2 (B) of the Daily Migration System experiment, wherein a conical passageway is used in Version 2 (B), 13 only. Detailed Description

Described generally herein, an apparatus for restricting cannibalism in a population of crustaceans farmed in an aquaculture system is disclosed. The apparatus is configured to hold feed and includes a culture vessel and a barrier. The barrier is configured such that it defines in the vessel, to respective sides of the barrier, a first (non-feeding) and second (feeding) zone. In the first zone, said crustaceans of the population can moult, and the second zone is for containing crustaceans of the population that have moulted (in a "post-moult phase") or are not about to moult (in an "inter-moult phase"). The barrier is fluid-permeable and the apparatus is operable to flow fluid from the second zone to the first zone to effect fluid current such that the fluid current carries a scent of the feed can travel thereacross from the second zone to the first zone. The barrier is further trafficable from the first zone whereby crustaceans in a post-moult or inter-moult phase in the first zone, can, under the attraction of said scent, transit to the second zone through the barrier, so as to be kept from cannibalising crustaceans in the first zone.

Embodiments of the invention will now be described with respect to Figures 1 to 6.

Figure 1 shows an embodiment of the apparatus wherein the culture vessel 10 takes the shape of a flat sided tank filled with water. It should be noted, however, that any culture vessel suitable for housing crustaceans (including tanks not filled with water, or of a different shape) can be used with the present invention. A barrier 40 can be seen to split the vessel 10 into separate regions, defined as a feeding 60 and non-feeding zone 70. The barrier 40 may be either one of a removable or permanent fixture in the culture vessel 10. The operation of the invention is such that all crustaceans are located in the non-feeding zone 70 at the commencement of rearing. The pathways 90 promote transit of crustaceans in one direction, i.e., from the non-feeding zone 70 to the feeding zone 60. The apparatus is operable such that water in the tank flows directionally, originating from the feeding zone 60 of the culture vessel 10, flowing through to the non-feeding zone 70 (see Figure 1). The flow of the water is provided by a pump, located within the vessel 60, configured to pump water to/through the vessel 60 or provided upstream of the vessel 60 to provide a flow of water thereto. In a preferred embodiment, the pump is one of a centrifugal or positive displacement pump, however it is understood that any suitable type of pump, for example axial-flow or plunger pumps, could be used without deviating from the present invention. Likewise, multiple pumps and/or pump types could be used. In an alternate embodiment, the flow of water is provided by an upstream source, such as a river or other moving/flowing body of water. The provision of fluid flow causes a fluid current to be effected in the vessel 60 such that fluid flows in a direction from the feeding zone 60, through the barrier 40 to the non-feeding zone 70. For P. ornatus, at the onset of the dark phase feed is provided in multiple rations to the feeding zone 60 of the culture vessel 10. A directional feed scent, which originates from feed held in or proximate the feeding zone 60 is carried by the fluid current through to the non-feeding zone 70. In vessels 10 not provided with water, a similar flow effect can be achieved through air. The scent attracts inter-moult crustaceans to actively pass through the pathways 90 in the barrier 40 and facilitates feeding in the feeding zone 60. The crustaceans that are about to moult are not attracted by the feed scent so remain behind in the non-feeding zone 70. Pre-moult animals remaining in the non-feeding zone 70 undergo their moult uninterrupted, and after a short period become attracted by the feed scent, and are competent to also transit through the pathway 90 to the feeding zone 60 to commence feeding. At this stage, they are not vulnerable to cannibalism by inter-moult animals.

Not pictured but present in this embodiment, the culture vessel 10 is also equipped with a lighting system. The lighting system provides light to crustaceans in a pre-moult phase, and provides darkness during the moulting phase. The lighting system may provide light to the vessel by any readily available means, such as by natural sunlight, or by powered/electrical lights. Similarly, darkness may be provided by removing power to the lights, or otherwise covering/shading the vessel 10. Alternatively, the light and dark subjections may be provided entirely naturally through the day and night cycle of the location/environment within which the vessel 10 is housed.

The culture vessel 10 is equipped with a feeding station. The feeding station provides feed, and thus feed scent, to the feeding zone 60 of the culture vessel 10. The feed is held in the feeding station, and the feeding station is positioned proximate a region of the vessel 10 which corresponds to the feeding zone 60. In preferred embodiments, the feeding station is positioned above the water level over the culture vessel. The dispensing of feed is in rations, and may be controlled via a timer or through manual operation, allowing the feed to be dispensed. The feed is dispensed in spaced time periods, giving the crustacean's time to moult. In some embodiments, it is necessary for the feed to be provided to different regions in the culture vessel as the feeding 60 and non-feeding zone 70 changes. This is achieved with a feeding station that is relocatable. In a preferred embodiment, the feeding station is self-relocatable, and relocated based on the same timer by which it dispenses feed. Alternatively, this may be achieved by having the feeding station fixed in location, and rotating the culture vessel 10 to provide the different zones 60, 70 with feed.

The barrier 40 and pathway 90 may take a variety of forms. Whilst the preferred embodiment features conical pathways 90 (as seen in Figure 3), it is understood that a variety of passageway shapes (see Figure 1), including perforated tubes, can be included (including at angles, see Figure 2) in the barrier 40 and will serve the same purpose. Both conical and inclined pathways 90 provide a biasing effect toward the feeding zone 60. The conical passageways are configured such that the exit is sufficiently large to permit egress of crustaceans from the passageway into the feeding zone 60, but small enough to obstruct ingress of crustaceans from the feeding zone 60 into the pathway 90, i.e., the entry into the passageway is larger than the exit out of the passageway. Similarly, the inclined passageways are configured such that, in order for a crustacean to move back to the non-feeding zone 70 from the feeding zone 60, it must travel upwards through the inclined passageway. Each of these biasing agents work in conjunction with the feed scent attracting the crustaceans in the direction of the feeding zone 60. Providing perforation in the pathway 90 allows the feed scent to disperse into a greater area of the non-feeding zone 70 and thus be more likely to reach and attract the crustaceans in said zone. The pathways 90 provided in the barrier 40 may further extend, as conduit, into one or each zone such that crustaceans cannot move, be pushed or drift into the incorrect zone incidentally. In place of a pathway 90, an embodiment of the invention may instead include doors, the doors being biased to a closed condition and urgeable to an open condition by crustaceans transiting from the nonfeeding zone 70 to the feeding zone 60. Such doors may be hinged at any location, or otherwise attached to provide an openable but biased closed condition.

Whilst the embodiments provided in the Figures each disclose barriers 40 with multiple passageways, it is understood that one passageway would also be functional in this invention. It is further understood that any such variation of shape that provides the benefits of the passageway forms disclosed may be used, such as, for example, a tapering square tube in place of a conical conduit. Due to the shape and size of the passageways and the direction of the water flow the intermoult animals are discouraged from returning to the non-feeding zone 70 to predate on the moulting animals.

In these embodiments, the culture vessel 10 and its parts are made from high density polyethylene, other materials may also be suitable, including acrylic, polyvinylchloride, fibreglass, polycarbonate, sheet metal or other manufacturing materials. Additionally, the, each or at least one pathway 90 through which the crustaceans may move between zones 60, 70, is configured to provide traction to crustaceans, and so assist in facilitating transit of the crustaceans between said zones 60, 70. A texture 100 provides roughness to the internal surface structure of the pathways 90 of the culture vessel 10 allowing the crustaceans to grip the surface and pull themselves through to from zone 70 to 60. A floor structure, being the surface whereon crustaceans may crawl, may singularly define the internal surface structure. Alternatively, any wall structure may define the internal surface structure, or a combination thereof such as a conical wall structure where the floor and wall structures together make up the internal surface structure of the pathway 90. In one embodiment (shown as Figure 6), the texture 100 is provided by way of addition of a bead of hot glue material, other methods for the addition of a surface to provide traction may be suitable, including by adding grooves, or adhering non-slip materials to the inner surface of the pathway 90. It is understood that any such additional texture or roughness, whether applied to the surfaces or inherent in the surface material, may provide this feature of the invention, including, for example, through corrugations in the surface, the adhesion of sandpaper to the surface or through the use of a compliant surface material.

The culture vessel 10 could be set up with any number of feeding and non-feeding zones 60, 70, to allow for cyclical operation of the method. The zone 60 or 70 does not have to refer to a fixed region in the vessel 10, and may be redefined during the course of operation of the method. The redefinition of the zones can include the daily reversing of the barrier 40 configuration, feed station and/or water flow prior to the next dark phase and such that which was the feeding zone 60 becomes the nonfeeding zone 70 and vice versa. In doing so animals are encouraged to move back to the former nonfeeding zone (now feeding zone) during the next dark phase when attracted by feed. Figure 4 shows an additional variation to the vessel in which the region defining the feeding zone 60 is encircled by the region defining the non-feeding zone 70. Turning now to Figure 5, the apparatus may also alternatively exist with use of a continuous directional flow vessel (circular, continuous raceway, etc) utilising at least three regions. This arrangement allows the crustaceans to move sequentially and continuously between regions, stimulated by feed scent from the upstream region (being at that time upstream from the feeding zone 60). As the arrangement continues, the zones are redefined in the regions such that the third region can, once said crustaceans are contained therein, become a first zone whereby said first zone (in another region) becomes a second zone. Summarily, an apparatus and method for reducing cannibalism in crustaceans is disclosed. The apparatus and method have the potential to reduce the incidence of cannibalism in mass scale rearing and thus allow tank-based commercial scale communal culture of crustaceans (in this case spiny lobsters).

Legend

Examples

The following examples are not intended to limit the invention as described herein.

Example 1 (Version 1 }

Version 1 of Crustacean walkthrough cannibalism reduction technology (before development of the passageway as disclosed in Figure 1) demonstrated the following key points:

• The proportion of moult events observed in the second zones and first zones were significantly different to the expected moult proportion location according to the distribution of the lobsters in the second zone and first zone (%2 = 15.47; df = 1; p = 0.00) (Table 1).

• In the second zone, 20% of moulting events led to cannibalism, whereas in the first zone this was lower at 14.5%. This is lower than that observed in a concurrent study being undertaken at IMAS, which documented 23.3% of moults lead to cannibalism in communal culture without this technology (T. Kelly unpublished data).

• This experimental work demonstrated that P. ornatus feeding behaviour changes before moulting and this can be used to lower cannibalism, i.e., behavioural segregation under the walkthrough technology. Table 1. Summary of moulting and cannibalism in the Daily Migration System according to the three iterations categorised.

Iteration

(days of treatment) Variable zone 2 zone 1 Combined

Il Successful moults 1 2 3

(20) Cannibalism 0 2 2

12 Successful moults 1 3 4

(19) Cannibalism 0 0 0

Successful moults 2 12 14

13 Unsuccessful moults* 1 0 1

(81) Cannibalism 1 1 2

Total cannibalism 1 3 4

Observed total moult events

(moults and cannibalism) 5 21 26

Proportion of total moult events (%) 19.23 80.77

Expected total moults 14.92 11.08

Mean proportion of population migrated daily to, and remained in the feeding compartment (%) 57.38 42.62

Example 2 (Version 2 )

Under experimentation of Version 2 (Iteration 2) of the present invention: videography of lobsters revealed guarding of the passageway/barrier (stopping other specimens from passing), and some specimens migrating both ways. These data led to the development of the passageway (in this iteration a conical passageway) on the barrier - designed to mitigate the ability of lobsters to migrate backwards through the system. Under Iteration 2 (conical passageway), five lobsters were held for 16 days, with 4 specimens moulting in the first zone and none on the second zone. After moulting in the first zone, three of the four lobsters migrated through to the second zone, with the fourth specimen observed to migrate through to the second zone once disturbed at the morning inspection time. During this time there were 66 migrations to the second zone (including the lobster that had moulted on Day 1 and moved across once disturbed); conversely in the first zone there was only 4 occasions when lobsters remained the following day, with one of these data points a specimen that had moulted and remained behind. There was no cannibalism in the experiment during this time. Videography each night of the 16 days of the experiment revealed no lobsters were able to pass through the conical passageways in the reverse direction. Further, when using the conical passage or other configuration passageways the proportion of lobsters in the second zone was greatly increased: 94% of the population instead of 45-72% (Figure 7).

This experimental work demonstrated that P. ornatus feeding behaviour changes before moulting and this can be used to mitigate cannibalism, i.e., behavioural, and physical segregation under the technology of the present invention.

Embodiments of versions of the apparatus according to the present invention can be seen in Figures 1 - 6, the transition backwards and forwards between two chambers (Figure 1) or the continuous movement to successive chambers (Figure 5) where feed is provided daily.