METHOD FOR PRODUCING FISH FRY FOOD AND COMPOSITIONS THEREOF

FIELD OF THE INVENTION

The present invention relates generally to the field of fish farming. In particular, the present invention relates to a method for artificially stimulating the hatching of zooplankton resting egg species, so as to provide a low-cost and efficient source of food for fish larvae.

BACKGROUND OF THE INVENTION

Fingerling production in inland fish culture very frequently follows the "mesocosm" approach that is based on filling earthen ponds (nursery ponds) and stocking them with fish fry in the proper timing. Fish fry feed primarily on zooplankton, whose most important species are Rotifera, Cladocera and Copepoda. The availability of zooplankton of appropriate size is critical for fish fry, so that several management techniques, mostly different fertilization procedures and specific zooplankton inoculation, are generally used.

In the fish-farming industry, there is a high demand for particular types of fish. A particularly serious difficult challenge is to secure a high survival rate of the hatched larvae of the species being cultivated. Expansion of the aquaculture industry requires that several problems be addressed, one of the most significant being the difficulty of supplying live prey organisms which provide a nutritionally adequate feed for the larvae. Larval fish in the wild consume a mixed population of plankton prey organisms which together provide a balanced nutrition. However, collecting plankton in sufficient quantities to meet the demand in aquaculture is not feasible. Other methods must be developed for supplying a sufficient and reliable amount of food for the fish fry.

In light of the above discussion, it is the main goal of present invention to describe a method for providing large quantities of zooplankton, as a source of food for fish fry. The present invention also relates to a method for artificially stimulating the hatching of eggs of plankton species, so as to provide a reliable source of food for fingerling fish.

SUMMARY OF THE INVENTION

Chemical communication is a well-known ecological phenomenon mediating interactions between organisms via infochemicals. Kairomones constitute the class of info-chemicals evoking a behavioral or physiological reaction in the receiver that is adaptively favorable for the receiver but not for the sender. Predator-derived kairomones play an important role in ecological and evolutionary processes that enable the prey to survive predation pressure. The term 'kairomone' refers in the present invention to any suitable kairomones, pheromones, chelating agents or a combination of the same.

The term 'pheromones' refers hereinafter to any chemical that triggers a natural behavioral response in another member of the same species, such as aggregation pheromones, alarm pheromones, epideictic pheromones, releaser pheromones, primer pheromones, territorial pheromones, trail pheromones, sex pheromones etc.

There are a wide variety of responses to predator chemical cues. The diversity of taxa which are responsive to predator kairomones in terrestrial, freshwater and marine habitats is broad. In aquatic ecosystems, planktonic organisms are able to detect the presence of potential predators through kairomones. This enables planktonic organisms to exhibit predator-specific responses that reduce predation risk. It is especially interesting to study predator-induced responses for planktonic prey, since there is little possibility of seeking a physical refuge from predators in the open water zone. It is known that behavioral, morphological and life-history changes in planktonic prey can offer refuge from predation. Chemically induced anti-predator defenses have been found in a wide range of different planktonic organisms among which are algae, ciliates, rotifers, insect larvae, and several planktonic crustaceans. (See Lass S. and Spaak P. "Chemically induced anti-predator defenses in plankton: a review" Hydrobiologia (2003) 491 : 221-239). Research has shown that, for example, Daphnia dispausing eggs adjust hatching in the presence of predator kairomones. (See Lass, S., et al., "Hatching with the enemy: Daphnia diapausing eggs hatch in the presence of fish kairomones", Chemoecology 2005, 15:7—12). Generally, research has been somewhat limited and highly specific to the type of plankton species and the specific type of system.

In the present invention, the approach is different and the main hypothesis is that similar high- pressure master factors occurring in most nursery ponds select identical or similar species and processes in the ponds. It is assumed that natural pulse systems colonized with fish are the

primary source for these zooplankton species, which are distributed worldwide by passive and anthropogenic dispersal. These convergent forces mask the divergent forces also acting in the ponds.

The dominant species found in all the different systems are: Brachiomis calyciflorus, B. angiilaris, B. plicatilis, Keratella tropica, Polyarthra vulgaris, Hexarthrafermica, H. intermedia, Ceriodaphnia comiita, Moina brachiata, M. micrura, Daphnia magna, Mesocyclops sp. There is good evidence that there is a large reserve of zooplankton resting stages in the sediments that can restore the planktonic population as conditions become suitable, and that have naturally pre-selected capabilities to participate in the new autochtonic or/and allochtonic community foundation.

There is also good evidence of the influence of predator kairomones (from fish present in the source of the filling water and from the fry stocked in the ponds) on the rotifer Brachiomis calyciflorus population regulation by resting eggs production and on hatching of resting eggs of rotifers and cladocerans. Such phenomena provide a valuable evolutionary advantage to avoid encounter with predators and/or allow an immediate anti-predator response. They can explain the pre-adaptive recruitment abilities of the zooplankton organisms that enable the colonization of the nursery ponds. Large species, preferred by fish larvae as prey, are more sensitive to such chemical clues than small species, as shown by the three zooplankton species Brachiomis angiilaris (the smallest), Brachiomis calyciflorus and Moina brachiata (the largest). There is also good evidence of chemical signals in the filling water that influence the hatching intensity of Brachiomis plicatilis from resting eggs, probably a valuable adaptation to predict reaching the carrying capacity of the system, and/or to reduce predation risk. In general the different responses of the zooplankton community reflect a selection compromise between food availability utilization and predation risk.

The explanation of succession based on competitive exclusion of small zooplankton species (Rotifers) by large ones (Cladocera) and the selective predation on large species by fish larvae ("size efficiency hypothesis") was herein found to be an over-simplification. Obvious indications of other competitive abilities related to environmental conditions, independent of species size and unrelated to the order of appearance of the different species in the succession, were found. Two principal simultaneously succession processes, that partly overlap but are not necessarily interdependent, could be identified. The first process is the irreversible appearance of a rotifer

"boom" community (boom- like reproduction), mainly of the filling water. The second one, dominated by the appearance of the cladoceran Moina brachiata that is supposed to replace the rotifers, is inconsistent and depends noticeably on the density of fish fry stocking. The conventional assumption that fish fry inserted into the developed communities of the nursery ponds "disturbs" the zooplankton succession process just by predation, is not correct. It is better to use a term such as "plastic succession" to express the versatile phenomena. Timing of fish fry stocking was found to be critical to create a proper match with zooplankton succession communities, and can explain (derived from match/mismatch situations) many of the inconsistent results documented in commercial fingerling production. Some simulated succession patterns showed situations of almost no direct influence of fry predation on zooplankton species. Mismatch situations have a further recruitment contribution to the "bank" of zooplankton resting stages in the sediment.

Zooplankton response to flooding and fertilization, in semi natural salty ponds in Zanzibar, was found similar to that of agriculture mesocosm systems. Kairomones have also been found to influence hatching of Brachionus plicatilis (Rotifera) resting eggs.

The term 'mesocosm' refers in the present invention to fresh water systems, brackish water systems, salt water systems, or any combination or mixtures thereof. The term also refers to macro and micro mesocosm systems. The term "micro-mesocosm" system refers in a non- limiting manner to e.g., a 0.5 to 5 cubic meter systems, specifically, e.g., 1 cubic meter water systems.

Separating the rotifer "boom" stage from the cladoceran stage is necessary for better management of the nursery mesocosm ponds. Using the mesocosm concept for zooplankton production only and its posterior transfer into tanks stocked with fry, as commonly done in marine institutes, is another interesting way to achieve better management. It is thus in the scope of the present invention to present a method for providing feed for fish larvae. The method comprises the steps of (a) providing an enriched sediment including one or more inactive zooplankton species; (b) adding to the sediment a solution containing at least one kairomone so as to result in hatching of the one or more inactive zooplankton species; and, (c) feeding fish larvae hatched species of zooplankton produced in step (b).

It is also in the scope of the present invention to present the method as described above, wherein the solution is added in an amount useful for providing a manipulated mesocosm of about 400

EUP/ml to about 1000 EUP/ml. It is further in the scope of the present invention to present the method as described above, wherein the solution is added in an amount useful for providing a manipulated mesocosm of about 400 EUP/ml to about 2000 EUP/ml climax density. It is further in the scope of the present invention to present the method as described above, wherein the solution is added in an amount useful for providing a manipulated mesocosm of about 40

ROT/ml to about 400 ROT /ml climax density.

It is also in the scope of the present invention to present the method as described above, wherein the zooplankton species are selected from the group consisting of Rotifera, Cladocera and

Copepoda.

It is also in the scope of the present invention to present the method as described above, wherein the method further comprises a step of adding to the enriched sediment at least one additive selected from the group consisting of vitamins, amino-acids, proteins, peptides, nitrogen-rich compositions, plants products and by products, animal processing products and by products, nutriating agents, minerals, salts, biocides, pigments, colorants, stabilizers, emulsifiers, or a combination of the same.

It is also in the scope of the present invention to present the method as described above, wherein the method further comprises the steps of obtaining a stackable incubation apparatus comprising; a liquid incubator bath, for incubating the enriched sediment; a cooling/heating circuit for controlling temperature of the bath; at least one growth pot immersed in the bath; a light source for directing light to the growth pots; and, an aerator for controlling oxygen in the inocula growth pots; propagating the one or more inactive zooplankton species in the growth pots; and, feeding the fish larvae with propagated zooplankton species.

It is also in the scope of the present invention to present the method as described above, wherein the stackable incubation apparatus additionally comprises a container for containing the kairomone solution.

It is also in the scope of the invention to present a fish larvae food produced by using a method comprising the steps of providing an enriched sediment including one or more inactive zooplankton species; adding a solution containing at least one kairomone to the enriched sediment; wherein the solution is adapted to stimulate hatching of the one or more inactive zooplankton species in a fish mesocosm.

It is also in the scope of the invention to present a fish larvae food as defined above, wherein the solution is added in an amount useful for providing a manipulated fish mesocosm of about 400 EUP/ml. to about 1000 EUP/ml; wherein the solution is added in an amount useful for providing a manipulated fish mesocosm of about 400 EUP/ml to about 2000 EUP/ml climax density; or wherein the solution is added in an amount useful for providing a manipulated fish mesocosm in an effective amount useful for providing a manipulated mesocosm of about 40 ROT/ml to about 400 ROT /ml climax density.

It is also in the scope of the invention to present a fish larvae food as defined above, wherein the zooplankton species are selected from the group consisting of: Rotifera, Cladocera and Copepoda.

It is also in the scope of the invention to present a fish larvae food as defined above, wherein the enriched sediment includes additives selected from the group consisting of vitamins, amino- acids, proteins, peptides, nitrogen-rich compositions, plant products and by-products, animal processing products and by products, nutriating agents, minerals, salts, biocides, pigments, colorants, stabilizers, emulsifiers, or a combination of the same.

It is also in the scope of the invention to present a fish larvae food as defined above, wherein the food is obtained using a stackable incubation apparatus; the apparatus comprising: a liquid incubator bath, for incubating the enriched sediment; a cooling/heating circuit for controlling the temperature of the bath; at least one growth pot immersed in the bath; a light source for directing ^" light to the growth pots; and an aerator for controlling oxygen in the inocula growth pots; wherein the stackable apparatus is useful for propagating the one or more inactive zooplankton species in the' growth pots, thereby providing food for feeding fish larvae. It is also in the scope of the invention to present a fish larvae food as defined above, wherein the stackable incubation apparatus additionally comprising a container for containing the solution. It is also in the scope of the invention to present a stackable incubation apparatus for use in the production of food for fish larvae, comprising ^' a stackable incubation apparatus. The apparatus comprising: a liquid incubator bath, for incubating the enriched sediment; a cooling/heating circuit for controlling temperature of the bath; at least one growth pot immersed in the bath; a light source for directing light to the growth pots; and, an aerator for controlling oxygen in the inocula growth pots; wherein the stackable apparatus is useful for propagating the one or more inactive zooplankton species in the growth pots, thereby providing food for feeding fish larvae.

The present invention also relates to a composition for artificially stimulating a colony of zooplankton, comprising at least one kairomone. The kairomone may be combined with any other suitable additives, such as, but not limited to proteins, stabilizers, etc... Additionally, the present invention relates to a fish larvae food, comprising zooplankton, wherein the zooplankton is obtained by providing enriched sediment including one or more inactive zooplankton species; and adding to the sediment an inoculating solution which contains at least one kairomone so as to result in timed and effective propagation of the one or more inactive zooplankton species.

The kairomone(s) may be artificially isolated and then ^' introduced into the system, or they may be presented via introduction of predetermined fish predator species known for producing specific kairomones. The zooplankton species which are propagated may be any species, such as, but not limited to, Rotifera, Claάocera and Copepoda.

It is further in the scope of the invention to provide mesocosm systems (e.g., fresh, brackish or salty waters) with a microcosm system, about 20,000 times smaller than the aforementioned correlated mesocosm system, and to manipulate the mesocosm system by means of kairomones, pheromones and chelating agents. In this manner the intended succession is provided, while intensification is applied. The intensification is achieved especially by introducing sufficient measures of organic additives.

It is further in the scope of the invention wherein the fish larvae food as defined in any o'f the above, further comprises additives. The additives are selected in a non-limiting manner from a group consisting of vitamins, amino-acids, proteins, peptides, nitrogen-rich compositions, plants products and by products,- animal processing products and by products, nutriating agents, minerals, salts, biocides, pigments, colorants, stabilizers, emulsifiers, or a combination of the same.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a brief description of the drawing, which is presented for the purposes of illustrating the development disclosed herein and not for the purposes of limiting the same. In order to understand the invention and to see how it may be implemented in practice, a preferred embodiments is now be described, by way of non-limiting example only, with reference to the accompanying drawing, in which

FIG. 1 is a schematic representation of an aspect of the invention; and FIG. 2 is a schematic representation of another aspect of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, various aspects of the invention will be described. For the purposes of explanation, specific configurations, examples and details are set forth in order to provide a thorough understanding of the invention. However, it will be also apparent to one skilled in the art that the invention may be practiced without specific details presented herein. Furthermore, well-known features may be omitted or simplified in order not to obscure the invention.

EXAMPLES

An inoculating stock solution containing inter alia Composition A, which is comprised of commercially available sediments, pre-collected natural occurring sediments or. mixtures of the same; Composition B, which is comprised of organic matter, such as yeast-based compositions; and

Composition C comprised of kairomones, pheromones, chelating agents or mixtures thereof. The inoculating stock is admixed in various manners, e.g., 50:150:2; 150:50:2; 75:75:5 weight ratio.

The stock solution is admixed with about 20 liters fresh water for 2 to 4 days, and then admixed in fresh water with various fish types, such as empire gudgeon, Melanotaema praecox etc. This fish larvae food yielded 70% surviving of larva, compared with 0 to 30% in control systems. A high growth rate and intensification of fish color were also achieved, relative to control systems.

Reference is now made to Fig. 1 which depicts in schematic form exemplary results of a simulation of a commercially manipulated earthen mesocosm, inoculated with aforementioned stocks of compositions A, B and C as above.

The left hand y axis peaks of Fig. 1 shows that the climax density of the manipulated (MAN in the figure) stage is much larger than the equivalent natural mesocosm stage -1000 EUP/ml vs. 20

EUP/ ml respectively.

The time before rotifers peak appearance shortened from day 14 to day 7-8. Climax density of the manipulated (MAN in the figure) stage is much larger than the equivalent natural mesocosm stage - 200 R0T/m"l vs. 20 ROT/ m"l respectively. (The two right hand y axis peaks)

Reference is now made to Fig. 2, which is a photograph of an incubation apparatus controlling temperature and aeration suitable for preparing and propagating stock solution inocula such as the above mentioned inoculating stock solution. The apparatus comprises a liquid bath enclosed in a housing about 50 cm deep and 100 cm wide. The bath rests on a removable tray, in which inocula growth pots 2.11 arranged in rows of about 3 deep of 8 pots per row are immersed. The bath may be removed for maintenance by removing panel 2.1 and sliding out tray 2.2. Growth conditions of the apparatus are principally maintained by the following: a. a light source 2.3; this may be a fluorescent light; b. a cooling circuit (2.41,2,2.43,2.45) for temperature control of the bath; and c. an aerator assembly 2.5 for controlling oxygen in the inocula growth pots.

The cooling circuit comprises, inter alia, 2.41 condensing coil, condenser 2.42 expansion valve, 2.43 evaporator coil, 2.45 compressor. It is acknowledged that in some embodiments the coolant may be ammonia, and in other embodiments the coolant may be another refrigerant fluid such as HCFC or R-22. Optionally a temperature sensor and/or thermostat is used to control the expansion valve for temperature regulation. Optionally, the cooling circuit may be adapted with means to function as a cooling/heating circuit.

The aerator comprises an air pump 2.5 which pumps air through aeration tubes 2.6. A programmable timer and electric switch 2.7 conveniently placed on the side of the apparatus are used to command the light source, cooling circuit and aerator. The device is provided with means to monitor and feedback data on oxygen levels in the growth pots to the aerator, and aeration or oxygenation may be regulated automatically or manually in some embodiments. In some embodiments the aerator may be adapted with means to bubble oxygen through the growth pots.

In some embodiments the functioning apparatus is stackable one on top of the other for efficient use of space.

Using the exemplar described above, about 4 gm of sediment material in about 1 liter of water incubated for 48 hours in the above apparatus will provide sufficient zooplankton for 1 liter of fish larvae.

While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub- combinations thereof. It is therefore intended that the following appended claim as and claims

hereafter introduced be interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.