GB2168231A - A method and plant for raising aqua culture organisms - Google Patents

Abstract

Aqua culture organisms, particularly fish, but also shellfish such as shrimps, are grown from fry into slaughter size in a plant comprising a suitable enclosure such as one or more vessels (10). The organisms are separated by means of a plurality of movable water penetrable partition walls (S1, S2, S3) which are moved relative to each other concurrently with the growth of the organisms in order to maintain the organism density in the enclosure relatively constant during the growth period. <IMAGE>

Description

SPECIFICATION A method and plantfor raising aqua culture organ isms The invention relatesto a method and a plantfor raising aqua culture organisms, from fry up to slaughter size. The invention is particularly intended for the raising of fish, but it may also be used for shellfish, for example, such as shrimps, crawfish, etc.

When raising fish in conventional plants the fish is usually confined in a substantially constant water volume during the entire growth period. The plant must therefore be dimensioned with a volume that is sufficiently large to secure thatthefish density, defined as the weight of fish per unit volume (kg/m3), will not be too high when the fish approaches slaughter size. In salmon and trout plants,forexampie, a fish density of about 40-50 kg/m3 is considered an optimum value. This involves that the plant during most of the growth period has an unused volume capacity, since the fish density in the fry stage and upwards is substantially below the optimum value, and usually only one fry generation peryear is grown into adultfish ready to be slaughtered, in one and the same plan.Alternatively, as the fish grows, it must be transferred into increasingly larger enclosures.

The main object ofthe present invention is to provide a plant system for raising aqua culture organisms, particularly fish, in which the volume capacity is optimally utilized at any time without the need of transferring the fish in a stressing and work-consumable manner. According to the invention this is achieved by using displaceabie, water penetrabel partition walls in the plant, as stated in detail in the accompanying patent claims.

With such a plant it will be possible to carry out an almost continuous slaughtering throughoutthe year of aqua culture organisms of relatively uniform size, by introducing in the plantthreeto five fry inputs during one growth cycle ofthe organism.

The invention is described in detail below with reference to the drawings in which: Fig. 1 shows an embodiment of a plant according to the invention as seen from above, Fig. 2 shows a section along the iine Il-Il offig. land Fig. 3-6 shows diagrammatically a preferred embodiment of a plant according to the invention seen from above in different stages.

Although the invention is described below in connection with the raising of fish, it is to be understood that its application is not limited to such organisms, rather, as previously mentioned it comprises aqua culture organisms in general. Thus, the plant as described may without substantial modifications just as well be used for raising shellfish.

The plant shown on fig. 1 and 2 comprises an enclosure in the form of avessel 10 having a substantially circular peripheral wall 11 and a conical lysteppped bottom 12. Lowermost in the peripheral wall lithe vessel has substantially tangential flowadjustable water inlet 13 covered by an inlet screen 14, and in the upper portion ofthe vessel there is a central outlet 15 with a screen 16 covering a concave weir plate 17 at the top of a down pipe 18 extending down through the vessel coaxiallytherein and outthrough the bottom of the vessel. A bottom screen 19 is disposed over a mud chamber 20 which is emptied through a mud removal pipe 21 externallyofthe vessel 10.The water level in the vessel 10 is indicated at 21, i.e. at the level of the upper edge of the weir plate 17.

The vessel 10 is normally adapted to be kept floating in the surface of a lake orsea area, but it may also be used in plants on land. Thevessel may also have a different ratio between diameter and height than that appearing from the drawing, for instance shallow vesselsforflatfish, shrimps etc.

Further, according to the invention, radially extend ing, water penetratable partition walls are disposed in the vessel displaceably relative to each other. The number of partition walls will depend on the number offry inputs, growth velocity of the organism and tolerable variation in slaughterweight. As an example three partition walls S1, S2 and S3, each consisting of a fine mesh stretched on a frame, are rotatablysup- ported on the central down pipe 18, so thatthewalls can rotate 360 in the vessel around the axis thereof.

Thus, the three partition walls S1, S2 and S3 divide the vessel 10 into three sectors or compartments l, ll and Ill of relatively variable size. According to the principle of the invention the smallest sector I may contain fish of a smallest size, requiring least space, sector II may contain fish of a medium size, while sector Ill contains fish of slaughter size or near slaughter size.

As the fish grows in the respective sectors I-Ill the partition walls S2 and S3 are roatated forwardly in the vessel, i.e. clockwise, such that the fish density in these sectors is always substantially constant on the desired level. The partition wall S1 is temporarily kept stationary, andthefish to be slaughtered is removed from sector Ill concurrently with the decreasing volume in this sector, such that also in sector Ill the fish density is kept substantially constant.

When S3 has been rotated all the way to S1 sector II has reached its maximum volume while the volume of sector Ill is zero, and all fish is removed from that sector. Atthistime the average weight ofthe fish in sector II will correspond to the average weight obtained by the fish in sector Ill at the starting point of the cycle. Similarly S2 will have reached an end position b, indicated with dash-point-line, in which sector I has a maximum volume andthefish in this sector has reached an average weight corresponding to the initial weight of the fish in sector II.

NowS1 is rotated an angleocclockwisetothe starting position 'a' of S2 to form, together with S3 which is now kept stationary, a new sector I, while S2 is rotated a corresponding angle a clockwise to the initial starting position 'd' of S3 to form a new sector 11 between S1 and S3, and a new cycle is started. The new sector I being filled with a new generation of fry, the fish that was in the initial sector I now being in the new sector 11, whilethefish in the initial sector II is now in ill.

Thus, in this initial condition ofthe plant sectors land II have their minimum volume and minimum average weight of the fish, while sector Ill has maximum volume and minimum average fish weight. When rotating S1 and S2 as described above for S2 and S3, and gradually removing fish to be slaughtered from sector Ill the fish density in the respective sectors l-lil is kept substantially constant in the vessel 10 in all the sectors or compartments l-lli. This implies that the volume capacity ofthe vessel 10 is fully utilized at any time, and largerproduction output is achieved than would be the case if the vessel 10 was used in a conventional mannerwithoutthe movable partition walls S1-S3, i.e. if itwasfilled with fish in a number intended to give the maximum allowable fish density when the fish has reached a weight close to the slaughter weight.

A preferred embodiment of a plant according to the invention is diagrammatically shown, seen from above, in figs. 3-6. The plant comprises four circular vessels A, B, C, D ofsubstantiallythe same design as the vessel 10 described above. Thefour circular vesselsA-D touches each othertangentially to define between them an area which togetherwith a suitable bottom forms a central basin M. The basin M is divided into four equally large chambers M1-M4 by stationary, orthogonally crossing partition walls 22 extending in planes passing through the axes of diagonallyoppo- site vessels A, C and B, D respectively.

Vessel A hasthree movable partition walls Si, S2, S3 like vessel 10 in the previous example, while vessel B, C and D have two movable partition walls S1 and S2.

Furthermore each vessel A-D, centrally in the vessel wall toward the basin M has a closable opening 23 which is halved by the outer end ofthe adjacent basin partition wall 22. The partition walls of the respective vessels A-D divide the plant as a whole into fou r volume variable compartments l-IV as explained in further detail below.

The above described plant is intended forthe growth of three fry generations yearly, for example rainbowtroat up to fish readyto be slaughtered, and continuous slaughtering through the year with a size variation below 25% of the weight of each single fish.

The operation ofthe system will now be explained with reference to a number example.

In the example each vessel A-D has a water volume of 1200 m3 which together with that of the central basin M represents a total watervolume of about 5000 m3. The fish density in the plant is intended to be kept on an optimal, substantially constant value of about 40 kg/m3, and intended total output perycar is 500 ton.

Other operational data in connection with the example are given in the following table.

sector I 11 III ": Sum Retention time i2' 120 120 Q-120 (days) Number of fishes 36.000 tO.Ou0 57.000 S;.000 Weight of each fish (kg) l.,5-0,3 0,3-1,0 1.0-2,5 2.$-4.0 Density (kgZm31 3e-4r 40 40 45 Total weight (ton) 3.2-11.9 11,9-60 60-114 114-0 103-196 Water volume (m ) 105-470 470-lS00 1500-2850 2850-0 4900-4800 Figs. 3-5 show the system in three different stages or phases during a growth period of about 120 days, while fig. 6 shews the plant atthe beginning of the next period of 120 days.At any time during the growth period the plant will have a partition wall in each vessel A-D oriented in a zero position aligned with the opposite, fixed basin partition wall 22, such that each vessel opening 23 is vertically bisected by the coinciding end edges of the vessel partition wall and basin partition wall. Th us, vessers 8 Bcan communicate through their respective opening halves into basin chamber M1; vessels B and C communicate via basin chamber M2 and vessels C and D communicates via basin chambers M3 while basin D can communicate with basin chamber M4, since the opening half of vessel A into chamber Mq will normality be closed.

Fig. 3 illustrates the plant in a starting or initial condition at the beginning of a growth period of 120 days, fig. 4 illustrates the situation about half way through the period, while fig. 5 illustrates the condition atthetermination ofthegrowth period. In the following description the reference sign of the respective vessels A-D has been placed in front ofthe reference sign forthe respective movable partition walls S1-S3 in orderto provide a simple way of stating the partition wall in question. Thus, AS1 means the partition wall S1 in vessel A, BS2 is the partition wall S2 in vessel B and on.

In the initial condition as shown in fig. 3 one partition wall S, in all fourvessels is oriented in zero position aligned with the basin partition walls 22. AS2 has been rotated about 30 forward, i.e. clockwise, relative to AS1 to define between those partition walls a compartment or sector I with a volume of about 105 m3. Sector I is filled with fry in a number of about 63 000 and having an average weight of 0,05kg, giving a fish density of about 30 kg/m3.At the same time AS2 and AS3 define a sector II about 141 corresponding to a watervolume of about 470 m3filled with fish of an average weight of about 0,3 kg, i.e. a fish density of about40 kg/m3, AS3 and AS1 + BS1 and BS2 via basin chamber M1 form a sector Ill of altogether about 4300 corresponding to a water volume of about 1500 m3, filled with fish of average weight 1,0 kg and fish density about 40 kg/m3, and finally BS2 and BS7 together with the entire vessels C and D via basin chambers M2 and M3togetherform a sector IV of about 810 corresponding to a watervolume of 2850 m3, filled with fish of average weight kg and a fish density of about 40 kg/m3.In this initial condition sectors 1, II and Ill have their minimum volume while sector IV has its maximum volume.

Asthefish grows the respective partition walls are rotated clockwise for gradually increasing the water volume in sectors 1,11 and Ill, and correspondingly gradual reducing the volume removed from sector IV to renderthefish density concurrently removed from sector IV to renderthefish density always up to about 40 kg/m3 in allfoursectors.

In fig. 4the positions ofthe movable partition wails are illustrated in an intermediate position which they occupy after about 80 days relative to the initial positions shown in fig. 3. AS2 is here moved clockwise all the way to join AS1 in zero position; BS2 is moved clockwise to zero position while BS1 is moved about 30 clockwise defining on one side togetherwith BS2, basin chamberM1,AS2andAS1 an extended sector II, and on the other side together with BS2, vessel C and via basin chamber M2 and DS1 and D52 via basin chamber M3 an extended sector Ill; while S1 and S2 on their other side in vessel D form an approximately halved sector IV relative to the initial condition offig.3,thefish content in the lattersector also being approximately halved to maintain approx imatelythe sarneffsh density In the final stage shown in fig. 5, i.e. 120 days after the condition shown in fig. 3, the respective partition walls have been moved clockwise to their end positions giving maximum water volume for sectors I, II and Ill, whilethewatervolume in sector IV is zero and all fish, with afinal weight of about4 kg, is removed from this sector.The fish in the three remaining sectors or compartments I, II and Ill have now an average weight of 0,3, 1,0 and 2,0 kg respectively.

Nowthe next 120 days growth period is started by shifting the various partition walls to the positions illustrated in fig. 6, i.e. with the plant in the same starting position as shown in fig. 3, but with different partition walls in the respective starting positions.

In this new starting condition ofthe plant a new generation of fry is introduced in the new sector I, the fish that initially. i.e. in the preceeding growth period, grew in sector I is now in sector II with an average weight of 0,3 kg, the fish initially in sector II is in new sector Ill with average weight 1 kg, and the fish in initial sector Ill in new sector IV with average weight 2 kg, and the above described cycle is repeated.

Thus, the transfer offish from one sector or compartment to the next simply takes place by moving the partition walls into new positions as explained above. The rotation of the partition walls during the 120 days period may be carried out manually or mechanically, more or less stepwise or continuously.

During a 120 days growth period, i.e. during the time between the stages shown in fig. 3 and 6, a more or less continuous sorting of the fish may be carried out by means of "sorting gates" which are swept through the various sectors, or by transferring the fish to the central basin M where it is sorted.

Although a system comprised of four circular vessels as in the above example is preferred, also systems comprising three, five or more vessels may be contemplated.

Claims (7)

1. A method of raising aqua culture organisms, particularly fish, from fry to slaughtersize in an enclosure comprising the steps of keeping organisms of different size separated by means of a plurality of movable water penetrable partition walls, and moving said partition walls concurrently with the growth ofthe orgamisms in orderto maintain the organism density ofthe enclosure relatively constant during the growth period.

2. A plant for raising aqua culture organisms, particularly fish, from fry to slaughtersize, compris ing an enclosurefor containing the organisms in the growth period, wherein said enclosure comprises movable. partitionwallsdividing said enclosure into a plurality of compartments having variablewater volume.

3. A plant according to claim 2, wherein the enclosure is in the form of a substantially circular vessel and that said partition walls extend radially relative to the axis of said vessel and are rotatable about said axis.

4. A plant according to claim 2, wherein said enclosure is in the form ofthree or more vessels engaging each othertangentially,each vessel having radialiy extending partition walls rotatable about the axis of said vessels, said vessels defining between them a common basin through which the vessels can communicate.

5. A plant according to claim 4, comprising four circularvessels, said common basin being divided into four chambers each communicating with two adjacent vessels.

6. A method of raising aqua culture organisms, particularly fish, from fry to slaughter size in an enclosure, substantially as herein described.

7. A plantfor raising aqua culture organisms, particularly fish, from fryto slaughtersize, substantially as herein described and as illustrated in any of the acompanying drawings.