PLANT FOR GROWING FISH

Abstract: A plant for growing fish comprises a number of adjacent pools (23) to which water is supplied at one end and which, at the other end, have a water outlet in the form of a narrow gap close to the bottom. Since the depth of the water in the pools (23) is relatively small, the fish are forced to move close to the bottom and, by their fin movements, keep the waste collected on the bottom in motion and cause it to move with the flowing water to the outlet opening into a space (20), the bottom of which is situated at a lower level than the bottom of the pools (23). The space has an overflow edge on a level with the water surface in the pools, thus causing the waste coming through the outlet to sink down to the bottom of the space from where it is conducted to a purification plant (38, 39), while clean water flows upwards over the overflow edge to an outlet duct (40) from where it is discharged into a lake or water course and/or recycled to the pool inlet.

Description: PLANT FOR GROWING FISH The present invention relates to a plant for growing fish, comprising adjacent pools in which a continuous flow of water is maintained. The growing of fish starts in a separate growing station where the roe is brooded and fry are raised to sufficiently large fish which are called seed-fish and sold to growers for further growing and, finally, slaugh¬ ter. Growing is normally conducted in net tanks, approxi¬ mately 4 m deep, each suspended in a so-called tank frame supported by floating bodies. On delivery, the seed-fish are two years old and have a minimum weight of 1 kg. Delivery usually takes place in May, whereas slaughter * takes place at the end of October in the same year, when the weight of the fish has increased to approximately 3 kg. The interest in growing fish has increased consider¬ ably in recent years, but the above-mentioned tank growing technique has serious disadvantages. Thus, it is not possible to recover, in a profitable manner, the waste which settles at the sea bottom below the tanks and contaminates the water, resulting in a continuous, mostly prohibited environmental pollution. Moreover, the fodder consumption is high since, frequently, there is no time for the fish to eat before the fodder falls through the meshes of the tanks. A further difficulty resides in the transportation of seed-fish from the seed-fish growing • station to the tank growing plant because the transport of 1 ton of seed-fish requires at least 8000 litres of water. This means that if a tank grower intends to produce 60 tons of fish, for which, as has been mentioned above, 20 tons of seed-fish are required, he will need 160 tons of water. Again, tank growing usually takes place in the sea and since salt water becomes supercooled- in winter, the fish must be slaughtered before then. As a result, all tank growers will be slaughtering at the same time, thus flooding t e market. A large part of the fish must therefore be frozen, by which process the quality is deteriorated. Finally, tank growing plants are vulnerable both to storms and sabotage. The object of the present invention is to provide a new type of fish-growing plant with pools which elimi¬ nates the above-mentioned problems and brings several advantages. This object is achieved in that the plant has means for supplying water at one end of each pool approximately uniformly over the cross-sectional area of the pool, and for discharging water and waste at the other end of the pool via an outlet gap provided with a grating and extending across the pool between the lower edge of an end wall and the pool bottom, and that control means are provided to maintain such a maximum depth of water in the pools that the fish therein are forced to move close to the pool bottom so as to cause, by their fin movements, the waste collected on the bottom to move with the flowing water to the outlet gap. The invention will be described in detail below, reference being had to the enclosed drawings showing an embodiment. Fig.1 is a schematic plan view of a plant according to the invention; Fig. 2 is a vertical section of the plant according to Fig. 1; Fig. 3 is a cross- section of the pool outlets; and Fig. 4 is a vertical projection, partly in section, of the whole plant. The plant shown in the drawings has a foundation wall 10 resting on a base plate 11. The foundation wall - is rectangular and has two long sides 12, 14 and two short sides 13, 18. The foundation wall 10 defines the pool space, as will appear from Fig. 1, but supports also the roof 45 of the plant,as will be seen from Fig. 4. The space defined by the foundation wall comprises three intermediate walls 15, 16 and 17 extending parallel to the long sides 12, 14 of the wall. The first intermediate wall 15 defines, together with the neighbouring long side O PΓ 12 of the wall, an inlet duct 19. Between the intermediate wall 15 and the second intermediate wall 16, eight pools 23 are arranged. The third intermediate wall 17 defines, together with the second intermediate wall 16, a water space 20 (Figs. 1 and 3) and with the other long side 14 of the wall 10, an outlet duct 21. Between the inter¬ mediate walls 15 and 16, partition walls 22 are extending which separate the different pools 23. The partition walls 22 may be stationary or movable. Inside the short side 18, a transverse intermediate wall 24 is arranged which forms the long side of the outermost pool 23, i.e. the lowermost pool in Fig. 1. Between the transverse intermediate wall 24 and the short side 18, a space is provided which com¬ prises, for example, a slaughtering and packing room 25, a freezing space 26 and a space 27 for a reserve power plant. In the corner between the short side 18 and the long side 12, a pump well 28 is arranged, which has at least two submersible pumps (not shown), one of which is a reserve pump. Water is led to the pump well 28 by means of a pipe 37 and is transported from the pumps to the inlet duct 19. The water supplied to the inlet duct 19 flows, via openings in the intermediate wall 15 forming the pool end wall, into the pools 23 and is distributed as uniformly as possible over the cross-sectional area of each pool 23. The water flowing into the pools 23 is led off at the opposite end of the pools by means of an outlet gap 30 - extending transversely of the pools and arranged between the lower edge of the intermediate wall 16 which forms • the other end wall of the pools 23, and the pool bottom 11 (Fig. 3). The outlet gap 30 is covered by an inclined grating having mesh size such that the fish in the pools will not be carried along by the outflowing water. The space 20 defined between the walls 16 and 17 merges at the bottom into a cavity arranged in the base plate 11 and having a wall 31 extending along and approximately • opposite the intermediate wall 17, a bottom 32 and a wall 33 which slopes, upwardly from the bottom and, in the area of the outlet gap 30, merges into the base plate 11. The bottom 32 has outlets 34 connected to a discharge pipe 35 opening into a vortex separator 38 which in turn is connected to a settling pond 39. The outlet duct 21 between the intermediate wall 17 and the long side wall 14 has an outlet connectible, by means of a conduit -40, to the pump well 28 for reuse of the water which has flown through the pools, and a further outlet connected to an outlet conduit 36 which leads to a lake or a water course. Provided that there is sufficient fall, approxi¬ mately 2.5 m, a turbine 41 driving a generator may be arranged in the last-mentioned conduit. Normally, the water is discharged by means of the conduit 36 during operation of the turbine 41, but especially in winter, the conduit 36 is used for circulating the water which by pumping can be kept at a temperature well above the freezing point. As indicated in Fig. 3, the intermediate walls 16 and 17 preferably consist of horizontal planks stacked upon one another on their long side edges and kept in position by means of intermediate U-sections 29. At . he top, the U-sections* 29 of the intermediate wall 16 support a rail (not shown) which together with a rail on top of the long side 14 of the wall, forms a track, on which a service car 42 is movable transversely of all pools as shown in Fig. 1. The car 42 is used for example for picking up fish to be slaughtered. ' Transversely of all pools, a work bridge 43 extends which, in a suitable * manner, is movable along the pools and is used, for example, for feeding the fish. At least some of the pools 23 have a grating wall 44 extending between the partition walls of the pools and having a mesh size related to the fish in the pool. The grating wall 44 is displaceable along the associated pool in order to define the space in which the fish can move, thereby establishing an appropriate fish density. The plant is used in the following manner for growing fish. The, in the drawing, lowermost pool 23 is slightly narrower than the other pools and is particularly intended for receiving fish fry, having the weight of- for example 5 g. At appropriate times, the growing fish are moved from one pool to the other. A special feature of the invention is that the depth of the water in the pools must not ex¬ ceed a predetermined limit which is set such that the fish are continuously forced to move close to the pool bottom and, by their fin movements, set the waste in motion such that it is carried along by the water flowing through the pool to the outlet gap 30. The arrangement of the water space 20, as illustrated in the drawing, causes the waste to sink to the bottom 32 of the space from where it can then be removed to the purification plant 38, 39 via the outlet 34 and the pipe 35. Between the outlets 34 in the bottom 32 of the space 20, walls inclining towards each other are arranged so that the falling waste will always be fed to an outlet 34. The water purified from waste by means of the purification plant 38, 39 may be led directly into a lake or water course. As illustrated by the arrows in Fig. 3, the major part of the outflowing water, which thus is essentially clean, flows up into the space 20 and over the edge of the wall 17 down .into the outlet duct 21, from where it is either led back to the pump well 28 via the conduit 40 or is discharged into a lake or water course after passing the turbine 41. It will thus be evident that the plant according to the invention causes no environmental problems. Contrary to conventional tank growing technique, the plant according to the invention requires energy for driving the pump, which may be regarded in and per se as a disadvantage, but this is well compensated for by the fact that the pumping of water prevents the plant from freezing so that fish can be grown throughout the year, and this is, of course, a condition for raising fry. However, it also means that the fish grower has work all the year round and can sell the fish when the demand is great. The pumping of water through the pools also makes it possible to treat the fish with suitable chemi¬ cals to eliminate, for example, attacks by parasites. It 5 should also be emphasised that the fish can consume all the fodder supplied, whereby considerable savings are obtained; for example, it has been calculated that in a 60—ton plant, 20 tons of fodder a year can be saved, that * is to say at least SEK 100,000. Furthermore, it should 0 be stressed that the turbine makes it possible to recover more than 50 % of the energy supplied. The invention has been described above with reference to a comparatively large plant with pools of concrete, but the principle of the invention is also applicable to 5 smaller plants, for example for raising fry, in which case plastic vats may be used as pools. In principle, these smaller plants are designed in the same way as the larger ones, although in the latter at least part of the purified outlet water is continuously recycled to the 0 inlet. . _O PΓ.

Claims: CLAIMS 1. A plant for growing fish, comprising adjacent pools (23) in which a continuous flow of water is main¬ tained, c h a r a c t e r i s e d in that means are provided for supplying water at one end of each pool (23) 5 approximately uniformly over the cross-sectional area of » the pool, and for discharging water and waste at the other end of the pool via an outlet gap (30) provided with a grating and extending across the pool (23) between the lower edge of an end wall (16) and the pool bottom (11), 0 and that control means are provided to maintain such a maximum depth of water in the pools (23) that the fish therein are forced to move close to the pool bottom (11) so as to cause, by ' their fin movements, the waste col¬ lected on the bottom to move with the flowing water to 5 the outlet gap (30). 2. A plant according to claim 1, c h a r a c ¬ t e r i s e d in that the outlet gap (30) opens in a water space (20) which is defined by the end wall (16) and a further wall (17) located at a distance therefrom 0 and having its upper edge on a level with the water surface in the pools (23, 31) and its lower, edge on a lower level than the bottom (11) of the pools, where said further wall (17) merges into the bottom (32) of the water space, said bottom, being connected, preferably 5 by means of a sloping wall (33), to the bottom (11) of the pools at the location of the outlet gap (30), whereby • any waste accompanying the water discharged through the outlet gap (30) is forced down to the bottom (32), while clean water.flows upwards and over the upper edge of said further wall to an outlet duct (21). 3. A plant according to claim 2, c h a r a c ¬ t e r i s e d in that a discharge pipe (35) is connected to the outlets (34) arranged in the bottom (32) of the water space (20) to lead the waste mixed with water to a purification plant., for example a vortex separator (38) with a settling pond (39), while the outlet duct (21) is connectible, by means of a return conduit (40), to said means for supplying water to the pools (23) for reuse of the water. 4. A plant according to claim 3, c h a r a c ¬ t e r i s e d in that the outlet duct (21) has a further outlet which communicates, via an outlet conduit (36), fcith a lake or water course at a lower level than the outlet duct (21), and that a turbine (41) driving a generator is connected in the conduit (36). 5. A plant according to any one of the preceding claims, c h a r a c t e r i s e d in that the pools (23) are defined by end walls (15, 16) and partition walls (22) extending therebetween, and that at least one and preferably all pools (23) have a transverse grating wall (44) movable in the longitudinal direction of the pool to define a fish space in which an appropriate fish density can be maintained. 6. A plant according to any one of claims 2-5, c h a r a c t e r i s e d in that the end wall (16) at -the other end of the pools (23) and said further wall (17) consist of horizontal planks which are stacked upon one another on their longitudinal edges and are kept in position by means of vertical U-sections (29), the U- sections of the end wall (16) supporting at their top a rail which, together with a further rail on a wall defining part of the outlet duct (21), forms a track on which a service car (42) is movable. 7. A plant according to any one of the preceding ' claims, c h a r a c t e r i s e d in that it is made up of a foundation wall (10) resting on a base plate (11) and having intermediate walls parallel to the long sides (12, 14) of the wall, the first of said intermediate - walls defining, together with the first long side (12), an inlet duct (19) and forming one end wall (15) of the pools (23), the second intermediate wall forming the other end wall (16) .of the pools, and the third inter ¬ mediate wall defining, together with said second inter ¬ mediate wall, the water space (20 ) and, together with the other long side (14), the outlet duct ( 21 ) , and that the roof (45) of the plant rests on the upper side of the foundation wall ( 10 ) .

Inventors: NYSTROEM STIG GOERAN, NYSTROEM, STIG, GOERAN
Applicants: NYSTROEM STIG GOERAN, NYSTROEM, STIG, GOERAN
Application year: 1984
Main classification: A01K61
IPC codes: A01K61