GB2026823A - Improvements relating to the rearing of fish and other marine creatures - Google Patents

Abstract

A floating raceway 10 for the rearing of fish comprises a fish-rearing region through which water is passed, the raceway having buoyancy which will support it such that when it is floating on water, the water in the fish-rearing region is at a higher level that the outside water on which it is floating, and the bottom 12 when the raceway is floating on water slopes downwardly from a water inlet to a water outlet. <IMAGE>

Description

SPECIFICATION Improvements relating to the rearing of fish and other marine creatures This invention relates to the rearing of fish and other marine creatures. In particular, the invention relates to a raceway which will float on expanses of water and in which the fish are contained for rearing.

There are areas of the world where intensive fishing has led to depletion of the natural stocks of fish and so there is an increasing interest in aquaculture or fish farming. In addition, when fishing boats have to travel long distances to obtain their catches, the cost of fish becomes higher because of increases in the price of oil.

Normally, fresh water aquaculture is carried out in land-based ponds filled with fresh water from various sources. Such systems are economical where flat land is readily available and inexpensive. However, where land availability is limited, aquaculture finds itself in competition with demand for land for housing and industry and also for agricultural purposes. Such a situation exists, for instance, in Hong Kong where the area of land in the vicinity of Deep Bay for fresh and brackish water pond systems is steadily being diminished under Government land resumption policies.

Salt water aquaculture is normally carried out by two systems. In one system, fish are contained in cages or netted enclosures within the sea or floating in the sea and the water changes necessary are effected by natural current and tidal flows. In the other system, fish are contained in tanks on land, close to the sea but above high water level and salt water is pumped to these tanks. This type of system is generally referred to as a raceway system and the energy cost of pumping is a significant cost item.

The invention has been made with these points in mind and it is an object of this invention to provide a raceway which can be used in fish rearing and farming which does not require too much energy for pumping water through the raceway.

According to the invention, there is provided a floating raceway for the rearing of fish or other marine creatures comprising a fish-containing region through which water is passed defined within outer walls and a bottom, the raceway having buoyancy which supports the raceway such that, when it is floating on water, the water in the fish-containing region is at a higher level than the outside water on which it is floating, and the bottom, when the raceway is floating in water, slopes downwardly from a water inlet to a water outlet.

Because the raceway floats on its surrounding water, the head of water to be pumped into the raceway is consistent, irrespective of the level of the surrounding water in relation to land and need only be a very small head; often a head of water of a few centimeters, e.g. 5 to 20cm, will be sufficient. This greatly reduces pumping energy requirements which is one of the major costs in fish farming.Thus the raceway of the invention can be used on the sea and the head of water will be constant irrespective of the state of the tide whereas if the raceway were installed on land, the minimum head of water be pumped could be no less than the normal for a raceway according to the invention when the tide was at its highest and would be increased by the rise and fall of the tide to a maximum at low tide which could be many times the head required for a raceway according to the invention. Equally, the raceway of the invention could be floated on inland water such as, for example, a pond, lakes or a reservoir where again the water levels may be subject to large changes.Again, if the raceway were to be positioned on land adjacent, say, a reservoir, then the head of water to be pumped could vary over a very large range and be very high when the reservoir was at a low level.

In a raceway according to the invention, it will be noted that the bottom is arranged to slope downwardly from the water inlet to the water outlet. The resulting gravitational fall induces a steady flow of water throughout the whole cross-section of the raceway. The slope can be quite small, e.g. from 1/2" to 5 and more preferably from about 1" to about 2".

In choosing the slope, one factor which should be considered is to try to provide a substantially constant depth of water from the inlet to the outlet As a result, good oxygenation of the water and good cleansing action of the base of the raceway, which aids the purging of debris and undesirable waste, will be achieved. These are most important in fish farming since hygiene is of the utmost importance where fish are stocked at a high biomass and good oxygenation of the water is also vital both for the health and efficiency of growth of the fish.

The raceway according to the invention has its own buoyancy which can be provided in a number of ways. Thus, separate buoyancy bags can be attached to the raceway or the raceway can have built-in buoyancy compartments. As a result of the buoyancy which is provided, water which is pumped into the inlet of the raceway can be arranged so that the internal water level slightly exceeds the external water level of the surrounding water. In addition, the buoyancy can be used to provide a barrier which prevents undue inundation from the external water by wave action and also ensures that in the case of totak inundation of the raceway, it will not sink.

Thus, it will often be desirable for the water pumped into the raceway to be different from that in which the raceway floats. For example, whilst one would not normally pump fresh water into a raceway floating on the sea, it might well be desirable to pump through the raceway seawater from an inlet positioned well out to sea or deep down so as to provide purer and fresher seawater than that on which the raceway is floating close to land.

In the floating raceway of the invention, water in which the fish are reared is pumped through the system. Thus the raceway does not rely on currents in the water on which it is floating to change the water in the raceway. Thus, a positive flow of water through the raceway is essential to farm the fish intensively so as to control the food given to the fish and use the food efficiently and also to control factors such as the degree of oxygenation and temperature of the water, all of which need to be chosen to obtain optimum growth results.

Because of the buoyancy of the raceway and the fact that the water level inside will be slightly higher than outside, it is possible for the outlet from the raceway to be no more than a vent which is below the external water level. In this way, by pumping the water into the raceway, it will flow by gravity through the raceway to the outlet and will then be vented. In addition, the venting is quite automatic so that if too much water is pumped in at the inlet or water enters the tank unintentionally through sea wave action, the excess will automatically leave via the vent without requiring special control apparatus.

A further advantage of the invention is that in places such as Hong Kong where flat land is at a premium, raceways according to the invention can be placed on reservoirs or on the sea and do not need to take up scarce flat land. This again results in an important cost advantage particularly in places where land is expensive.

The raceway of the invention can be constructed from a wide range of materials. Thus, for example, the raceway could be made from rigid materials such as ferrocement, glass reinforced plastic (g.r.p.) orwood. In an alternative construction, the raceway could be made from a flexible material such as a fabric reinforced rubber or plastics material rather akin to an inflatable dinghy. In such a case, the raceway may comprise an inflated collar which provides the buoyancy and defines the periphery of the raceway and a base which would be a thin sheet of impermeable or semi-permeable material.

The choice of a rigid or a flexible material will largely depend upon the environment in which the raceway is to be placed. Thus, for example, if the raceway is to be placed in sheltered or inland waters, a rigid construction may well be more satisfactory, whereas for raceways to be placed at sea, a flexible construction is preferred so that the raceways are capable of absorbing the effect of waves, tidal movements and buffetting against adjacent raceways or floating debris.

One advantage of a rigid raceway is that it provides for relatively easy management of the fish.

Thus, a large number of raceways can be closecoupled together and where the water depth within the raceway is low, e.g. a meter or less, workers can easily enter the raceway and stand up in itto carry out work such as cleaning or sampling the fish.

The raceway of the invention can be constructed in any convenient shape provided there is a reasonably uniform flow of water through the raceway and so a progressive fall from the inlet to the outlet. By way of example, the raceway, whether rigid or flexible could be of a rectangular shape when viewed in plan, particularly an elongated rectangular shape with the water entering at one end and leaving at the other end. Alternatively, the raceway, particularly when made of flexible material, can be of circular or regular polygon shape with the water injected substantially tangentially near the periphery and extracted near the centre so that the water adopts a spiral or helical flow from the outside to the centre of the raceway.In the case of a flexible raceway, the bottom of such a circular or polygon-shaped raceway will automaticallytake up a regular slope from the periphery to the centre due to the pressure of the internal water whereas in the case of a rectangularshaped tank, the sloping bottom will normally be produced by an appropriate shape of the raceway.

Alternatively, however, with a rigid raceway, the required slope for the bottom can be provided by adjustment of the buoyancy of the raceway as between the inlet and the outlet end of the raceway.

There are a number of possible arrangements for the water outlets which can be used aione or in combination. Thus, a simple hole or combination of holes through the wall of the floating raceway can be placed below the external equilibrium water line.

Such a simple arrangement, although not exclusively useful with rigid raceways, ensures that the internal water in the raceway is always maintained close to equilibrium level, even in the event of pump failure.

In another arrangement, a standpipe overflow venting system with the entry to the standpipe placed at or above the equilibrium level. The advantage of the standpipe exit system is that with pumped water inlet systems, the depth of water in the raceway can be adjusted easily by increasing the depth of the standpipe.

A further arrangement consists of a syphonic outlet system with the water entry inlet to the syphon being set at or below the equilibrium fill level, the water outlet being set at or below the external water line. If the head of the syphon is set below the maximum possiblefill ievel,the syphon will be selfpriming. The pressure drop driving the system is close to the water level difference between the internal water level under equilibrium and the external water level. The syphonic outlet system has a number of advantages. The inlet and outlet levels of the syphon can be adjusted over a wide range; thus the inlet level can be set close to the floor of the raceway, creating a suctioning effect for debris.The outlet level of the syphon can be set well below the external water level, thus depositing outflowing debris close to the bottom of the pond, lake or reservoir in which the raceway is floating. If either the inlet level or the outlet level is set so that periodically, the syphon is broken by air entering the syphon through wave action, or if a deliberate small air bleed ultimately breaks the syphon, then the syphon will restart when the fill water level exceeds the head of the syphon. Under these conditions, high purging flow will take place for a short period at either random or regular intervals and this will aid cleaning action and this also avoids stale and stagnant areas of water in the fish-containing region.

A high level overflow orifice can be combined with such a syphonic arrangement to provide either random or regular purging floating debris.

At the water inlet to the fish-containing region of the raceway, the water entry arrangement may be free fall water entry using a pumped water source.

The advantage of such a system is the facility to improve oxygenation of the water through either free fall or a forced jet system. Alternatively, a syphonic water entry system may be used with the inlet level being set below the equilibrium water level. The advantage of a syphonic water input system is that one can use a low pumping head and hence mainimum pumping energy requirements are experienced with this arrangement, provided that adequately oxygenated source water is available.

Where the raceway if floating on the sea which is subject to tidal movements, it is possible to use a system where the pumping head for the water is provided by sea water entrapped at high tide and allowed only to flow away under gravity to the raceways with the raceways floating in an enclosed region from which the water is evacuated at low tide and then sealed against entry from the rising tide.

Such a system requires very little operating energy consumption, energy being required only to open and shut seawater valves and gates which would be possible with manual labour. Such a system would be particularly suitable for developing countries and remote locations.

The invention will now be illustrated, by way of example, with reference to the accompanying drawings, in which: Figure lisa longitudinal section through a rigid raceway according to the invention shown floating on water; Figure 2 is a section on the line 2-2 of Figure 1; Figure 3 is a cross-section through a flexible raceway according to the invention shown floating on water; Figures 4to 6 are sectional details showing three different forms of simple water outlets; Figures 7and 8 are sectional details showing two possible types of standpipe water outlet; and Figures 9 and 10 are sectional details showing two alternative forms of syphonic water outlet from a raceway according to the invention.

The raceway 10 shown in Figures 1 and 2 is in the form of a rigid tank which in plan view is cylindrical.

It has a bottom 12 which slopes from the end adjacent a water inlet 14 to the end adjacent a water outlet 16. The angle of slope is not great but is of the order of 1" to 2".

The tank has longitudinal side walls 18 and end walls 20. Integrally formed with or attached to the side and end walls adjacent their tops is buoyancy 22.

Conveniently, the tank could be of the order of 15 to 30m long and 2 to 5m wide whilst the maximum depth could be of the order of 1 to 2m.

The raceway 10 is shown floating in surrounding water, the level 24 of which is below the level 26 existing within the raceway. Water is pumped into the raceway through the inlet 14 by means of a pump (not shown) and is automatically vented through the outlet 16 which is positioned below the outside water level 24. The venting occurs automatically because of the greater head of water within the raceway.

The raceway 30 shown in Figure 2 is of flexible construction and is substantially circular as viewed in plan. The raceway includes a flexible sheet shaped so as to form when filled with water, side walls 32 and a sloping floor 34. The upper ends of the side walls 32 are attached to and pass over an annular inflated buoyancy ring 36.

The material of the walls and the inflated buoyancy can be, for example, a fabric reinforced rubber or plastics material and be akin to that used in the making of inflatable life rafts and the like.

As with the raceway shown in Figure 1, the water pumped in through the inlet 40 fills the raceway 30 to a level 26 which is above the level 24 of the surrounding water on which the raceway floats. At the centre of the sloping floor 34, there is an outlet 46 through which the water leaves. Because of the extra head of water within the raceway, the water leaves through the outlet 46 automatically and the floor 34 takes up a curved or sloping shape such that the bottom falls in the direction from the edge to the vent.

The water circulates through the raceway 30 in a spiral fashion and the water entering can, if desired, be given a component tangential to the periphery of the raceway. The water therefore circulates around within the raceway and spirals progressively inwardly until it leaves through the outlet 46 and so traverses a path, the floor of which slopes towards the outlet 46.

By way of example, the raceway 30 could be 10 to 20m in diameter, have a maximum depth of water of 0.5 to 1 m and have a ring 36 whose diameter is 0.5 to 1m.

The outlet 16 in the embodiment shown in Figures 1 and 2 and the outlet 46 in the embodiment shown in Figure 3 are both covered with suitable mesh or netting to prevent the fish contained within the raceway from leaving. in addition and particularly with the raceway 30, the area within which the fish swim can be surrounded by a net so as to prevent the escape of the fish in the event of swamping of the raceway.

The outlet from a raceway according to the invention can conveniently be a simple water vent whose outlet is positioned below the surrounding level 24 of water. Figures 4,5 and 6 show three simple outlets 16a, 16b and 16c, respectively which can, for example, be used with the raceway 10 shown in Figures 1 and 2. Because the water level 26 is higher within the raceway than the surrounding water level 24, the water will automatically discharge from the raceway.

Figures 7 and 8 show outlets in the form of standpipes and such outlets can be used with any form of raceway according to the invention. For example, the outlet, shown in Figure 7, includes an upright standpipe 50 positioned within a surrounding open-topped and open-bottomed pipe 52. In this way, the water enters the lower end of the pipe 52 and then spills over the top of the upright pipe 50 and leaves through the bottom of that pipe.

If desired, the pipe 50 can have a downward extension 50a as shown in Figure 8 so that the water is discharged from the raceway at a location remote from the raceway, e.g. some distance away from and/or some distance below the raceway.

Further possible outlets are shown in Figures 9 and 10 which illustrate the use of syphon outlet pipes 60 and 62. These pipes have inlets positioned below the water level 26 within the raceway and outlets positioned outside the raceway and beneath the surrounding water level 26 within the raceway and outlets positioned outside the raceway and beneath the surrounding water level 24. Once primed such syphons will operate to discharge water from the raceway.

In the case of the syphon pipe 60 shown in Figure 7, this syphon can operate intermittently. Thus once the water level reaches somewhere near the top of the side walls 20, the pipe 60 is self-priming and water can be discharged at a high rate which is faster than the rate of entry of the water until the inlet 60a of the syphon becomes exposed to the air when the water level in the raceway is reduced sufficiently.

The pipe 60 will not then discharge again until the water in the raceway covers the top of the pipe 60.

Claims (13)

1. Afloating racewayforthe rearing offish or other marine creatures, comprising a fish-containing region through which water is passed and which is defined within outer walls and a bottom, the raceway having buoyancy which will support it such that, when it is floating on water, the water in the fish-containing region is at a higher level than the outside water on which it is floating, and the bottom, when the raceway is floating on water, sloping downwardly from a water inlet to a water outlet.

2. A raceway as claimed in Claim 1, in which the bottom, when the raceway is floating on water, slopes at an angle of rom to 5 relative the horizontal.

3. A raceway as claimed in Claim 1 or Claim 2, in which connected to the water inlet is a water conduit having an inlet remote from the location of the raceway and water is arranged to be pumped from that remote inlet to the fish-containing region of the raceway.

4. A raceway as claimed in any preceding claim in which the outer walls and bottom are made of rigid materials.

5. A raceway as claimed in any of claims 1 to 3, in which the outer walls and bottom are made of a flexible material and the buoyancy is provided by an inflated collar which additionally imparts shape to the raceway.

6. A raceway as claimed in any preceding claim which, in plan view, is of generally rectangular construction, the water inlet being adjacent one end of the rectangle and the water outlet being adjacent the other end so that the water in the fish-containing region passes along the length of the rectangle.

7. A raceway as claimed in any of claims 1 to 5 which, in plan view, is of generally circular or regular polygon shapes, the water inlet being adjacent the outer wall of the fish-containing region so that the water enters substantially tangentially, and the wates outlet being adjacentthe centre of the base so that the water in the fish-containing region passes in a spiral or helical fashion from the outside to the centre.

8. A raceway as claimed in any preceding claim, in which the water outlet is a.vent positioned below the water level of the surrounding water on which the raceway floats.

9. A raceway as claimed in any of claims 1 to 7, in which the water outlet comprises a standpipe overflow vent, the entry to the standpipe being at the desired level of water at the outlet from the fishcontaining region.

10. A raceway as claimed in any of claims 1 to 7, in which the water outlet is a syphon whose inlet is at or below the desired level of water at the outlet from the fish-containing region and whose outlet is at or below the level of the surrounding water.

11. A raceway as claimed in Claim 10 in which the means are provided to break the syphon effect through the syphon periodically.

12. A raceway as claimed in any preceding claim, in which the pumping headforthewaterforthe fish-containing region is arranged to be provided by sea water entrapped at high tide and allowed to flow by gravity to the raceway, the raceway being arranged to be floating on an enclosed region from which the water is evacuated at low tide and then sealed against entry from the rising tide.

13. Afloating raceway substantially as herein described with reference to Figures 1 and 2, Figure 3 or Figures 1 and 2 or 3 as mcdified by anv of Figures 4to 10, of the accompanying drawings.