Abstract:
A recirculated marine aquaculture system and process for growing crustaceans or other fish within a body of water. Water from the body of water is treated by stripping carbon dioxide and biological byproducts and by oxygenating the water. A water treatment unit may be provided to treat the water and provide movement to the body water. The water treatment unit can be configured to provide cavitation to the water, which aids in the removal of carbon dioxide and biological byproducts. Water may also be cycled through a deflocculation tank to reduce the floc of bacteria within the body of water to acceptable levels for optimal growth of crustaceans or other fish within a body of water. Using the system and the deflocculation tank has the advantage of significantly reducing the water exchange rates and even the water effluent, while maintaining acceptable water quality for growing crustaceans or other fish.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of U.S. application Ser. No. 12/028,097, entitled “SYSTEM FOR GROWING CRUSTACEANS AND OTHER FISH,” filed Feb. 8, 2008 now U.S. Pat. No. 7,682,504, which is incorporated herein by reference in its entirety, which in turn claims all available benefits of U.S. provisional application Ser. No. 60/904,262 filed Mar. 1, 2007. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to aquaculture systems for commercially raising fish, particularly crustaceans including, but not limited to, crayfish, crabs, lobster and shrimp. 
     In recent years the world has witnessed an alarming decline in commercial fisheries, the result of over fishing and environmental degradation. Over the years, many of the traditional sources for fish, i.e. lakes, rivers, streams, etc., have become contaminated with pollutants generated by the public. As a result, fewer fish are available in such sources; and, in addition, fish that are able to survive in the contaminated waters often themselves become contaminated and unfit for human consumption. According to the Food and Agriculture Organization (FAO) of the United Nations, nearly 70% of the world&#39;s commercial marine fisheries species are now fully exploited, overexploited or depleted. Based on anticipated population growth, it is estimated that the world&#39;s demand for seafood will double by the year 2025. Therefore, a growing gap is developing between demand and supply of fisheries products, which results in a growing seafood deficit. Even the most favorable estimates project that in the year 2025 the global demand for seafood will be twice as much as the commercial fisheries harvest. 
     It is very clear that the only way to meet the world&#39;s growing needs in fisheries products is through marine aquaculture systems—the farming of aquatic organisms in controlled environments. In response to the situation, global aquaculture production is expanding quickly. Aquaculture&#39;s contribution to the world&#39;s seafood supplies increased from 12 to 19% between 1984 and 1994. Worldwide, it is estimated that in order to close the increasing gap between demand and supply of aquatic products, aquaculture will need to increase production three-to-four-fold during the next two and a half decades. In this context, there is a compelling motivation to develop aquaculture systems of improved and commercially viable character for high volume production of aquatic species and environmental sustainability. 
     In an effort to eliminate the effects of marine aquaculture on the environment, and to optimize aquaculture production, an environmentally acceptable aquatic farming technology has emerged: the use of recirculated marine aquaculture systems (RMAS), in which the same water is continuously reused in operation of the system. These systems have many advantages over non-recirculating systems which typically require periodic water exchanges. There are drawbacks to periodic water exchanges; namely, additional water usage, waste material generation that may be adverse to the environment, and an increased cause of stress to the cultured aquatic species. Water re-use in the RMAS minimizes any adverse environmental burden created by the aquaculture system since there is minimal net waste material generation, and what waste is generated is easily handled by local sewer systems, or can be used as fertilizer. RMAS offer flexibility in location options including urban, rural, and inland, since they are not confined to coastal areas or open oceans. Unlike free-floating pens, process conditions can be better controlled within a RMAS. In addition, RMAS minimizes the stress caused to the cultured aquatic species by management of the waste material generation (carbon dioxide, protein, nitrates, nitrites, etc.) and preservation of the floc of beneficial bacteria without breaking the floc. Systems that break the floc of beneficial bacteria must be given additional time and fine tuning to create an effective relative proportion of beneficial bacteria to water. 
     RMAS typically includes a container containing a large quantity of water in which the fish are raised, and a filtration system for cleaning the water in the container. Such filtration systems typically include a particulate filter and a bio-filter. The particulate filter is used to remove solid particulate materials, such as fish waste and uneaten food, from the water. The bio-filter contains bacteria which removes ammonia and nitrates from the water, and also is used to oxygenate the water. Various types of filters have been used as particulate filters in aquaculture, including rotating drum filters. The use of rotating drum filters in aquaculture, however, has been limited by their high cost, their need for frequent maintenance, and the difficulty in cleaning the filtering surface of the filtering media. The filtering surface must be continuously cleaned to prevent the filtering surface from being clogged by the particulate matter. 
     In general, aquaculture systems of the prior art are not well designed for use in connection with crustaceans. As a result, the commercial aquaculture systems developed to date are highly variable in efficiency and output of product. Such systems are subject to numerous processing and operational deficiencies, including: sub-optimal production of fish; absence of control of process conditions; process instability; susceptibility to environmental pathogens; susceptibility to pollution; loss of stock; and the lack of well-defined optimal conditions for achieving maximal growth and production of the aquatic species being raised in the aquaculture system. 
     Despite the various features and benefits of the structures of the prior aquaculture systems, there remains a need for a recirculated marine aquaculture system and process that is specifically designed for crustaceans, including, but not limited to, crayfish, crabs, lobster and shrimp. There remains a specific need for a low-cost system that can grow crustaceans from an early post larval stage to a market ready stage at a well defined time interval that can be repeatedly cycled for optimum return on the system investment. 
     SUMMARY OF THE INVENTION 
     These several needs may be satisfied by a recirculated marine aquaculture system and process for growing crustaceans or other fish within a body of water. The RMAS system can include a water treatment unit suspended above, and at least partially submerged, within a body or container of water such as a fisheries tank, pool, pond or lake. A portion of the water is removed from the container in order to be treated by one or more components. Preferably, the water is treated with a single water treatment unit as described herein. The water treatment unit can include a stand pipe with a first propeller adapted to pump a portion of the body of water and a second propeller, elevated above the first propeller, adapted to cavitate water to be treated. The cavitation of water permits the removal of at least one of biological byproducts such as protein and carbon dioxide from the water. During cavitation, a plurality of microbubbles is generated to permit a larger interface between air and water. Dissolved and suspended biological particulates adhere to the surface of the microbubbles and are then removed from the container. The stand pipe can include one or more laterally directed openings positioned above the second propeller. These openings are where through the pumped water flows after cavitation. The openings are elevated above the upper surface of the body of water to allow the water to fall to the upper surface of the body of water, where the water mixes with air drawn into an air inlet of the water treatment unit for oxygenation of the water. Water is then returned to the container. 
     The body of water can be provided with a floc of beneficial bacteria to break down organic matter, e.g., wastes from the crustaceans or other fish, and convert ammonia into nitrites and nitrites into nitrates. The floc is measured periodically with a measurement device suitable to measure settling solids, such as an Imhoff cone. To reduce the floc of beneficial bacteria to suitable relative proportions for optimal growth of crustaceans or other fish (e.g., 20-40 ppt), without breaking the floc, the RMAS system may also include a deflocculation tank. The body of water of the RMAS can be cycled through the deflocculation tank coupled to the body of water. The deflocculation tank has an inlet for receiving water from the body of water for treatment. The deflocculation tank includes a floor and sidewalls extending upward from the floor to define a cavity that is filled with the body of water to be treated. A first column and/or a second column extend upright within the cavity. The first column has a bottom sealably attached to the floor and a top opening with a passageway extending therebetween. Water is directed from the inlet to the top opening of the first column to flow in a toroidal pattern around the first column for a sufficient period of time to reduce the relative proportion of the floc. The second column is sized to fit within the passageway of the first column in order to define a space between the columns that is capable of receiving water from the body of water after flowing between the area between the inner walls of the tank cavity and the first column. The second column has top and bottom openings with a passageway extending therebetween. The top opening of the second column extends beyond the top opening of the first column, and the bottom opening of the second column is elevated above the bottom of the tank to form a gap for receiving water from the passageway of the first column. A gas bubble source can be positioned within the first column at the bottom of the tank in alignment with the passageway of the second column. The gas bubble source is capable of directing air bubbles in the passageway of the second column in order to lift the water therethrough above at least the top opening of the first column for exiting out of the top opening of the second column. The treated water with a reduced level of floc of bacteria is then returned to the body of water. The flow rates of the return may be maintained to control the period of flow with the tank. In other system embodiments, a RMAS includes the water treatment unit, the deflocculation tank, or various embodiments of both. 
     Furthermore, several processes are provided herein. In a first process embodiment, a process for growing crustaceans or other fish in a RMAS comprises: housing crustaceans or other fish in a container containing a body of water, having a bottom and a side extending upward to a top edge located above an upper surface of the body of water; removing a portion of the body of water from said container for treatment; cavitating said treatable portion of water to strip at least one of a biological byproduct such as protein and carbon dioxide from said treatable portion of water; mixing said treatable portion of water with air for oxygenation thereof; and returning said treatable portion of water to the body of water within said container. Other aspects include: pumping a portion of said body of water to an elevated position above the upper surface of the body of water for the mixing step; removing a portion of the body of water for reducing a relative proportion of floc of beneficial bacteria in the body of water, and afterwards returning the portion of water to the body of water; maintaining a proportional characteristic of the body of water within a predetermined range, the characteristic including at least one of: temperature in the range of about 80-90° F.; oxygen in the range of about 1-10 ppm; carbon dioxide in the range of less than 15 ppm; ammonia in the range of about 0.1-3 ppm; nitrites in the range of less than 2 ppm; nitrates in the range of about 0.1-20 ppm; salinity in the range of about 5-35 ppt; alkalinity in the range of greater than 150 ppm; pH in the range of about 7-9; and beneficial bacteria in the range of about up to 40 ppt. 
     In a second process embodiment, a process for reducing a floc of bacteria in a RMAS includes moving a treatable portion of water into the cavity of the deflocculation tank through the inlet of the deflocculation tank, the treatable portion of water having a head pressure, and directing the treatable portion of water from the inlet to the top opening of the first column to flow in a toroidal pattern around the first column within the cavity for a sufficient period of time to reduce the relative proportion of floc of beneficial bacteria. Other steps may include: activating the gas bubble source of the deflocculation tank; moving the treatable portion of water into the passageway of the first column from the top opening to the gap near the bottom opening of the second column; lifting the treatable portion of water through the top opening of the second column; and returning the treatable portion of water to the body of water within the container by movement of the treatable portion of water through the outlet of the deflocculation tank. The flow rate of the treatable portion of water that is returned to the body of water within the container can be maintained between about 5 gpm to about 15 gpm, and the sufficient period of time to reduce the relative proportion of floc of beneficial bacteria can be between about 20 minutes to about 40 minutes. The deflocculation tank can be used as needed or periodically, such as weekly, to reduce the relative proportion of floc of beneficial bacteria in the body of water to about 20 to 40 ppt. 
     Using various aspects of the system and process has the advantage of reducing the water exchange rates, while maintain acceptable water quality for growing crustaceans optimally. It has been found that the various systems and processes described herein provide a significantly reduced amount of water effluent (about 5-10 gallons per week or about 0.065% to 0.18% for a 5700-7700 gallon container) in the form of the withdrawn foam. This has little to no adverse impact on the environment, as not only is there no further treatment needed for the water effluent before being reintroduced to the environment, but also the withdrawn foam is enriched with protein and organic compounds that can be used as fertilizers in greenhouses or other applications. Other features of the present invention and the corresponding advantages of those features will become apparent from the following discussion of the preferred embodiments of the present invention, exemplifying the best mode of practicing the present invention, which is illustrated in the accompanying drawings. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like referenced numerals designate corresponding parts throughout the different views. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic sectional view of a recirculated marine aquaculture system that includes a water treatment unit embodying the present invention. 
         FIG. 1A  is a close-up view of an embodiment of propellers of a system impeller used with a water treatment unit. 
         FIG. 2  is an elevation view, partially in section of a portion of a water treatment unit. 
         FIG. 3  is an elevation view, partially in section of another portion of a water treatment unit. 
         FIG. 4  is a sectional view of another portion of a water treatment unit. 
         FIG. 5  is a schematic of a recirculated marine aquaculture system that includes a water treatment unit and a deflocculation tank. 
         FIG. 6  is a schematic sectional view of a deflocculation tank used with a recirculated marine aquaculture system tank. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     A first embodiment of a recirculated marine aquaculture system  10  is shown schematically in  FIG. 1  that includes a water treatment unit  12  situated within a fisheries tank  14 . Preferably, the system  10  is a closed system with suitable recirculation of the tank water that essentially eliminates water exchanges, while maintaining acceptable water quality for optimal growth of aquatic species. The water treatment unit  12  can also be situated in a pool, pond, lake or other body of water with equal effect, and the illustration here of a tank  14  is not intended to be limiting in any way. The water treatment unit  12  has a first chamber  16  that is situated below the water surface  18  in the body of water. A stand  20  can be coupled to a bottom surface  22  of the first chamber  16  to space the first chamber  16  above the bottom  24  of the body of water. The first chamber  16  has a floor  26  and a ceiling  28  which are made of a material that is generally water impenetrable, such as stainless steel or fiberglass reinforced plastic. A filtering wall  30  connects the floor  26  and ceiling  28 . The filtering wall  30  permits water to flow from the body of water in the fisheries tank  14  into the first chamber  16 . The filtering wall  30  is made of a filtering material that will exclude the desired species of crustaceans or other fish from the first chamber  16 , but will permit small particulate materials that may be present in the body of water  14  to pass into the first chamber  16 . The filtering material can be a fine screen of stainless steel or a polymer. The filtering wall  30  can be in the form of discrete replaceable panels or in the form of a continuous wall that completely surrounds and connects a perimetral edge  32  of the chamber floor  26  to a perimetral edge  34  of the chamber ceiling  28 . A gas bubble source  36  can be situated adjacent to a lower edge  38  of the filtering wall  30  to provide an upward sweeping flow of bubbles that can help maintain the outside of the filtering wall  30  free from litter. The gas bubble source  36  can be supplied by any conventional source of compressed air. The lower edge  38  of the filtering wall  30  can extend below the chamber floor  26  to provide a protected zone  40  under the chamber floor  26  for enhanced microbial activity to break down some of the waste products of any crustaceans or other aquatic species in the body of water  14 . 
     The water treatment unit  12  also includes a second chamber  42  situated above the first chamber  16  as shown schematically in  FIG. 1 . The second chamber  42  has a base  44 , a sidewall  46  extending upward from the base  44 , and a top  47  that can be located above the water surface  18  in the tank  14 . The second chamber base  44  can be spaced above the first chamber ceiling  28 , or can rest directly on the first chamber ceiling  28 . The second chamber  42  also has at least one water outlet  48  in a lower portion  50  of the second chamber  42 . The water outlet  48  from the second chamber can take the form of one or more outlets  48  through the second chamber base  44 . A directionally adjustable pipe  52  can be coupled to the outlet  48  from the second chamber  42  so that the outflow from the second chamber  42  can be used to develop a desired water flow pattern within the body of water  14 . An air inlet  54  is provided in an upper portion  56  of the second chamber. The air inlet  54  can be in the form of a lateral slot  58  formed between a central opening  60  in the second chamber top  47  and a plate  62  situated immediately below the central opening  60 , but in spaced relation from the second chamber top  47 . An outlet  64  can be provided in the second chamber upper portion  56  to allow for withdrawal of excess foam and air enriched in carbon dioxide from the second chamber  42 . 
     The water treatment unit  12  also has a stand pipe  66  coupled between the first chamber  16  and the second chamber  42 . The stand pipe  66  has a lower end  68  that opens into the first chamber  16  and an upper opening  70  adjacent to the top  47  of the second chamber  42 . The upper opening  70  of the stand pipe  66  can take the form of a plurality of openings  72  that can direct a flow of water laterally adjacent to lateral slot  58 . An impeller  74  is connected to the stand pipe  66  to move water from the first chamber  16  up through the stand pipe  66  and out through the upper opening  70  of the stand pipe  66  into the second chamber  42 . The impeller  74  can take the form of a motor  76 , such as a ¾ HP electric motor, coupled to the stand pipe  66  and a shaft  78  coupled to the motor  76  and to at least one propeller  80  situated within the stand pipe  66  below the water surface  18  in the body of water in the fisheries tank  14 . Suitable bearings can be provided between the shaft  78  and the plate  62 , as well as at the lower end of the shaft  78  to ensure stability of the rotating shaft  78  with respect to the vertical center of the stand pipe  66 . The size of the stand pipe  66 , upper opening  70 , motor  76 , and propellers  80  are desirably selected so that between about 600 to 1000 gallons of water per minute, preferably 800 gpm, can be pumped from the first chamber  16  into the second chamber  42 . At this rate, about 0.8 to about 1.4 pounds of oxygen per hour are added to the body of water by the water treatment unit. 
       FIG. 1  shows the tip diameter of the propellers  80  being about the same dimension as the inner diameter of the stand pipe  66 .  FIG. 1A  illustrates a close-up view of an alternative orientation of the propellers  80 ,  80 A. Propeller  80  can be dimensioned and positioned such that the diameter formed by the tips of the blades is slightly less than the inner diameter of the stand pipe  66 . Thus, water can enter into the stand pipe  66  through the propeller  80  which is configured to lift the water from the first chamber  16  to the second chamber  42 . Although the propeller  80 A can also be configured to add lift to the water, preferably the propeller  80 A is configured to form cavitation within the stand pipe  66 . To this end, the propeller  80 A can be then dimensioned and positioned such that the diameter formed by the tips of the blades is substantially less than the diameter of the stand pipe  66 , shown as a radial distance  81 . This gap thus permits cavitation of the water passing therethrough, which allows for the generation of microbubbles, subsequent growth and collapse of the microbubbles. Dissolved and suspended biological particulates adhere to the surface of the microbubbles and are then carried with the water through the outlet  72  and into the second chamber  42 . The water and microbubbles then fall within the second chamber to interface with foam already present in the chamber. Large amounts of interface between the water and air via the microbubbles form a part of foam fractionation where carbon dioxide and biological byproducts, such as protein, is stripped from the water. Portions of the foam can then be removed through the outlet  64 . In one example, where the stand pipe has an inner diameter of 8 inches, the propeller  80  has a tip diameter at the tips of the blades of slightly less than 8 inches, and the propeller  80 A has a tip diameter that is 20-30% (preferably about 25-27%) less than the inner diameter of the stand pipe  66 . 
     In a preferred embodiment shown in  FIG. 1A , a cylindrical ring  83  having outer and inner surfaces has its outer surface attached to the inner surface of the stand pipe  66 . Propeller  80  is positioned to be within the cylindrical ring  83  so that the tip diameter of propeller  80  is slightly less than the inner diameter of the cylindrical ring  83 . The tip diameter of the propeller  80 A can be about 20-30% (preferably about 25-27%) less than the inner diameter of the stand pipe  66 . Propeller  80  and propeller  80 A can even be the same size, with the radial thickness of the cylindrical ring making up the difference. For example, for a stand pipe having an inner diameter of about 8 inches, the outer diameter of the cylindrical ring is about 8 inches and its inner diameter is about 5⅞ inches (for a radial thickness of about 2⅛ inches), and the tip diameter of both propellers  80 ,  80 A is about 5⅞ inches. 
     The pumping of water from the first chamber  16  up through the stand pipe  66  causes water to be drawn through the filtering wall  30  into the first chamber  16 . The pumping of water from the first chamber  16  into the second chamber  42  through the upper openings  70  causes the water to turbulently mix with air drawn in through the lateral slot  58 , thereby increasing the level of oxygen in the water in the second chamber  42 . The turbulent mixing also releases some carbon dioxide from the water within the second chamber  42  which can be removed through outlet  64 . The pumping of water from the first chamber  16  into the second chamber  42  creates a head represented by the difference in level of the water surface  82  in the second chamber  42  as compared to the water surface  18  in the fisheries tank  14 . A small difference in water level can also be observed between the areas inside and outside an inner wall  124 . The head within the second chamber  42  forces some of the water in the second chamber  42  out through the water outlets  48  in the lower portion  50  of the second chamber  42 . By suitably directing the directionally adjustable pipes  52  the water coming out the water outlets  48  can cause any desired water flow pattern within the fisheries tank  14 . An upward flow out of the adjustable pipes  52  can cause a toroidal flow of water within the body of water  14  around the water treatment unit  12 , the flow of water being of a volume sufficient to provide a living environment for growing crustaceans or other fish within the body of water  14 . 
     Two sub-assemblies of the water treatment unit  12  are shown in  FIG. 2 . The first chamber  16  of the water treatment unit  12  has the ceiling  28  and the floor  26  connected by vertical ribs  25  that are located on the inside of the screen forming the filtering wall  30 . The screen forming the filtering wall  30  can be clamped around the periphery defined by the ceiling  28 , floor  26  and vertical ribs  25 . The floor  26  also includes a down-turned peripheral flange  23 , which in a preferred embodiment extends downward about 5 cm below the floor  26 . The gas bubble source  36  can be attached to the peripheral flange  23  using a plurality of brackets or clamps  37  so that the bubble source  36  is situated adjacent to the lower edge  38  of the filtering wall  30 . The first chamber  16  of the water treatment unit  12  is shown in section to reveal the stand  20  supporting the bottom surface  22  of floor  26 . A lower portion  84  of the stand pipe  66  can be seen to extend downward below the ceiling  28  of the first chamber  16  so that a lower end  68  of the stand pipe  66  rests on the floor  26  of the first chamber  16 . The portion  86  of the stand pipe  66  residing within the first chamber  16  includes a plurality of lateral intake openings  88  sized to permit an essentially un-restricted amount of water to flow from the first chamber  16  into the stand pipe  66 . A coupling  85  can be provided at the upper end  87  of the lower portion  84  of the stand pipe  66  to facilitate the assembly to additional elements of the water treatment unit  12 . A secondary screen can be provided immediately surrounding the stand pipe surface to trap organic debris in the first chamber  16 . A high surface area filler can be added to a lower portion of the first chamber  16  to facilitate the digestion of any trapped organic debris. 
     The base  44  of the second chamber  42  is shown to be coupled to the lower portion  84  of the stand pipe  66  spaced some distance above the ceiling  28  of the first chamber  16 . One or more flanges  90  can be cemented, bonded, or otherwise fixed to the stand pipe  66  and one or more fasteners  92  can penetrate the base  44  of the second chamber  42  and the flange  90  to secure the base  44  to the stand pipe  66 . Thus, the lower portion  84  of the stand pipe  66  and the base  44  of the second chamber  42  can be handled as a unit to permit easy assembly and disassembly of the water treatment unit  12 . In particular, the portion  86  of the stand pipe  66  can slide into and be lifted out of the opening  27  in the ceiling  28  of the first chamber  16  to permit easy assembly and disassembly of the unit  12 . A gasket or flange  29  can be situated on the stand pipe  66  to minimize or inhibit any inflow of water into the first chamber  16  at the junction of the ceiling  28  and stand pipe  66 , thereby ensuring a proper filtering of the water through the filtering wall  30 . 
     The pipes  52  coupled to the water outlets  48  in the base  44  of the second chamber  42  are shown to comprise a first pipe  92  and a second pipe  94 . The first pipe has a first end  96  cemented, bonded, or otherwise fixed to the base  44  to receive water from the outlet  48 . The second pipe  94  has a first end  98  coupled to the second end  100  of the first pipe  92 , so that the second pipe  94  can be rotated to a desired position relative to the first pipe  92  whereby water exiting the second chamber  42  out through the second end  102  of the second pipe  94  can be variously directed to obtain desirable water current conditions within the body of water  14 . 
     A further sub-assembly of the water treatment unit  12  is shown in  FIG. 3  that includes an upper portion  104  of the stand pipe  66 , which is capped by plate  62 . The lower end  106  of the upper portion  104  is intended to be coupled to the coupling  85  at the upper end  87  of the lower portion  84  of the stand pipe  66  shown in  FIG. 2 . The upper end  108  of the upper portion  104  can include a flange or tabs  110  that can be coupled to the plate  62  by means of fasteners  112 . Additional fasteners  114  can be provided to define the size of the lateral slot  58  that creates the air inlet  54  to the second chamber  42  shown in  FIG. 1 . Arcuate mounting blocks  116  can be provided to mount the motor  76  above the plate  62  by a defined spacing. A coupling  118  can be provided to couple the motor  76  to a shaft  78 . A suitable bearing  120  can be mounted to the plate  62  to receive the shaft  78 . The openings  72  are seen to comprise three rows of openings that are substantially equally spaced around the upper portion  104  of the stand pipe  66  adjacent to the plate  62 . A depending flange  63  can be provided on a lower surface  65  of the plate  62 . The depending flange  63  can intercept and downwardly direct water flowing from the openings  72 . The downwardly directed water entrains air coming through air inlet  54  to elevate the level of oxygen dissolved in the body of water  14 . In a preferred embodiment the depending flange  63  can extending downward about 6 cm from the lower surface  65  of plate  62 . 
     In  FIG. 4 , a further sub-assembly is shown that consists generally of the sidewall  46  and top  47  of the second chamber  42 . The lower edge  122  of the sidewall  46  is intended to fit reasonably snuggly around the perimeter of the base  44  of the first sub-assembly so that water outflow from the second chamber is essentially entirely through the adjustable pipes  52  seen in  FIG. 2 . An inner wall  124  can be provided that depends from the top  47  generally in a uniformly spaced relation from the sidewall  46 . A suitable space between the inner wall  124  and sidewall  46  has been found to be about 5 to 10 cm. The lower edge of the inner wall  124  can be located below the lower edge of the depending flange  63 , and in a preferred embodiment can be located 1 to 5 cm below the water surface  82  within the second chamber  42 . 
     A second embodiment of a recirculated marine aquaculture system  110  is shown schematically in  FIG. 5  that includes a water treatment unit  12 ′ situated within the fisheries tank  14  and a secondary, deflocculation tank  150 . The water treatment unit  12 ′ can perform several functions with individual equipment, even though the water treatment unit  12  alone can be configured to perform all of the functions. To this end, as described in further detail below, the water treatment unit  12 ′ can include features that can perform one or more of the functions. 
     For example, the water treatment unit  12 ′ can include a filter  130 , e.g., the filter  30 , to exclude the desired species of crustaceans or other fish from entering into the water treatment unit, but will permit small particulate materials that may be present in the body of water  14  to pass into the water treatment unit for further treatment. A heat source  140 , described in greater detail below, may also be associated with the tank in order to heat and maintain the body of water of the tank to a desirable level. A pump source  141 , e.g. the impeller  74 , is provided to lift the water from the tank through the water treatment unit. A foam fractionation source  142  is provided, e.g., the combination of the cavitational propeller  80 A and the bubbles and foam created by the drop of water from the openings  72  elevated from the water level. The carbon dioxide and byproducts in the form of foam can be removed via the outlet  64  that can be aided by a suitable vacuum pump. An aerator  143  is also provided, e.g., the air entrained through the air inlet  54  during the drop of the water from the openings  72 . A flow generator  144  is provided, e.g., from the outflow from the conduits  52  of the water treatment unit  12  to develop a desired water flow pattern within the body of water. 
     The deflocculation tank  150  is configured to reduce the relative proportions of beneficial bacteria in the water, while preserving the floc of beneficial bacteria (i.e., avoiding “breaking” the floc). Crustaceans or other fish produce wastes that break down to create ammonia in water, which is highly toxic to the crustaceans or other fish. Beneficial bacteria can be provided in water to convert ammonia into nitrites and nitrites into nitrates, as well as breaking down organic matter (waste feed and crustacean or fish waste). Thus, one type of bacteria that make of the floc is heterotrophic bacteria that build a colony around some organic or inorganic particle and then breakdown organic matter. A second type of bacteria that make of the floc is nitrifying bacteria that also grow on these colonies. The nitrifying bacteria can include nitrosomonas bacteria one the oxygenated areas of the floc that break down the ammonia into less toxic nitrites, while consuming oxygen that is within the water, and nitrobacter bacteria on the anoxic portions of the floc that break down the nitrites into nitrates, which also consume oxygen in the water. The floc of beneficial bacteria may continue to thrive and grow until reaching undesirable relative proportions, such as, e.g., 20-40 parts-per-thousand (ppt), in which case the relative proportions of beneficial bacteria in the water may be removed preferably without breaking the floc. The floc levels may be measured periodically, such as daily, by use of a device configured to measure settling solids, such as a one-liter Imhoff cone, allowing a period of time, e.g., 15 minutes, of settling before measuring the level of settled solids. 
       FIG. 6  depicts an exemplary way to couple the tank  14  to a preferred embodiment of the deflocculation tank  150 . The tank  14  includes fluid outlet  151 , such as a tap or spigot, coupled through the wall of the tank  14  for permitting the tank water to drain out. A conduit  152 , such as a hose, is coupled between the tank fluid outlet  151  and a fluid inlet  154  in the deflocculation tank  150  such that the fluid outlet  151  and fluid inlet  154  are sealably connected. A first column  156  is cemented, bonded, or otherwise fixed to the bottom of the cavity  158  of the deflocculation tank and extending upright. The bottom  160  of the first column and the bottom  153  of the deflocculation tank  150  are effectively sealed to inhibit water from entering from the bottom. This causes the water to circulate in a flow pattern around the first column  156 . The water preferably circulates at a desired flow rate for a desired period of time for treatment before entering from the top  161  of the first column in the spaced defined between the first column  156  and a second column  162 . The second column  162  is inserted through the passageway of the first column  156 . In one example, the first column  156  is 4-inch PVC pipe and the second column  162  is 2-inch PVC pipe, although it can be appreciated to those skilled in the art that the sizes can vary so long as the inner diameter of the first column is larger than the outer diameter of the second column. The second column  162  extends toward the bottom  160  of the first column  162  but not all the way in order to allow enough space for water to enter therethrough. The second column  162  also extends past the top  161  of the first column  156  and preferably mounts to the top  155  of the deflocculation tank  150 , shown cemented, bonded, or otherwise fixed at the center of the deflocculation tank. The top  164  of the second column  162  has a fluid outlet  166  where water exits the deflocculation tank  150  to preferably enter back into the tank  14  via a return conduit  167 . A fluid flow meter (not shown) may be associated with the return conduit  167  in order to measure the flow rate of return water through the return conduit. Another port  168  may be associated with the top  164  of the second column  162  for receiving an air conduit  170 , such as air tubing, having an outlet  172  that is placed within the first and second columns. The air conduit  170  is preferably attached to a source for compressed air  174 . 
     A gas bubble source  176  may also be located along the bottom  160  of the first column  156 ; and preferably in alignment with the passageway  163  of the second column  162 . The gas bubble source  176  can be an airstone or air diffuser typically used with water and fitted with an air fitting for coupling to the outlet  172  of the air conduit  170 . The gas bubble source  176  is configured to diffuse oxygen or air into the tank for oxygenation of the water and to lift the water past the water level  178  into the fluid outlet  166 . The pumping action to lift the water above the water surface level in the deflocculation tank  150  should be sufficient to permit the treated water to exit the fluid outlet  166  at a desired flow rate. The return flow rate can be in the range of about 1 gallons-per-minute (gpm) to about 30 gpm; preferably 5-20 gpm; and most preferably 15 gpm. Thus, for a deflocculation tank having a 300-gallon capacity and a return flow rate of 15 gpm, the amount of time for a portion of water to cycle through the deflocculation tank would be 20 minutes. The pressure from the air pump can be increased or decreased accordingly to effectuate the desired flow rate, e.g., the air pressure can be in a range of about 3 pounds-per-square inch (psi) to about 6 psi. 
     It has been found that the lower flow rates, especially 5-15 gpm, can enhance the preservation of the floc of bacteria. In other words, too low of a flow rate does not sufficiently reduce the relative proportion of floc of bacteria, which leads to more treatment, and too high of a flow rate breaks the floc of bacteria. After a period of operating the deflocculation tank  150 , the relative proportion of the beneficial bacteria can be reduced to sufficient levels, e.g., about 20-40 ppt. This can avoid the conventional matter of changing the water completely by draining the “old” water from the tank  14  and filling the tank with “new” water, which can break the existing bacteria flocs. The retention time and the flow rate within the deflocculation tank depends on the relative proportion of the floc of bacteria, and one skilled in the art can determine the time and return flow rate necessary to reduce the relative proportion of the floc to suitable levels for the size of the tank and the deflocculation tank. 
     For optimal growth of crustaceans or other fish, the water quality of the body of water within the tank is regulated to provide an aquatic environment for optimal growth of the crustaceans or fish. Various aspects of the quality of water can be sensed and regulated, including: temperature, oxygen, carbon dioxide, ammonia, nitrites, nitrates, salinity, alkalinity, pH, bacteria proportions, or the like. Therefore, various means for sampling and sensing the various aspects of the body of water can be provided as appreciated by those skilled in art. 
     The temperature of the water of the tank  14  may be maintained in the range of about 80° F. to about 90° F., preferably 83° F. to about 87° F., and most preferably 85° F. The water may be heated by a heat source in the form of an external or an internal heat source. For instance, the external heat source can include a convection heat fan unit that applies heated air to the surface of the tank, and the internal heat source can include an electric heater or pipes carrying a heated fluid media from an external water heater within the body of water. For example, the heat source  140  can comprise a water pipe configuration (not shown), such as about 300 feet of pipe in a coiled configuration, located within the first chamber  16  of the water treatment unit such that the water is heated while being pumped through the water treatment unit  12 . The pipe configuration is then fluidly coupled to an external water heater (not shown). A thermostat can be associated with the body of water and coupled to the water heater so that the temperature of the water can be controlled by cycling the heater on-off or proportionally changing the temperature of the heater to maintain the temperature within acceptable levels. In some instances, heat generated by operation of the impeller  74  may by sufficient as a primary source of heat or at least sufficient as a supplemental heat source to the heater. 
     The salinity of the water can also be regulated such that the salt is between 5 ppt to about 35 ppt, preferably from 7 ppt to 25 ppt, and most preferably at 10 ppt, striking a balance between having an acceptable salinity for optimal growth, while minimizing operation costs of maintaining a higher salinity. Additional salt may be added to the water of the tank  14  to increase the salinity; for example, sea salt mix available from Tropic Marin. Alkalinity of the water of the tank  14  may also be regulated to maintain at least 150 parts-per-million (ppm). The pH of the water can be between about 7-9, and preferably about 7-7.5. When the alkalinity of the water is below this threshold, or pH is too high, a sufficient amount of carbonates and/or bicarbonates, such as sodium bicarbonate, can be used to increase the alkalinity of the water to levels above 150 ppm or reduce the pH to acceptable levels. 
     Other properties of the water of the tank  14  can be sampled periodically to monitor environmental changes. For example, samples of the water can be taken to measure the oxygen, ammonia, and nitrite levels of the water. The oxygen levels can be maintained between about 1 ppm to about 2 ppm and 10 ppm; and preferably maintained in the range between about 5-8 ppm. The ammonia levels can be maintained as high as about 2 ppm to about 3 ppm and as low as 0.1 ppm and preferably maintained at about 0.5 ppm. Similarly, the nitrite levels can be maintained less than 2 ppm, and the nitrate levels can be maintained as high as about 10 ppm to about 20 ppm and as low as 0.1 ppm and preferably maintained at about 0.5 ppm. The various aspects of the quality of water are summarized in Table 1. 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Water Variable 
                 Range 
                 Preferred 
               
               
                   
                   
               
             
             
               
                   
                 Temperature 
                 80-90° F. 
                 85° F. 
               
               
                   
                 Oxygen 
                 1-10 ppm 
                 5-8 ppm 
               
               
                   
                 Carbon dioxide 
                 less than 15 ppm 
               
               
                   
                 Ammonia 
                 0.1-3 ppm 
                 0.5 ppm 
               
               
                   
                 Nitrites 
                 less than 2 ppm 
               
               
                   
                 Nitrates 
                 0.1-20 ppm 
                 0.5 ppm 
               
               
                   
                 Salinity 
                 5-35 ppt 
                 10 ppt 
               
               
                   
                 Alkalinity 
                 greater than 150 ppm 
               
               
                   
                 pH 
                 7-9 
                 7-7.5 
               
               
                   
                 Bacteria floc 
                 up to 40 ppt 
                 20 ppt 
               
               
                   
                   
               
             
          
         
       
     
     During operation, the pumping of water from the second chamber  42  through the upper openings  70  that can cause cavitation before the water turbulently mixes with air drawn in through the lateral slot  58 . This not only increases the level of oxygen in the water in the second chamber  42  at about 1.1 pounds of oxygen per hour, but also creates microbubbles to form a body of foam enriched with carbon dioxide and biological byproducts on the water surface  82 . The inner wall  124  preferentially traps a significant, and generally dominant, portion of the foam between the inner wall  124  and the sidewall  46 . An outlet  64  can be coupled to the space between the inner wall  124  and the sidewall  46  of the second chamber  56  to permit withdrawal of excess foam and air enriched in carbon dioxide from the second chamber  42 . The outlet  64  can be aided by a suitable vacuum pump facilitating the withdrawal of the foam and carbon dioxide enriched air through the outlet  64 . The outlet  64  can also include a downwardly extending water drain line  128  permitting the return of some of the water separated with the foam to the fisheries tank or other body of water  14 . The water drain line  128  preferably extends downward so that a lower end  130  of the water drain line  128  is at least at or below the water surface  18  to ensure an adequate vacuum to facilitate withdrawal of the foam and carbon dioxide enriched air from the second chamber  56  through the outlet  64 . It has been found that the various systems and processes described herein provide a significantly reduced amount of water effluent (about 5-10 gallons per week or about 0.065% to 0.18% for a 5700-7700 gallon container) in the form of the withdrawn foam, with the exception of water vaporization. However, the water effluent may even be negligible if returned to the deflocculation tank for cycling back into the body of water. Regardless, the total amount of water exchanges is significantly reduced. Consequently, this has little to no adverse impact on the environment, as not only is there no further treatment needed for the water effluent before being reintroduced to the environment, but also the withdrawn foam is enriched with protein and organic matter and can be used as a fertilizer in greenhouses or other applications. 
     Periodically, the relative proportions of bacteria will become “thick” or above 40 ppt, in which case the relative amount of bacteria may be too high and adversely affects the oxygen levels of the water and growth of the crustaceans or other fish. To counteract this problem, the deflocculation tank  150  can be arranged adjacent to the tank  14  and the conduit  152  can be fluidly coupled to the two tanks by sealable attachment between the outlet  151  of the tank  14  and the fluid inlet  154  of the deflocculation tank  150 . The valve of the outlet  151  can be opened to permit the water of the tank  14  to flow into and fill the deflocculation tank  150 . The water level  178  of the deflocculation tank  150  will rise until rising above the height of the first column  156  where water will then fill the passageway of the first column  156 . Water within the deflocculation tank  150  should cycle in a flow pattern, such as toroidal pattern, around the first column  156  for a predetermined amount of time and flow rate before entering the second column. Water will also enter into and fill the passageway  163  of the second column  162  as the water fills the first column  156 . With the air conduit  170  coupled to the compressed air source  174  and the gas bubble source  176 , the air source  174  is turned on and the air pressure is adjusted to operate the gas bubble source  176  such that the desired flow rate of water exiting the fluid outlet  166  of the deflocculation tank  150  is obtained, e.g., 5-15 gpm. Preferably, the water is then returned to the tank  14 . This operation can continue to run until the bacteria thins out to an acceptable relative proportion, such as 20-40 ppt, without breaking the floc. The deflocculation tank  150  may also be movable so that it can be fluidly coupled to other tanks. 
     Example 1 
     Water is added to an 18-foot diameter tank having 52-inch sidewalls to substantially fill the tank to about 5700-7700 gallons. The water temperature is heated and maintained at about 85° F. Sea salt is added to the water in the tank to increase the salinity to about 10 ppt. The water treatment unit is then activated to begin cycling and moving the water in a toroidal pattern. Generally, the water treatment unit is operated for a period of time sufficient to normalize the environment of the tank water before supplying the crustaceans or other fish. As described previously, the water treatment unit not only sufficiently aerates the tank water, e.g., 1.1 pounds of oxygen per hour, but also strips carbon dioxide and biological byproducts from the tank water and removes them from the system. To increase the growth rate of bacteria, a sufficient amount of ammonia, nitrites and/or nitrates may be added to the tank water. Samples of the tank water are taken to measure various aspects of the quality of water to ensure that the tank water is ideal for growing crustaceans or other fish. 
     A plurality of shrimp (quantity of about 12,000 to 15,000), with an average weight of about 1 gram, is placed in the tank water. The shrimp are fed several times of day (e.g., 3 times a day) with a sufficient amount of feed typically associated for growing shrimp, such as from Zeigler&#39;s Bros., Inc., Gardners, Pa. After 6 to 8 weeks of feeding, the shrimp become market size and ready for shipment, e.g., weighing about 16.7 grams to about 27.3 grams. 
     During the growth period of the shrimp, water quality is monitored to ensure that the water is sufficient for optimal shrimp growth. In particular, samples of tank water are taken periodically, such as daily, to measure the relative proportions of ammonia, nitrites, and/or nitrates. As described previously, the relative proportions of these are maintained within their ranges. Samples of tank water can also be taken to measure the relative proportions of oxygen, carbon dioxide, salinity, and alkalinity or pH in order for them to be maintained within their ranges. It is preferable that the water quality is maintained within their preferred ranges. It can be appreciated that the water quality can be monitored with equipment and processes suitable for such measurements and adjusted as known in the art. 
     While these features have been disclosed in connection with the illustrated preferred embodiment, other embodiments of the invention will be apparent to those skilled in the art that come within the spirit of the invention as defined in the following claims. Further, it will be appreciated that in very large ponds or lakes, it may be convenient or necessary to employ two or more water treatment units  12  and/or deflocculation tanks  150  to ensure a total water flow volume sufficient to provide a living environment for growing crustaceans or other fish within the entire body of water.