Fish cage

A fish cage having a frame structure defining an enclosure with a top and a bottom and an intersecting side. The frame is adapted to rest on the bottom of an outdoor body of water and is covered with a first netting on the top and side but not the bottom. The first netting has mesh openings sized to permit ambient water and suspended particles therein to circulate through the cage but prevent predators and competitors for food of the fish under study from entering the cage. A second netting covers the bottom of the enclosure. The second netting has second mesh openings larger than the first mesh openings and sized to prevent the fish being studied from leaving the enclosure as well as permit plant and animal life at the bottom of the body of water to enter the enclosure, thereby providing a more natural environment for the fish under study. The enclosure includes a door to permit access to the interior of the enclosure.

FIELD OF THE INVENTION
 This invention relates generally to the field of fish containment devices
 and, more particularly, to an improved open water fish cage.
 BACKGROUND OF THE INVENTION
 Aquatic net cages or pens of various shapes and sizes have been used for
 many years to contain fish for the purposes of research, breeding and
 raising fish for food. Cages designed for the breeding and/or raising of
 fish for consumption either float or rest at the bottom of an outdoor body
 of water. Generally, such cages have an access opening in the top of the
 cage and are often designed to retain man-made fish food within the cage
 by providing an overlay of netting on the cage bottom with a mesh size
 that is substantially smaller than the other netting that covers the cage.
 Such cages may also include fish grading screens of either netting or
 parallel bars to separate the smaller fish prior to harvesting the larger
 fish.
 Aquatic net cages for research purposes are also known. For example, some
 cages are designed to study the effect of pollutants on fish growth.
 However, such cages are often designed to isolate the different species
 being studied from each other and/or predators. Thus, such cages have a
 very specialized research purpose and a relatively complicated
 construction. In other studies, round cages suspended in a body of water
 may be used to study the predatory behavior of fish populations.
 It is also known to use cages that rest at the bottom of a body of water to
 study in situ fish growth. Fish growth is affected by environmental
 conditions, such as the availability of food, dissolved oxygen
 concentrations, water temperature, pollutants, etc. Therefore, in contrast
 to cages in which fish are raised for consumption, in fish growth studies,
 preferably, all of the food should come from the local environment; and no
 man-made food should be provided. Cages to study fish growth are often
 bottomless, so that the plant and animal life is readily available as food
 for fish being studied. However, a bottomless cage has several
 disadvantages. First, access to the cage is through a relatively small
 opening or door generally in the top of the cage, and thus, removal of
 fish from the cage must be done with a dip net or suction gun. In turbid
 water in which the visibility is limited, the removal of fish from a
 bottomless cage with a dip net or other device is very difficult and time
 consuming. In very turbid water with close to zero visibility, such a task
 is almost impossible. Further, deploying and retrieving fish in a
 bottomless fish cage in turbid water from a boat is also very difficult if
 not impossible. Therefore, fish growth studies using bottomless cages must
 be limited to less turbid or shallower waters. Further, in view of the
 difficulties in handling fish in a bottomless cage, such cages are often
 made smaller, thereby severely limiting available food supply and thus,
 the number of fish that can be studied in each cage.
 Therefore, there is a need to provide an improved fish cage for in situ
 fish growth studies that does not have the disadvantages of known cages.
 SUMMARY OF THE INVENTION
 The present invention provides an improved fish cage that permits fish to
 be easily handled during in situ fish growth studies that are performed in
 deeper waters and in turbid waters, even waters having zero visibility.
 Further, the above is achieved by a fish cage design that protects the
 fish being studied from predators and competitors for food while
 permitting both ambient water with suspended particles to circulate
 through the cage and plant and animal life on the bottom of the water to
 enter the cage. Thus, the fish in the cage of the present invention can
 live for extended periods of time in their natural feeding environment.
 The fish cage of the present invention has the further advantage of
 permitting the cage to be easily removed from the water with complete
 retrieval of the fish being studied. Another advantage is that the cage
 may be made relatively large so that larger fish populations can be
 studied, and in addition, advantageously, the fish cage of the present
 invention is economical, simple to manufacture and has a durable long
 life.
 In accordance with the principles of the present invention and in
 accordance with the described embodiments, the present invention provides
 a fish cage having a frame defining an enclosure having a top, a bottom
 and an intersecting side wall. The frame is adapted to rest at the bottom
 of an outdoor body of water and is covered with a first netting on the top
 and side wall but not the bottom. The first netting has mesh openings
 sized to permit ambient water and suspended particles therein to circulate
 through the cage but prevent predators and competitors for food of the
 fish under study from entering the cage. A second netting covers the
 bottom of the enclosure, and the second netting has second mesh openings
 larger than the first mesh openings. The second mesh openings of the
 second netting are sized to first, prevent the fish being studied from
 leaving the cage and second, to permit the natural environment of plant
 and animal life at the bottom of the body of water to enter the enclosure,
 thereby providing a more natural environment for the fish under study. The
 enclosure includes a door permitting access to the interior of the
 enclosure.
 In one aspect of the invention, the frame is multilateral, for example,
 rectangular, and made from perforated plastic tubing. In another aspect of
 the invention, the door is a flap of netting cut from the wall or the top
 of the enclosure. In a still further aspect of the invention, a second
 door of a netting material covers the first door.
 These and other objects and advantages of the present invention will become
 more readily apparent during the following detailed description together
 with the drawing herein.

DETAILED DESCRIPTION OF THE INVENTION
 Referring to the FIGURE, the fish cage 20 is adapted to rest at the bottom
 22 of an open body of water 24. The fish cage 20 is comprised of a frame
 structure 26 covered by a netting or other net-like material 28. The frame
 26 defines the outer boundaries of the fish cage 20 and is normally
 multilateral, for example, rectangular. The frame 26 is preferably made of
 an extruded pipe or tubing material having perforations 30 permitting
 water to enter the interior of the pipe, thereby removing any buoyancy the
 pipe may have and causing the frame 26 to rest on the bottom 22. The frame
 is constructed by connecting a plurality of straight pipe sections 32 with
 molded double elbow fittings 34 and molded double T-fittings 35. The
 straight pipe sections 32 can be connected to the fittings 34, 35 by any
 known technique including adhesives, welding, fasteners, etc. Preferably,
 the pipe 32 and fittings 34, 35 are made from a one inch diameter
 polyvinyl chloride, however, they may be made from any other plastic
 material as well as a metal or a pressed paper material. Further, the
 frame 26 may be made of materials having a noncircular shape as well as
 materials of different sizes. In addition, the frame may be made from
 concrete reinforcing bar or another solid bar instead of tubular
 materials; however solid materials weigh more and will make the cage more
 difficult to handle. In the example of the present invention, the frame
 has two side walls 36, 37, two end walls 38, 39, a top wall 40 and a
 bottom wall 41; and the frame 26 has a length 42 of approximately 60
 inches, a width 43 of approximately 40 inches and a height 44 of
 approximately 20 inches.
 The netting or net-like material 28 may be any commercial netting material,
 for example, a "VEXAR" polyethylene or polypropylene plastic netting
 material commercially available from DuPont. The netting in the FIGURE is
 schematically shown as having a square mesh, however, as will be
 appreciated, any mesh shape, for example, diamond or other quadrilateral,
 hexagonal, octagonal, and circular or other curved mesh shapes, etc. may
 be used. The first netting 31 for the sides and top of the cage is chosen
 to have a mesh size large enough to permit ambient water and suspended
 particles therein to circulate through the cage. However, the mesh size of
 the first netting 31 must be small enough to prevent predators from
 entering the cage as well as nonpredators who compete with the fish being
 studied for the available food supply within the cage. If the mesh size of
 the first netting 31 is too large, competitors for food and potential
 predators may enter the cage early in a growth cycle, and after growing in
 the cage, become significant competitors for food or predators of the fish
 being studied. For example, after molting, a blue crab is very flexible,
 can squeeze through small openings and may enter the cage. However, after
 entering the cage, the crab may grow to a size too large to leave the cage
 and become a predator of the fish being studied in the cage. Therefore,
 the mesh size of the netting 31 on the sides, ends and top of the cage is
 chosen first, to permit water currents to wash plant and animal life into
 or onto the cage on which the fish being studied can forage and second, to
 prevent other fish competing for food and predators and competitors for
 food of the fish under study from entering the cage 20. If, for example,
 the fish being studied are juvenile croaker having a length in the range
 of approximately 90 millimeters ("mm") to 120 mm, then a mesh size for the
 first netting 31 on the sides 36, 37, ends 38, 39 and top 40 of the cage
 20 is chosen to be in the range of approximately 0.25 inches to 0.375
 inches.
 After the frame 26 is constructed, the netting may be applied to the frame
 in many different ways, and one such process will be described in detail.
 A piece of first netting 31 is cut to a length that is slightly longer
 than twice the cage length 42 and the cage width 43. The netting 31 is cut
 to a width that is slightly greater than the cage height 44 plus more than
 half the cage width 43. Thus, given the frame size example recited above,
 the netting 31 is cut to a length of approximately 206 inches and a width
 of approximately 43 inches. One end of the first netting 31 is connected
 to one corner post, for example, post or frame member 46, with tie-wraps
 48 such that the edge of the netting 31 is flush with the bottom and the
 netting 31 extends above the top of the cage by a distance greater than
 one-half the height 44, for example, using the current example,
 approximately 23 inches.
 A tie-wrap 48 is an elongated plastic member having one end that is looped
 around objects to be joined and then passed through an opening in the
 other end, thereby progressively tightening the tie-wrap around the
 objects. Thus, an end of the tie-wrap 48 is looped around post 46, through
 openings in the netting 31 and then through the other end of the tie-wrap
 48. The one end is then pulled tight, thereby securing the netting within
 the tie-wrap 48 around the pipe section.
 The length of the first netting 31 is then successively wrapped around the
 rear side 36, the right end 38, the front side 37, the left end 39 and
 around the post 46 to overlap with itself on the rear side 36. The wrapped
 netting 31 is then tie-wrapped to the post 46, and the overlapping loose
 end of the netting 31 is then stitched to the underlying netting on the
 rear side 36 using 20 pound fish line. At this point, the sides 36, 37 and
 ends 38, 39 of the fish cage are in place, however, netting extends above
 the frame 26 approximately 23 inches on all four sides. That extended
 netting is then cut at the four corners to provide four flaps of extended
 netting contiguous with the sides 36, 37 and ends 38, 39.
 The extended netting 50 on the forward side 37 of the cage 20 is folded
 toward the rear side 36 and the extended netting 52 on the rear side 36 is
 folded forward so that the folded netting portions 50, 52 cover the top 40
 of the cage 20 with an overlap 54 of approximately 5 inches with the
 folded front side 50 located beneath the folded rear side 52. The
 overlapping folded netting 50, 52 may be tie-wrapped or partially stitched
 to hold it in place while the ends are folded and a door is made. The
 extended netting 56 at one end, for example, the right-hand end as viewed
 in the FIGURE, may be left as is or trimmed so that it extends above the
 top of the cage by a lesser amount. The extended netting 56 is folded over
 the top 40 of the cage 20, and the netting 56 is tie-wrapped to upper
 frame members, and the edges of the netting 56 are stitched together using
 20 pound fish line 57.
 The top at the left end of the cage as viewed in the FIGURE is next
 provided with a cage door. First, it is desirable that the extended
 netting 58 at the left end extending above the top 40 of the cage 20 be
 cut or separated from the netting portions 50, 52 folded over to form the
 top 40 of the cage 20. In addition, it is desirable that the extended
 netting 58 be in the form of a simple flap that is extendable over the top
 40 of the cage. Therefore, extra netting at the corners of the extended
 netting 58 is cut away to form the desired flap configuration. The left
 end flap 58 is then folded to the left, away from, and off of the top of,
 the cage 20. The edges of the folded side pieces 50, 52 extending over the
 top 40 of the cage 20 are then stitched together as desired using 20 pound
 fish line 57. However, the edges of the netting pieces 50, 52 that are
 located where a door in the top of the cage is to be located are not
 stitched. Next, two parallel cuts are made from the forward edge of the
 netting piece 52 toward the rear side 36 of the cage 20, thereby forming a
 flap or door 62 in the top wall 40 of the cage 20. The door 62 provides
 access to the cage 20 via an opening 63 through which fish are placed in,
 and retrieved from, the enclosure of the cage 20. Preferably, the door 62
 is located close to the left side 39 of the cage such that when the end
 flap 58 is folded over the top 40 of the cage 20, the flap 58 covers the
 door 62 completely, thereby forming a secondary door.
 The secondary door flap 58 provides additional protection for the first
 door flap 62. The door flap 62 is secured closed in the field, often in a
 boat rocking in swells, and must be done relatively quickly. Therefore,
 the first door flap 62 is often less tightly secured, and the second door
 flap 58 is effective to provide additional security to prevent predators
 and competitors for food from entering the cage. Further, the secondary
 door flap 58 provides additional physical security. It is common for
 objects to be dragged over the top of the fish cage and for boat hulls to
 pass over and contact the top of the fish cage. Thus, without the
 secondary door flap 58, it is possible for such an object to catch onto
 and partially or fully open the first door 62. Once again, the secondary
 door flap 58 provides additional protection for the first door 62 from
 items contacting the cage in a manner tending to open the door flaps 62
 and 58.
 Next, the bottom 41 of the cage 20 is made. It is desired that the bottom
 41 of the cage permit animal and plant life 64 to enter the cage from the
 bottom wall 41 so that the fish 66 being studied may forage on the natural
 food 64. However, the size of the mesh of the netting 68 of the bottom 41
 of the cage must be small enough so that the fish 66 being studied cannot
 escape when the cage 20 is removed from the bottom 22 of the water 24.
 Normally, the fish being studied are not exposed to predators coming
 through the bottom of the cage. In the example above, where the fish 66
 being studied are juvenile croaker having a length in the range of
 approximately 90 mm to 120 mm, then a mesh size for the netting 68 on the
 bottom 41 of the cage 20 is in the range of approximately twice the size
 of the mesh on the sides 36, 37, ends 38, 39 and top 40, that is, 0.50
 inches to 0.75 inches. The netting 68 for the bottom 41 is cut so that the
 area of the netting corresponds to the length and width of the cage plus
 approximately 6 inches in each direction. Thus, the bottom netting 68
 covers the bottom of the cage and extends up and overlaps the two side
 walls 36, 37 and the two end walls 38, 39 by approximately 3 inches.
 After, the bottom netting 68 is located with respect to lower sections of
 the frame 26, tie-wraps 48 are used to connect the netting 68 to the lower
 frame sections, and the peripheral edges of the bottom netting 68
 overlapping the side and end walls 36-39 are stitched to the underlying
 side and end walls with 20 pound fish line 57. The cage construction is
 now complete, and the cage 20 is ready for use.
 In use, the cage 20 may be deployed from the shore or from a boat. The
 construction of the cage is particularly advantageous when being deployed
 from a boat and in turbid water. When being deployed from a boat, the
 right end 38 is placed in the water 24 with the door 62 being left above
 the surface of the water 24. The flaps 58, 62 are pulled back and the cage
 20 is stocked with the fish 66 being studied. The inner door or flap 62 is
 then stitched shut and the outer flap or door 58 is held shut with either
 stitches or one or more bungee cords. The cage 20 is lowered into the
 water 24 and located on the bottom 22. The cage 20 is then manipulated to
 push it into the top layer of silt on the bottom 22, thereby bringing the
 animal and plant life 64 through the larger mesh of the netting 68 into
 the cage 20. Thus, the netting 68 having the larger mesh on the bottom 41
 of the cage is as effective as a bottomless cage in providing available
 food for the fish being studied. By optimizing the animal and plant life
 64 available to the fish 66, the most natural possible environment is
 provided. Therefore, the effect of different environmental factors in the
 water 24, including pollutants on the growth rates of the fish 66, can be
 more accurately determined. After the cage 20 is in place, it is anchored
 by tying it to concrete blocks or other weights at the four corners only
 one of which is shown schematically by a block 70. Anchoring the cage 20
 prevents it from being turned over by stronger currents. If the cage turns
 over, the fish being studied are exposed to predators that can penetrate
 the larger mesh of the bottom netting.
 At the end of the growth study period, for example, three weeks, the
 anchors 70 are removed; and the cage 20 is lifted from the bottom 22 and
 into the boat. The cage 20 is set on its left end 39, or the end with the
 door 62. The fish being studied drop to the lower end 39 of the cage 20
 next to the doors 58, 62. The door flaps 58, 62 are quickly released, and
 fish being studied are removed from the cage 20.
 As will be appreciated, the fish cage 20 is a substantial improvement over
 other in situ fish cages previously used to study the effects of
 environmental conditions on fish growth rates. The fish cage 20 of the
 present invention has the advantage of being able to stock and easily
 retrieve all of the fish from the cage whether being deployed from a boat
 or in turbid waters. Further, the fish cage 20 provides the fullest
 natural environment to the fish being studied, thereby allowing the fish
 to live on natural food in the environment over extended study periods.
 Further still, the fish cage 20 more effectively prohibits predators and
 competitors for food from entering the cage. In addition, the cage may be
 made relatively large so that larger fish populations can be studied. The
 fish cage of the present invention has the further advantage of being
 simple and economical to manufacture and has a durable, long life.
 While the invention has been set forth by a description of the preferred
 embodiment in considerable detail, it is not intended to restrict or in
 any way limit the claims to such detail. Additional advantages and
 modifications will readily appear to those who are skilled in the art. For
 example, as will be appreciated, the cage 20 can be any size that is
 appropriate for the fish being studied. Further, the mesh size of the
 first netting 31 on the sides 36, 37, ends 38, 39 and top 40 of the cage
 20 and the mesh size of the second netting 68 on the bottom 41 of the cage
 20 will vary with the nature of the study being done. However, as a
 general rule, the mesh size of the second netting 68 on the bottom 41 of
 the cage 20 will be substantially larger than the size of the mesh of the
 first netting 31 on the other sides of the cage 20. While a rectangular
 multilateral shape of the cage 20 is described, as will be appreciated,
 the cage 20 may have other shapes, such as hexagonal, octagonal, etc., as
 well as a cylindrical shape. Further, in the preferred embodiment, all of
 the edges of the netting overlap with an adjoining piece of netting,
 however, as will be appreciated, the edges of the netting may butt with
 each other so that there is no overlap.
 In the described example, tie-wraps 48 are used to secure the netting to
 the frame 26 of the cage 20. As will be appreciated, other ties, for
 example, flexible wire, water proof string, rigid wire clips, or any other
 known securing device or connecting clip may be used instead. Further, in
 the described example, the cage 20 is left in place during the full term
 of the experiment. However, if desired, the cage 20 may be lifted off the
 bottom 22, and the fish 66 removed for measurement at periodic intervals
 during the term of the experiment.
 Therefore, the invention in its broadest aspects is not limited to the
 specific detail shown and described. Consequently, departures may be made
 from the details described herein without departing from the spirit and
 scope of the claims which follow.