Abstract:
A fish grading device is provided including a framework of substantially rigid elongate members pivotably interconnected to form a plurality of loops, wherein each the loop is formed from a plurality of the substantially rigid elongate members and defines an aperture not exceeding predetermined dimensions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application claims the priority of a United Kingdom patent filed May 11, 1999 under application number 9926195.0. 
   The present application claims priority of a UK application filed Nov. 5, 1999 under the following serial number: 9926195.0, which is incorporated herein by reference in its entirety. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to fish grading devices and relates particularly, but not exclusively, to fish grading devices for incorporation into fishing nets. 
   BACKGROUND OF THE INVENTION 
   Fish grading devices are known which consist of a fishing net having a mesh size such that fish above a certain size cannot swim through the net and are therefore retained in the net, while smaller fish can escape through the apertures in the net. Known fish grading devices of this type suffer from the disadvantage that fish can be injured by becoming snagged on the net while trying to pass through the apertures. 
   BRIEF SUMMARY OF THE INVENTION 
   Preferred embodiments of the present invention seek to overcome the above disadvantages of the prior art. 
   According to an aspect of the present invention, there is provided a fish grading device comprising a framework of substantially rigid elongate members pivotably interconnected to form a plurality of loops, wherein each said loop is formed from a plurality of said substantially rigid elongate members and defines an aperture not exceeding predetermined dimensions. 
   By providing a plurality of loops formed by interconnected substantially rigid members such that each loop is pivotable relative to the or each loop adjacent thereto, this gives the advantage that fish are less likely to become snagged on the substantially rigid elongate members than on threads of a fishing net, but the fish grading device is still sufficiently flexible that it can be wound onto a reel or otherwise made compact for convenient handling or transport. 
   In a preferred embodiment, each said substantially rigid elongate member can rotate about its longitudinal axis. 
   This provides the advantage of minimising the risk that a fish will become snagged on one of the substantially rigid elongate members while trying to pass through one of the apertures of the device. 
   Each said substantially rigid elongate member may be tubular. 
   The substantially rigid elongate members may be interconnected by means of elongate flexible members. 
   In the case of tubular substantially rigid elongate members being interconnected by elongate flexible members, this provides the advantage that the fish grading device is flexible when not under tension, but becomes rigid when under tension such that the apertures remain of substantially constant dimensions. 
   The or each said elongate flexible member may be a string or thread. 
   The or each said elongate flexible member may form a respective loop corresponding to each said loop of said interconnected substantially rigid elongate members. 
   At least one said substantially rigid elongate member may be slidable longitudinally relative to the corresponding elongate flexible member. 
   In a preferred embodiment, a plurality of said loops of elongate members are each formed from four said substantially rigid elongate members. 
   Each of said loops of substantially rigid elongate members is preferably substantially rectangular. 
   According to another aspect of the invention, there is provided a fishing net including a fish grading device as defined above. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     A preferred embodiment of the invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings, in which:— 
       FIG. 1  is a schematic elevation view of part of a fish grading device embodying the present invention; 
       FIG. 2A  is a perspective view of a first embodiment of fishing net incorporating the fish grading device of  FIG. 1 ; 
       FIG. 2B  is an enlarged view of part of the fishing net of  FIG. 2A ; and 
       FIG. 3  is a schematic elevation view of a second embodiment of fishing net incorporating the fish grading device of  FIG. 1 . 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , a fish grading device  1  is formed from an array of generally rectangular apertures  2 , each of which is formed by two long tubes  3  and two short tubes  4  of plastics material mounted to a loop of fishing net  5 . Each loop of fishing net  5  is formed by crimping the ends of the loop by means of a metal crimp  6 . Each of the tubes  3 ,  4  can rotate freely about its longitudinal axis, so that a fish brushing against a tube  3 ,  4  will cause the tube to rotate, and will therefore avoid becoming snagged on the tube. 
   Tubes  3 ,  4  defining two adjacent apertures will have two loops of fishing line  5  passing therethrough, for example as shown at locations  7 . When the fish grading device  1  is placed under tension, the dimensions of apertures  2  are prevented by tubes  3 ,  4  from being reduced, but when the device  1  is not under tension, it is relatively flexible, and can therefore be handled easily, for example would onto a reel on a fishing boat. 
   Referring now to  FIG. 2A , a fishing net  10  for use in the commercial fishing sector is dragged by means of lines  11  by a boat (not shown) such that fish are drawn into mouth  12  of the net  10 . The net  10  is provided with a number of panels formed by fish grading devices  1 , three such panels being shown in  FIG. 2A , two of which are in the central location of the net  10 , and one of which is at cod end  13  of the net ( FIG. 2B ). 
   The operation of the net shown in  FIGS. 2A and 2B  will now be described. 
   When the net  10  is dragged behind a boat, fish are drawn into the net  10 , and only fish that are sufficiently small to pass through apertures  2  ( FIG. 1 ) can escape from the net. As a result, larger fish are retained in the net, while smaller fish can escape. 
   As the net  10  is dragged behind the boat, the loops  5  of the fish grading device  1  are placed under tension, as a result of which the tubes  3 ,  4  are drawn closer together and the rigidity of the tubes prevents the dimensions of the apertures from reducing. At the same time, if a fish is trying to pass through one of the apertures  2  and is caused by other fish to be pressed against one of the tubes  3 ,  4 , the tube  3 ,  4  can rotate about its longitudinal axis, which reduces the risk of a fish becoming injured by becoming snagged on the threads of the fishing net. 
     FIG. 3  shows a sweep net for use in the aquaculture industry in confining fish to a selected volume of water, for example within a sea cage or shore tank system of a fish farm. The sweep net  20  is formed by a net  21  suspended from float  22 , and incorporating a fish grading device  1  as shown in  FIG. 1 . 
   It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.