the present invention provides methods to guide the displacement of aquatic crustaceans . the method for attracting aquatic crustaceans to move close to a predetermined place for hiding or staying after theses crustaceans are fed full but prior to the status that these crustaceans are hungry again comprises the step of generating the effect of bright and dark contrast at the predetermined place within the water body of culture . the aforesaid predetermined place can therefore be distinguished by its composition of one or more first brightness sub - areas and one or more second brightness sub - areas . the bright and dark contrast is the contrast between an above - said first brightness sub - area and an above - said second brightness sub - area . the aforesaid first brightness sub - areas are brighter than the aforesaid second brightness sub - areas . the predetermined place within the water body of culture is the place , presenting the visual effect , chosen from the bottom surface , the walls , or any space from bottom up to the water surface of the water body of culture . within the above - said chosen region , the bright and dark contrast can be generated , projected , painted and / or spread , on any floating attachable material and / or any fixed attachable material . the above - said effect of bright and dark contrast is generated by one or many light - emitting sources directly or , modified by reflection of one or more combinations of painted figures and / or one or more sets of protrusions , and / or by filtration of one or more filters with various filtration effects . such light - emitting sources , light - reflecting or light filtering apparatuses / materials can be installed onto the above - said predetermined place directly , the nearby space above water or even the exterior side of the container &# 39 ; s bottom layer as long as the effect of bright and dark contrast generated , projected , spread and / or painted at the predetermined place can be received by the cultured crustaceans . the size and depth of a container carrying the water body of culture can vary according to the species and size of aquatic crustaceans reared in practice without specific limitations . for white shrimps , litopenaeus vannamei , they can be cultured in a water body of about 10 cm depth , which is much less than the 60 cm to 200 cm depth in traditional marine culture for shrimp like blue shrimp , penaeus setiferus , white shrimp , litopenaeus vannamei , tiger shrimp , penaeus monodon , and kuruma shrimp , panaeus japonicus . the first brightness sub - areas and the second brightness sub - areas can be regularly or irregularly arranged and produced simultaneously or in an unsynchronized fashion . modifying position or angle of the light reflecting / filtering apparatuses ( such as the aforesaid painted figures , protrusions and filters ) and / or the coexisted illuminating sources or changing the arrangement of the light emitters is capable of altering the brightness or the shape of each first or second brightness sub - area . moreover , shapes , arrangements and reflection levels of the figures , the structure and characteristics of the filters are also ready to be adjusted in order to create the desired brightness in both first and second brightness sub - areas . the brightness of each first or second brightness sub - area is constant or changeable . neither all first brightness sub - areas are necessarily of same brightness nor all second brightness sub - areas are necessarily of same brightness , if number of the first brightness sub - area and / or the second brightness area is larger than one . the bright and dark contrast can be produced directly from a light - emitting source directly ( see fig2 a and 2 b ), or with a filter plate ( see fig3 ), a light - reflecting painted figure ( see fig1 ) and light reflection networks of protrusions ( see fig4 and 5 ). when a light - emitter like leds or fluorescent / incandescent light is selected , it could be used as the light emitting source for generating the contrast effect directly and can be closely deployed at a predetermined place . single or multiple said emitters , with / without same brightness , are both able to be utilized to generate the bright and dark contrast . on / off manipulations of the emitters , the differences between the emitters &# 39 ; brightness and the brightness differences between the surrounding less illuminated places and the places lighted by emitters all can produce aforementioned bright and dark contrast . the preferred embodiment adopts multiple numbers of emitters , like fig2 a and 2 b , with on / off manipulations , producing effective contrast of bright and dark . considering high burn - out consumption of emitters due to repeatedly turning them on and off , an area deployed with persistently glowing emitters in a loosely arranged pattern with space in between is preferred . this loose pattern of emitters can be made by a plurality of individual emitter or emitter group irregularly dispersedly or regularly arranged . on the other hand , on / off manipulations of single or multiple emitters , which is grouped or not , is also sufficient to produce the bright and dark effects , and emitters in such condition , can flash synchronously , alternatively or totally in an unsynchronized fashion . as known in the art , a transparent structure or material ( not shown in the figure ) may cover over the light emitters to prevent them from immersion in water . when a light - reflector / filter is chosen , such as the flat area with painted figures of different reflection levels , see fig1 , protrusions which form shadows by reflecting a portion of illuminating light , see fig4 and 5 , a filter which has sub - areas with different light transparencies ( between and including 100 % and 0 %) and can thus serves as a sieve that creates an effective image of dark and bright contrast through and onto the bottom of the water body of culture , see also fig3 , there should be an auxiliary illuminating source , outside and / or inside the water body of culture . the first brightness sub - areas and the second brightness sub - areas derived from the light emitting sources directly or with filters , or from the light reflecting sources can be shaped into linear , square , round , hexagon - like or any kind of geometric or non - geometric figures and arranged into rows , circles , grids or regular / irregular styles . the illuminating sources used to shine on filters , painted figures or protrusions are commercially available light bulbs or leds ; normally , light that generates a light intensity at 1 - 300 lux at the surface of or within the water body of the culture is used . position of the light filter is chosen between bottom of the culture container and the illuminating source in order to form a light pattern mixed with shadow and lighted spots at the bottom or through the water body of culture , see fig3 . in one preferred embodiment , this filter can be installed under the water surface of the water body of culture to further providing the cultured crustaceans with a tangible and attachable structure for hiding and staying . both the brighter areas , defined as the first brightness sub - areas derived from the illuminating light passing through the high - transparency openings in the filter , and the less - bright areas , defined as the second brightness sub - areas derived from the illuminating light blocked by the none - opening , or less - transparent , areas of the filter , jointly result in the formation of the bright - dark contrast . the painted figures , images created by light filters and / or protrusions can be deployed directly into the predetermined place . areas surrounding the predetermined place can be further lighted with even or graded intensities to enhance the attracting effects built into the predetermined place . the aquatic crustaceans in the present invention include , but not limited to , shrimp and crab ; wherein litopenaeus vannamei , penaeus monodon , penaeus setiferus and panaeus japonicus are preferable . in one embodiment , the cultured aquatic crustacean is white shrimp , litopenaeus vannamei , depth of the water body is of 10 cm . a filter plate , containing perforations of one size or various sizes at 0 . 2 to 2 cm in diameter , is placed 4 to 9 cm deep into the water . a fluorescent illuminating light source evenly reaches to the water surface with a light intensity at 10 - 60 lux shines to the underwater filter plate . while light reaches to the filter , a part of it goes through perforations and the rest of it is blocked by the none - opening portion of the filter , an effect of bright and dark contrast is thus created at the predetermined place . for white shrimp , a bright and dark contrast with 25 lux at the first brightness sub - areas and 5 lux at the second brightness sub - areas has been found very effective . that is white shrimp of various weight ( each of 0 . 05 to 40 g ) are observed to approach the predetermined place effectively after feeding . moreover , the shrimp of large numbers can be seen to hide under this properly arranged light - filter plate as short as 30 minutes after feeding . the overall apparatuses for generating the effects of bright and dark contrast are shown in fig1 ˜ 5 and described in following embodiments . in embodiment 1 , see fig1 , strip - like dark colored figures , constructed with dark paint or adhesive tape , are combined into a grid - like pattern 110 deployed onto a predetermined place 130 at the bottom 101 of the container 100 . the deep - colored regions 132 and the un - painted region 131 at the predetermined place 130 respectively construct the aforesaid second brightness sub - areas and the aforesaid first brightness sub - areas , jointly these sub - areas constituting the bright and dark contrast under the illuminating source 120 . in embodiment 2 , see fig2 a , light - emitters 210 a arranged into an array is the direct origin of the bright and dark contrast . the emitter 210 a can be a led , a fluorescent light bulb , an incandescent light bulb or any of other light sources . a led is preferred here because it is economical and durable . however , the fluorescent light bulb is also preferred considering its low price and availability . the emitter 210 a &# 39 ; s array is placed at the bottom 201 a of the container 200 a . and the predetermined place 230 a can thus be distinguished into several less illuminated sub - areas 232 a , intended to be the second brightness areas , and several illuminated sub - areas 231 a , intended to be the first brightness area . the emitters glow persistently or alternatively and their brightness is constant or changeable . in this embodiment , a plurality of individual led glowing persistently is preferred because of its easy installation and management . in embodiment 3 , see fig2 b , light - emitters 210 b arranged into an array is the origin of the bright and dark contrast . the emitter 210 b can be a led , a fluorescent light bulb , an incandescent light bulb or any of other light sources . a led is preferred here because it is economical and durable . however , the fluorescent light bulb is also preferred considering its low price and availability . the emitter 210 b &# 39 ; s array is not placed at the bottom 201 b of the container 200 b like the case in embodiment 2 but instead placed above surface of the water body of culture loaded into container 200 b . with the emitter 210 b &# 39 ; s array image projecting on , the predetermined place 230 b can thus be distinguished into several less illuminated sub - areas 232 b , intended to the second brightness areas , and several illuminated sub - areas 231 b , intended to the first brightness areas . the emitters glow persistently or alternatively and their brightness is constant or changeable . in this embodiment , a plurality of individual led glowing persistently is preferred because of its easy installation and management . in embodiment 4 , see fig3 , a perforated filter plate 310 with 100 % light transparency at its perforations 311 and 0 % light transparency at the rest of the plate surrounding perforations 311 is adopted to sift the illuminating light 320 . several light columns 340 are formed and therefore the filter plate produces simultaneously several illuminated sub - areas 331 , intended to be the first brightness sub - areas , and the under illuminated sub - areas 332 , intended to be the second brightness sub - areas . both sub - areas jointly constitute the effect of bright and dark contrast at and above the predetermined area 330 on bottom 301 of container 300 . the filter plate 310 can be an opaque round plate of pvc - like material constructed as a horizontal light filter , but its shape , material and position angle respectively are not limited to be round , pvc and horizontal . other shapes , materials and / or position suitable for generating intended effects are usable . shape of the opening 311 is not limited to be a round hole and size of each opening 311 is of one size or various sizes of 0 . 1 to 8 cm in diameter . the distance of 0 . 1 to 8 cm between neighboring perforations 311 has been tested to be effective . the perforations 311 , although they have 100 % light transparency in this embodiment , other materials / structures contributing to different light transparency can be adopted . the light transparency of the filter plate itself is also adjustable . position of the filter 310 is located between the bottom layer 301 and the illuminating source 320 , either above the surface of or immersed in , the water body of culture loaded in container 300 . when this light - filtering plate immersed into the water 2 - 9 cm deep , it has been proved to be effective not only for attracting fed white shrimp but also creating a tactile sensation that enhances penaeus setiferus and litopenaeus vannameis hiding behavior at predetermined place 330 where the said bright and dark contrast is present . in embodiment 5 , see fig4 , a network of thin - wall protrusion 410 is installed on bottom 401 of container 400 at a predetermined place 430 . this network of protrusion 410 is formed by interlacing thin - wall plates into a grid - like pattern sitting vertically on the predetermined place 430 at bottom 401 of container 400 . the height of the network of protrusion 410 in this embodiment is of 0 . 1 to 8 cm and the distance between two neighboring parallels of protrusion plates is of 0 . 1 to 8 cm . a bright and dark light contrast effect can be produced by projecting light source 420 in an angle toward network 410 . range of the aforesaid height of and distance between protrusion plates can be adjusted depending on size and species of the cultured animals and / or angles of the illuminating light . shadow sub - areas 432 derived from shade of the network of protrusion 410 under illuminating light 420 are intended to be the second brightness sub - areas which constitutes the bright and dark contrast when in combination with lighted sub - area 431 , intended to be the first brightness sub - areas . this embodiment has an additional advantage that it also provides habitable shelters facilitating the staying and hiding activities of aquatic crustaceans at predetermined place 430 after they have been attracted to it . in embodiment 6 , see fig5 , within container 500 , a network of cone like protrusion 510 is constructed at a predetermined place 530 on container bottom 501 as a variation of the present invention . shape of the protrusion 510 includes , but not limited to , a column - like or a taper shape . the network of protrusion 510 forms lighted sub - areas 531 and casts shadowed sub - areas 532 under angled illuminating light 520 . the shadowed sub - areas 532 are intended to be the second brightness areas and the lighted sub - areas 531 are intended to be the first brightness sub - areas . both , the first and second sub - areas combined , constitute the effect of bright and dark contrast . height of the protrusion 510 in this embodiment is of 0 . 1 to 8 cm and distance between two neighboring protrusions 510 is 0 . 1 to 8 cm . range of the aforesaid height and distance can be adjusted depending on size and species of the cultured animals and / or angle of illuminating light 520 . the area of the predetermined place depends on species and size of animals reared and the size of culture container in use . it is preferred to have the area of the predetermined place and the rest of the container &# 39 ; s bottom in a ratio like 1 : 1 ; in one culture test , such ratio has led to lowered cannibalization incidents . thus , the area surrounding the predetermined place with brightness of even or gradually grading quality may be further applied into the above - mentioned embodiments to facilitate movement of none - molted crustaceans searching for their hiding place at the predetermined place and leave alone newly molted mates who have backward retraction ability to move and stay in the area surrounding but away the predetermined place . with the present method , construction of a tank having at least one predetermined area expressing the effect of bright - dark contrast can culture aquatic crustaceans at an increased density and at a reduced depth of the culture container to almost 10 cm still with cannibalization under control . a multi - layered culture system construction is therefore feasible due to reduction of water body in each culture layer . for culturing aquatic crustaceans and other animals , being able to have multi - layered culture greatly increases the space utilization efficiency of each square meter of a production area . the results generated in one embodied multi - layered system while culturing litopenaeus vannamei are shown in table 1 . the culture density of each square meter production floor is calculated as the total weight of shrimp cultured in 10 - layered culture system , with 10 individual culture layers stacking one above the other , divided by the square area covered by the culture system which is equal to the bottom area of each individual culture layer . this table depicts that by using this 10 - layered culture system with technology of the present invention in place , a very high production efficiency at a density of 10 kg or more litopenaeus vannamei per square meter production floor can be attained with reduced cannibalism ( expressed as nearly 100 % survival rates ). this is a significant improvement over the density of 0 . 73 kg marine shrimp produced over per square meter pond area ( calculated by the data published in the annual report of taiwan , r . o . c . council of agricultural affairs on fishery in 1987 , which is the most successful year of marine shrimp culture in taiwan and the yield was 80 , 000 tons for 11 , 000 hectares of land used ). the inventive subject matter being thus described , it will be obvious that the same may vary in many ways . such variations are not to be regarded as a departure from the spirit and scope of the inventive subject matter , and all such modifications are intended to be included within the scope of the following claims .