Device and method for selecting substrates with appropriate particle sizes for schizothorax fries

Abstract

The invention provides a device and a method for selecting substrates with suitable grain sizes for schizothorax fries. The device comprises a cylindrical water tank, a separation assembly and a life support system. The water tank is divided into a central larva fish throwing area and a plurality of fan-shaped substrate areas by partition assemblies, and gravel substrates with the same gradient particle size (1-30 cm) are laid in the symmetrical areas; the life support system maintains the water temperature to be 16-18 DEG C, the dissolved oxygen to be 6-7 mg / L and the water flow to be stable. The method comprises the steps that a substrate is laid, environment parameters are adjusted, 100-200 healthy larva fishes are put in, after adaptation, a baffle is pulled away so that the substrate can be freely selected, after one hour, the baffle is put back for partition counting, and the appropriate particle size is determined through a preference degree formula (P = (n / N) * 100%). Free selection and accurate counting are achieved through the detachable baffle, the problem of observation deviation of a traditional device is solved, and the result provides reference for sediment construction of a schizothorax spawning site.

Description

Technical Field

[0001] This invention relates to the field of ecological water conservancy science, specifically to a device and method for selecting suitable particle size substrate for schizothorax larvae. Background Technology

[0002] Currently, research on fish substrate preferences generally employs the flume experiment method, which determines preferences by recording the time fish spend in different substrate areas, the frequency of their presence, or the proportion of individuals (for larvae). Existing technologies have relatively mature substrate selection devices for larvae and adults, but dedicated devices for larvae are scarce, mainly because most fish do not require substrate protection during their larval stage.

[0003] For the unique schizothorax fish of the Qinghai-Tibet Plateau, their newborn larvae lack the ability to swim independently and need to hide under gravel of a specific size to avoid predators and improve their survival rate. Therefore, they have special requirements for substrate selection devices. However, existing devices and methods have significant limitations and cannot meet the experimental needs of schizothorax larvae, specifically:

[0004] The device design is mismatched with the behavior of the larvae: Existing devices (such as Rose CN201621373405.0 and Duan Ming CN202010479504.1) mostly rely on perforated partitions or "X"-shaped partitions to allow fish to actively cross the partitions or enter specific areas to make selections. However, larvae of the Schizothorax fish do not have the ability to swim independently and cannot actively complete the crossing or selection process. They may remain in areas of non-preferred substrate due to obstruction by the partitions, leading to increased experimental errors.

[0005] There are blind spots in the observation method: Existing devices (such as Bao Chunpeng CN202420314415.5, Feng Guangpeng CN200920070636.8, and Rose CN201621373405.0) all use cameras mounted on the top to capture fish tracks. Due to the obstruction of gravel, they cannot capture the activity of larvae hiding under the gravel. They are only suitable for fish that move above the bottom substrate and are completely unsuitable for larvae of schizothorax fish that hide under the bottom substrate.

[0006] Lack of specialized equipment: In the existing technology, there is a severe lack of experimental equipment for substrate selection of schizothorax larvae, which cannot meet their biological characteristics of "requiring substrate protection", making it difficult to carry out related research.

[0007] The survival of schizothorax fish faces the dual threats of human activities and climate change. Habitat protection is central to their species conservation, with spawning ground protection being of paramount importance. Currently, research on schizothorax spawning grounds is extremely limited. Their requirements for substrate particle size are fundamental data for restoring original spawning grounds and constructing artificial spawning grounds, and larval substrate selection experiments are an important scientific supplement to obtain this data. Therefore, the limitations of existing technology hinder the effective advancement of research on schizothorax larval substrate preferences and spawning ground particle size requirements. There is an urgent need for a specialized device that can accurately determine the suitable substrate particle size for schizothorax larvae to support research on larval protection and spawning ground restoration.

[0008] In summary, existing technologies cannot meet the special biological needs of schizothorax larvae, resulting in a significant technological gap. The present invention is of great significance in filling this gap and promoting the conservation of schizothorax and the study of spawning grounds. Summary of the Invention

[0009] The purpose of this invention is to provide a device and method for selecting suitable particle size substrates for schizothorax larvae, in order to solve the problems of restricted larval activity, inaccurate statistics, obstructed observation, and unstable environment in the existing schizothorax larvae substrate selection experiments, and to achieve accurate determination of suitable particle size substrates for schizothorax larvae.

[0010] To achieve the above objectives, the technical solution of the present invention is as follows:

[0011] A device for selecting suitable substrate size for schizothorax larvae includes an experimental tank, a life support system, and a partitioning component. The experimental tank has an opening at the top and is connected to the life support system via an inlet pipe and an outlet pipe. The inlet of the inlet pipe is located at the center of the experimental tank, and the water flows evenly from the center to the edge. Both the inlet and outlet pipes are equipped with flow control valves. The partitioning component divides the inner cavity of the tank into multiple areas. The central area is a circular larvae placement area that can cover the length of the larvae, and the remaining areas are fan-shaped substrate placement areas arranged around it. The bottom of each fan-shaped substrate placement area is covered with gradient-sized gravel substrate, and the substrate particle size is the same in symmetrical areas.

[0012] Furthermore, the experimental tank is cylindrical in shape, with a diameter of 1.5m-2m and a height of 1m; the central fry release area has a diameter of 5cm-10cm, forming a closed adaptation area through partitions; the substrate release area is covered with gravel substrate with a thickness of 10cm-20cm, and the substrate in each area can be replaced individually.

[0013] Furthermore, the separating component includes a "T"-shaped baffle and an annular baffle, both perpendicular to the bottom surface of the experimental tank. The annular baffle is placed in the middle of the experimental tank, and its top is provided with multiple slots at intervals. The locking strip at one end of the "T"-shaped baffle is locked into the slot of the annular baffle for fixation; the locking strip at the other end is locked into the slot at the top of the experimental tank. The space formed by the inner wall of the annular baffle constitutes the fry release area, and the space formed by two adjacent "T"-shaped baffles and the outer wall of the annular baffle constitutes the fan-shaped substrate release area. The separating component is placed when laying the substrate to prevent mixing. During the experiment, the separating component is removed for the fry to choose freely, and the separating component is put back when counting to prevent cross-dwelling.

[0014] Furthermore, the life support system maintains stable water quality in the tank through inlet and outlet pipes, controlling dissolved oxygen at 6-7 mg / L, water temperature at 16-18℃, and water flow rate at 3-5 cm / s. The gravel substrate in the substrate placement area is disinfected by ultraviolet irradiation or chemical soaking before use.

[0015] A method for selecting suitable substrate particle size for schizothorax larvae, using the aforementioned apparatus, includes the following steps:

[0016] Substrate preparation and environmental preparation: Remove the separator components and lay gradient gravel substrate of the same thickness in 8 fan-shaped areas. Fill the submerged substrate with water to 5-8 cm and start the life support system to adjust the water quality parameters to stabilize.

[0017] Fry stocking and acclimatization: Select 100-200 healthy schizothorax fry with a body length of 9-11mm and place them in the central fry stocking area. After acclimatizing to the water temperature and water quality conditions in the device, remove the separator to allow the fry to freely enter each substrate stocking area.

[0018] Zone separation and counting: 1-2 hours after the fry are released, the separating components are put back into the card slots, the gravel substrate of each zone is removed, and the number of fry in each substrate release zone is counted.

[0019] Data statistics and preference analysis: The preference degree was calculated according to the formula P=(n / N)×100, where P is the preference degree, n is the number of larvae in the area, and N is the total number of larvae released. The preference range of larvae for different particle size bottom substrates was determined through repeated experiments.

[0020] Furthermore, the gradient particle size substrate is symmetrically distributed in the steps. After the separation components are put back in the steps, it must be ensured that there are no larvae swimming together in each area. The experiments are repeated in the steps using larvae of the same size and substrate treatment method to verify the reliability of the results.

[0021] The present invention has the following beneficial effects:

[0022] 1. Removable baffle design to protect the natural selection behavior of fry.

[0023] The design employs a detachable baffle, allowing larvae to freely enter various substrate areas after adapting in the central adaptation zone. This accurately reflects their natural selection behavior and effectively avoids experimental errors caused by channel obstruction or human restriction in existing devices, which result in larvae staying in non-preferred areas.

[0024] 2. To prevent fish fry from escaping during statistical analysis and improve experimental accuracy.

[0025] By using detachable baffles for flexible control during the experiment, the problem of inaccurate experimental data caused by fish fry escaping into other areas when counting fry in traditional devices is solved, ensuring the stability of the statistical process.

[0026] 3. Directly count larvae hidden in the substrate, solving the problem of obstructed observation.

[0027] After the experiment, the partitions were reinstalled to achieve isolation, and the substrate was then removed from each partition to directly count the larvae hidden in the gravel gaps. This completely avoided the shortcomings of traditional optical observation methods, which could not accurately count the larvae under the substrate due to gravel obstruction, and significantly improved the reliability and accuracy of the data.

[0028] 4. Integrated life support devices ensure a stable experimental environment.

[0029] Adding a life support device to the apparatus can effectively maintain the stability of environmental parameters such as water quality and dissolved oxygen in the tank, reduce the interference of environmental fluctuations on the behavior of fry and experimental results, and provide controllable and suitable conditions for the experiment.

[0030] 5. A cylindrical water tank is used instead of the traditional square water tank to optimize the experimental environment simulation and ease of operation, as detailed below:

[0031] (1) Eliminate boundary effects and ensure experimental randomness

[0032] Cylindrical tanks avoid the interference of the boundaries, corners, and top effects of square tanks on the behavior of larvae, allowing the target fish to swim randomly without physical restrictions. This ensures that the selection of preference factors is not affected by non-target environmental factors, thus improving the scientific nature of the experimental design.

[0033] (2) Simulate natural open water areas to enhance the realism of the environment.

[0034] The circular tank structure can better simulate the open water conditions in the natural environment, reduce the interference of artificial devices on the natural behavior of larvae, make the experimental results closer to the substrate selection preferences of schizothorax larvae in their natural habitat, and enhance the ecological relevance of the experimental conclusions.

[0035] (3) Optimize the laying and maintenance of the substrate to improve the ease of operation.

[0036] The circular bottom shape of the water tank is conducive to the uniform laying of substrates with different particle sizes. Compared with square water tanks, it is easier to achieve a consistent substrate thickness and density distribution. At the same time, the circular structure facilitates the replacement and maintenance of substrates in the later stage, reduces the difficulty of experimental operation, and improves experimental efficiency. Attached Figure Description

[0037] Figure 1 This is a three-dimensional structural schematic diagram of a substrate selection device for suitable particle size of schizothorax larvae according to an embodiment of the present invention;

[0038] Figure 2 This is a top view of a substrate selection device for suitable particle size of schizothorax larvae according to an embodiment of the present invention;

[0039] Figure 3 This is a schematic diagram of the bottom partition of a substrate selection device for suitable particle size of schizothorax larvae according to an embodiment of the present invention;

[0040] Figure 4 This is a diagram of the baffle structure of a substrate selection device for suitable particle size of schizothorax larvae according to an embodiment of the present invention;

[0041] Figure 5 This is a graph showing the number and preference data of small-headed naked carp larvae in different substrate particle size regions according to an embodiment of the present invention;

[0042] Figure 6 This is a graph showing the number and preference data of Schizothorax heterodon larvae in different substrate particle size regions according to an embodiment of the present invention.

[0043] Figure 7 This is a graph showing the number and preference data of giant schizothorax larvae in different substrate particle size regions according to an embodiment of the present invention. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Please see Figure 1 This invention provides a device for selecting suitable particle size substrate for schizothorax larvae, comprising an experimental tank 1 and a life support system 2 connected to each other.

[0046] In this embodiment, the experimental tank 1 is equipped with a partition component 14. The experimental tank 1 is connected to the life support system 2 via an inlet pipe 3 and an outlet pipe 4. The outlet of the inlet pipe 3 is 0.5 meters below the horizontal plane at the top of the experimental tank. Flow control valves are installed on the inlet pipe 3 and the outlet pipe 4 to control the water flow. The inner cavity of the experimental tank 1 is divided into 9 areas by the partition component 14. The central area is a circular larvae placement area 5, which can cover the length of the larvae. The remaining 8 areas are fan-shaped substrate placement areas (6-13). The bottom of each fan-shaped substrate placement area 6-13 is covered with gradient-sized gravel substrate, and the substrate particle size is the same in symmetrical areas. Figure 3 As shown, in one embodiment, reference numerals 6 and 10 represent areas without substrate, reference numerals 7 and 11 represent gravel substrates with a particle size of 1 cm to 10 cm, reference numerals 8 and 12 represent gravel substrates with a particle size of 10 cm to 20 cm, and reference numerals 9 and 13 represent gravel substrates with a particle size of 20 cm to 30 cm.

[0047] In one embodiment, the experimental tank 1 is cylindrical with an open top, and its central area is set as a closed adaptation area by a partition, serving as the fry release area 5. The tank has a diameter of 2m and a height of 1m.

[0048] The partition component 14 is a splicing connection method, which facilitates the adjustment of the substrate area division according to experimental needs. Specifically, the partition component 14 includes a "T"-shaped baffle 14-1 and an annular baffle 14-2, both of which are perpendicular to the bottom surface of the experimental tank 1. The annular baffle 14-2 is placed in the middle of the experimental tank 1, and the top of the annular baffle 14-2 is provided with multiple slots 14-4 at intervals. The locking strip 14-3 at one end of the "T"-shaped baffle 14-1 is locked into the slot 14-4 of the annular baffle 14-2 for fixation, and the locking strip 14-3 at the other end is locked into the slot 14-5 at the top of the experimental tank 1. The space formed by the inner wall of the annular baffle 14-2 constitutes the larvae release area 5, and the space formed by the outer walls of two adjacent "T"-shaped baffles 14-1 and the annular baffle 14-2 constitutes the fan-shaped substrate release area 6-13.

[0049] When laying the substrate, place the separator component 14 to prevent mixing. During the experiment, remove the separator component 14 to allow the fry to choose freely. When counting, put the separator component 14 back to prevent them from swimming together.

[0050] The thickness of the substrate filling layer in the substrate placement area (6-13) is 30cm, and the substrate material in each substrate placement area (6-13) can be replaced individually.

[0051] The substrate in the substrate placement area (6-13) must be washed and disinfected before use. The disinfection method is ultraviolet irradiation or chemical soaking.

[0052] This invention also provides a method for selecting suitable particle size substrate for schizothorax larvae, which uses the aforementioned apparatus and includes the following steps:

[0053] (1) Remove the baffle, lay the same thickness of substrate, and make the substrate evenly distributed; fill the water to submerge the substrate by 5-8 cm, and run the life support system to make the dissolved oxygen 6-7 mg / L, the water temperature 16-18℃, and the flow rate 3-5 cm / s.

[0054] (2) Select 100-200 healthy, uniformly sized schizothorax fry and place them in the fry release area 5 to allow them to adapt to the same water temperature and quality conditions as the device. Then, by removing the ring baffle 14-2, the fry can freely choose different bottom areas.

[0055] (3) After the fry are released, wait 1 hour and then put the separator 14 back into the slot to separate the area and observe the distribution and number of fry in different particle size substrate areas.

[0056] (4) Data recording and analysis: During each observation, the number of larvae in each area (6-13) was recorded in detail and compiled into a data table. Through statistical analysis, the proportion of the average number of larvae staying in different particle size substrate areas to the total number of larvae released was calculated, i.e., the preference. Based on the changes in data of each area (6-13) in multiple experiments, the preference of the schizothorax larvae for different particle size substrates was determined, and the substrate particle size range that is more suitable for the schizothorax larvae to live was determined.

[0057] Formula: P = (n / N) * 100%

[0058] Where P is the preference degree, n is the number of times the experimental fish appears in each region, and N is the total number of experimental fry.

[0059] (5) Throughout the experiment, environmental conditions such as water temperature, water quality, and light were strictly controlled to keep them relatively stable, reducing the interference of external factors on the behavior of larvae in selecting substrate. At the same time, to ensure the accuracy and reliability of the experimental results, at least three repeated experiments were conducted. Each experiment used larvae of the same origin and size, as well as the same substrate treatment method. The most accurate suitable substrate size for schizothorax larvae was obtained by analyzing the data from multiple experiments.

[0060] Implementation Case 1

[0061] Experiment on substrate selection of juvenile smallhead naked carp with different gravel sizes

[0062] Remove the separator component 14 and lay gravel substrate with particle sizes ranging from no substrate (control), 1-10cm, 10-20cm, and 20-30cm in different zones, ensuring even distribution and consistent thickness across zones. Fill the zones with water to submerge the substrate by 5-8cm and operate the life support system to maintain dissolved oxygen at 6-7mg / L, water temperature at 16-18℃, and flow rate at 3-5cm / s. Select 100-200 healthy, uniformly sized small-headed naked carp larvae and place them in the larvae stocking area 5 to allow them to acclimatize to the same water temperature and quality conditions as the device. Then, remove the annular baffle, allowing the larvae to freely choose different substrate areas. One hour after stocking, replace the separator component 14 in the slot, separating the zones and preventing the larvae from re-entering the substrate areas with different particle sizes. Observe the distribution and number of larvae in the substrate areas with different particle sizes, and compile the data as shown below. Figure 4 As shown

[0063] Experimental results show that juvenile small-headed naked carp have a clear preference for gravel substrate with a particle size of 1-10 cm.

[0064] Implementation Case 2

[0065] Experiment on substrate selection of different gravel sizes for larvae of *Schizothorax heterodon*

[0066] Remove the baffle and lay gravel substrate with particle sizes ranging from no substrate (control), 1-10cm, 10-20cm, and 20-30cm in different zones, ensuring even distribution and consistent thickness across zones. Fill the zone with water to submerge the substrate by 5-8cm, and operate the life support system to maintain dissolved oxygen at 6-7mg / L, water temperature at 16-18℃, and flow rate at 3-5cm / s. Select 100-200 healthy, uniformly sized schizothorax fry and place them in the fry release area to acclimate to the same water temperature and quality conditions as the device. Then, remove the ring baffle, allowing the fry to freely choose different substrate areas. One hour after fry release, replace the separating component 14 back into the slot, separating the areas and promptly preventing fry from re-entering substrate areas of different particle sizes. Observe the distribution and number of fry in substrate areas of different particle sizes, and compile the data as shown below. Figure 5 As shown.

[0067] Experimental results show that juvenile *Schizothorax heterodon* have a clear preference for gravel substrate with a particle size of 1–10 cm.

[0068] Implementation Case 3

[0069] Experiment on substrate selection of larvae of the giant schizothorax with different gravel sizes

[0070] Remove the baffle and lay gravel substrate with particle sizes ranging from no substrate (control), 1-10cm, 10-20cm, and 20-30cm in different zones, ensuring even distribution and consistent thickness across zones. Fill the zone with water to submerge the substrate by 5-8cm, and operate the life support system to maintain dissolved oxygen at 6-7mg / L, water temperature at 16-18℃, and flow rate at 3-5cm / s. Select 100-200 healthy, uniformly sized schizothorax larvae and place them in the larvae introduction area to acclimate to the same water temperature and quality conditions as the device. Then, remove the ring baffle, allowing the larvae to freely choose different substrate areas. One hour after introduction, replace the separating component 14 back into the slot, separating the areas and preventing larvae from re-entering different substrate areas. Observe the distribution and number of larvae in different substrate areas, and compile the data as shown below. Figure 6 As shown

[0071] Experimental results show that juvenile *Schizothorax heterodon* have a clear preference for gravel substrate with a particle size of 1–10 cm.

[0072] This invention has the following features and effects:

[0073] 1. Zoning Design and Free Choice: The circular tank is divided into a central larvae release area and eight fan-shaped substrate areas by a partition component. With the addition of a detachable baffle structure, the larvae can freely enter each substrate area, avoiding the obstruction of larvae movement by the partition holes in traditional devices. This truly reflects their natural selection behavior and reduces experimental errors.

[0074] 2. Accurate counting and prevention of cross-dwelling: After the experiment, the fry can be directly counted by putting them back into the partitioned area and removing the gravel. This solves the statistical bias caused by gravel obstruction in traditional optical observation methods and ensures data accuracy.

[0075] 3. Stable environment simulation: The life support system controls parameters such as water flow, water temperature (16-18℃), and dissolved oxygen (6-7mg / L) through the inlet pipe (central water inlet) and outlet pipe. The circular water tank design reduces boundary effects and is closer to natural open water. The bottom substrate is evenly laid and can be replaced individually, improving the reliability of the experiment.

[0076] 4. Spawning Ground Construction Reference: By analyzing preferences, the suitable substrate particle size for larvae is determined, providing a scientific basis for the restoration and artificial construction of schizothorax spawning grounds.

[0077] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A device for selecting suitable substrate particle size for Schizothorax fish larvae, characterized in that: The utility model relates to a fish larvae and juvenile rearing device and method, which comprises an experimental tank (1), a life support system (2) and a separation component (14). The experimental tank (1) is open at the top and is connected to the life support system (2) through an inlet pipe (3) and an outlet pipe (4). The inlet of the inlet pipe (3) is located at the center of the experimental tank (1), and the water flows uniformly from the center to the edge. Both the inlet pipe (3) and the outlet pipe (4) are equipped with flow control valves. The separation component (14) divides the inner cavity of the experimental tank into multiple areas. The middle part is a circular fish larvae releasing area (5) that can cover the length of the fish larvae. The remaining parts are fan-shaped substrate releasing areas (6-13) arranged in a ring. The bottom of each fan-shaped substrate releasing area (6-13) is paved with gradient particle size gravel substrate. The particle sizes of the substrates in the two symmetrical areas are the same.

2. The apparatus of claim 1, wherein: The experimental tank (1) is in the shape of a cylinder with a diameter of 1.5-2 m and a height of 1 m. The fish larvae releasing area (5) in the center is 5-10 cm in diameter and is formed into a closed adaptive zone by a partition. The substrate releasing areas (6-13) are paved with 10-20 cm thick gravel substrate. The substrates in each area can be replaced individually.

3. The apparatus of claim 1, wherein: The separation component (14) comprises a "T"-shaped baffle (14-1) and a ring-shaped baffle (14-2), both of which are perpendicular to the bottom surface of the experimental tank (1). The ring-shaped baffle (14-2) is located in the middle part of the experimental tank (1). Multiple clamping grooves (14-4) are arranged at the top of the ring-shaped baffle (14-2). The clamping strip (14-3) at one end of the "T"-shaped baffle (14-1) is clamped into the clamping groove (14-4) of the ring-shaped baffle (14-2) for fixation. The clamping strip (14-3) at the other end is clamped into the clamping groove (14-5) at the upper part of the experimental tank (1). The space formed by the inner wall of the ring-shaped baffle (14-2) constitutes the fish larvae releasing area (5). The space formed by the outer wall of the ring-shaped baffle (14-2) and the two adjacent "T"-shaped baffles (14-1) constitutes the fan-shaped substrate releasing area (6-13). The separation component (14) is placed when paving the substrate to prevent mixing. The separation component (14) is pulled out during the experiment to allow the fish larvae to choose freely. The separation component (14) is put back when counting to avoid straying.

4. The apparatus of claim 1, wherein: The life support system (2) maintains the stability of the water quality in the experimental tank through the inlet pipe (3) and the outlet pipe (4). The dissolved oxygen is controlled at 6-7 mg / L, the water temperature is controlled at 16-18℃, and the water flow rate is controlled at 3-5 cm / s. The gravel substrate in the substrate releasing areas (6-13) is disinfected by ultraviolet irradiation or chemical agent soaking before use.

5. A method for selecting suitable particle size substrate for schizothorax larvae, using the apparatus described in claims 1-4, characterized in that... The method comprises the following steps: (1) Substrate paving and environment preparation: remove the separation component (14), pave the same thickness of gradient particle size gravel substrate (particle size 1-30 cm, divided into 4 gradients) in the 8 fan-shaped areas, fill water to 5-8 cm above the substrate, and start the life support system (2) to adjust the water quality parameters to stable; (2) Fish larvae releasing and adaptation: select 100-200 healthy Schizothorax fish larvae with a body length of 9-11 mm, place them in the central fish larvae releasing area (5), and after adapting to the water temperature and water quality conditions in the device, pull out the separation component (14) to allow the fish larvae to enter each substrate releasing area (6-13) freely. (3) Area separation and counting: After 1-2 hours of fry release, the separation component (14) is returned to the card slot separation area, the gravel substrate of each area is removed, and the number of fry in each substrate release area (6-13) is counted; (4) Data statistics and preference analysis: The preference degree is calculated according to the formula P=(n / N)×100, where P is the preference degree, n is the number of fry in the area, and N is the total number of fry released. The preference range of fry for different particle sizes of substrate is determined through multiple repeated experiments.

6. The method of claim 5, wherein: In step (1), the gradient particle size substrate is symmetrically distributed, and in step (3), the separation component (14) is returned to ensure that there is no fry swimming between areas, and in step (4), the same size fry and substrate treatment method is used for repeated experiments to verify the reliability of the results.

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