A method for guiding Japanese eels using light

Abstract

To provide a method for guiding Japanese eels using light. [Solution] The light-based guiding method for Japanese eels of the present invention is a method for guiding the behavior of Japanese eels that are cultivated in a designated enclosed area. It is characterized by shining blue light into the water in the designated area from one direction and shining red light from a different direction from the blue light, creating blue areas irradiated with blue light and red areas irradiated with red light in the water in the designated area, thereby causing the Japanese eels to move from the blue area to the red area.

Description

[Technical Field]

[0001] This invention relates to a method for guiding Japanese eels using light to control their movements. [Background technology]

[0002] Fish farming is an important means of making up for food shortages that will accompany future population growth. Relying solely on natural resources will put some species at risk of extinction, but by increasing their numbers through aquaculture, it is possible to protect species while using them sustainably. In particular, the Japanese eel, an endangered species, is a prime example of how aquaculture can preserve resources while ensuring a stable supply. Furthermore, aquaculture also leads to the creation of local industries and jobs, and as a sustainable fisheries industry, it contributes to "protecting the abundance of the seas and oceans" (SDG 14). In a study conducted last year, it was discovered that the "splash-splash" sound on the water surface causes fish to exhibit a repelling behavior, and it was also confirmed that the effect was greatly enhanced when blue or green light was used in combination (Patent Document 1). This year, we worked to put these results to use at aquaculture farms. Initially, we focused on the problem of feed waste, but after interviews with several aquaculture sites, we heard many people say, "Feed waste is not a big issue, the work of landing the fish is more difficult," so we switched the focus of our research to landing the fish. In actual aquaculture sites, it is difficult to gather the fish in one place because they tend to run away, and the hard work of manually driving them in is a common issue. Incidentally, Patent Documents 2 to 4 and Non-Patent Document 1 state that red is a repellent color for many fish species, including filefish, sweetfish, and salmon. An experiment was conducted in an aquaculture tank (23 tons of water, 7m diameter, 60cm depth) (Kanagawa Prefectural Fisheries Technology Center, Jogashima) where 3,000 artificial chub mackerel were kept.The fish were found to have a significant repelling behavior due to the "splash-splash" sound, but the repelling behavior due to the color of the light alone was weak, and it appeared that blue light was more repulsive than red. Furthermore, in experiments at a land-based Japanese eel farm (Hiranuma Suisan, Kamisato-machi, Kodama-gun, Saitama Prefecture) and subsequent experiments in a simple pool, it was confirmed that the eels were unresponsive to sound, but showed aversion to blue light. Having discovered that the repellent response differs depending on the fish species, we identified the fish species as Japanese eels and worked on controlling their movements using light. Figure 8 shows photographs showing a preliminary experiment on Japanese eels using different light colors. [Experimental conditions] We used an LED panel capable of emitting multicolored light. Two aeration devices were installed in a vinyl pool measuring 166 cm long x 100 cm wide with a water level of 9 cm. Dechlorinated fresh water was used and 10 Japanese eels (approximately 30 cm in length) were placed inside. Blue, white, green and red light was shone on one side of the pool and we observed whether the Japanese eels would move to the other side. We also covered one side with an aluminum plate to create a dark area where the Japanese eels would feel safe, and tested whether the Japanese eels would move underneath this aluminum plate. The results of the experiment are shown in Figure 9. While observing the reactions of Japanese eels to different colors of light, we also experimented with the colors of light that Japanese eels avoid, the direction of the light, the time of day when the reaction is strongest, and the light-dark contrast of the background. [Experimental Results] 1. Effect of light color (monochromatic light) Red light (640nm-770nm), green light (490nm-550nm), and blue light (430nm-490nm) were irradiated individually, and behavioral changes were observed. Blue light evoked a particularly strong aversion response, with the entire school clearly moving away from the light source. Green light tended to evoke a repellent response, although not as strongly as blue light, while red light evoked almost no aversion response, or was sometimes accompanied by approach or excited behavior. Curiously, when Japanese eels were exposed to red light, fighting between the eels was often observed. Purple light evoked a certain degree of aversion behavior, although not as strongly as blue light. White light was excluded from this experiment because it has been described as a repellent light in many publications. 2. Effect of water temperature Differences in water temperature affected the strength of the reaction to light. The avoidance behavior was particularly active at water temperatures of around 15-17°C. Furthermore, the avoidance behavior of Japanese eels tended to weaken when the water temperature fell below 15°C, which is considered low but not low enough to hibernate. At temperatures of 11°C, the avoidance behavior was no longer present. (Japanese eels stop feeding when the temperature falls below 10°C, and appear to hibernate at 8°C or below.) Research has shown that the optimal water temperature for Japanese eels is 20-28°C, and that they enter full hibernation at 5-8°C. It appears that Japanese eels move in response to blue and green LEDs when the water temperature is appropriate. Figure 10 shows the experimental results with the influence of water temperature. 3. Time of day influences When comparing daytime and nighttime, Japanese eels were found to be more sensitive to light stimuli in the evening and at night, and a strong aversion was observed when light stimuli were applied, especially after 6 p.m., when it was already dark. During the day, their response was somewhat weaker, perhaps because they were accustomed to the brightness of their surroundings. Figure 11 shows the experimental results with the influence of time of day. 4. The influence of ambient brightness (contrast) The greater the difference between light and dark in the background, the more clearly the behavioral changes caused by light stimuli were noticeable. When strong light was shone locally in a dark environment, Japanese eels tended to recognize the light more accurately and avoid it quickly. On the other hand, in bright environments, the reaction was weaker, perhaps due to the reduced contrast between the light and the background. Blue light was repulsive regardless of the light or dark environment, but the repulsive behavior was stronger in dark surroundings. Green light was also repulsive in dark conditions, although not as repulsive as blue light, and the reaction was slower in bright surroundings. 5. The effect of light habituation The next thing I focused on was "getting used to light." Non-patent document 2 reports that when fish were observed to be attracted to blue light between 7:00 PM and 3:00 AM, they found that fish were more likely to be attracted to blue light during the dark hours of the night and early morning, and that the effect weakened after sunrise. However, I thought, "By shining the blue light continuously for eight hours, the fish became accustomed to the light and learned that it was not dangerous, and eventually their curiosity changed and they came closer, wondering, 'So what is this light?'" So, I exposed 10 Japanese eels to blue light, which is a repellent light, from 9:00 p.m. to 6:00 a.m. and observed their behavior every hour. Date and time: Wednesday, May 21, 2025, outside temperature 23℃, water temperature 22℃ Method: Ten Japanese eels were placed in a plastic pool on the balcony of a house and exposed to a repellent blue light for nine hours from 9 PM to 6 AM. Their behavior was observed every hour. The size of the pool, the size of the Japanese eels, and the aluminum lid were the same as in the previous experiment. 21:02 Preliminary test: Immediately after the blue light irradiation started, all 10 mice moved to the dark area of ​​the aluminum plate (strong repellent reaction). As a preliminary experiment, we confirmed that blue light effectively repels insects. 21:06 Start of experiment. Blue light was irradiated. Immediately after the start, all Japanese eels showed a strong repellent reaction. 21:08 All Japanese eels have been evaded 22:00 Two of them get used to it and go outside 23:00 2 fish No change (not repellent) 0:00 4 (not repellent) 1:00 5 fish Nearly half felt that the light was not dangerous (not repelling them) 2:00 Eight of them went outside, reaching the maximum number. Their discomfort with the light faded, and it may be that their "habituation," "curiosity," and "peak activity" all coincided. 3:00 5 (not repellent) activity begins to calm down 4:00 4 (not repelled) Dawn is approaching and they may be returning to their nest as part of their daily routine. 4:19~4:22 7 (not repelled) As soon as it started to get light outside, the number of 7 increased. Is it because the way they "see" blue light has changed? It's possible that as the surroundings became brighter, they once again became suspicious of the blue light. 4:37 Six (not repelled) starting to return to their nest? 5:00 5 (not repelled) move towards end of activity 5:26 2 (not repelled) behavior ends 5:59 2 animals (not repellent) experiment completed As shown above, immediately after the blue light was turned on, all of the Japanese eels were clearly repelled by the dark side. However, they later became accustomed to the light and began to come towards the blue light. In other words, it was found that Japanese eels can become accustomed to light that they dislike. 6. Difference between flashing and steady light Even with the same light intensity, there were many cases where the fish responded more strongly to flashing light than to steady light. With blue and green light in particular, the more irregular the flashing, the more likely the fish were startled and the more likely they were to exhibit avoidance behavior. In particular, in our experiments, the most effective combination of blue light, a dimming value of 1023, an on-time of 4 μs, and a flashing pulse of approximately 250 kHz was found. 7. Effect of light intensity There was a tendency for the intensity of the reaction to increase with increasing light intensity, but once the light intensity reached a certain level, further increases did not significantly change the reaction. However, the most effective light intensity was a dimming value of 1023 (the maximum light intensity of the light source manufactured by Levox Co., Ltd.). 8.Reaction characteristics of Japanese eels When a spot light was shone on the eyes of Japanese eels for 5 seconds, no noticeable reaction was observed and they appeared unresponsive, but when the light was shone on the entire body, there was a clear change in behavior. In fact, when a Japanese eel entered a pipe with only its head sticking out (its body was inside the pipe and not exposed to the light), the eel showed no reaction and did not retract its head into the pipe. This suggests that the light shining on its eyes alone is not enough to "repel" the eel. Figure 12 shows a photograph of a Japanese eel when a spot of light was shone on its eye. Figure 12(b) shows the image 5 seconds after irradiation, compared to Figure 12(a). The Japanese eel showed no reaction when the light was shone on its eye. This suggests that Japanese eels likely sense light not only with their eyes, but with their entire skin. This suggests that they sense light in a way other than by seeing with their eyes. Therefore, we thought that the most effective way to repel Japanese eels with repellent light would be to shine the light from above. This is because, when I thought about it, "Eels naturally slither across muddy or swampy ground, so wouldn't their enemies come at them from above, rather than slithering towards them from the front?", I naively thought that it would be safe to assume that the object they avoid (the angle at which they perceive the repellent light) would also be from above. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7623781 [Patent Document 2] International Publication No. 2020 / 116504 [Patent Document 3] Special Publication No. 46-5016 [Patent Document 4] U.S. Patent No. 6,203,170 [Non-patent literature]

[0004] [Non-Patent Document 1] Matthew J Hansen, Dennis E Cocherell, Steven J Cooke, Paul H Patrick, Michael Sills, Nann A Fangue. "Behavioral guidance of Chinook salmon smolts: the variable effects of LED spectral wavelength and strobing frequency." CONserv Physiol. 2018 Jun 25;6(1):coy032. doi: 10.1093 / cONphys / coy032 https: / / pmc.ncbi.nlm.nih.gov / articles / PMC6016652 / [Non-patent document 2] Yoko Tanuchi, Yasusumi Fujimori, Susumu Shimizu, and Yasutsugu Katakura, "Behavior of the Japanese Rockfish (Sebastes taczanowskii) under LED Light Irradiation in Indoor and Outdoor Experiments," 2021 Autumn Meeting of the Japanese Society of Fisheries Science (Fukui Prefectural University), 2019. Summary of the Invention [Problem to be solved by the invention]

[0005] Preliminary experiments revealed that Japanese eels exhibit aversion to blue light. However, there are thousands to tens of thousands of Japanese eels in aquaculture farms. If blue light were used to repel the eels, it would be necessary to install a large number of pipes to ensure dark areas for them to escape to, but preparing that many pipes is not realistic from the perspective of equipment and operating costs. Therefore, we felt it was necessary to establish a guidance method that was not dependent on pipes. At that time, I remembered a phenomenon often used when studying for exams: "If you highlight text with a blue marker and then place a red sheet on top of it, the text becomes invisible." I wondered if this mechanism could be applied to light combinations, and decided to newly examine the effect of overlaying red light on blue light. This invention is based on the idea of ​​using red light in combination with blue light, as it is possible that Japanese eels may find it harder to see the blue light if red light is superimposed on blue light. If we could use light to guide the movements of Japanese eels, not only would it reduce the labor required for landing them, but it would also enable us to manage their growth, for example by conducting health checks on farmed fish and checking their growth rate, which we thought would lead to sustainable, efficient, and stable farming of Japanese eels.

[0006] The purpose of this invention is to propose a method for guiding Japanese eels using light. [Means for solving the problem]

[0007] The light-based guiding method for Japanese eels of the present invention described in claim 1 is a light-based guiding method for Japanese eels that is cultivated in a closed, predetermined area, and involves shining blue light from one direction into the water in the predetermined area. By lighting At the same time, red light is irradiated from a different direction than the blue light. By blinking The device is characterized by shining light onto the water in a specific area, creating a blue area illuminated with the blue light and a red area illuminated with the red light, thereby causing the Japanese eel to move from the blue area to the red area. Claim 2 The present invention as described The light-based guiding method for Japanese eels is a method for guiding the behavior of Japanese eels that are cultivated in a designated enclosed area, in which blue light is irradiated into the water in the designated area from one direction and red light is irradiated from a different direction to the blue light, creating a blue area irradiated with the blue light and a red area irradiated with the red light in the designated area, and causing the Japanese eels to move from the blue area to the red area. The blue and red lights are irradiated for a predetermined period of time, and then the blue and red lights are turned off, causing the Japanese eels to tread water. [Effects of the Invention]

[0008] According to the light-based guiding method for Japanese eels of the present invention, it is possible to guide Japanese eels from the blue area to the red area, thereby reducing the burden of landing work. [Brief explanation of the drawings]

[0009] [Figure 1] Photograph showing the device used in the experiment on the light-guiding method for Japanese eels of the present invention. [Figure 2] A photo showing a Japanese eel in the septic tank pipe at the top left [Figure 3] Figure showing the experimental results when the red and blue light conditions were changed [Figure 4] Figure showing the experimental results when conditions other than the two colors of blue and red light were added. [Figure 5] Photograph showing the violet light experiment [Figure 6] A photo showing an experiment in which a light-blocking board was used to separate the tank in the center. [Figure 7] A photo showing how to induce Japanese eels to tread water [Figure 8] Photograph showing preliminary experiment on Japanese eels using different light colors [Figure 9] Experimental results [Figure 10] Figure showing the experimental results of the influence of water temperature [Figure 11] Figure showing the experimental results depending on the time of day [Figure 12] A photo of a Japanese eel with a spotlight shining on its eye DETAILED DESCRIPTION OF THE INVENTION

[0010] The light-based guiding method for Japanese eels according to the first embodiment of the present invention is a method for guiding the behavior of Japanese eels cultivated in a closed, predetermined area, by shining blue light from one direction into the water in the predetermined area. By lighting At the same time, red light is irradiated from a different direction than the blue light. By blinking The device illuminates a designated area of ​​water, creating a blue area illuminated with blue light and a red area illuminated with red light, causing Japanese eels to move from the blue area to the red area. Previous studies have shown that many fish species exhibit aversion to red light, but Japanese eels exhibit aversion to blue light. Furthermore, Japanese eels, which showed no noticeable behavior when exposed to red light alone, were found to gather in the red area when exposed to both blue and red light. Japanese eels can be guided using only blue light, but by creating a red area in addition to the blue area, it is possible to guide many Japanese eels into the red area in a short period of time. Therefore, it is possible to move a large number of Japanese eels in a short amount of time without using pipes or other structures that Japanese eels like to enter. This reduces the burden of landing the eels and is thought to reduce stress on the Japanese eels compared to chasing them with nets. In addition, making the flashing cycle of the red light longer than that of the blue light is more effective in attracting Japanese eels.

[0011] The present invention No. 2 Embodiments of the present invention The light-based guiding method for Japanese eels described above is a method for guiding the behavior of Japanese eels cultivated in a designated enclosed area. The method involves irradiating the water in the designated area with blue light from one direction and irradiating it with red light from a different direction, creating blue areas irradiated with blue light and red areas irradiated with red light in the designated area of ​​water, and moving the Japanese eels from the blue area to the red area. Japanese eels are made to tread water by shining blue and red lights on for a set period of time, then turning off the lights. After shining the blue and red lights for a specified period of time, the Japanese eels all swam vigorously toward the water surface, performing movements that appeared as if they were treading water. In this way, by making them all swim vigorously toward the water surface or tread water, it is possible to measure their length and check the color of their bellies, for example, which makes it possible to manage the growth of the Japanese eels, such as by checking their health and rate of growth. [Example]

[0012] Figure 1 shows the device used in the experiment to demonstrate the light-based guidance method for Japanese eels of the present invention. In Figure 1, blue light is being irradiated from the top right of Aquarium 1 by LED Light 2, and blue light is being irradiated from the top left of Aquarium 1 by LED Light 3. Figure 1(a) shows the time when irradiation began, Figure 1(b) shows 10 seconds after irradiation began, and Figure 1(b) shows 20 seconds after irradiation began. Seven Japanese eels (approximately 30 cm in length) were placed in Aquarium 1. As shown in the photograph in Figure 1(a), when the red and blue light irradiation began, the Japanese eels were scattered all over the left and right sides of Tank 1. As shown in the photograph in Figure 1(c), 20 seconds after the start of irradiation, all of the Japanese eels moved from the blue area on the right to the red area on the left.

[0013] Next, we will explain the experiment in which LED lighting 2 was flashing from the upper right corner of aquarium 1. For the flashing LED lighting 2, a three-wavelength LED fiber optic light source unit (SLG-450TSL series manufactured by Lebox, Inc.) was used. In the following explanation, μs (microseconds) represent the length of time a single flash lasts, and frequency (Hz) represents the number of flashes per second. An "on-time of 4 μs" means that a single flash lasts for 4 microseconds, which corresponds to a frequency of approximately 250 kHz (approximately 250,000 flashes per second). Similarly, an "on-time of 99,999 μs" corresponds to approximately 10 Hz (approximately 10 flashes per second). With this three-wavelength LED fiber optic light source unit, the strongest light is "dimming value 1023" and the weakest light is "dimming value 1." This dimming value is a software value set on the device's operation screen and does not represent the actual illuminance (lx).

[0014] This three-wavelength LED fiber light source unit was used for LED Light 2, which illuminates from the top right of Aquarium 1, with a blue light source dimming value of 1023 pulses, an on-time of 4 μs, and approximately 250 kHz. A red LED panel (commercially available) was lit for LED Light 3, which illuminates from the top left of Aquarium 1. When the blue pulse from LED Light 2 on the top right was turned off for a moment, the Japanese eels in the red area on the left returned to the right, but when the blue light was immediately turned on again, they fled to the left, and this cycle repeated. This result suggests that the cells repelled the blue pulse and moved towards the red light. After the experiment was completed, there were four fewer Japanese eels in Tank 1 than there were at the start of the experiment. Four Japanese eels escaped into the septic tank through a pipe near the red LED panel. It is thought that the Japanese eels had a stronger aversion reaction to the light stimulus of the "pulsed flashing" rather than the "on" light. It is also thought that the stimulus from the repeated on and off of the blue pulsed light had a significant effect. The photo in Figure 2 shows a Japanese eel in the septic tank pipe in the upper left.

[0015] Figure 3 shows the experimental results for different red and blue light conditions. The experimental results shown in Figure 3 indicate that the stronger the intensity of the red light, the greater the effect. Based on these results, we hypothesized that red light could cancel out blue light, causing Japanese eels to mistake the red area for a safe zone. The fact that the Japanese eels were attracted to the red side of the two colors of light, "blue light" and "red light," raised the following questions: "Is it correct to conclude that behavior is being controlled by two colors of light, or is height related to the experimental conditions? What would happen if the "blue area" and the "red area" were at the same height? Or what would happen if the "red" were higher and the "blue" were lower?"

[0016] So I experimented with changing the positions of the blue and red areas, and the differences between blue light patterns and red light patterns. Figure 4 shows the experimental results when conditions other than the two colors of blue and red light were added. The experimental results showed that blue and red light can enhance the induction effect by setting the optimal wavelength to match the visual characteristics of Japanese eels. Furthermore, by combining not only constant light but also flashing (pulse irradiation) and light intensity, the reaction speed and induction probability were improved. To repel Japanese eels, a "short" pulse flashing cycle (in the experiment, an on-time of 4 μs, approximately 250 kHz) and a light intensity of 1023 were effective, but to attract Japanese eels, a "long" pulse flashing cycle (in the experiment, 99,999 μs, approximately 10 Hz) was more effective. By combining these, it was possible to find effects not only with the color but also with the flashing method.

[0017] When red and blue are mixed together, the color becomes "purple," but we conducted an experiment to see if this phenomenon occurs, where the color does not become the mixed purple but rather becomes closer to the solid purple color. Figure 5 is a photograph showing an experiment using violet light. The purple light was irradiated from the upper left of Tank 1. Figure 5(a) is a photograph taken at the start of irradiation, and Figure 5(b) is a photograph taken a few seconds after irradiation. As shown in Figure 5, when illuminated with monochromatic purple light, Japanese eels move to the left. This shows that Japanese eels exhibit a repulsive behavior toward purple light.

[0018] Figure 6 shows an experiment in which the tanks were separated by a light-blocking board in the middle. However, a gap was left between the bottom of the board and the bottom of Tank 1 to allow the Japanese eels to move around. Furthermore, the front side remained untouched because it required observation, and Tank 1 was surrounded by black panels to minimize mixing of the "red light" and "blue light." Furthermore, the windows of the sunroom where Tank 1 was placed were covered as much as possible with black sheets during the experiment. The Japanese eels moved from the right side of the divider (blue area) to the left side of the divider (red area). Therefore, by using a divider to separate the "blue area" and the "red area," it becomes easier to gather the Japanese eels in the red area. From these experimental results, it appears that the optimum settings for blue light (approximately 460 nm) are a dimming value of 1023, an on-time of 4 μs, and approximately 250 kHz, and the optimum settings for red light (approximately 630 nm) are a dimming value of 1023, an on-time of 99999 μs, and approximately 10 Hz. It is believed that the blue light is most effective when irradiated from above the water surface, and the red light is irradiated from near the bottom of the water, perpendicular to the blue light.

[0019] Figure 7 is a photograph showing how to induce Japanese eels to tread water. Figure 7(a) shows the state with blue light irradiated, and Figure 7(b) shows the state with the blue light turned off. When a strong light is shone on them and then turned off, Japanese eels all exhibit a "treadmill response," swimming vigorously to the surface. When exposed to blue light, the Japanese eels immediately began to crawl along the bottom (swimming low to the bottom of Tank 1), and as the light continued, some of them began to move toward the surface. When the light was turned off, many of the Japanese eels began to tread water (a soft, treading swim) before settling on the bottom. Furthermore, when blue and red light was shone on them, they began to "crawl along the bottom" and gathered in the red area from the moment the light was turned on. When the light was turned off, many Japanese eels began to "tread water" and then settled on the bottom. Furthermore, Japanese eels continued to crawl along the bottom for a longer period of time when only blue light was irradiated than when both blue and red light were irradiated. Being able to make Japanese eels tread water at certain times could be used, for example, to determine their health by observing the condition of their bellies and fins. [Industrial Applicability]

[0020] This invention not only reduces the labor required for pond-lifting work at aquaculture farms, but can also be used in a wide range of applications, such as safely guiding eels into fishways at dams and water intakes to help protect resources, efficiently gathering schools of eels in the direction of a desired catch in fisheries, temporarily gathering individuals to reduce the burden on them during ecological surveys or specimen collection in research sites, and educational exhibits at aquariums where visitors can see how light can be used to move schools of eels. [Explanation of symbols]

[0021] 1 aquarium 2, 3 LED lighting

Claims

1. A light-based guidance method for Japanese eels that guides the behavior of Japanese eels cultivated in a closed, predetermined area, A blue light is lit and irradiated from one direction into the water in the predetermined area, and a red light is flashed and irradiated from a different direction from the blue light. In the predetermined area of ​​water, a blue area illuminated with the blue light and a red area illuminated with the red light are created, and the Japanese eel is moved from the blue area to the red area. A method for guiding Japanese eels using light.

2. A method for guiding Japanese eels using light to guide the behavior of Japanese eels cultivated in a designated enclosed area, comprising: A blue light is irradiated from one direction into the water in the predetermined area, and a red light is irradiated from a direction different from the blue light. A blue area illuminated with the blue light and a red area illuminated with the red light are created in the water in the specified area, and the Japanese eel is moved from the blue area to the red area. After irradiating the blue and red lights for a specified period of time, the blue and red lights are turned off, causing the Japanese eel to tread water. A method for guiding Japanese eels using light.

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