Fish Ethology
Topic outline
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The nature of fish behaviors is closely related to their habitat and form of predation. For example, some fish swim toward a stream of water or approach light upon sensing it. Also, some fish see small moving objects as bait and engage in predatory behavior. Historically, people learned about the nature of such fish behaviors through empirical observations and developed ways to catch fish by taking advantage of these. This includes using fishing weirs to capture sweetfish by taking advantage of their inclination to move towards the water flow, squid fishing that takes advantage of their nature of approaching light, and using lures in fishing.
Fish ethology is the study of the nature of such fish behaviors and elucidates their relationship with the habitat of fish and baiting ecology. This knowledge is important, especially in the field of fisheries, to design fishing gear for catching fish. Furthermore, modern fisheries requires selective fishing technology to protect resources, in which only the fish needed are caught and the fish that are not needed or are small/immature are released. Therefore, the knowledge of fish behaviors is utilized in such situations.
Here, we would like you to learn the basic functions that support the nature of fish behaviors, as well as to see how they are applied to current fishing technologies.
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This explains the sensory functions that control the behaviors of fish.
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You can see the result of simulating the movement of the fish in the aquarium in the video.
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Fish behavior is closely related to their habitat and foraging. This knowledge is important in designing fishing gear. By improving techniques to efficiently catch only the species and ages of fish targeted for fishing, we can prevent bycatch of young fish and non-target species, thereby reducing the waste of resources. Through this, we hope to contribute to SDG 14 (LIFE BELOW WATER).
The United Nations has designated the decade starting in 2021 as the "Decade of Ocean Science," with the aim of contributing to SDGs. Ocean science, as defined by the UN, includes the field of fisheries.
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The most common use of light in fisheries is as fishing lights. Fishing with fishing lights uses the fish behavior that is attracted to and localized by light stimuli. In Japan, it has been used in various forms for a long time, and more than 30 species of fish have been targeted. The light source began with the torch in earlier times and later changed to oil lamps, incandescent lamps, halogen lamps, and metal halide lamps as light-emitting technology progressed. In recent years, Light Emitting Diode (LED) has been gaining attention as a new light source. Compared to other light sources, LED lamps have a longer life, which reduces labor and costs related to maintenance and management, and they are smaller and occupy less space. Furthermore, its characteristics are very different from those of light sources previously used in the fishing industry, and it can emit light at specific wavelengths. For example, incandescent lamps emit a large proportion of long-wavelength components of visible light to infrared light, while LED light can produce specific light with a narrow wavelength range of 460–500 nm for blue, 500–570 nm for green, and 610–780 nm for red, and is characterized by high energy efficiency. Many researchers believe that these characteristics of LED lights and the color preference and light sensitivity of fish can be used to control fish with lower energy consumption and effectively guide or repel them.
Studies conducted on the use of LED light
1. Use in squid jigging fishery and saury stick-held dip net fishery
In the case of squid jigging fishery, the results of a practical test showed that the use of blue LED lamps instead of halogen lamps for a part of the fishing lamps for squid, which are highly sensitive to blue light, reduced fuel costs and increased the catch (Demonstration Test of Energy Saving by LED Fishing Lights on a Medium Size Squid Fishing Boat. 有限会社旺貴水産, Ishikawa, 2010). In addition, the conversion to LED lights is underway in saury stick-held dip net fishery, where light is actively used as in the case of squid jigging fishery.
2. Use to reduce bycatch
Codends equipped with LED lights and a special escapement port on trawl gear have been reported to reduce bycatch of Chinook salmon (Oncorhynchus tshawytscha) and fish of the genus Sebastes by guiding fish to the escapement port by light (Larsen et al., Fisheries Research, 2018; Hannah et al, Fisheries Research, 2015; Lomeli et al., Fisheries Research, 2012) Many other utilization studies have been conducted.
In addition to the fisheries industry, this technology is also being considered as a technique for preventing fish from wandering into water intake facilities, using the fact that Chinook salmon and red seabream (Pagrus major) tend to avoid red lights (Cooke et al., Conservation Physiology, 2018).
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Here, you will see how light color affects fish behavior based on a case study of the experiment conducted using the observation window on the submarine floor of the Mombetsu Okhotsk Tower, an ice sea observation tower in Mombetsu City.
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This is a video of white-edged rockfish gathering around a blue LED underwater light source, taken with a camera set up directly above the light source.
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The physiological state of an organism often has a cycle of approximately 24 hours. For example, the body temperature of a mammal has a constant cycle of temperature changes, the cycle being 24 hours. However, if the animal is placed in a permanently dark or permanently light environment with a constant temperature, the phase of the body temperature change can advance or delay. However, the cyclic temperature change is maintained. This endogenous rhythm generated by the biological clock, which is independent of the external environment and has a cycle of about 24 hours (close to 25 hours in the case of humans), is called a circadian rhythm.
The behavior of many marine organisms also has a periodicity in the amount of daily activity. In many cases, the periodicity is due to circadian rhythms, and when light is present in the living environment, the light-dark cycle is a tuning factor, as in many animals. Biological rhythms that are lost in constant dark or light are not endogenous and are distinguished as diurnal rhythms rather than circadian rhythms.
Fisheries have empirically made use of the horizontal and vertical migrations associated with the diurnal behavior of organisms. For example, these behaviors of target organisms play an important role in determining the location and depth of trawl nets, gill nets, longlines, traps and pots, etc. The cycle of feeding behavior is also linked to the periodicity of these behaviors. In angling fisheries, it is important to understand such time periods.
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Adult walleye pollock live in deep water, but during the juvenile stage they are found in the middle of the water, where they make daily vertical migrations. The factors that contribute to this behavior have been discussed in relation to water temperature, light, and predators, all of which indicate the importance of the role of light. We will illustrate the diurnal activity of juvenile walleye pollock by presenting a case study to show whether it is strongly dependent on exogenous (day-night) or endogenous (circadian) rhythms.
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