Conservation of Freshwater Fish Diversity in Japan

Abstract

The current situation for Japanese freshwater fishes is discussed in terms of biodiversity by comparing the Red List and the Red Data Book (Japanese versions). As a threat to Japanese freshwater fishes, rice paddy field remodeling to improve the efficiency of rice cultivation is thought to have the greatest negative impact. This can be shown by the fact that 24 out of 75 species (32%) categorized as “Critically Endangered” and “Extinct,” live around paddy fields. Furthermore, Largemouth Bass Micropterus salmoides and Bluegill Sunfish Lepomis macrochirus introduced from the United States of America are having serious negative effects on small native cyprinids. Steps to protect Japanese freshwater fishes are proposed by referring to “in situ conservation,” “ex situ preservation,” and “social enlightenment.”

1 Introduction

The Japanese Archipelago is located at latitudes 20–46° north and consists of islands of various sizes, with its main islands comprising Hokkaido, Honshu, Shikoku, Kyushu, and the Ryukyu Islands. The archipelago is long and narrow from north to south, and the Oyashio cold current from the north and the Kuroshio warm current from the south carry various fishes of marine origin along the Pacific coast. From a meteorological point of view, the archipelago can be classified as a heavy rain zone belonging to the temperate monsoon. The annual rainfall is about 1800 mm, which is about twice the world average. When heavy rain falls on rivers in Japan, floods are frequently caused and create diversified habitats including temporal breeding grounds for freshwater fishes. In addition to this, the Japanese Archipelago has been connected to the Asian continent, and several continental strains of freshwater fishes have been established in the archipelago. These geological circumstances have resulted in a relatively diversified freshwater ichthyofauna in Japan.

Unfortunately, many Japanese freshwater fishes are now declining in various areas of the archipelago as result of excessive anthropogenic activity, and some are on the verge of extinction. In this chapter, the current situation of Japanese freshwater fishes is reported first, and then steps to protect them are discussed. In the following pages freshwater fishes are defined as the primary and secondary freshwater fishes (sensu Myers 1938).

2 Freshwater Fishes in the Red Data Book

To promote the protection of wildlife, it is prerequisite to objectively grasp the current situation of species and to scientifically analyze the factors that threaten their habitat. The “Red List” (RL) and the “Red Data Book” (RDB) are important indicators for this purpose regardless of the taxon. The former contains a list of endangered species, and the latter is its commentary.

It is well known that the RL and RDB each bears red on its cover. This binding color was originally selected by the International Union for Conservation of Nature (IUCN) in Switzerland in 1966 according to the degree of danger of endangered organisms on the earth. Since then, “red” has become the symbol color of endangered species (Fig. 23.1a).

Fig. 23.1

IUCN Red List and Japanese Red Data Book. (a) The IUCN Red List Categories and Criteria, version 3.1 (2001) translated into Japanese; (b) Red Data Book—Threatened Wildlife of Japan 4. Pisces–Blackish and Freshwater Fishes, Ministry of the Environment (2015)

2.1 Publication of the Red Data Book

In 1991, the Environment Agency (now the Ministry of the Environment), Government of Japan published the RDB for the first time entitled “Japanese Endangered Wildlife: Vertebrates” (Environment Agency 1991). Since then, many local governments such as prefectures or municipalities have followed the policy of the Environment Agency, and each published their own RL and RDB. In addition, the Fisheries Agency published a similar version, the “Databook on Rare Wild Aquatic Organisms in Japan” (Fisheries Agency 1998).

The RDB of the Ministry of the Environment has been selected and revised four times by 2015 and has become a Japanese standard, the most important and reliable source in both name and reality (Fig. 23.1b).

The selection criteria for the RL of the Ministry of the Environment were reviewed for the first time in 1997. The quantitative evaluation criteria by the IUCN were adopted from the second RL in the same year (Ministry of the Environment 2003) and now follow the IUCN criteria ver. 3.1 second edition (IUCN 2012; Fig. 23.1a). However, qualitative requirements are also used to prevent underestimation due to a lack of quantitative data (Ministry of the Environment 2020a).

2.2 Definition of Threatened Species

In the RL of the Ministry of the Environment, each species falls into one of eight categories (Fig. 23.2). Aside from “extinct,” not all categories on the RL indicate “threatened.” Strictly speaking, threatened species are limited to three categories: endangered IA, IB, and II. These categories are defined by how “the current state was brought about.” In addition, if the negative factors continue to act, species ranked in these categories are estimated as having difficulty in surviving in the wild. In fact, fishes ranked in IA are facing an “extremely high risk of extinction in the wild in the very near future,” and IB is “as much as IA.” Endangered species II may move to the category of “endangered species I” in near future, if the negative factors that brought about the current state continue to act as “species with an increased risk of extinction.” Quantitative criteria are defined by (A) reduction rate, (B) area, (C) mature population + reduction rate, (D) mature population, and (E) extinction probability. In the case of the Ministry of the Environment RL, qualitative criteria have been used in addition to quantitative criteria as well.

Fig. 23.2

Category classification and hierarchy structure in the Red List, issued by the Ministry of the Environment, Government of Japan

At first, regarding the handling of fishes in the RDB of the Ministry of the Environment, freshwater fishes, brackish water fishes, and some seawater fishes migrating to inland water for some life stages were comprehensively considered. However, at present, two special committees are set up to treat “freshwater fishes” and “seawater fishes” independently, though its sorting of some brackish water fishes to be charged, is tough and very confusing on affiliation.

In Japanese biota, freshwater fishes are in a particularly critical situation among various threatened animals. The RDB 2014 version (Ministry of the Environment 2015) preceded as the RL in 2013 lists a total of 167 threatened species of freshwater fishes (IA, IB, II). About 500 species of Japanese native freshwater fishes were evaluated. The total number of threatened species of freshwater fishes on the list exceeds 40% of the total number of native freshwater fishes. This ratio is significantly higher than in other fields or taxa such as insects and plants. Unfortunately, the number of listed species has clearly increased with successive revisions (Fig. 23.3). This increase includes the number of species examined and taxonomic subdivision, but it is true that the number of threatened species of freshwater fishes has increased in the last 20 years or so.

Fig. 23.3

Changes over time in the total number of categorical ranks of blackish and freshwater fishes listed on the Red List of the Ministry of the Environment, Government of Japan. (Modified from Hosoya et al. 2016)

Fig. 23.4

Japanese freshwater fishes categorized as Extinct (a–c) and Extinct in the wild (d). (a) Acipenser medirostris (photo by Ryu Uchiyama); (b) Gnathopogon elongatus suwae (photo by Kazumi Hosoya); (c) Pungitius kaibarae (photo by Kazumi Hosoya); (d) Kunimasu Oncorhynchus kawamurae. (Photo by Tetsuji Nakabo)

2.3 Application of IUCN Criteria

Currently, 36 out of a total of 123 species (29.3%) that are classified as endangered IA and IB on the Ministry of the Environment RL, and the oldest RLs (ver. 2.3, not the current standard ver. 3.1) were also evaluated by the IUCN. Among them only two species [Parabotia curtus , Ministry of the Environment version IA; Parahucho perryi (listed as Hucho perryi), IB; 1.6%] correspond to IUCN IA and IB, respectively. Overall, there are few contradictions in the difference between the global (IUCN) evaluation and that of Japan about widely distributed species not endemic to Japan. In the current situation where only Parabotia curtus , which was newly evaluated as IA in November 2015, is listed at the top of the IUCN list among Japanese endemic species, and the crisis and conservation status of Japanese freshwater fishes are being discussed worldwide. International evaluations by the IUCN and others have triggered a great deal of domestic attention, as seen with Anguilla japonica and Parabotia curtus . Furthermore, international information sharing on the biodiversity crisis is an important criterion for clarifying the issues and responsibilities of Japan in ratifying the “Convention on Biological Diversity” and realizing more appropriate conservation measures and efforts. The main idea is that the creation of a system in which valuable information compiled by the Ministry of the Environment is effectively reflected in the IUCN RL should be led by the national government, not by individual researchers. For that purpose, it is strongly desired that the Ministry of the Environment considers its approach, especially in the handling of qualitative requirements.

On the other hand, the Japanese versions of the RL or the RDB differ in that they have two major features regarding taxonomic targets compared with those of the IUCN. First, the Japanese versions cover even undescribed species as targets that are tentatively included by indicating these as “sp.” or “type.” For example, Musashi-tomiyo, a ninespine stickleback, is confined to small area near Tokyo and categorized as IA, under the name of “Pungitius sp. 1” without proper scientific name. In addition, the Japanese version is unique in including an extra category “Lp,” which stands for a local population of the species possibly classified as “Least concerned” or “Data deficiency.” This approach focuses on the protection of peripheral populations of some species that are candidates as new subspecies.

3 Threats to Japanese Freshwater Fishes

There are 33 causes that threaten the survival of wildlife listed by the Ministry of the Environment, Government of Japan in the RDB (edited by the Ministry of the Environment 2015). The causes of the decrease differ depending on the fish species, but all causes have human activity at the root (Fig. 23.5).

Fig. 23.5

Threats to Japanese freshwater fishes

3.1 Dam Construction and Crossing Work

The biggest threat to fish species is that the natural environment is being converted to artificial structures by various developments. In fact, the Japanese Archipelago, which has a small land area, is even more susceptible to this.

When geographic structures such as dams are created in rivers, they affect the run-up of migratory fishes that make a round trip between a river and the sea. Arctic Lamprey Lethenteron camtscaticum is a typical anadromous species whose life history cannot be completed unless the parent fish return to the breeding ground to lay eggs in the river and then migrating down the river after the fry have grown. The designation of this species as Endangered on the third RL, 2007 suggested that it is more difficult for mature adults from the sea to reach their breeding grounds. Though the lamprey mainly occurs in Hokkaido, they are distributed along the coastal area of the Sea of Japan southward to the San-in and Hokuriku districts in Honshu where the decrease in individuals has accelerated.

The extinction of Japanese sturgeon, Acipenser medirostris (Fig. 23.4a), which was rated as it was in 2007, once had run-up large rivers in Hokkaido emptying into the Sea of Japan such as the River Teshio and the River Ishikari (Hosoya 2016).

3.2 Rice Paddy Field Remodeling

The impact of agricultural modernization is also enormous throughout the Japanese Archipelago. Remodeling rice paddy fields is thought to have the greatest negative impact on Japanese freshwater fishes (Hosoya 2009). Widespread public works to improve the efficiency of rice crops started from the 1960s. Since then, about 60% of paddy fields in Japan have been changed to unnatural structures, characterized by unification of several small traditional paddy fields to a large modern one in a rectangle; separation of canals into drainage and water injection in some cases even replaced with irrigation pipelines; expansion of the heading distance by more than 1 m between paddy fields and drainage channels; three-sided concrete walling of canals; and alternation from small soil grooves to U-shaped concrete grooves (Fig. 23.6).

Fig. 23.6

Comparison of a traditional rice paddy field (a) and modern one during remodeling in the winter (b) in Gifu Prefecture, Japan

As a result, the parental fishes cannot move from the drainage channel or stream to the paddy field, which should be their spawning ground. Thus, the reproduction of fishes is inhibited. Furthermore, because the waterways for drainage are protected by concrete on three sides, there is no sediment, and it becomes difficult for aquatic plants to grow. As a result, the flow becomes too strong and rapid, and fishes that use these plants as a refuge and feed on them cannot remain in the drainage canals anymore. These construction methods have left even medaka fishes Oryzias latipes and Oryzias sakaizumii , which are so-called symbol fishes of paddy fields, as endangered species (Category II).

The total number of freshwater fish species inhabiting the Japanese Archipelago is 512, including exotic species (Hosoya 2019). Of these, 115 species live around paddy fields, which is equivalent to 22% of freshwater fishes in Japan. On the other hand, there are 71 species categorized as “Critically Endangered” (Fig. 23.3) and four species as “Extinct” (Fig. 23.4) in the Ministry of the Environment version of RL (2020a), of which 24 species live around rice paddy fields, accounting for 32% of IA plus extinct species. These facts show how many freshwater fishes live around paddy fields in the Japanese Archipelago, but now are in danger of extinction.

In fact, Parabotia curtus once successfully used the areas around rice paddy fields as an alternative to floodplains but has found it difficult to coexist with modern agriculture (Abe et al. 2007). Early rice cultivation that requires the start of irrigation earlier than the spawning season of this species has become common. Due to rice paddy field remodeling, the number of reliable breeding sites for P. curtus has now decreased to only three (Abe et al. 2007; Watanabe et al. 2009).

3.3 Invasion of Alien Species

The introduction of alien species has had irreparable consequences for native ecosystems. In Japan, the heavy negative effects of Largemouth Bass Micropterus salmoides and Bluegill Sunfish Lepomis macrochirus have become a major problem. After introduced from the United States of America, they have been secretly released into rivers and lakes for sport fishing. Some endangered species such as Acheilognathus cyanostigma , Acheilognathus typus , Pseudorasbora pumila , and Gnathopogon caerulescens , which are all small cyprinids with a maximum total length of about 8–15 cm, have been severely damaged in ponds, lakes, rivers with weak currents, and agricultural waterways. It is thought that the rank up to Endangered IA is mainly due to the feeding damage by these predatory sunfishes. The habitat of A. typus has already disappeared in the Kanto region in central Honshu, and it is believed that there fewer than ten habitats remaining in the Tohoku region in northern Honshu. This rapid reduction in habitat has been accelerated by ecological competition with another alien bitterling, Rhodeus occelatus occelatus as well which happened to be contaminated into the seedlings of Chinese four major carps from the River Yangtze to the River Tone in the Kanto region, Japan to increase food production during the World War II.  All these remaining habitats are irrigation ponds as the last fort because alien fishes cannot invade over high mounds. In recent years, Smallmouth Bass Micropterus dolomieu , which can live in running water, have been released illegally, and the distribution area is expanding rapidly from eastern Japan to western Japan. This results in accelerating the decrease and deterioration of Japanese biodiversity by the two species of Micropterus.

These foreign-derived exotic fishes should be called foreign exotic fishes. However, in practice, the distinction between exotic and native fishes must be made within and outside the natural distribution of individual species, not inside or outside a country border. This means that even fishes native to Japan, such as Carassius cuvieri endemic to Lake Biwa, will turn into exotic fish if they are transplanted to other areas beyond the original distribution area, and these should be called domestic exotic fishes (Hosoya and Takahashi 2006).

3.4 Ornamental Fish Boom

In Japan, there are a few cases where freshwater fishes have been overfished for food purposes, but collection for viewing purposes is frequent. Acheilognathus cyanostigma , which is a relatively slender bitterling with a maximum total length of about 10 cm, has a habit of spawning in bivalves, but in the habitat of the Lake Biwa/Yodo River system, bivalves that raise eggs and fry have been poached. The threatened freshwater fishes listed in the RDB are all pretty and relatively easy to breed. However, personal collection of these freshwater fishes for viewing purposes is no longer necessary in many habitats. Even if it is not directly involved in collecting but the demand for rare freshwater fishes is high, it will lead to an increase in collecting pressure by traders and indirectly reduce the number of rare freshwater fishes. It is now time for the collection and sale of rare wildlife for commercial purposes to be severely restricted (See Sect. 23.5).

In 1993, Japan ratified the Convention on Biological Diversity, a global treaty aimed at preserving biodiversity. Since then, the government has been presenting a national strategy to protect Japan’s native organisms, with several revisions. Among them, the goals are the idea of nature conservation, expansion of the scope of protection, nature restoration, concrete proposals for that purpose, cooperation, and collaboration. Unfortunately, the number of animals and plants listed on the RL and the RDB has continued to increase since then, and the results of efforts cannot be read from them. This is probably because many protection measures are not sufficiently effective.

3.5 Water Pollution

Water pollution cannot be overlooked as a cause of deteriorating habitats of freshwater fishes. This includes eutrophication, inflow of industrial wastewater, sewage, and mine wastewater, and the toxic effects of pesticides. Of the four extinct freshwater fishes in Japan, Oncorhynchus kawamurae originally inhabited only Lake Tazawa in Akita Prefecture (Fig. 23.4d). This species became extinct in 1940s when the water from the River Tama was introduced into Lake Tazawa for hydroelectric power generation. This is because the water from Tamagawa-Onsen hot spring, which is known for its hypochlorous acid water, had begun to flow into Lake Tazawa. Later, it was found that individuals of O. kawamurae transplanted from Lake Tazawa to Lake Saiko, Yamanashi Prefecture before the World War II still survive (Nakabo et al. 2011). Therefore, this finding compels the Ministry of the Environment to change the category of O. kawamurae from “Extinct” to “Extinct in the wild” based on the extant distribution out of original site.

Certainly, the water quality of Japanese rivers has improved dramatically since the 1980s due to the development of sewage treatment plants, legislative restriction of water pollution, and increasing public awareness of environmental protection. The achievement rate of the public environmental standard for organic water pollution by 2019, reached 94.1% of 2572 waters in rivers in BOD while it remains in 50% of 188 waters in lakes in COD (Ministry of the Environment 2020b). These changes in aquatic circumstances appear to lead to improved habitats for Japanese freshwater fishes.

On the other hand, various kinds of synthetic organic chemicals have been utilized in the terrestrial environments and flow into the aquatic ones including freshwater and marine water area, recently. For example, pesticides including oraganophosphates (fenitrothion, diazinon, dichlorvos, IBP, etc.), neonicotinoids (acetamiprid, clothianidin, imidacloprid, etc.), and fipronil (phenylpyrazole) have been much applied. Since the 1990s, neonicotinoids and fipronil, which are effective for rice cultivation, have been much used, and drastically reduced the number of aquatic organisms such as dragonfly larvae and Daphnia that freshwater fishes feed on. The EU already prohibited to use some neonicotinoids in 2013 after heavy colony collapse disorder (CCD) of honeybees. It has been warned that this effective pesticide not only acts directly on pests, but also has unpredictable negative effects on ecosystems through the food chain. In fact, neonicotinoids have been reported to act indirectly not only on arthropods but also on vertebrates (Frank and Tooker 2020). In Lake Shinji, Shimane Prefecture, the biomass of zooplankton and chironomid larvae, has plummeted since the beginning of the application of neonicotinoids to agricultural fields in the 1990s. This phenomenon may be the indirect negative impact to fishes represented by commercially caught fishes through trophic cascades (Yamamuro et al. 2019). For example, the catch of Hypomesus nipponensis and Anguilla japonica has dropped sharply since 1993. That time coincided with the time when neonicotinoid insecticides were started to use. Many kinds of pesticides have been applied in the terrestrial environment and are introduced into aquatic one. The levels of these pesticides in river water were generally less than the acute toxic concentration in fishes (Kawai et al. 2018). However, neonicotinoids and organophosphorus pesticides act on the nervous system of vertebrates and invertebrates, especially on acetylcholine esterase receptor that has very important role of excitatory transmission in animals. Therefore, these pesticides may affect behavioral activity of aquatic organisms such as fishes, and researches concerning behavioral ecotoxicological approaches seem to be essential (Kurokawa and Kawai 2019).

On 11 March 2011 the Pacific coast of northern Honshu was attacked by a huge tsunami caused by a large earthquake. This caused heavy damages to human lives and a significant disastrous impact on various ecosystems including the hydrosphere, both directly and indirectly. Unfortunately, the Fukushima First Nuclear Power Station of TEPCO (Tokyo Electric Power Company) located on the tsunami-attacked area was given serious damages in this disaster. This resulted in the scatter of huge amounts of radioactive materials into the air which highly contaminated the surrounding land and water bodies. As a result, radioactive cesium was detected in Plecoglossus altivelis at 3093 Bq/kg wet and Pseudaspius hakonensis at 2500 Bq/kg wet, compared with 100 Bq/kg wet as a standard value, in the River Mano, Soma City, Fukushima Prefecture. Freshwater fishes seem to bioaccumulate radionuclides through the food chain from pelagic fishes to demersal fishes, and from omnivorous fishes to carnivorous fishes (Mizuguchi 2012). Among radioactive substances, cesium-137 released has been confirmed to be highly concentrated in the waters around the Tohoku region and adjacent areas. Moreover, high level of radio cesium (¹³⁴Cs and ¹³⁷Cs) was detected in Salvelinus leucomaenis in a river close to the Nuclear Power Station at the level of 25,600 Bq/kg wet (Wada et al. 2019). Cesium-137 has a long half-life, or decay period, of about 30 years. It was revealed that the factors affecting radio cesium levels in riverine organisms did not necessarily influence radio cesium levels in organisms from lakes (Ishii et al. 2019). Namely, feeding habits had a major influence in the case of piscivorous fishes in lakes, but not in rivers. These findings show that biotic and abiotic factors affecting radionuclide accumulation in fishes are clearly dependent on the ecosystem. After the Fukushima nuclear power plant accident, managing environmental radionuclide contamination efficiently has become greatly important because of two reasons, one is the acute and chronic effects of radionuclide to all animals including humans, of course, and the second is the effect on the inland fisheries for safe supply of fishes.

Overall, regarding the recent negative effects of environmental changes on Japanese freshwaters, it is necessary to carefully monitor how they affect freshwater fishes, not only the health hazards to humans.

4 Red List Challenges

The RL and its manual, the RDB, are an important collection of data that can be used in various forms as statistical data on the current situation and factors for the critical situation of species diversity for each taxon.

The purpose of creating the RL should be to accurately comprehend endangered species and spread this understanding to the public so as not to lead to artificial extinction of wildlife. It has been pointed out that selection does not impose any legal restrictions, so the disappearance of habitats due to development will not end, and the value of rare organisms will increase. Nevertheless, when viewed comprehensively, many experts judge that it has the effect of promoting efforts toward biodiversity conservation. However, there are various issues even when focusing on fishes, and it is necessary to understand them to a certain extent when using the RL.

4.1 Insufficient Basic Data

A problem frequently seen in the evaluation process is the lack of basic data for quantitative criteria that are important in determining the rank of endangered species. To address this issue, qualitative requirements are also provided for evaluation. However, there is a common understanding that evaluation should be carried out objectively, leading to a way only using quantitative criteria. From a scientific point of view, fishes are animals that live freely in water, and it is generally difficult to make reliable estimates of populations across habitats. Even if catch statistics are available, it is not uncommon to know how many individuals exist outside the fishing grounds, and it is not uncommon for multiple species to coexist, such as “sardines.” Furthermore, even for countable species, no system has been established for continuous monitoring at a national level. In other words, it is extremely difficult to obtain accurate quantitative information for most species. At present, it is necessary to take into consideration that the tendency to underestimate extinction risk does not occur while making good use of qualitative evaluation, and environmental administration will promote the construction of a system to focus on scientific research.

In addition, the rate of decrease that is emphasized in the evaluation is stipulated as a longer period of 10 years or three generations. However, as is the case with many Japanese freshwater fishes, it is often inappropriate to apply this criterion to species that declined earlier and are now in minority equilibrium. This is because freshwater fishes that once proliferated in the plains may have already declined from the 1960s to the 1980s, when rice paddy field remodeling was active (Hosoya 2009), or from the 1980s to 2000s, when Largemouth Bass was released nationwide (Hosoya and Takahashi 2006). This is because the rate of decrease is expected to be underestimated. Therefore, in such organisms, it is difficult to individually predict the causes of extinction such as loss of habitat due to development, introduction of alien species, and overfishing before problems occur on the biological side such as genetic deterioration and demographic fluctuations. However, the anthropogenic factors that have been involved pose a far greater threat. This is not limited to freshwater fishes in minority equilibrium, but in assessing species for which quantitative data are lacking, we are fully aware of the endangering nature of anthropogenic factors.

5 Protection Measures

Listing on the RL itself is not subject to legal restrictions. In the RDB published in February 2015, species with the highest priority for protection were defined as those where necessary protective measure will be taken, such as designating it as a domestic rare wild animal and plant species based on the “Act on the Conservation of Endangered Wild Animal and Plant Species” (Ministry of the Environment 2015). However, only four species, Tanakia tanago , Acheilognathus longipinnis , Rhodeus smithii , and Parabotia curtus had been designated at first, then Acheilognathus tabira nakamurae , Cobitis striata hakataensis , Cobitis takenoi , Neosalanx reganius , and Gymnogobius nakamurae were added in 2020. Finally, total number remains at only 15% of the endangered IA species. At the same time, Hemigrammocypris neglecta were designated as the “Specified second species” under the act which prohibits sales for commercial purposes but permits sampling for research and conservation activities. The purpose is to inform the plight of endangered rare wildlife as well as to publish the RL and the publication of the RDB, and to proceed with protection from there. Of course, there are various possible developments in protection (e.g., Hosoya 2002). However, the concrete steps are left specified and are not connected to efficient protection. It is necessary to promptly respond to the challenges posed by the RL.

5.1 Three Basic Steps for Protection

“Protection” can be defined as the way to protect threatened species (Hosoya 2008; Yokoi 2009; Kitagawa 2018). Protection methods include “in situ conservation” which conserves the field habitat where a threatened species is originally located, and “ex situ preservation” which maintains the strain of threatened species in a research facility. In addition, to implement “protection,” the value of the threatened species must be socially promoted as a prerequisite. Therefore, in “protection” of threatened species, “in situ conservation” and “ex situ preservation,” plus “social enlightenment” can be compared to three basic steps (Hosoya 2002, 2008) (Fig. 23.7). All three steps are indispensable, and each must have an organic connection.

Fig. 23.7

Scheme for the protection of threatened species using three basic steps: “in situ conservation”, “ex situ preservation”, and “social enlightenment”

5.2 In Situ Conservation

This refers to the conservation of threatened species that live in an original distribution area in their natural state. Many threatened fishes occur in rural areas including paddy fields, streams, and ponds (See Sect. 23.2.2). To conserve these fishes, it is desirable to isolate the population in a fish sanctuary to block the negative effects of anthropogenic activities. However, these fishes are often unevenly distributed in now open habitats without being conserved. The current situation is that they are directly susceptible to human influences such as rice paddy field remodeling, excessive spraying of pesticides, and disorderly release of foreign fishes such as black bass (Largemouth Bass and Smallmouth Bass), Bluegill Sunfish, and Mosquitofish Gambusia affinis. To conserve native threatened fishes, local governments need to give some rating to local groups and impose legal restrictions. In fact, they are on the RL of each local government, but no effective decree that imposes penalties has been found so far.

5.3 Ex Situ Preservation

This refers to accommodating threatened species in zoos, aquariums, research institutes, etc. to maintain the lineage, and plays the role of “Noah’s Ark.” In fact, this term is internationally confusing. For example, the IUCN per se consistently uses the term “ex situ conservation” (IUCN/SSC 2014), whereas the World Resources Institute and the United Nations Environment Program uses “ex situ preservation” (WRI et al. 1992; see Frankel and Soulé 1981 as well). Like the IUCN, the Ministry of the Environment also follows the term “ex situ conservation.” It is undeniable that the reason for this was the excessive interference of ecologists with terms in the protection measures for rare organisms in Japan. Though it can be admitted that “ex situ conservation” can be contrasted with “in situ conservation” as a word, it is not realistic as a concept. Because the properties that can be extracted from within a habitat are always limited, and the act of protecting the lineage is preservation itself, as shown by cryopreservation of sperm (Frankel and Soulé 1981).

It is well known that having a small number of breeding parents reduces the genetic diversity of the offspring. For example, it was reported Oryzias latipes became completely clonal populations after 20 generations (Arii et al. 1987). Such long-term sub-cultured populations carry the risk of being transformed into a population that is genetically different from the wild population. This tendency is even more likely to appear in small freshwater fishes, which have a short lifespan and a fast generation rate. The goal of “ex situ preservation” is how to faithfully maintain the genetic traits of wild populations.

5.4 Social Enlightenment

Japan is traditionally a fishing nation, and fishermen and officers have used fish seedings. In the name of environmental education, artificially improved varieties of Oryzias latipes such as “Himedaka” were released into natural waters where native O. latipes had disappeared (Munakata et al. 2020). This activity was often reported as positive news. The easy transfer of artificially improved varieties of unknown origin and wild O. latipes from other regions clearly deviates from the idea of biodiversity protection. Because the addition of heterogeneous elements will have some negative effect on the stability of the ecosystem, and if crossed with a native wild O. latipes population, genetic disturbance is inevitable (Nakao et al. 2017).

Unfortunately, the public is not aware of O. latipes, and few people understand the plight of wild O. latipes. In many cases, fry of common cyprinid species such as Opsariichthys platypus and Pseudorasbora parva , or Gambusia affinis of a specific exotic species are mistaken for O. latipes. Even in textbooks whose educational goal should be nature maintenance, the explanation of wild O. latipes is not sufficient. It is required now to have the public accurately understand the uniqueness and diversity of not only wild O. latipes but also other native freshwater fishes in Japan.

On the other hand, there are many NPO bodies for O. latipes conservation activities. In Kanagawa Prefecture, the “Fujisawa Medaka School Creation Association” and the “Odawara Medaka Protection Association” actively protect the local native O. latipes. Higashiyama Zoo and Botanical Garden in Nagoya City, the Medaka Museum, is noteworthy as an aquarium specializing in O. latipes. Finally, it is deeply desired that the circle of these protection and enlightenment activities will expand.