担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：CSIRO PUBLISHING  

Adults of the marine-originated amphidromous goby (Gymnogobius petschiliensis) inhabit both freshwater and brackish-water areas, unlike many other amphidromous species, which spend their entire lives, except the larval stage, in freshwater. Furthermore, adult G. petschiliensis individuals incur higher osmoregulatory costs in freshwater than those in hypertonic brackish water under laboratory conditions, suggesting that the ecology of the species is largely dependent on high-salinity (ancestral) environments. Therefore, a detailed information on the ecology of G. petschiliensis will help elucidate the diversity and evolution of amphidromy. Here, this study assessed the habitat use and freshwater dependency of G. petschiliensis in two streams in central Japan. Year-round surveys showed that adult density was higher in freshwater than in brackish water during the non-spawning season. This implies that adults chose salinity habitats according to ecological conditions (e.g. inter- and intraspecific competition, and predation risk) without being bound by physiological preferences. Conversely, most egg clutches were found in brackish water. Furthermore, adult density in brackish water increased with the increase in spawning events, suggesting that the adults migrated downstream for spawning. This preference for spawning in brackish water rather than in freshwater may be attributed to the constraints of their reproductive physiology.

DOI： 10.1071/MF21181

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Society of Fisheries Science  

To conserve the Japanese eel Anguilla japonica, damaged estuarine habitats need to be restored, because the estuaries are essential for not only growth of the species, but also as areas for silver eels to acclimate to seawater prior to migrating into the ocean for spawning. As a first step towards improving and restoring estuarine habitats, this study aimed to reveal the preferred gap structure within stone piles by eels at each life history stage. Compari-son of the number of individuals among Ishikura nets with different-sized stones (large, 30 cm in major axis; medi-um, 20 cm; small, 10 cm) found that the immature adults (elvers and yellow eels) preferred those with small-sized stones the most. In contrast, the maturing adults in the middle of downstream spawning migration (silver eels) uti-lized only the Ishikura nets with large and medium-sized stones. These findings suggest the importance of estab-lishing estuarine habitats with various-sized stones to allow many eels to survive to maturity in stream areas.

DOI： 10.2331/suisan.21-00043

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY  

This study aimed to reveal the salinity preference of juveniles of an amphidromous goby, Sumi-ukigori Gymnogobius petschiliensis, while migrating to a freshwater area. Salinity choice experiments revealed that juveniles of this species significantly prefer brackish water (salinity 20) to freshwater (salinity 0) when acclimated to a salinity of 20 in advance. Additional experiments revealed no preference between brackish water and seawater (salinity 35). Since body size was not correlated with the strength of preference for brackish water, and adults of this species are also known to prefer brackish water at a salinity of 20 to freshwater, the preference for saline water may be consistent after migration to a freshwater area. Considering that juvenile G. petschiliensis would often migrate to freshwater areas just after entering streams, the migration should be against its salinity preference. This directly contrasts with other diadromous species, which prefer the salinity of destination areas during and after migration. Adult and juvenile G. petschiliensis may take advantage of high euryhalinity to choose habitats where such ecological costs, such as high predation risk and interspecific competition, are low (i.e., freshwater areas).

DOI： 10.1111/jfb.14351

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER JAPAN KK  

The study of changes in intraspecific habitat use when closely related species coexist aids our understanding of the relationships between intra- and interspecific interactions in fishes. However, evidence of this phenomenon is few and shown in a very limited number of taxa. In particular, the stream goby [Rhinogobius flumineus (Mizuno, 1960)] is known for intraspecific variation in habitat use. We used underwater visual surveys to investigate this species' size-dependent habitat use, both in isolation and in the presence of a sympatric congener, Rhinogobius nagoyae Jordan & Seale, 1906. A generalized linear mixed model and multiple comparison tests revealed that in the absence of R. nagoyae, R. flumineus body length was positively correlated with river flow velocity. This correlation disappeared when R. flumineus coexisted with R. nagoyae. Additionally, R. nagoyae density increased with flow velocity. Observations of interspecific territorial behavior revealed that larger individuals dominated in male-male competition regardless of species combination. Of the two species, R. nagoyae is significantly larger, so it was likely to exclude even relatively big R. flumineus individuals from fast riffles, the habitat preferred by both species. This study demonstrated that interspecific competition dominates intraspecific competition under sympatric conditions with larger related species.

DOI： 10.1007/s10228-019-00684-y

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER  

The floating goby Gymnogobius petschiliensis Rendahl is an amphidromous fish, which migrates upstream from the sea in the juvenile period and then inhabits not only freshwater areas but also brackish water. Most of the species that have such migratory polymorphism switch their osmoregulatory mechanism in synchrony with the timing of migration, but in G. petschiliensis it is known that even individuals living in freshwater areas behaviourally prefer brackish water to freshwater conditions in a laboratory. To clarify whether this species lives in freshwater areas with high osmoregulatory cost, the relationship between physiological cost and salinity was investigated using adult fish of the species captured in a freshwater area. Adults were kept individually in 13 L tanks with various salinity levels under fasted conditions. Their loss of body weight in freshwater conditions was more rapid than in 2/3 seawater, whereas the frequencies of horizontal and vertical movement in 13 L tanks did not differ significantly between freshwater and 2/3 seawater conditions. This suggests that the weight loss reflects not behavioural performance but physiological cost. In addition, no adults died even when transferred from freshwater to seawater conditions, indicating that they have high tolerance to salinity change in estuarine areas even after migrating to freshwater areas. These results support the hypothesis that G. petschiliensis migrates to freshwater areas while maintaining high hypo-osmoregulatory ability and paying a high physiological cost. Because G. petschiliensis phylogenetically originates from the coastal species, this example of migration without completely switching the osmoregulatory mechanism may help us to understand the diverse processes of up-stream migration in marine fish.

DOI： 10.1016/j.jembe.2019.03.014

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER JAPAN KK  

Adults of three amphidromous gobiid fishes, Tridentiger brevispinis, Rhinogobius similis, and Gymnogobius petschiliensis, are euryhaline and generally found in both freshwater (FW) and brackish water (BW) areas. The determining factors for their choice of habitat with different salinity have never been explored. In this study, a salinity-choice experiment was conducted using the above species captured in the FW region of the Isazu River, northern Kyoto Prefecture. For comparison, the fluvial goby Rhinogobius flumineus and BW-acclimated G. petschiliensis were also tested. We found that the three euryhaline species, including BW-acclimated G. petschiliensis, preferred BW to FW, whereas R. flumineus preferred FW. These results suggest that salinity preference did not determine habitat in these euryhaline gobiids, which were found in FW. Surveys were also conducted focusing on competitors and predators in their potential habitats. Thus, net sampling captured many other gobiid species, and an environmental DNA method detected Japanese temperate bass, a voracious predator, in the estuarine areas, suggesting that biotic factors are major determinants in the distribution of euryhaline species.

DOI： 10.1007/s10164-017-0510-3

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記述言語：日本語   会議種別：口頭発表（一般）  

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記述言語：日本語   会議種別：口頭発表（一般）  

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記述言語：英語   会議種別：ポスター発表  

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記述言語：英語   会議種別：ポスター発表  

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記述言語：日本語   会議種別：口頭発表（一般）  

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記述言語：日本語   会議種別：ポスター発表  

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