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Online ISSN : 2434-2882
Print ISSN : 0503-1540
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  • Keita MARUYAMA, Hiroshi KOHNO
    2020 Volume 58 Issue 3-4 Pages 51-57
    Published: 2020
    Released: May 19, 2021
    JOURNALS OPEN ACCESS
    To evaluate the habitat function for fish of an artificial sandy beach constructed in the inner Tokyo Bay, occurrence patterns of Plecoglossus altivelis altivelis were examined based on samples collected monthly at both low and high tide from March 2018 to February 2019, using a small seine net in the sandy beach of Furuhama Park, Ota City, Tokyo. The number and mean body length(± SD)of specimens collected were 1,817 and 20.6 mm(5.4 mm)at high tide and 218 and 17.4(3.5 mm)at low tide, respectively. Because these sizes correspond to the phase of growth where fish gain swimming ability, they are considered to migrate positively to and from the sandy beach of Furuhama Park and the canal on the flow and ebb tides, respectively. The results suggest that the sandy beach of Furuhama Park has a habitat function as a nursery ground for P. altivelis altivelis at least.
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  • Akira ONODERA, Keita MARUYAMA, Kana TAKEYAMA, Hiroshi KOHNO
    2020 Volume 58 Issue 3-4 Pages 59-69
    Published: 2020
    Released: May 19, 2021
    JOURNALS OPEN ACCESS
    Occurrence patterns of fishes were compared between net cages(0.5 × 0.4 × 0.4 m) with three internal materials(nylon net, bamboo shoot and oyster shell)placed at surface and bottom layers along a seawall at the Furuhama Park in innermost Tokyo Bay from April 2016 to March 2019. A total of 1,574 individuals of 17 species representing 9 families were collected, fishes collected at the surface numbering 1,189 individuals of 13 species(13.2 ind./cage)and those at the bottom 385 individuals of 11 species(4.2 ind./cage).The dissolved oxygen was 6.2 ± 2.26(mean ± SD)mg/L and 4.2 ± 2.58 mg/L at the surface and bottom layers, respectively, and the respective times when the hypoxic oxygen water of 3.0 mg/L and lower appeared were 4 out of 88 cages and 33 of 89 cages at the surface and bottom layers. Three gobiids, Tridentiger obscurus, Chaenogobius gulosus and Tridentiger trigonocephalus, were dominant species occupying ca. 90% of the total individuals collected in this study; however, the first and third were collected by both the surface and bottom cages, but the second species occurred at the surface layer only. This study suggested a possibility that a certain structure created at the surface layer of a seawall would become a habitat for some fishes during the time when hypoxic waters arises.
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  • Ryousuke ONUMA, Seiya KANEKO, Hiroaki TOYODA, Kouki KANOU
    2020 Volume 58 Issue 3-4 Pages 71-82
    Published: 2020
    Released: May 19, 2021
    JOURNALS OPEN ACCESS
    In order to clarify fish assemblage structures in small fragmented seagrass beds inside harbors facing the open sea, daytime seine net sampling was conducted over a seagrass bed and adjacent bare sandy area in Hiraiso Harbor, Ibaraki Prefecture, eastern Japan, from May to August 2014. A total of 1126 fish individuals from 29 species and 562 individuals from 20 species were collected in the seagrass bed and sandy area, respectively. Despite the lack of significant differences in environmental properties(water temperature, salinity, turbidity and dissolved oxygen), except for mud content, between the seagrass bed and sandy area, the mean numbers of fish species and individuals per haul were significantly higher in the former throughout the study period, with species composition also differing remarkably between the two habitats.Larger-sized individuals also tended to be more abundant in the seagrass bed compared with the sandy area. These results indicated that fragmentary and small seagrass bed may provide an important habitat for some species.
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  • David E. ANGMALISANG, Keita MARUYAMA, Ayumi HIHARA, Hiroshi KOHNO
    2020 Volume 58 Issue 3-4 Pages 83-99
    Published: 2020
    Released: May 19, 2021
    JOURNALS OPEN ACCESS
    Occurrence patterns and ontogenetic intervals based on the development of swimming and feeding functions were investigated on the endangered goby, Eutaeniichthys gilli, collected from Obitsu-gawa River estuary in the inner Tokyo Bay. A small seine net and two set nets were used for the samplings at the main stream from May 2005 to April 2006 and at the creek on the tideland from July 2009 to June 2010. Individual numbers of E. gilli collected were 94 ranging from 2.8 to 34.5 mm BL with the mean ± SD = 7.7 ± 3.9 mm BL and 7 from 6.4 to 33.9 mm BL with 17.1 ± 12.3 mm BL at the tidal flat in the lower and middle streams, respectively, although no specimen was collected at the upper stream. On the other hand, 1,127 individuals of 10.1-39.5 mm BL with 27.5 ± 7.2 mm BL(n = 464)were collected from the creek. Based on the development of swimming- and feeding-related characters of 3.5-39.1 mm BL(n = 100) cleared and stained specimens, the following three swimming and feeding phases were recognized: caudal fin propulsion from 3.5 to 5.0 mm BL, whole body propulsion from 5.0 to 10-11 mm BL, and functional, juvenile swimming over 10-11 mm BL; sucking and biting from 3.5 to 5-6 mm BL, improved sucking and biting abilities from 5-6 to 10-12 mm BL, and functional, juvenile feeding over 10-12 mm BL. Based on the occurrence patterns and functional development, the spawning ground is considered to be formed in the tideland including the creek of Obitsu-gawa River estuary, and the hatched larvae are drifted and dispersed toward the sea. The forehead tidal flat at the lower stream is one of nurseries for early stage larvae. No nursery and growing habitats are formed in the main stream, but the juveniles of about 8 mm BL and larger migrate shoreward to and grow in the tideland of the Obitsu-gawa River estuary. This study revealed that Obitsu-gawa River estuary is almost the only major spawning ground and provides nursery and growing habitats for E. gilli in the inner Tokyo Bay.
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  • Mao SHIBATA, Seiya KANEKO, Seiji USUI, Wataru HYAKUNARI, Kazunori ARAY ...
    2020 Volume 58 Issue 3-4 Pages 101-114
    Published: 2020
    Released: May 19, 2021
    JOURNALS OPEN ACCESS
    Seasonal patterns of larval and juvenile fish assemblage in a limnetic zone of Lake Kitaura, a shallow large inland-sea lake(7 m maximum depth, 36 km ²)in Ibaraki Prefecture, eastern Japan, were examined by monthly larval net sampling at surface and middle layers from April 2010 to March 2012. A total of 5,272 individuals representing 8 families and 11 species were collected during the study period. Mean numbers of fish species and individuals were more abundant from spring to summer, with non-occurrence in most months during late autumn and winter. The most abundant species were Japanese icefish Salangichthys microdon, pond smelt Hypomesus nipponensis and three gobiids Tridentiger brevispinis, Rhinogobius sp. and Acanthogobius lactipes. Of these, icefish and pond smelt occurred abundantly at both layers in early spring(March and April), whereas three gobiids at middle layer in most months during late spring and summer(May to September). Species composition also differed between early spring and late spring to summer. Occurrence patterns and developmental stages of the five abundant species suggested that they would disperse from spawning grounds in littoral habitats and/or inflowing rivers and have more or less different pelagic larval duration and swimming layer in the limnetic zone.
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  • Sota KIRIHARA, Yumi HENMI, Gyo ITANI
    2020 Volume 58 Issue 3-4 Pages 115-123
    Published: 2020
    Released: May 19, 2021
    JOURNALS OPEN ACCESS
    Ecological studies of the facultatively symbiotic goby Acentrogobius sp. 2(sensu AKIHITO et al., 2013)are important because there is limited knowledge on the facultative relationship in goby-shrimp symbiosis in the Pacific. The present study surveyed the surface activity of Acentrogobius sp. 2 around the burrows of snapping shrimp(Alpheus brevicristatus)by quantitative observation on a tidal flat during high tides in southern Japan. Acentrogobius sp. 2 used the area in front of the burrow entrance for approximately 30% of the 10-min observation period only. Acentrogobius sp. 2 sometimes went farther than 10 cm from the burrow entrance, but most gobies returned to the burrow entrance. Surveys conducted at low tides confirmed that the goby showed surface activity in tidepools, but with a reduced time than that at high tides. The burrow-retreating bouts by the goby were triggered by approaching omnivorous and carnivorous fish and crab species. Future studies on shrimp burrow use by closely related Acentrogobius species may elucidate the evolutionary process of the facultative relationship of this genus.
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