A list of fishes found on the oyster farming rafts by the underwater visual census in northern Hiroshima Bay, Seto Inland Sea, Japan

カキ筏には多様な付着生物が生育することが知られており，魚類にとっても寄り付きやすい環境であることが示唆されている。しかし，カキ筏に具体的にどのような魚類が出現するのかについての知見は乏しい。そこで，カキ筏が数多く係留されている広島湾北部の江田島沖合において，カキ筏に出現する魚類の潜水目視調査を2011年8月と10月に実施した。マガキの垂下された水深5-9mを筏に沿って約50m 遊泳しながら，水中構造内に存在する魚種と個体数を記録した。各月とも，マガキの成長した筏とマガキが垂下されて間もない筏について調査し，のべ400分の潜水観察により総計16科24種の魚類を確認した。そのほぼすべてが，沿岸岩礁域およびガラモ場にみられる魚種であった。クロダイ，アカオビシマハゼ，アミメハギ，カワハギの４種は，調査を実施した筏すべてにおいて出現が認められ，カキ筏環境への順応性の高さが伺われた。出現魚種数および出現個体数は，マガキの成長した筏が有意に高く，マガキの成長に伴い，より多様な魚が数多く寄り付きやすくなることが示唆された。The oyster farming rafts occupy 200ha of the water surface in Hiroshima Bay. Each floating raft (ca.11m wide x 26m long) hangs a total of 600 wires (ca. 10m depth) each attaching 40 oysters’ collectors, providing a complex underwater structure. Though the raft structure has been suggested to provide nursery habitats for fishes, information of fishes found around the oyster raft has been very limited hitherto. In order to obtain data of the species composition and the abundance of fishes occurring on the raft structure, we conducted visual census at off Eta-shima Island, northern Hiroshima Bay, during the daytime on August 5 and October 3, 2011. The collecters were dropped in 0-15m depth from floating rafts. Five observers swam for 52m along the outer edge of the raft in 5-9m depth, with recording fish species and individual numbers occurring within the structure (ca. 100min observation for each raft). The underwater survey was conducted for two types of the rafts in each survey month; a raft with well-grown oysters after overwintering (called the late raft) and one with oyster spats (called the early raft). A total of 24 fish species (16 families) were confirmed and almost of them (23 species) have ever been known as occurring on rocky reefs in Hiroshima Bay. Four fishes, a sparid Acanthopagrus schlegelii, a gobiid Tridentiger trigonocephalus, monacanthids Rudarius ercodes and Stephanolepis cirrhifer, commonly occurred in all four surveyed rafts, suggesting their high abilities in fitting for the environmental conditions of the oyster rafts. The late rafts maintained significantly higher values both in mean fish species numbers and in mean fish abundance than the early rafts, implying that the environmental conditions would become attractive for fishes as a nursery habitat in accordance with the growth of oysters mooring for longer periods.本研究は平成23年度広島大学地域連携推進研究事業の支援を受け，プロジェクト「魚類によるカキならびにアサリの食害防除に関する生物学的研究」の一環として実施したものである

Fish Fauna in Coastal Area of Kashima Island on Border Zone between Hiroshima Bay and Aki-Nada Sea <Short Report>

瀬戸内海中西部水域において,近年冬期の海水温の上昇傾向が確認され,水中環境への影響が危惧されている。そこで浅海魚類群集の現況把握を目的に,2011 年9 月から2012 年8 月にかけて,広島湾最南部に位置する鹿島の沿岸2 定点において潜水センサス法による魚類相調査を実施した。総計24 科50 種の魚類を確認した。より南方の水域を主要分布域とする魚種は,イシガキダイ,オヤビッチャ,ゴンズイの3 種のみであった。いずれも高水温期に出現し,冬の低水温期に消失していた。各月の出現魚種数と水温との間には有意な正の相関関係が認められ,9 月に最多の32 種を,2 月に最少の7 種を記録した。他水域における魚類相データと本研究との魚種共通率から,鹿島は温帯水域と高い類似性を有することが確認された。本調査水域においては,現状においても,冬期の水温条件が南方系魚類を含め浅海性魚種の生存に大きな制約的影響を与えていると考えられた。Within the mid-western zone of the Seto Inland Sea including Hiroshima Bay and Aki-nada Sea, environmental changes such as the recent appearance of tropical/warm temperate fish have been observed. This phenomenon is associated with the warming of the water temperature especially during winter. To obtain basic data on the present conditions of the fish fauna, we conducted a year-long underwater fish census on two shallow water sites around Kashima Island from September 2011 to August 2012. A total of 50 species (24 families) were recorded in our monthly surveys, including three species (Plotosus japonicus, Abudefduf vaigiensis, Oplegnathus punctatus) normally occurring in tropical/warm temperate waters. These three species appeared during the warm water season and subsequently disappeared in winter. We found a positive correlation between the number of fish species and water temperature recorded each month (r = 0.85, p < 0.05). The diversity of fish recorded in the present study was very similar to the diversities of fish in temperate waters. Because of the rapid decrease in species number during winter, we suggest that the low water temperature during winter strongly restricts the number of survivors in the fish community even in the temperate waters of the mid-western area of the Seto Inland Sea

Kazuya NAGASAWA

Abstract Anglerfish Lophius litulon (Jordan) caught commercially in the East China Sea off western Japan were found to be infected with the chondracanthid copepod Acanthochondria spiriger

On the abnormally morphological forms in Mola sunfish (Mola spp. A and B) taken from Japanese coastal waters

2007年6月から2008年12月までの日本近海におけるマンボウ属2種（ Mola spp. A and B）の調査の中で（全145個体），胸鰭変形7個体，背鰭短縮2個体，背鰭軟条配置異常1個体，舵鰭臀部側欠損1個体，舵鰭欠損1個体，人為的な損傷3個体，精巣肥大2個体，幼形形態1個体を得た。これら異常がみられた18個体の内訳には先天的な奇形，捕食生物による損傷，人為的な損傷，寄生虫による変形などがあり，また長期間飼育された個体（1個体）は天然水域の個体と体形が異なる可能性が示唆された。人為的な損傷がみられた3個体と長期飼育された1個体を除く，天然水域で採集された異常個体（14個体）は採集された全体の約1割（14/145）で，ある程度は天然水域にも存在するものと推測された。Of 145 ocean sunfish specimens obtained from Japanese coastal waters between June 2007 and December 2008, morphologically abnormal forms were confirmed in a total of 18 specimens. Seven had transformed pectoral fins; two had shortened dorsal fins; one had abnormally arranged dorsal soft rays; one was missing the lower part of the clavus; one was missing the whole clavus; three had partially damaged bodies or fins, probably because of artificial cutting; two had hypertrophied testes; and one was a young fish in the juvenile-specific morphological form. These abnormal forms were thought to have occurred as a consequence of congenital malformation or damage by predation, parasites, humans, or other factors. One suffered a transformation in body shape from a natural form, probably because it was reared for a long period of time in an aquarium. According to the frequency of non-artifically abnormal individuals (ca. 10%, 14/145), the occurrence of abnormalities is not rare in natural populations

潜水センサスを用いた瀬戸内海倉橋島における浅海魚類相 : 出現魚種の季節的消長 <原著論文>

瀬戸内海の倉橋島において，潜水センサスによる魚類相の周年調査を行った。本調査により，8目29科53種の魚類を確認した。これらは周年定住種16種，季節的定住種37種に分けられた。近年，瀬戸内海で報告されている暖海性魚類と思われる種は確認されなかった。月毎の出現魚種数は，9・10月の41種が最多であり，1・2月の18種が最少であった。冬期には，9・10月に認められた多くの季節的定住種はその姿を消し，周年定住種を中心とした魚類群集が形成された。本調査海域の冬期の最低水温は10℃であり，低水温が種数の変動に影響し，暖海性魚類の出現を制限する要因になっていると考えられた。We conducted a year-long underwater census to survey fish fauna on a reef off Kurahashi Island in the Seto Inland Sea. A total of 53 species (8 orders, 29 families) were recorded; 16 species were residents, 37 were seasonal residents. No tropical/warm-temperate fish were confirmed. The total number of fish species (41) peaked in September and October, but drastically decreased to just 18 species in January and February because of the disappearance of most seasonal residents. These seasonal residents appeared to be prevented from continuing residence in the central part of the Seto Inland Sea because of the low water temperature in winter.※誤植訂正のためPDF差し替え(2018年3月20日

Critical Population Trend of the Small-scale Sillago Sillago parvisquamis (family Sillaginidae) at Nakatsu Tidal Flat, Suo-nada Sea, Western Seto Inland Sea, Japan, 2016-2018

キス科の絶滅危惧種アオギスSillago parvisquamis について，最大の生息地である瀬戸内海周防灘南部（豊前海）の大分県中津干潟において2016 ～ 2018年の繁殖期に緊急調査を実施し，本種の生息状況や年齢構成などを明らかにした。2016年，2017年，および2018年の釣CPUE（個体数/3 時間/ 人；平均値±標準偏差）は，それぞれ0.80 ± 1.3（n＝13），4.3 ± 2.9（n＝18），および0.33 ± 0.65（n＝9）の低値を示した。依然として，繁殖活動が認められるものの，個体数の減少は著しく，危機的な生息状況にあることが明らかになった。The small-scale sillago Sillago parvisquamis (family Sillaginidae) has been evaluated as one of the endangered species in Japan. The only largest local population exists at Nakatsu tidal flat in the southern part of the Suo-nada Sea (Buzen-kai Sea), Seto Inland Sea. The population structure of the species on the tidal flat was investigated in 2016-2018 to determine recent population trends. As a result, no dominant year class was observed in the population. Catch per unit effort (CPUE) (indiv./3 hours/person; mean ± SD) by rod and line fishing during the spawning seasons in 2016, 2017 and 2018 showed low values, at 0.80 ± 1.3 (n = 13), 4.3 ± 2.9 (n = 18) and 0.33 ± 0.65 (n = 9), respectively. Histological examination of ovaries of the females captured in 2018 indicated that spawning had occurred as yet. These findings suggest that the small-scale sillago stock has decreased to a critical level in Japan

東シナ海産キアンコウにおけるトゲナシツブムシAcanthochondria spirigeraの寄生状況

東シナ海で漁獲されたキアンコウLophius litulonの口腔壁にカイアシ類ツブムシ科のトゲナシツブムシAcanthochondria spirigeraの寄生を認めた。キアンコウは本寄生虫の新宿主である。トゲナシツブムシを含むAcanthochondria属のカイアシ類は魚市場等で食品衛生的な問題を起こすことがあるため，その寄生状況を観察した。全検査魚における寄生率は72％で，キアンコウ1尾当たり普通1～2個体が寄生していた。寄生部位は口腔壁で，鰓への寄生は見られなかった。1尾当たり寄生数は魚体長が増すほど，また季節的には秋（9～11月）に多くなる傾向がみられた。Anglerfish Lophius litulon (Jordan) caught commercially in the East China Sea off western Japan were found to be infected with the chondracanthid copepod Acanthochondria spirigera Shiino, 1955. Lophius litulon is a new host for this copepod. We made an observation on the occurrence of A. spirigera on anglerfish because the copepods of the genus Acanthochondria cause food hygiene problems at fish markets in Japan. Overall prevalence of infection with A. spirigera was high (71% of 31 fish examined), and one or two copepods were usually found on an infected fish. Their attachment site was the roof and floor of the buccal cavity of the fish. The number of copepods per fish showed an increasing tread with fish size and during the fall months (September to November)