著者

木村 清志 Kimura Seishi

出版者

三重大学水産学部

雑誌

三重大学水産学部研究報告 (ISSN:02875772)

巻号頁・発行日

no.14, pp.p113-235, 1987-09

被引用文献数

6

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イサキは一本釣や定置網の対象魚種として非常に重要であり,また栽培漁業の適種のひとつにもあげられている。ところが,近年漁獲量の減少や,魚体の小型化など資源の安定性に問題がおこり,本種の資源特性や資源状態を解明することが必要となってきた。このような現状から,著者は特に三重県熊野灘沿岸のイサキについて種々の資源生物的特性を明らかにする目的で研究を行ってきた。本報告は9章から成り,まず第1章では全国的なイサキ漁業の概観と三重県前島地方のイサキ漁業の実態について述べ,第2章では本種の地理的分布や移動について検討した。第3章から第6章までは資源生物学的知見として最も重要な年齢・成長,年齢組成・生残率,成熟・産卵,および食性について論述した。第7章では人工種苗生産に関する諸問題について検討を加え,この研究で得られた卵,仔稚魚を使用して第8章では本種の初期生活史,特に卵から若魚に至る期間の形態形成過程について述べた。最後に,第9章ではこれまでに得られた知見を総合して本種の資源解析を行い,資源の維持・管理および増殖を行う施策について検討した。これらの研究によって得られた知見を要約すると次のようになる。 1.漁 業 (1) 漁場は黒潮および対馬暖流域でかつ天然礁がよく発達した海域に形成される。代表的な漁法は一本釣で,このはか定置網や刺網などでも混獲されている。主漁期は全国的に4月,5月から10月,11月であった。 (2) 三重県前島半島沿岸では年間150~160トン程度の漁獲量があった。一本釣漁獲量は1982年をピークにして減少傾向を示し,魚体の小型化も認められた。 2.分布・移動 (1) わが国における通常の分布域は太平洋沿岸では千乗県~鹿児島県,対馬暖流域では新潟県~鹿児島県であった。国外では韓国南部や台湾,中国大陸東シナ海,南シナ海沿岸に分布が認められた。分布の特徴として,暖流性,外海性があげられた。また本種は沿岸性が強く,いわゆる「大陸棚固有種」であると考えられた。 (2) 本種は大規模回遊は行わないが,季節的に局所的な向岸一向沖移動は行っていると考えられた。 3.年齢・成長 (1) 年齢表示形質として鱗、耳石,椎体,主鰓蓋骨,上後頭骨背側隆起板の5硬組織を観察した。 (2) 本種の鱗は典型的な櫛鱗で,被覆部には明瞭な輪紋が形成されていた。体各部の鱗には相似的に輪紋が形成され,どの部位の鱗であっても年齢形質として利用できると考えられた。 しかし,実際には体中央部(胸鰭後端付近の側線直下)の鱗が最も大形で,かつ外形の歪みも少ないことから,輪紋の読取りはこれが最良であった。鱗の輪紋は年2回,1月~2月と6月~7月に形成された。 (3) 耳石は比較的大きく,明瞭に透明帯と不透明帯が観察された。この不透明帯の幅は著しく狭く,線状であった。このような耳石の帯構造は,15%中性ホルマリンで固定した場合,数ヶ月後でも観察可能であった。耳石の輪紋(不透明帯の外縁)は年1回6月~7月に形成された。この期間は産卵期と一致しているため,輪紋数は直接満年齢を表していると考えられた。 (4) 椎体の後方陥人面には不明瞭ではあるが透明帯と不透明帯がみられた。しかし,この輪紋は相似性が悪く,また輪紋が欠落している場合も認められた。 (5) 主鰓蓋骨の帯構造は極めて不明瞭であった。また,上後頭骨は明瞭な帯構造が認められるが,不透明帯数は大形魚でも2帯しか認められなかった。 (6) このような観察結果から,これら5硬組織のうち年齢形質として適当であるのは鱗と耳石で,他の3硬組職は不適当であると判断された。鱗と耳石を比較すると,高年齢魚での輸紋の明瞭さや複輪,偽輪の出現率の点で耳石の方が優れていた。 (7) 耳石の輪紋から年成長を推定した。平均的な年成長は(13)式で表され,大部分の個体がこの式で表した値の前後 3cm以内の成長を示すと考えられた。 (8) 耳石の縁辺成長率から,季節的な体長の増大は8月から10月にかけての期間が最大であった。 (9) 成長補償作用が確認された。 (10) 飼育実験の結果から,孵化後1日から407日までの初期成長は(28)式,(29)式で表された。 4.年齢組成・生残率・自然死亡係数 (1) 一本釣で漁獲されたイサキの年齢組成をいくつかの方法で推定し,比較した。その結果,年齢査定法と繰返し計算法によって得られた値が最良であった。 (2) 年齢組成から最近の生残率は0.25程度であると推定された。 (3) 自然死亡係数は0.5~0,6と推定された。 5.成熟・産卵 (1) 本種の生殖腺は左右不相称である個体が全体の半数強を占め,このうち石偏の個体が左偏の個体よりも多かった。 (2) 生殖腺の成熟状態は部位に関係なく,はぼ均一であった。 (3) 2歳魚以上の卵巣内には卵黄胞期以下の成熟段階の卵が周年存在した。第1次卵黄球期以上に成熟した卵は5月から8月まで出現し,特に胚胞移動期以上の卵は2歳魚では6月に,3歳魚以上では6月から8月にかけて出現した。 (4) 精巣の成熟段階を精子形成準備期,精子形成期,精子放出期,精子吸収期の4期に分けた。精子形成準備期は12月あるいは1月から4月,精子形成期は4月から5月,精子放出翔は6月から8月,精子吸収期は9月から12月であった。 (5) 生殖腺組織の観察やGIの変化および水槽内での産卵実験の結果から,産卵期や産卵時刻,最小成熟年齢などについて次のように推定した。産卵期は6月から8月で,若齢魚の産卵期間は高齢魚よりも短い傾向が認められた。日本国内での産卵期に顕著な地域差は認められなかった。産卵水温は通常20~28℃であった。産卵時刻は20時をピークとして前後1時間程度であった。最小成熟年齢は雌雄とも満2歳で,生物学的最小形は雌で尾叉長16cm,雄で15cm程度であった。 (6) 性比は成長にともなって雌よりに偏る傾向を示し,これは雌雄の生残率の差に原因していると考えた。各年齢群の性比を(34)式,(35)式で表した。 (7) 産卵前後の卵巣の重量差と卵巣卵数から産卵数を推定し,(40)式に表した。また個体群としての産卵量は3歳魚が最大であると推定された。6.食 性 (1) 釣と定置網で漁獲された標本の胃内容物を比較した結果,定性的には明瞭な差は認められなかったが,空胃率は明らかに釣獲標本の方が高かった。 (2) 摂餌活動には季節的な周期性がみられ,夏季には活発になり,冬季には活動が低下した。 (3) 未成魚・成魚の主餌料はキビナゴやマイワシ,カタクチイワシなどの魚類および橈脚類や端脚類などであった。これらのことから,本種の食性は幅広い肉食性であると考えられた。 (4) 後屈曲期仔魚の餌料はすべて橈脚類であった。稚魚期になると,これに加えて二枚貝幼生や橈脚類などを捕食するようになり,さらに若魚期では,これらのほかヤムシ類や尾索類およびカタクチイワシのシラス期仔魚などを餌料としていた。 (5) 餌料動物の大きさを捕食者体長との相対値αで表した。αの最大値は0.6前後で,典型的な魚金魚と比較するとかなり小さい値を示した。 (6) 摂餌量に関する問題について飼育実験を行い,次のような結果を得た。魚体の大きさと最大摂餌量との関係は(44)~(46)式で表された。摂餌量は水温と密接に関係し,12℃以上では有意な正相関が認められた。また,生殖腺の成熟にともなって摂餌量が減少する傾向がみられた。 (7) 摂餌後の胃内容物の減少速度に関する実験を行った。その結果,胃内容物減少率は水温が高いほど,また魚体が小さいぼど高くなる傾向がみられた。 (8) 捕食・消化器官の形態は全体的に特化の程度が低く,これは食性自体の特化程度が小さいためであると考えた。ただ,鰓耙上の針状突起はよく発達し,これによって,橈脚類などの捕食が可能になると考えられた。 7.種苗生産 (1) 本種は漁獲直後の親魚から自然採卵することが可能であった。 (2) 孵化率は通常50~100%であった。孵化率と浮上卵率や卵径の変動係数との関係には有意な相関がみられ,これらは卵質判定の指標になると考えられた。 (3) 胎盤性性腺刺激ホルモンは.畜養親魚を用いる限り,有効性は認められなかった。 (4) 孵化率は卵収容容器の表面積に対する卵密度と逆相関するが,20粒/cm2以下の範囲内では密度の影響を受けなかった。 (5) 最適孵化水温・塩分はそれぞれ22.6℃,34.2‰と推定された。孵化率と水温・塩分との関係は(65)式で表された。 (6) 水温18℃~28℃の範囲内では,孵化に要する積算温度は一定で,孵化時間と水温との関係は(67)式で表された。 (7) 孵化後30日から407日までの体重の増加を(68)式で表した。 8.初期生活史 (1) 受精卵は球形の分離浮遊卵で,卵径は0.78~0.85mm,卵黄は無色で表面に亀裂があった。油球は単一であった。受精後40分で2細胞期になり,28~30時間後に孵化が始まった。 (2)孵化仔魚は全長1.50~1.65mmで,3日後に卵黄を吸収し終り,関口した(全長2.71~2.80mm)。全長約5.5mmで脊索の屈曲が開始し,約12mmで鰭条総数が定数に達して稚魚に移行した。全長約35mmで体がはぼ完全に被鱗し,若魚になった。 (3) 仔魚期の形態的特徴は,前期仔魚では油球が卵黄の後下方に位置していること,肛門が卵黄から離れていること,膜鰭縁辺に黄色素胞が発達することなどで,また前屈曲仔魚でほ全体に黒色素胞が少ないこと,後関節骨後端や肛門直前の膜鰭に塊状黒色素胞があることなどであった。 (4) 本種特有の暗色縦帯は稚魚期に発現し,若魚期に完成した。この縦帯は人工種苗の方が天然稚魚に比較して小さな体長で形成された。 (5) 仔魚期から若魚期における体各部の相対成長を(70)~(86)式に表した。人工飼育魚と天然魚の相対成長を比較した結果,人工飼育魚の体形は本質的には天然魚と大差ないと考えられた。 (6) 鰭の形成過程を観察し,次のような結果を得た。原基が形成される全長は胸鰭2.8mm,尾鰭4mm.背鰭,臀鰭6mm,腹鰭8mm前後であった。全長12mm付近で鰭条総数が定数に達し,18mm前後になると棘数も定数に達した。各鰭軟条の分枝過程が完了するのは全長140mm前後であった。 (7) 鱗の形成は全長16mm程度から開始され,35mm前後で吻以外は被鱗した。吻まで完全に被鱗し,鱗形成が完了するのは全長130mm程度であった。 (8) 腸管の施回は全長3.1mm付近から開始され,3.7mm前後で完了した。胃の伸長や幽門垂の形成は全長12.7mm付近から開始された。全長22.5mm程度で幽門垂数が定数に達し,消化管の形態は成魚とほぼ同様になった。 9.資源の現状と管理および増殖 (1) これまでに得られた生物学的知見と漁獲資料から,三重県志摩町沿岸のイサキ資源の解析と診断を行った。1歳魚以上の資源尾数は約660万尾と推定された。現状の資源における雌親魚数と産卵数はそれぞれ処女資源の41.2%,16.4%に減少し,この資源は濫獲状態にあると判断された。 (2) 現在の濫獲状態を是正し,最大持続生産を行うためには漁獲努力量を3690boat・day 程度に減少さすか,あるいは漁獲最小尾叉長を17~18cm程度まで引上げるという2方法の漁業規制が考えられた。(3)さらに積極的に資源を増殖させるためには種苗放流も効果的であると予想された。The threeline grunt Parapristipoma trilineatum (Pisces : Perciformes : Haemulidae) is a valuable species as an edible fish along the coasts of southern Japan. The present report deals with the fishery biology of this species, with particular reference to its fishery, geographical distribution and migration, age and growth, age composition and survival rate, maturity and spawning, feeding habits and morphology of feeding and digestive organs, artificial spawn taking and larval rearing, embryonic and larval developments, and stock assessment. The materials used in these studies were mainly caught from coastal areas of Kumano-nada (Kii Peninsula, Mie Prefecture) during the years from 1978 to 1984. The rearing experiments were carried out at the Fisheries Research Laboratory, Mie University. The results obtained are summarized as follows : 1. Threeline Grunt Fishery Fishing grounds of this fish were formed in the rocky reefs along the warm currents, or Kuroshio (Pacific coasts) and Tsushima Current (coasts of East China Sea and Sea of Japan). This species was caught representatively with hook and line, and allso with set nets and gill nets. The fishing season generally began in April or May, and continued until September or November. The commercial landing of the threeline grunt with hook and line, set nets, and gill nets was totally estimaled at 150 to 160 metric tons per year at the Pacific corst of Sakishima Peninsula, Mie Prefecture in 1982 and 1983. The catchin weight with hook and line increased rapidly during the years from 1979 to 1982, but it decreased in 1983. The average length of the fish caught with hook and line became smaller during the years from 1979 to 1983. 2. Geographic Distribution and MigrationThe threeline grunt was distributed in southern Japan, the southern coasts of the Korean Peninsula, Taiwan, and along the East and South coasts of mainland China. But this species did not inhabit the sea along the Ogasarwara Islands, Ryukyu Islands, nor the Philippines. This fish was one of the representative submarginal continental endemic species. ln Japan, the fish normally inhabited the area from Kagoshima Prefecture to Chiba Prefecture along the Pacific coasts, and from Kagoshima Prefecture to Niigata Prefecture along the coasts of the East China Sea and the Sea of Japan. This species preferred warmwater temperature, high salinity, and rocky shores. The threeline grunt did not make a large-scale migration which was observed in the tunas Thunnus spp., the yellow tail Serlola quinqueradiata, or the saury Cololabis saira, but made a seasonal offshore-inshore migration in limited areas.3. Age and GrowthThe scale, otolith, centrurn, opercle, and supraoccipital crest were observed in detail in order to select the most suitable hard tissue for age determination of the threeline grunt. The scale was a representative ctenoid, and ring marks were shown clearly on the embedded part. The ring marks formed similarly on scales taken from any part of the body. Although any scale on the body could have been used for age determination, the scale taken from a row beneath the lateral line just posterior to the tip of the pectoral fin (B-region in Fig. 10) was the most suitable for mark reading because of having the largest scale radiusand less distorted shape. Ring marks on scales formed twice in a year, both in summer (June or July) and in winter (January or February).The otolith was fairly large and was removed very easily from the cranium. Hyaline and opaque zones were shown clearly without grinding or sectioning. The opaque zones were very narrow and shown as opaque lines. Otoliths preserved in 15 % buffered formalin for some months were sufficiently readable. Ring marks on the otoliths (outer margins of opaque zones) formed once a year in June or July. Because such months coincided with the spawning period of the fish, the number of ring marks on the otolith represented the full age of the fish.Ring marks on the longitudinal sections of the centra were very obscure, and lack of ring marks frequently appeared. Zonation of the opercle was extremely indistinct. The supraoccipital crest had distinct hyaline and opaque zonss, but only two opaque zones could be recognized in any large fish. From such observations, the author concluded that only scales and otoliths could be used for age determination of this species among those five hard tissues. The otolith was more suitable than the scale because the ring marks were showndistinctly even for older specimens, and lack or duplication of ring marks were very few. From otolith reading, average length growth of the fish was expressed by the following eduation : Lt = 357.5(1-exp (-0.2855( t +0.2909))), where L = fork length in mm and t =full age. Range of the length growth was estimatedby the mean values and standard deviations of calculated fork lengths at the time of each ring formation. The growth for about 95% of the fish was within the limits of the following two equations : Lt = 362.1(1-exp (-0.3377( t +0.3622)))) and Lt = 355.8(1-exp (-0.2427( t +0.1283))). The length growth was more rapid during the months frorn August to October than the other months. The growth compensation was obsered in the growths of 2‐ to 4‐age‐groups. The early length growths were estimated from rearing experiments and these were expressed by the followilg two equations : TL=0.00986t2 + 0.0734t + 2.43(t≦30) and TL=324(1-exp (-0.00983(0.127t+5.26+8.53 sin (0.0172 t -20.0))))(t>30),where TL = total length in mm and t = days after hatching.4. Age Composition, Survival Rate, and Natural Mortality Coefficient Age composition of the threeline grunt caught with hook and line was estimated by otolith reading for the sampled fish, by analyzing the polymodal frequency distribution of the fork length, by solving simultaneous equations based on the length compositions of each age-group and the length composition of commercial catch, and by an iterative calculation method based on the market size or length compositions of each age-group and the length cornposition of commercial catch. Good results were obtained by otolith reading and the iterative caluculation methods. Survival rate was estimated at 0.25 from the age composition of the fish by LEA's (1930) and DOI's (1975) methods. Natural mortality cosfficient was calculated at 0.5-0.6 by DOI's (1977) and PAULY's (1981) methods.5. Maturity and SpawningThe larger half of speciments had a pair of gonads bilaterally asymmetrical in weight. Of these, the speciments with dextral gonads dominated over the specimens with sinistral ones. The developement or maturity of ovarian eggs proceeded uniformly throughout the ovary. According to the degreee in advancement toward ripeness, the ovarin eggs were divided into the following nine stages ; (1) peripheral nuleolus stage, (2) yolk vesicle stage, (3) early yolk globule stage, (4) middle yolk globule stage, (5) later yolk globule stage, (6) migrating nucleus stage, (7) pre-maturation stage, (8) maturation stage, (9) ripe egg stage. The ovarian eggs at peripheral nucleolus and yolk vesicle stages were present throughout the year in the ovaries of the groups older than age2. The eggs at yolk globule stages or more mature stages appeared during the period from May to August, especially the eggs at migrating nucleus stages or more mature stages were found only in June in 2-age- group and between June and August in the groups aged older than 3. From the histological observation, the process of testicular maturation was divided into the following four phases ; (1) preparative phase : the testis was occupied mainly by spermatogonia, (2) spermatogenesis phase : primary and secondary spermatocytes were dominant in the testis, (3) discharging phase : spermatozoa filled up in the testis, (4) resorptive phase : spermatozoa resorbed by the seminiferous epithelial layer. The testes of such phases appeared in the following months ; (1) preparative phase : December or January to April, (2)spermatogenesis phase : April and May, (3) discharging phase : June to August, (4) resorptive phase : September to December. The spawning season began in early June, and continued until mid-August. The younger fish (2- and 3- age-groups) finished their spawning earlier than the older ones. The water temperature of the spawning ground ranged from 20 to 28℃. The time of actual spawning in a day usually fell at around eight p.m. The group maturity rates of both sexes for each age-group were estimated as follows ; 1-age-group : 0% in both sexes, 2-age-group : 43% in females and 83% in males, 3-age-group : 95% in females and 100% in males, 4- to 8-age-groups : 100% in both sexes. The biological minimum sizes were about 160 mm in fork length in females and about 150mm in males. The sex ratio of males to females declined with their growth, and this charge was attributable to the difference of the survival rates between both sexes. The percentage occurrence of females in each age-group (Pf) were expressed by the following equation : Pf = 100/(1+1.921・0.788t), where t = age. The number of eggs spawned in a year by a single female ( = fertility) was estimated from the difference of the ovary weight between samples of pre-spawning and spent conditions. The fertility (Fe) was given by the following equaion: Fe = 4.759L5.281・10-8, where L = fork length in mm. The total amount of eggs spawned by the 3-age-group was the largest among the all age-groups. 6. Feeding Habits Empty stomachs occurred more frequently in the samples collected with hook and line than in those with set nets. The feeding activity was intense during the period from May to September, and declined after October. Main foods of the adult and subadult fish, larger than 100 mm in fork length, were clupeoid fishes ( Spratelloides gracilis, Sardinops melanostictus, Engraulis japonicus, etc. ), but crustaceans also were fed on abundantiy in March, June, November, and December. Clupeoid fishes appeared as the prey animal in almost all seasons. In crustaceans, copepods chiefly appeared in spring and autumn, while amphipods in sumrner. Postflexion larvae fed on only copepodspecies (Corycaeus spp., copepodid larvae, etc. ). Juveniles became to feed on branchiopods and larval bivalves in addition to copepods. The main foods of young were an arrow worm Sagitta sp., copepods (Eucalanus spp., etc.), larvaldecapods (mysis and zoea larvae, etc), protochordates (Oikopleura dioica, etc.), and larval anchovy Engraulis japonicus. Maximum value of the size preference (αmax=PLmax / L, where L = fork length of the predator and PL.max = maximum size of the prey animal) was 58% in the fish of 50 to 100 mm in fork length. The value of αmax decreased with growth for the fish larger than 100 mm. This value of the threeline grunt was fairly smaller than that of a piscivorous fish as theJapanese bluefish Scombrops boops. Maximum amount of food ingested (Fmax) was given by the following equation : log Fmax=0.842 log W-1.026, where W = body weight in g. The amount of ingestion was positively related to the water temperature. There was a little decrement of the amount of ingestion according to the gonadal development. The gastric emptying rate tended to increase with rising environmental temperature, while the rate varied inversely with the size of fish. The feeding and digestive organs (teeth, jaws, gill rakers, stomach, pyloric caeca, and intestine) of this species were less specialized owing to its unspecialized feeding habits. But the needle ‐like processes on the gill rakers ( = secondary gill rakers) were well developed, and they enabled the fish with only a small number of gill rakers to feed on such small crustaceans as copepods.7. Artificial Spawn TakingSpawning was observed twenty times or more during the period from early June to mid ‐July. It was possible to collect the fertilized eggs from non‐reared parental fish. Even injection of gonadotropin (HCG) took no recognizable effect.Hatching rate usually ranged from 50 to 100 %. The rate was significantly related to the ratio of floating eggs and inversely to the coefficient of variance of the egg diameter. Accordingly, the ratio and the coefficient of variance could be indicators appraising the quality of eggs spawned. The hatching rate was inversely related to the areal density of the eggs in a hatching vessel, but the rate independent of the areal density within less than 20 eggs/cm2 and of the voluminaldensity of eggs in the vessel.Optimum temperature and salinity for hatching were estimated at 22.6 ℃ and34.2‰, respectively. The relationship between the hatching rate(Hr,%), temperature (T,℃)and salinity (S,‰) was expressed by the following equation : Hr = -1.984 T2 - 4.125 S2 + 70.92 T + 269.9 S - 0.5475 TS - 530. The total effective temperature ((T - T0) Ht, where Ht = time to hatching in h, T = water temperature in ℃, and T0 = biological zero in ℃ ) was almost constant within the limits of water temperature ranging from 18 to 28 ℃. Consequently, incubation time was given by the following equation : Ht = 241.5/(T-13.2).The weight growth curve for the juvenile and young stages was expressed by the following equation : W = 449 (1-exp (-0.00983 (0.127t + 5.26 + 8.53 sin(0.0172t - 20.0))))3.07, where W = body weight in g and t = days after hatching.8. Embryonic, Larval and Juvenile DevelopmentFertilized eggs, measuring 0.78 ‐ 0.85 mm in diameter, were buoyant, spherical, and transparent. The yolk was segmented partly and contained a single oil globule. Hatching oocurred at 28 to 30 h after spawning when incubation temperatures ranged from 20.5 to 21.5 ℃. Total lengths (TL) of newly hatched larvae ranged from 1.50 to 1.65 mm. In yolk‐sac larvae, a single oil globule rested on infra‐posterior portion of the yolk sac, the anus opened away from the yolk, and xanthophores developed on the dorsal and anal margins of the finfold. The yolk and oil globule completely absorbed in three or four days after hatching, and the larvae became preflexlon stage. The notochord flexed at about 5.5 mmTL in 19 days after hatching. Aggregate numbers of all finrays were completed at about 12 mm TL, and they became juveniles. Squamation was almost finished in specimens of about 35 mm TL, and they changed to the young. Specific longitudinal bands started to form in the juvenile stage and completed in the young stage. The bands appeared in smaller specimens of reared juveniles than those of wild ones. There was little difference in the relative growths of some body parts between reared juveniles and wild ones. The larvae and juveniles of the threeline grunt bore close resemblance to those of Haemulon pulmieri and Orthopristis chrysoptera rather than those of Plectorhynchus pictus and P.cinctus.The anlages of each fin formed at 6 mm TL (dorsal and anal), at about 4 mm (caudal), at about 2.8 mm (pectoral), and at about 8mm (pelvic). Aggregate numbers of all finrays and the numbers of fin spines were completed at 12 mm TL and 18 mm, respectively. Segmentation of the softrays occurred at 9 to 17 mm TL in dorsal fin, at 8.5 to 15 mm in anal fin, at 6.4 to 9.6 mm in caudal fin, at 9.5 to 60 mm in pectoral fin, and 12 to 16 mm in pelvic fin. Branching of the softrays was observed at 24 to 130 mm TL in dorsal fin, at 20 to 140 mm in anal fin, at 12 to 18 mm in caudal fin, at 24 to 130 mm in the pectoral fin, and at 14 to 34 mm in pelvic fin. Scales appeared at about 16 mm TL. The head and body except the snoutwere almost covered with scales when juveniles attained to about 35 mm. The snout was covered by scales and squamation was completed perfectly at about 130 to 140 mm. Convolution of the alimentary canal started at about 3.1 mm TL and finished at 3.7mm. The pyloric caeca formed at about 12.7 mm, and completed in number at about 22.5 mm.9. Stock AssessmentBased on the above data, the present parameters of the threeline grunt stock at the coast of Sakishima Peninsula were estimated as follows : natural mortality coefficient(M) = 0.6 , survival rate(S) = 0.25, total mortality coefficient (Z) = 1.39, fishing mortality coefficient (F) = 0.79, rate of exploitation (E) = 0.504, and availability of 1-age-group (Q) = 0.058, catch in number for 1‐ to 8‐age‐groups (C) = 1,275,400, fishable population size in number for 1- to 8‐age-groups (Nc) = 2,966,000, population size in number for 1-age‐group (N1) = 3,861,500, and total population size in number for 1‐to 8‐age-groups (N) = 6,603,500. From the stock size estimates, the population size of mature females and total number of eggs spawned in the present stock decreased to 41.2 % and 16.4% of those in unexploited stock, respectively. Accordingly, it seemed that the present fishing intensity more or less exceeded the optimum level. And further, such two methods as reducing the fishing effort to 3690 boat・day in a year, and rising the length at first capture to 17 ‐ 18 cm in fork length, were conceived in order to manage the stock at the optimum level.

著者

小林 裕 Kobayashi Hiroshi

出版者

三重大学水産学部

雑誌

三重大学水産学部研究報告 (ISSN:02875772)

巻号頁・発行日

no.13, pp.p25-133, 1986-11

被引用文献数

1

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この研究は,深海性サメ類と深海底延縄との関わり,および,分布と生態的な特性を解明するため,熊野灘海域(本州南東岸)において、主として底延縄による漁獲試験を行い,つぎの諸点を明らかにした。1.漁獲試験を行った水域は,長鳥沖,尾鷲沖,および,阿田和沖に存在する海底谷,あるいは,その近傍を主とする水域(3漁場)である。これらの海域の深海(200~1100m)における海洋環境(水温,塩分量)は,周年安定していて,漁場間の相遵もきわめて微少である。また,溶存酸素極小層の酸素量は,1.6~1.7mL/Lで1500mに至ると約2.1mL/Lまで増加する。長島沖,および,尾鷲沖漁場の海底地形は,海底谷をやや離れた比較的平坦な水域であったが,阿田和沖漁場は海底谷の真上,および,その近傍の海底傾斜の急峻な凸凹のある複雑な水域であった。海底を覆う底質は3漁場とも細かい砂を含んだ泥土であった。2.底延縄の海底における縄成り(枝縄の水中形状)は,漁具性能を決定する重要な要素の一つであり,浮子とロープの浮力,その海水抵抗,沈子の固定力とその流水抵抗,および,海底における流速などによって決まる。理論計算の結果,枝縄は,海底においてほぼ直立状態にあると考えてよいことが分かった。3.この研究によって,熊野灘海域から生息が確認された底層性サメ類は,これまでに,この海域から確認されている種,この海域で初めての種,稀にしか漁獲されない種など8科20属31種(底延縄が3科10属19種,底刺網が7科13属17種)に達した。これらの中から,ツノザメ科サメ類9属18種を,これまでに,他海域(銚子沖と駿河湾)において記録されているツノザメSqualidae科のサメ類(TANIUCHI、田中、TANAKA,YANO and TANAKA)と比較すると,隣接海域の共通性は駿河湾を挟さんだ銚子沖と熊野灘海域の共通性に比べて高い。4.長島沖,および,尾鷲沖漁場ではへラツノザメDeania calceaが,阿田和沖漁場ではタロウザメ Centrophorus acus が最も多獲され最優占種の地位にある。漁場によって第2優占種以下の種が異なる。種組成を類似度指数Cλ(Morisita)を適用し比較すると,長島沖漁場と尾鷲沖漁場の類似性はきわめて高い。しかし,これらの2漁場と阿田和沖漁場の類似性は低く,サメ類相は種組成においても量的組成においても明瞭な相違がある。5.底層性サメ類(主としてツノザメ Squalidae 科のサメ類)の深度別釣獲率(分布)を種に関係なくみると,どの漁場においても釣獲率の一つのピークが,300~500mに存在する。この深度を越えると漸次減少傾向に移行するが再び増加し,長島沖漁場では,1000mを超える深海に,きわめて高い釣獲率域の存在が確認された。これは1000m以探における高い密度域の存在の示唆と考える。また,魚種組成は異なるが釣獲率の変化傾向は,どの漁場においてもほぼ同じであった。さらに,この結果はインド洋西部で Foster et al. が,行った漁獲試験結果とよく対応する。釣獲率を種別にみると,分布水域は種間で重なりを持つが,高釣獲率域は,種によって異なり,多獲される種は,漁場と深度によって特定される。また,漁獲種数は深度によって異なる。これらの結果は、深度によってサメ類相が質的にも量的にも相適することを示すものと考える。6.タロウザメ Centrophorus acus は、等深線の尾根付近の比較的傾斜の緩やかな水域を,モミジザメ Centrophorus squamosus は海底谷の傾斜の急峻な水域を主分布域とする。両種の混獲関係には,負の相関性が認められた。また,フトカラスザメ Etmopterus priceps とニセカラスザメ Etmopterus unicolor とは,分布の重なりは全くなく,明瞭にすみ分けていることが分かった。さらに,タロウザメ C. acus は、海底地形の急峻な水域で,へラツノザメ Deania calcea は比較的平坦な水域で多獲され生息域に地形的な相違があることが分かった。このように,深海性サメ頬は、地形や深度によって独自の生活場所を形成している。7.延縄に沿った漁獲傾向を調べた結果,一回の操業で延縄が敷設された限られた水域における,深海性サメ類の水平的な分布のパターンは,ランダム分布で近似できるが,種によって所々に濃密な分布域が存在することが分かった。8.枝縄に沿った漁獲傾向から,深海性サメ類は,必ずしも,常に着底生活を営むものでないこと,どのサメ類も海底から,10数メートルを越えて上昇し摂餌していることが推定された。9.海洋環境と漁獲の関係を検討した結果,深海性サメ類の海洋環境への適応の幅は,比較的広いことが推定された。また,タロウザメ C.acus, へラツノザメ D.calcea, および,カラスザメ E.pusillusなどの探海性サメ類は,急激な海洋環境の変化に対する耐性が強いことが推定された。 このような特性を持つ深海性サメ域の構成種を,制限し決定する要因の一つとして,海洋環境が,強く関与しているとは考えにくい。地形的な相遼が結果したものと考えられる。10.夜縄と昼縄の漁獲を比較したところ,釣獲率は昼縄に比べて夜縄の方が著しく高い。この結果は,深海性サメ類の摂餌活動が,昼間より夜間に活発化することの現われであり,夜間に摂餌活動が活発化する種の多いことを物語る。11.深海性サメ類の加害生物は,食害の痕跡から腐食性生物(Scavenger)が目立つ。サメ類も加害魚として関わりを持つ。しかし,サメ類の漁獲と食害魚との間に相関性を認めることばできなかった。これは,サメ類が食害を受けにくいことを示すものと考える。サメ類の食害率は,低く平均5.2%であった。12.生物調査結果 a.フジクジラ E.lucifer,および,へラツノザメ D.calcea の全長組成のモードの位置は,雌雄で明らかに相違(雌の方が大型である)する。また,タロウザメ C.acus,モミジザメ C.squamosus,へラツノザメ D.calcea,ニセカラスザメ E.unicolor,および,ビロウドザメ S..squamosus では,複数の位置にモードがみられ,モードの位置より小さい側で漁獲個体数が少ない。これは,漁具の選択性によるものと考えられる。へラザメ A platyrhynchus とフトカラスザメ E. princeps は資料が少なくモードの位置は明確でない。 b.全長と体重の問には,明瞭な曲線関係が存在する。両者の関係は,Table14の通りである。へラツノザメ D.calceaの雌では,調査した月(5月と10月)によって体重の相違が認められたが,どの種についても全長と体重関係の調査月による相違は肯定できなかった。 C.肝重比(体重と肝臓重量の比)は種によって異なる。また,同種であっても個体間のバラツキが大きい。へラザメ A platyrhynchus の平均肝重比は10%に満たない。フジクジラ E.lucifer は約12~13%であるが,アイザメ Centrophorus 属のサメ類では20数%に達し,この海域で漁獲されたツノザメ Squalidae 科のサメ類の申で最も大きい。サメ類の肝臓機能(Baldridge,Castro,Compagno)を考えると,肝重比の大小は,種による行動能力の強弱を強く反映しているものと考える。また,へラツノザメ D.calceaとフジクジラ E.luciferの肝重比は,明らかに調査した月によって相違が認められた(Fig.32参照)。 d.胃内容物の目視観察を行った結果、深海性サメ類は,底層を基盤として生活するサメ類であるが,底層から表層付近に至る幅広い生物を捕食していた。アイザメ Centrophorus属のサメ類,および,へラツノザメ D.calceaからは,表層および中層性の魚類が観察された。落下物を捕食した可能性もあるが,これらのサメ類の肝重比は大きく,行動能力との関連が考えられる。 e.一般に,この海域で漁獲されたサメ類の性成熟の大きさは雌の方が大きい。フジクジラ E.lucifer,および,ニセカラスザメ E.unicolorなどで明瞭な相違が認められた。年を通してみた,この海域における大部分のツノザメ Squalidae 科のサメ類の性比は1:1であるが,へラツノザメD.calceaとフジクジラE.luciferでは調査した月によって違いが認められた。 繁殖生態に関する調査と観察の結果,オシザメ P.microdonlの産仔様式が非胎盤性胎生(卵胎生)であること,胎抒の栄養吸収方は卵食性でないことが確認された。 また,交接器,子宮,生殖巣を観察した結果,タロウザメC.acus,および,モミジザメ C.squamosusは,未熟個体に限られた。大部分のへラツノザメ D.calceaは未熟であったが,成熟した雌2個体が確認された。へラザメA platyrhynchus(卵性)の輸卵管内には周年卵殻が観察された。また,フジクジラE.luciferは8月に胎仔が,どの季節にも大型卵巣卵,子宮内下降卵が観察された。ニセカラスザメ E.unicolorでは4月に胎仔が,5月と10月に大型卵巣卵が観察された。これらのサメ類の雄の精巣は膨大していて,周年精液が確認された。このように,種によって繁殖生態の一端を知ることができたが,多くの種については,断片的な資料にとどまり,多くの未解明な事項がのこされた。今後の課題として他梅域を含む調査と研究が望まれる。 13.深海底延縄漁業は,他の漁業との競合が少なく,地形的制約を受けることも少ない。また,小人数で小型の船を用いて行うことができる。したがって,現在,利用度のきわめて低い熊野灘海域における深海漁場の開発とその利用は、現漁業の延長として十分考えることができる。また,深海性サメ類は,残された数少ない未利用水産資源の一つであり,その適正な漁獲と利用は,今後の地域漁業の発展を考える上に取組まなければならない重要な課題の一つと考える。This study was performed in the Kumano-nada region along the Pacific coast of Japan, mainly, by fishing tests using bottom longline, in order to clarity distribution and ecological characteristics of deep-sea shark and their relationship with deep-sea bottom longline. The following are the results obtained. 1. Areas of fishing tests are located at 5 - 15 miles lrom the coasts of Nagashima, Owase and Atawa. Marine environment (water temperature and salinity) of deep-sea in these regions (200 - 1,100m) was stable the whole year, and difference among fishing grounds were also quite small. The dissolved oxygen was 1.6 - 1.7mL/L, and it, reached to 2.1mL./L at 1,500m - depth. Bottom topgraphy of the fishing ground of Nagashima and Owase offshores was relatively plateau at a distance from a submarine valley, but the region of the fishing ground of Atawa offshore was just over the valley or over uneven steep slopes around the valley. Sea bed was covered with fine mud. 2 . Shapes of branch-lines of bottom longline on the sea bed is an impor tant facter for the evaluation of efficiencies of fishlng gear, and it is determined by buoyancy of floats and ropes, their current-resistance, the fixing power of sinker and its current-resistance and the speed of current on the sea bottom. Theoretical calculation based on our data showed that branch-lines on the sea bottom would be almost in a vertical position. 3 . Deep-sea sharks, confirmed for their inhabitation in Kumano-nada region through this study, reached to 31 species covering 24 genera of 8 families ( 3 families, 10 genera, 19 species by bottom longline and 7 families,13 genera, 17 species by bottom gill net) including known, new and rare species in this region. Among them, dogfish sharks (18 species of 9 genera)were compared with the sharks of squalidae reported so far in different region (Choshi-offshore and Suruga-Bay; Taniuchi, Tanaka and Yano ).Commonness of the species in adjoining region were high compared to those in the separated regions (Choshi and Kumano, separated by Suruga-Bay). 4 . Needle dogfish, Centrophorus acus, and birdbeak dogfish, Deania calcea, were the highest catches and the first dominant species in fishing grounds of Nagashima and Owase offshores (former species ) and Atawa offshore (latter one ), relatively. Second and less dominant species varied depending on the fishing ground. When content of the species were compared by the Morisita's Cλ fishing ground of Nagashima and Owase offshores showed quite high similarity, while Atawa offshore showed a low similarity compared to the former two grounds. Consequently, the shark biota were clearly different depending on the fishing grounds in terms of both the contents in their species and amounts. 5. Hooked-rate at different sea depths (distribution) were checked on deep-sea sharks (mainly dogfish shark ) independently of the species. A peak ofthe hooked-rate was found at 300 ~ 500m in each fishing ground. The ratio deereased gradually as the depth exceeded this level, but increased again; alayer with quite high hooked-rate was found at more than 1,000m-depths at the Nagashima fishing ground. This could be an indication that there wouldbe a layer (s) with high density of sharks under futher deepend area. These change in the depth were basically the same in all the studied fishing grounds, although the species-content was different. ln addition, these results corresponded well with another result of fishing tests of Forster et al. (1970) performed in a western area of the Indian Ocean. As regarding the species, their distribution areas were overlapping, their areas of high hooked-rate differed and the species with frequent catchingwere spesified by the fishing ground and sea depth. Catches in number regarding species and their varibility differed depending on the fishing ground. It was also found that shark biota changed with sea depth. 6. The main distribution region of needle dogfish , Centrophorus acus, was located around the axes of the valley and leafscalegulpershark, Centrophorus squamosus, were located around the ridg of countourelines, respectively. A negative correlation was found between the two species on their simaltaneous catching. Aiso, no overlap was found with regard to the distribution of great lanternshark, Etmopterus princeps, and Brown lantern shark, Etmopterus unicolor, clearly indicating their habitat segregation. Deep-sea shark, thus, were forming their habitat independent from each other by each own specific conditions of topography and depth. 7. Based on the catching tendency along the longline, it was found that spatiai distribution of deep-sea sharks on the sea bed is approximated atrandom. Based on the catching tendency along the branch-line, it was found that dogfish sharks were not always leading a bottom-clinging life; all speciesshow feeding activity asending over 10 meters from the sea bed. 8 . Results of an examination on the relationship between marine environ ments and catches indicated that the adaptation ability of deep‐sea sharksinto marine environments was relatively high. lt seems reasonable that the topographic characteristics, but not a marine envirornent, are concerned with these specific species or deep - sea shark asfactors which restricted and identified them into one group. 9. Hooked‐rate for night operation was remarkably high compared to day operation. This result indicate that feeding activity of dogfish sharks is morefrequent at night than day. 10. Scavengers were found to be the most frequent natural enemy of dogfish sharks judging from the signs of damage, in addition to some sharks as the enemy fish. No prey‐predator correlations, however, were found among caught sharks. Rate of damaged sharks was low (5.2% in average). This result seem to indicate that sharks are highly tolerant againist natural enemies. 11. Biological examination and observation a) Positions of mode or T.L.. composition were clearly different between male and female (female was bigger) in the case of birdbeak dogfish, Deania calcea and blackbelly lanternshark, Etmopterus lucifer. Two modes were observed for needle dogfish, C. acus, leafscale gulpershark, C. squamosus, birdbeak dogfish, D. calcea, brown lanternshark, E..unicolor,and velvet dogfish, Scymnodon squamulosus,.Their catches in number were low at smaller side of the mode's position, although the results could be explained as matter of selecting the rishing gear. The Position or the mode of spatularsnout catfish, Apristurus platyrhynchus, and great lanternshark, E.princeps, were unclear because of insufficient data. b) A distinct relationship on a curved line was observed between the total length and weight. The equational relationship is shown in Table 14. The relationship varied depending on the investigated months (season) in the case of birdbeak dogfish, D. calcea, and blackbelly lanternshark, E.lucifer. c) L/B (ratio of body weight to liver) was species‐dependent, but the rate fluctuated widely even among strain of the same species. Mean valuesof the L/B of spatularsnout catfish, Apristurus platyrhynchus, and blackbelly lanternshark, E..lucifer, were below 10% and 12 ~ 13%, respectively. Sharks of the genus Centrophrus showed over 20% of the rate; this was the highest value among sharks of family Squalidae which had been fished in this region. Based on the liver function of sharks (Baldridge, Castro and Compagno) the size in the L/B seemed to be reflecting strongly each species strength of action ability. In addition, obvious changes in the L/B were observed depending on the investigated month (season) in the case of birdbeak dogfish, Deania calcea, and blackbelly lanternshark, E. lucifer (see Fig.32). d) Macroscopic observation of stomach contents indicated that deep‐sea sharks were praying upon many creatures ranging from the sea bottom to the surface layer despite the fact that they were deep‐layer living sharks. Surface‐living fishes, were found in stomachs of birdbeak dogfish, D.calcea,and sharks of the genus Centrophorus. The L/B of these sharks were high, reflecting their high action abilities. e ) The size of sexual maturation was generally large in females among sharks fished in this region, and this difference was remarkable especially in blackbelly lanternshark, E. lucifer, and brown lanternshark, E..unicolor.Most sharks of fhe family Squalidae in this region showed a sex ratio of 1: 1 for a whole year, although some monthly (season) variations were found in bridbeak dogfish, D. calcea, and blackbelly lanternshark, E..lucifer. The mode of reproduction of false catshark, Pseudotriakis micrdon, was the mode of non-placental type and the nutritional type of embryo was not oophagous. Observation of the clasper, uterus and sexual gland confirmed that all the examined strains of needle dogfish, C. acus, and leafscale gulpershark, C.squamosus, were immature. Most birdbeak dogfish, D. calcea, were immature, and only two matured females were observed. The egg case was observed for a whole year in the oviduct of spatularsnout catshark, Apristurus platyrhynchus, (oviparous ). In the case of blackbelly lanternshark, E. lucifer, embryo was found in Augast and large ovarian eggs and fertilized eggs were observed for a whole year. In the case of brown lanternshark, E. unicolor, an embryo and large ovarian eggs were observed in April and in May and October, respectively. Testis of the male of these sharks was swelling, and seminal fluides were observed for a whole year. But the data on most species were still fragmentary. In order to fulfill these unsettled term, further studies are required expanding the investigation regions. 12. Bottom longline in the deep-sea has very little competitions with other fisheries, topographic limitations are negligible and it can be performed bya small number of people using a small boat. Therefore, development and application of deep-sea fishing ground in the Kumano-nada region, which has very little utility value at present, can be considered as an extention of present fisheries. Since deep-sea sharks are one of the few remaining fisheries resources undeveroped, proper fishing control and application will be the important subjects we have to solve considering future developments of local fisheries.

著者

上野 隆二 奥村 雅人 阪中 和紀 堀口 吉重 Ueno Ryuji Okumura Masato Sakanaka Kazuki Horiguchi Yoshishige

出版者

三重大学水産学部

雑誌

三重大学水産学部研究報告 (ISSN:02875772)

巻号頁・発行日

no.12, pp.p167-173, 1985-10

被引用文献数

1

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我が国の魚介類養殖の発展に従って、発生する種々の疾柄を防御、治療するため多様な水産用薬品が用いられている。その様な薬品が、食品としての魚介類の体内に蓄積した場合、人間におよぼす影響は食品の品質こおいては言うまでもな〈、栄養学上、食品衛生学上重要な問題と言わざるを得ない。本研究は、食品としての魚介類を対象とし、それらの微量汚染物質の体内残留について検討し、前報(上野ら1984)では養殖ウナギのホルマリン薬浴による体内残留について報告した。そこで、本研究では、アユ、ウナギのビブリオ菌感染症の治療薬として用いられるミロキサシンを、試験的に餐殖ブリに経口投与した場合の体内残留および残留期間について、高速液体クロマトグラフィー(HPLC)を用いて検討した。The present work was undertaken to investigate the residue of miloxacin,5,8-dihydro-5-methoxy-8-oxo-2H-1,3-dioxolo(4,5-g) quinoline-7- carboxylic acid, in the tissues of cultured yellowtail,Serioa quinqueradiata, by oral administration.The concentration of miloxacin and its metabolites,M-1,5,8-dihydro-8-oxo-2H-1,3-dioxolo(4,5-g) quinoline-7-carboxylic acid, and M-2,1,4-dihydro-7-hydroxy-1,6-dimethoxy-4-oxoquinoline-3-carboxylic acid, were determined by high performance liquid chromatography. The recovery of miloxacin was 87,83 and 84% from the muscle, liver and blood, respectively. The maximum levels in these tissues were reached within 3 hours after administration of miloxacin at 10 and 40 mg/kg,and no miloxacin could be detected within 3 days following administration.Only one of the metabolites,M-1, was found in these tissues and still remained in the liver for 7 days after administration of miloxacin at 10 and 40 mg/kg.

著者

森 浩一郎 船越 進 Mori Koichiro Funakoshi Susumu

出版者

三重大学水産学部

雑誌

三重大学水産学部研究報告 (ISSN:02875772)

巻号頁・発行日

no.8, pp.p97-106, 1981-10

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The present authors have made taxonomical and ecological investigations of the white fish, Salangichthy microdon BLEEKER, in spawning period. The material for this study was collected at Akasuka, Kuwana City, located in the mouth of the Nagara River, during the period of February to April in 1980. The results obtained are summarized as follows. The present specimens were identified as Salangichthys microdon BLEEKER, because of having such specific characteristics as 12~13 dorsal fin rays, 25~27 anal fin rays,14~17 pectoral fin rays, 17~18 anal scales in male, 11~16 mandibular teeth and 7~11 palatine teeth. From the results of the examination of body length, it can be said that males usually exceed females in body length. The range of body length is 60.1~85.3 ㎜ in males and 61.5~79.5 ㎜ in females, and the mean value of the same is 78.6 ㎜ in males and 73.7㎜ in females. The mode of body length in males is 74~76 ㎜ and that in females 68~70㎜. The rerationships between body length (L in ㎜) and body weight (W in g) in males and females are expressed by the following equations : log W = 3.00 log L-5.31 ( r = 0.90) for male, log W = 3.03 log L-5.44( r = 0.87) for females. The condition factors (W/L3 × 106) in seasonal change ranges 4.67~ 5.22 in males and 3.57~4.48 in females, and the values appear somewhat higher in males.The mean value of the gonad indexes (GI=GW/L3×107); GW , gonad weight in g) is 0.124~0.252 in males and 6.21~15.17 in females, and any characteristic tendency was not recognized in the seasonal changes of gonad indexes. The mean value of the egg diameter measured by the season ranges 0.75~0.93 ㎜ with the excepiton of the case in February 19 , the value showed a tendency to somewhat decrease toward the end of the fishing period. Although the number of the ovarian eggs is 153 ~2,040 and largely varies among individuals, no significant correlation between the number of eggs and body length was recognized. Regarding the food of the white fishes, Calanus cinicus is predominantly found in their digestive tract. That Calanus cinicus, one of the marine copepods, is abundantly distributed in the saline bottom waters in the mouth of the Nagara River from November to February.著者等はシラウオについて分類学的検討、および生態学的研究を行い概略次のような結果を得た。なお本研究材料は1980年2月~4月の期間、長良川河口域で計9回の採集により得たものである。本研究で取扱った魚は、背鰭条数12~13、臀鰭条数25~27、胸鰭条数14~17、雄の臀鰭鱗数17~18、下顎歯数11~16、口蓋歯数7~11と計測されたので、Salangichthys microdon BLEEKER と同定された。体長組成の研究結果よりみて、雄の方が体長が大きい。すなわち雄の体長範囲は61.5~85.3mm、雌のそれは61.5~79.5mm、また、平均体長は雄で78.6mm、雌では73.7mmである。また雄の体長のモードは74~76mm、雌のそれは68~70mmであった。また、体長の頻度分布をみれば、雌雄ともに単一のモードを構成し、同一年齢群であると考えられる。体長(L)-体重(W)関係をあらわす場合、雌雄はそれぞれ次式であらわされる。雄:log W=3.00 log L-5.31 (r=0.90) 雌:log W=3.03 log L-5.44 (r=0.87) 肥満度の時期的変化をみてみると、雄では4.67~5.22、雌では3.57~4.48の間で変化し、雄の方がやや大きい値を示した。生殖腺指数の平均値は雄では0.124~0.252、雌では6.21~15.17であり、その時期的変化には特徴ある傾向は認められなかった。各時期別の卵の平均長径は0.75~0.93mmであり、2月19日の場合を例外として、終漁期に向ってやや下降する傾向がある。卵巣内の卵数は153~2,040で、大きく変化し個体による差が大きい。また孕卵数と体長、体重との相関関係は認められなかった。産卵期のシラウオの摂飼活動は、その消化管内容物の種類と量よりみて、不活潑であるといえよう。また捕食された餌料生物中では海産橈脚類の Calanus sinicus が卓越していた。この種は11月から2月にかけて長良川河口水域の塩分の濃い低層水中に多数分布することが知られている。

著者

木村 清志 中村 行延 有瀧 真人 木村 文子 森 浩一郎 鈴木 清 Kimura Seishi Nakamura Yukinobu Aritaki Masato Kimura Fumiko Mori Koichiro Suzuki Kiyoshi

出版者

三重大学水産学部

雑誌

三重大学水産学部研究報告 (ISSN:02875772)

巻号頁・発行日

no.10, pp.p71-93, 1983-10

被引用文献数

3

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1980年4月から1982年5月までの期間に,三重県英虞湾湾口部のアマモ場で,ビームトロールにより魚類の採集を行い,このアマモ場の魚類相とその季節的変化について,次のような結果を得た。1. 採集された魚類は13目53料117種27,293個体であった。個体数はゴンズイ,ギンポ,アミメハギ,ハオコゼ,ヨウジウオ,アナハゼの順に多く,この6種で全体の8割程度を占める。 2.各魚種の出現状態から,これらを周年定住種,季節的定住種、偶発種に分け,さらにいくつかのグループ,サブグループに細分した。 3. 種数は夏から秋に増加し,冬に減少する。4. 個体数のピークは5,6月,8月,10,11月,1,2月の年4回みられ,これらほスジハゼ,アミメハギ,ハオコゼ,アナハゼ,アサヒアナハゼ,ゴンズイ,ギンポ,サビハゼ,カワハギなどの変動に起因している。 5. このアマモ場の魚類相は,ヨウジウオ,ハオコゼ,アミメハギの周年にわたる出現,冬から春のギンポ,アナハゼ,6月のサビハゼ,8月のゴンズイの大量出現,夏から秋にかけてのベラ料やヒメジ科魚類の多種にわたる出現によって特徴づけられる。このような魚類相は暖流外海性の特徴で,黒潮沿岸各地のアマモ場の魚類相と共通性が高い。しかし,一方でほそれぞれのアマモ場の魚類相には特異性もみられる。 6. ギンポの大量出現ほ伊勢湾周辺のアマモ場の特徴である。 7. 英虞湾湾口部のアマモ場では有用椎幼魚の出現比率が低い。したがって魚類生産に関する限り,このアマモ場の水産的価値は小さいと判断される。Fish fauna of the Zostera bed at the mouth of Ago Bay, Mie Prefecture were studied by monthly samplings with a small beam trawl from April 1980 to March 1981 and from June 1981 to May 1982. The results obtained are summarized as follows : 1 ) 27,293 individuals (13 orders, 53 families, 117 species ) were collected in the Zostera bed. Plotosus lineatus, Enedrias nebulosus, Rudarius ercodes, Hypodytes rubripinnis, Syngnathus schlegeli,and Pseudoblennius percoides were dominant species. About 80 percent of the specimens collected belonged to these six species. 2 ) Each species of fish collected was divided into three categories, i. e. residents, seasonal residents, and casual species. Residents and seasonal residents were subdivided into a few of groups and subgroups as follows : (I) Residents ; fishes appearing in the Zostera bed all the year round. Group A ; fishes residing during the major part of their life cycle, and using the Zostera bed as their nursery, feeding and spawning grounds. Group B ; fishes inhabiting mainly during juvenile stage, and using the Zostera bed principally as a nursery ground. Group C ; fishes inhabiting chiefly during adult and subadult stages, and using the Zostera bed primarily as a feeding ground. Group D ; fishes universally distributed in the bay and commonly appearing in the Zostera bed. Group E ; fishes which may reside during all seasons in a very small number in the Zostera bed. (II) Seasonal residents ; fishes which spend a certain definite season in the Zostera bed. Group F ; fishes residing during juvenile and young stages and using the Zostera bed only as a nursery ground. Subgroup a ; fishes which spend a long perid of time ( more than four months) in the Zostera bed. Subgroup b ; fishes which spend a short period of time ( less than three months) in the Zostera bed. Group G ; fishes residing from juvenile to adult or subadult stages. Subgroup c ; fishes which inhabit the Zostera bed in a large number, and which use the Zostera bed as nursery, feeding, and spawning grounds. Subgroup d ; fishes which reside in the Zostera bed principally as a nursery ground. (III) Casual species ; fishes appearing casually in the Zostera bed. 3 ) Number of species increased from summer to autumn by recruitment of juveniles belonging to seasonal residents and casual species, and then decreased in winter. 4 ) Total number of individuals increased in May or June, August, October or November, and January or February. This fluctuation was caused by seasonal changes of populations of the following nine species ; Acentrogobius pflaumi, Rudarius ercodes, Hypodytes rubripinnis, Pseudoblennius percoides, P. cottoides, Plotosus lineatus, Enedrias nebulosus, Sagamia geneionema, and Stephanolepis cirrhifer. 5 ) The fish fauna of the Zostera bed at the mouth of Ago Bay was chracterized by the following : ( 1 ) Syngnathus schlegeli, Hypodytes rubripinnis, and Rudarius ercodes residing all year round. ( 2 ) Appearance in great number of Enedrias nebulosus and Pseudoblennius percoides from winter to spring, of Sagamia geneionema in June, and of Plotosus lineatus in August. ( 3 ) Subsistence of many species of fishes belonging to Labridae and Mullidae from summer to autumn. 6 ) Appearance of Enedrias nebulosus in large number was a peculiar feature of the fish fauna of the Zostera bed in and around Ise Bay, central Japan. 7 ) As far as the fish production in concerned, the Zostera bed at the mouth of Ago Bay had little significance for inshore fishery because there the juveniles of useful fishes were very few.

著者

木村 清志 有滝 真人 Kimura Seishi Aritaki Masato

出版者

三重大学水産学部

雑誌

三重大学水産学部研究報告 (ISSN:02875772)

巻号頁・発行日

no.12, pp.p181-192, 1985-10

被引用文献数

4

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1983年と1984年に三重大学水産学部附属水産実験所において,イサキの水槽内自然産卵に関する実験を行い,次のような結果を得た。1.産卵は6月上旬から7月中旬までの期間に20数回行われた。また,本種の場合は,漁獲直後の親魚から採卵することが可能であった。2.産卵行動の観察などから,本種の産卵時刻を19時から21時であると推定した。3.雌体重1g当りの産卵数は約500粒であった。4.卵径は0.76~0.87mm(平均0.815,標準偏差0.021)で,産卵終期の高水温期には小さくなる傾向がみられた。油球径は0.16~0.21mm(平均0.190,標準偏差0.008)で,卵径と正相関が認められた。5.孵化率は通常50~100%であった。孵化率と水温 卵径,産卵数との関係に有意性は認められなかった。孵化率と浮上卵率および卵径の標準偏差との関係では有意な相関が認められる場合もあった。6.胎盤性性腺刺激ホルモンは,畜養親魚を用いる限り,有効性は認められなかった。7.孵化率は卵収容容器の表面積に対する密度と逆相関するが,20粒/cm2以下の範囲では,密度の影響を受けなかった。The present report with the natural spawning in tanks of the threeline grunt, Parapristipoma trilineatum (Pisces: Perciformes: Haemulidae). The experiments were carried out at the Fisheries Reserch Laboratory,Mie University in 1983(Group A) and 1984(Group B and C). The majority of Group A and minorities of Group B and C were caught by hand line a few days before the experiments.The other parental fish were reared in a net cage for one year or more.The fish of Group A and B were injected in the epaxial musculature with gonadotropin(HCG) in order to induce their spawning.The results obtained are summarized as follows: 1) Spawning were observed twenty times or more for each group during the period from early June to mid-July. 2) It was possible to collect the fertilized eggs from non-reared fish. 3) Females spawned ca. 500 eggs per 1 g body weight during the spawning season. 4) Egg diameter ranged from 0.76 to 0.87mm (av. 0.815 and s.d. 0.021) and became smaller at the end of the spawning season.Diameter of oil globule ranged from 0.16 to 0.21mm(av.0.190 and 0.008)and correlated significantly with egg diameter. 5)Hatching rate usually ranged from 50 to 100%. There were no significant relations hatching rate to water temperature, egg diameter,nor number of eggs spawned. Relationships between hatching rate and ratio of floating eggs and standerd deviation of egg diameter were significant only in Group A. 6)Effectiveness of injection of gonadotropin was not observed for reared fish. 7) Hatching rate decreased with increment of areal density of eggs within more than 20 eggs/cm². The rate was independent of voluminal density.