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アイテム
エゾアワビの種苗生産技術体系とその基礎となる生物学的研究
https://fra.repo.nii.ac.jp/records/2007425
https://fra.repo.nii.ac.jp/records/200742530226a38-f269-4b17-be7b-daca9d5cc673
| Item type | 紀要論文 / Departmental Bulletin Paper(1) | |||||
|---|---|---|---|---|---|---|
| 公開日 | 2024-06-10 | |||||
| タイトル | ||||||
| タイトル | エゾアワビの種苗生産技術体系とその基礎となる生物学的研究 | |||||
| 言語 | ja | |||||
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| 言語 | jpn | |||||
| 資源タイプ | ||||||
| 資源タイプ識別子 | http://purl.org/coar/resource_type/c_6501 | |||||
| 資源タイプ | departmental bulletin paper | |||||
| アクセス権 | ||||||
| アクセス権 | metadata only access | |||||
| アクセス権URI | http://purl.org/coar/access_right/c_14cb | |||||
| 著者 |
關, 哲夫
× 關, 哲夫 |
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| 抄録 | ||||||
| 内容記述タイプ | Abstract | |||||
| 内容記述 | Transplantation of artificially produced seeds of important fisheries species into appropriate fishing grounds have been consistently practiced in Japan with the aim of resource enhancement. So far successful results have been obtained for several species such as salmon, sea bream, black sebastes fish, Japanese scallop and kuruma shrimp. Since mortality during the early developmental stages of many marine animals is very high and their initial recruitment fluctuates, further efforts to use seed production for new species have also been enthusiastically continued. The northern Japanese abalone, Haliotis discus hannai is one of the most valuable seafoods in Japan and is historically over 2,000 tons are harvested every year. Initially the transplantation of naturally collected seed was practiced in 1960's and later artificially produced seed have been released. However the annual catch of this species has been declining year by year. Therefore a detailed analytical study on the rocky reef ecosystem and the role of the algal community as well as the qualitative improvement of seed abalone by means of a systematic improvement of seed production technology is required. Abalone seed production remained in a primitive and small scale stage for a long period. This was partly because of difficulty in planning spawning and the high mortality in the early developmental stage. A series of innovative studies, however, has enabled to ensure mature spawners are available throughout the year. This has made it possible to repeat investigations on the early developmental stages until the causes of mortality were solved. Rearing equipment and facilities for mass production such as the large scale supply system of filtered seawater and efficient design of large scale rearing tanks were also devised along with the progress in biological understanding. The objective of the present study was to establish an engineering system for abalone seed production based on the biological requirements during the early embryonic and larval stages. As a basis of this proposal, the developmental morphology, behavior and biological requirements of abalone larvae during settlement and metamorphosis were studied. Results of this study were applied to improve the technology for the abalone seed production system, and the causes of mortality during the embryonic and pelagic stages of abalone were entirely prevented by promptly providing the proper conditions required for each developmental stage. The observations and experimentation of this study were undertaken from 1970 to 1992 at both the Oyster Research Institute (Karakuwa, Motoyoshi, Miyagi, Japan) and the abalone seed producing test farm of Tohoku Hatsuden Kogyo Co. Ltd. at the electric power station site of Tohoku Electric Power Co. Ltd. (Shichigahama-cho, Miyagi, Japan). The eggs and larvae used in the observation were prepared based on the method KIKUCHI and UKI (1974a, b). Fertilization and egg washing were identical to those undertaken by SEKI and KAN-NO (1977). Juvenile abalone used in this study were produced in identical facilities as described in KUSHIMA (1974). Results are summarized as follows: 1. Morphological changes during the early developmental stage. After fertilization, embryos develop through 41 externally distinct morphological features until the fourth tubules of cephalic tentacles are formed in the veliger larvae. These morphological features and the order of their appearance are commonly observed in both H. discus and H. gigantea larvae. Externally recognized 11 features that appear following to the appearance of the cilia in the mantle cavity are confirmed to be the characteristics occurring before metamorphosis, although they were observed and reported differently in previous studies (CROFTS 1937, 1955, INO 1952, OHBA 1964) as characteristics occurring after metamorphosis. These results provide a morphological key to determine the precise developmental stage of abalone larvae and enable the preparation of proper conditions required by each developmental stage promptly. That is, the discarding of unused sperm after fertilization and the removal of egg membrane after hatchout are undertaken before decomposition occurs. The prediction of time required until the developmental stage when the larvae become suitable to be handled using sieves at the rearing seawater exchange due to the larval shell completion. As a result, most of the causes of mortality during the early embryonic and pelagic stages were removed. 2. Relationship between water temperature and developmental speed of abalone larvae. The relationship between water temperature and the developmental speed until four distinct morphological features, hatchout, larval retractor muscle, 90˚ twisting of cephalo-pedal mass during torsion, and first epipodial tentacle were determined. The biological zero temperature of early development in H. discus hannai is 7.6˚C. The developmental zero temperature obtained in the same way for H. discus and H. gigantea are 8.5˚C and 9.0˚C respectively. The approximated equation formula of required time until each developmental stage was calculated under different temperatures. Based on the formula, the appropriate timing of required treatments were adjusted during the daytime by controlling the rearing water temperature. This enabled a highly systematized management of the early developmental stage in the artificial seed production of abalone. 3. Behavior of abalone larvae at settlement and morphological changes after settlement. Abalone larvae exhibit characteristic behavior on settlement, such as exploration, inspection, and orientation movements before metamorphosis occurs, in a similar manner to many other marine invertebrate larvae. In the first phase of settlement, veliger repeatedly swim and then crawl for a period of time on various spots on the substrata. The repeated swimming and crawling in search of a favorable surface are characterized as exploration. When the larvae arrive at a favorable spot, crawling continues within the area, although the speed decreases. This behavior is characterized as inspection. After this phase, the larvae stop crawling and stay in one spot, occasionally reorientating the body position. This orientation movement continues until metamorphosis started. In the final phase of orientation, the larvae show a typical series of actions. The anterior part of the cephalic tentacles touches to the substrata surface, and the larval shell is raised at the rear. Then highly viscous mucus is secreted through the groove between velum and propodium. This mucus anchors the anterior cephalo-pedal portion of each larva firmly onto the settling spot until the larva began crawling again. The swimming veliger larvae become able to crawl at 925˚C-hours of effective accumulative temperature (EAT), when a pair of protrusions, a rudimentary snout, appeared beside the mouth opening. Subsequently, the larva became able to metamorphose at 1,030˚C-hours EAT, when the third tubules of the cephalic tentacles were formed. When the veliger formed the fourth tubules on the cephalic tentacles, further development then ceased unless the larvae encountered a favorable substrata as a settling site. During metamorphosis, 12 succeeding morphological changes occurred, beginning with discarding the velum. 4. Inducers of settlement and metamorphosis. The veliger of H. discus hannai settle on the mucus trail of four Japanese abalone species in a genus-specific manner, but did not settle on the mucus trail of three intertidal gastropods, Haloa japonica, Monodonta labio, Cantharidus jessoensis. In addition, both grazing-trail and crawling-trail mucus of abalone had a high settlement-inducing effect, whereas mucus obtained from the sole of the foot of an abalone after the sole had been irritated or scrubbed had no effect on settlement. Significant settlement occurred on a grazed algal community that was grown as a monolayer before it was grazed. The settlement inducing effect was also confirmed with several macroalgae such as Ulva pertusa, Hizikia fusiformis, Dictyopteris divaricata, Callophyllis crispata, Shizymenia dubyi, and Carpopeltis prolifera. The effects of various temperature and desiccation conditions on the relative stability of grazing-trail mucus as an inducer of settlement and metamorphosis were determined. Moderate treatments, such as 4 hours of desiccation at room temperature or 3 hours of desiccation at 65˚C, caused partial loss of the settlement-inducing effect. Autoclaving and treatment with UV light destroyed the inducing effect. However, the inducer was not affected by freezing, soaking in fresh water, or soaking in running seawater. These results provided the required conditions for settlement control and a means to maintain its efficacy. Uniform distributions of settled larvae on collectors were achieved in the abalone seed production hatchery based on these findings of the settlement inducer. 5. Required phycological conditions of the substrata surface for settlement. Growth of the algal community and the changing pattern of its composition on the abalone rearing plate surface were also studied. The filamentous type of algal community which consisted of Navicula spp. and Nitzschia spp. primarily grew on the plastic sheets in the juvenile rearing raceway. Then the algal community growing in a monolayer such as Myrionema sp., Ulvella lens, and Cocconeis spp. increased and dominated secondarily when juvenile abalone were introduced to the sheet with a primary algal community growing. The surface of the secondary algal community that increased under grazing of juvenile abalone was fully effective for settlement, metamorphosis, and initial growth of plantigrade juveniles. Settling substrata of this surface was prepared by removing the juvenile abalone from the rearing sheets. Then, diatoms of the primary algal community again increased due to the decreased grazing intensity while the newly settled juveniles were growing on the rearing sheets. These diatoms are the essential food for the further growth of the early juveniles after the functional snout with a mouth opening diameter larger than 10 μm was formed. A rational technological system to prepare effective substrata for larval settlement, metamorphosis, and later growth were thus biologically established. 6. Harmful factors for larval development and their effect. Heavy metal ions of copper and zinc can pollute the larval rearing seawater through the pipeline system in a hatchery. Concentrations higher than 50 μg/L of copper ions and 100 μg/L of zinc ions caused the loss of fertilization ability for both male and female gametes. It also causes abnormal larval shell formation and disruption of the morphogenesis of the epitherial and visceral tissues resulting in high mortalities. | |||||
| 言語 | en | |||||
| 抄録 | ||||||
| 内容記述タイプ | Abstract | |||||
| 内容記述 | 水産生物の資源を増大する方法として,人工的に生産した種苗を自然の漁場へ放流,添加することが,サケ,マダイ,クロソイ,ホタテガイ,クルマエビなどで行われ,成果を挙げている.発生の初期の段階は減耗が多く,そのために初期添加量が年によって大きく変動して,計画的生産が挙げにくい水産生物では年ごとに一層多くの種類で種苗の人工的生産や放流が行われようとしている.本研究で対象としたエゾアワビは,日本のアワビの漁獲の約半数を占め,毎年2,000トン以上漁獲される水産上重要な磯根資源である.このため,古くは移植により,また,最近では種苗の人工生産とその放流による増殖が行われている.しかし,漁獲は年々減少しており,放流の効果は必ずしも明らかでない.このため,単に放流する種苗の量を増やすばかりではなく,アワビの種苗生産の技術水準を体系的に改善して種苗の質の向上を計ることなどが求められている.アワビは種苗生産が難しい種類であるとされてきた,計画的な採卵が難しく,初期発生期の減耗が多いばかりでなく,種苗として放流が可能になる大きさに育つまで長期間の飼育が必要である。しかし,これまでのエゾアワビの一連の研究成果によって,成熟した親貝の確保が四季を通じて可能となり,初期発生期の課題について繰り返し研究することが容易になった.また,濾過器,飼育設備の開発も進み,大量の濾過海水を用いエゾアワビの種苗を量産する態勢が整っている.本研究は,エゾアワビの発生初期から初期稚貝までの発生段階の形態変化と行動生態,着底時の行動生態と着底基質との関係,初期稚貝の生育に必要な飼育用餌料板上の藻類学的条件,ならびに発生と生育を阻害した2つの事例の要因を実験的に明らかにすることによって,発生段階に応じた生育条件を明らかにし,その生態を利用して大量の種苗を生産できる体系的な技術を確立することを目的として行った.さらに,受精直後から浮遊期,着底期,底棲期のそれぞれの段階について,これまで報告されていなかった形態上の特徴,行動生態あるいは餌料藻類との相互関係を明らかにするとともに,これらの知見を応用して,種苗を生産する技術に必要な条件を実験的に検討した.本研究は1970年から1992 年の間に宮城県本吉郡唐桑町のかき研究所と宮城県宮城郡七ヶ浜町の東北電力株式会社仙台火力発電所構内の東北発電工業株式会社開発部,温排水利用アワビ種苗生産実験所の2ヵ所で行った.観察·実験に用いたアワビの卵と幼生は,菊地·浮(1974a)にしたがって成熟親貝を育成し,菊地·浮 (1974b) にしたがって産卵誘発して受精させた.媒精と洗卵の方法は関·菅野(1977)にしたがった.実験に用いたアワビ稚貝は,串間(1974)の設備ならびに飼育装置と同様のものを用いて行った.得られた主要な知見を要約すれば次の通りである。初期発生の過程と形態の変化:エゾアワビは受精後,頭部触角上に第4の小突起を形成して被面子幼生としての形態を完成するまでの発生過程で,41項目の外部形態上の特徴が認められることを示した.これらの特徴は,クロアワビおよびマダカアワビの発生でも共通して認められる.これらの形態上の特徴のうち,面盤後方の体背部から外套腔内にかけて生ずる織毛が出現した後に現れる11項目の変化はこれまでの観察では変態の開始前後にまちまちに記載されていたが,本観察により変態以前に出現する被面子幼生の特徴であることが確認された.この観察の結果,幼生の発生の進行段階を外部形態の観察によって正確に判定することができ,飼育海水の水質を悪化させる原因となっていた余分な精子や卵膜などの除去,飼育海水の交換処理を必要な段階に正確に行なうことを可能にした.これにより,浮遊期の減耗要因をほぼ完全に取り除くことができた.水温と発生速度:発生過程に見られる外部形態の特徴のうち,エゾアワビの孵化,幼生牽引筋形成,頭足部90°の捩れ,および第1上足触角形成までの4項目の特徴を形成する段階に達するまでの水温と発生速度の関係を求めた.初期発生期の生物学的零度はエゾアワビでは7.6℃であった.クロアワビ,マダカアワビで,孵化,頭足部90°の捩れ,眼点の出現までの3項目の形態上の特徴を形成するまでの水温と発生速度を求めた結果,生物学的零度はそれぞれ8.5℃および9.0℃であった.また,これらの発生段階に達するまでの所用時間と水温の近似式が得られ,水温を調節して幼生の飼育管理に必要な処置を昼間に行なう作業の工程化を可能にした。着底·変態以後の発生:被面子幼生が基質に接触してから底棲に移行し,周口殻を形成して底棲期の初期形態を備えるまでの間に,浮遊期の幼生に見られる41項目の外部形態上の変化に引き続いて,新たに12項目の形態上の変化が認められることを示した.幼生が着底基質に接触した後,面盤細胞を脱離して変態を開始するまでの間は形態上の変化を生じない。エゾアワビ幼生は,腹足類が底棲へ移行する時に共通して見られる探索,検査,定位の各行動を示し,定位行動は,幼殻後部を持ち上げ,体前方の幼殻殻縁と頭部触角先端部を基質に接して静止しながら行われることを明らかにした.吻の一部になる突起が形成される925℃·時間期から着底が可能となり,頭部触角上に第3の小突起を生ずる特徴を備えた1,030℃·時間期以降に変態を開始することが可能になることを示した.この結果,幼生を着底基盤に接触させるべき時期を正確に予測して採苗器となる着底基盤を用意し着底させることが可能となった.アワビ足蹠粘液によるエゾアワビ幼生の着底·変態の誘起:エゾアワビ被面子幼生は,腹足類が基質上を匍匐する時に分泌する粘液のうちアワビ属の匍匐跡の粘液に属特異的に選択して着底することを実験的に明らかにした.このアワビの粘液は,匍匐時あるいは摂食行動時に分泌された場合に有効であり,外界の刺激を受けて密着した場合や足蹠をこすりつけて得られた場合には無効であった.藻類の群落をアワビが摂食した跡も強い着底誘起効果を持つことも明らかにした.類似の誘引作用はアナアオサ,ヒジキ,エゾヤハズ,ヒロハノトサカモドキ,ベニスナゴおよびコメノリなどの海藻類でも認められた.アワビの摂食跡が持つエゾアワビ幼生の着底誘起効果は,65℃以上の温度や紫外線照射処理で失活したが,海水中の2日程度の保存,凍結処理,淡水処理では失活しないことを示した.この結果,幼生の着底誘起条件とその維持方法が明らかになり,短時間で均質に幼生を飼育板上に付着させる採苗技術が可能となった.着底板の藻類学的条件:アワビを飼育している水槽の餌料板上に繁殖する藻類は,アワビの存在によって次第に変化する.出現してくる植物相の付着と繁殖様式の違いから,飼育板上に立体的な群体を形成して繁殖する一次藻類群落と板表面に密着して平面的に一層に繁殖する二次藻類群落に分類できる,二次藻類は,アワビの摂食行動が旺盛に行われ歯舌による基質表面の搔き取り作用を受けながら増殖することを明らかにした.また,二次藻類の摂食跡はエゾアワビの着底·変態を誘起する好適な着底基質であり,変態後の稚貝の生育には一次藻類の摂食が重要であることを実験的に明らかにした.この結果,エゾアワビ幼生の着底誘起作用をもつ基盤を稚貝の飼育の過程で創生し,この上に着底した稚貝の良好な成長を計る人工採苗技術を可能にした。発生と生育の阻害例とその要因:銅および亜鉛イオンは,飼育海水を供給する給水系の金属材料と接して混入することがあり,過剰の場合はエゾアワビの精子,卵子の受精能力を失わせた.また,幼殻の形成を阻害し,濃度の増加と共に阻害の程度が大きくなり斃死が見られる.銅イオンは50μg/L以上,亜鉛イオンは100μg/L以上でエゾアワビの発生が阻害されることを示した,周囲に人口が多い内湾にあるアワビ種苗の生産場では,砂濾過した海水のpHが,飼育水槽に供給された時点で7.3~8.4の範囲で変化する.1978年から1991年までの14年間pHの連続測定記録を行った結果,1986年以降,日毎の pH の変化が大きく,不安定になり,藻類を餌料とするアワビの飼育水槽内を通過した後の海水のpHが,供給時よりも低くなる日が多いことを認めるようになった.この現象の発生と同調して,着底以後に珪藻類を主な餌料として飼育しているアワビ稚貝の生残率が著しく低下した。この現象は,周囲の水質汚染が進行し,飼育水槽での藻類の繁殖の阻害によって生じたものと考えた.エゾアワビの発生と生育を阻害する要因を回避するため水質管理の重要性を指摘した. | |||||
| 言語 | ja | |||||
| 書誌情報 |
ja : 東北区水産研究所研究報告 en : Bulletin of Tohoku National Fisheries Researh Institute 巻 59, p. 1-71, ページ数 71, 発行日 1997-03-31 |
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| 出版者 | ||||||
| 出版者 | 東北区水産研究所 | |||||
| 言語 | ja | |||||
| 出版者 | ||||||
| 出版者 | Tohoku National Fisheries Researh Institute | |||||
| 言語 | en | |||||
| ISSN | ||||||
| 収録物識別子タイプ | PISSN | |||||
| 収録物識別子 | 0049-402X | |||||
| 書誌レコードID | ||||||
| 収録物識別子タイプ | NCID | |||||
| 収録物識別子 | AN00167637 | |||||
| 情報源 | ||||||
| 識別子タイプ | Local | |||||
| 関連識別子 | tnf_k_59_1 | |||||
| 関連サイト | ||||||
| 識別子タイプ | URI | |||||
| 関連識別子 | https://agriknowledge.affrc.go.jp/RN/2010552816 | |||||
| 言語 | ja | |||||
| 関連名称 | 日本農学文献記事索引(agriknowledge) | |||||
