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Study on cost reduction in Skipjack pole-and-line Fishery
Full text linkSkipjack pole-and-line fishery (SPLF) is an industry that occupies an important position in the domestic fisheries industry, which aims to provide a stable supply of Skipjack for sashimi. The fishery requires safe rearing of the Japanese anchovy (Engraulis japonicus), which is used as live bait during operations, during voyages. Particularly in pelagic fishery, where fish are raised onboard fishingboat, it is customary to cool the rearing water to the optimal water temperature for Japanese anchovies, 15°C, which tends to increase the fuel cost required to cool the rearing water. Additionally, operational losses due to the lack of a stable supply of anchovies and soaring costs for live bait are also becoming major problems. In addition, fuel costs, which account for a large portion of operating costs, are soaring due to the influence of the global situation, which is causing problems for the SPLF industry.
This study is a compilation of the research results that the author has worked on as a basis for reducing management costs in the SPLF. It consists of an introduction (Chapter 1), followed by Chapters 2 to 5, and a comprehensive discussion (Chapter 6). In Chapter 2, we investigated the high water temperature tolerance and low oxygen tolerance of Japanese anchovies in an attempt to raise breeding water temperature and reduce fuel costs. In Chapter 3, we clarified the ammonia tolerance of Japanese anchovies in an attempt to reduce the amount of water exchanged and fuel costs. In Chapter 4, based on the research results obtained in Chapters 2 and 3, we examined the feasibility of long-term feeding and tolerance to non-feeding. In the following Chapter 5, in order to verify the effectiveness of artificially produced Japanese anchovies using two methods, we calculated the cost and investigated the survival rate on board the ship and the catch rate of Skipjack (Katsuwonus pelamis).
Chapter 2 We conducted a test to find out whether it is possible to safely rear fish on a boat at a temperature higher than the 15°C rearing water temperature used in Pelagic fishery. As a result, the semi lethal water temperature for Japanese anchovies in a short period of time was estimated to be 27.3 to 28.5°C, and it was found that the current breeding water temperature could be raised by 5 to 10°C. We also investigated the oxygen consumption of Japanese anchovies at different water temperatures and clarified their hypoxic tolerance. The results revealed that it is safe to keep the dissolved oxygen level above 5 mg/L, and that the rate of oxygen consumption increases as the water temperature increases.
Chapter 3 A test was conducted with a focus on ammonia tolerance in order to find out whether it is possible to safely raise Japanese anchovies onboard ships even if the high water exchange rates used in pelagic fisheries are lowered. As a result, the short-term lethal concentration of undissociated ammonia nitrogen was 0.706 to 0.770 mg/L at the current rearing water temperature of 15°C. The concentration was estimated to be 0.450 to 0.634 mg/L at 25°C which is 10°C higher than the current rearing water temperature. It became clear that the current water exchange rate was too high and was wasting energy.
In addition, in order to prevent the mass mortality of Japanese anchovies that occurs during periods of high water temperature in inshore fisheries, a test was conducted to find out whether it is possible to raise Japanese anchovies without changing the water using cooled rearing water. The results revealed that short-term breeding is possible with intermittent water changes.
Chapter 4 The findings obtained in Chapters 2 and 3 evaluated acute environmental responses over short periods of time and under non-feeding conditions. Therefore, tests must be conducted under feeding conditions for 50 days of pelagic fishery at water temperatures of 20°C and 25°C. When we conducted a test to find out if breeding was possible, the survival rates after 50 days were 91 % and 81 %. Furthermore, since the tests conducted in Chapters 2 and 3 were both conducted under non-feeding conditions, starvation may have been a factor in the death of the test fish. When starvation tolerance tests were conducted at 20°C and 25°C to eliminate this problem, the number of dead fish began to increase rapidly after 23 and 14 days, respectively. From this, it became clear that starvation was not included as a cause of death during the short-term test.
Chapter 5 In recent years, departures have often been delayed due to a lack of a stable supply of anchovies to load onto ships. The price of live bait is also rising. In order to solve these problems, we aimed to clarify the production cost of Japanese anchovies and their effectiveness on board using two methods: cultured live bait by capturing and raising whitebait, and cultured live bait by artificially collecting eggs and producing seedlings. A test was conducted. As a result, compared to wild live bait, the production cost of cultivated live bait (Japanese anchovy produced by farming whitebait) was almost the same, but cultured live bait (Japanese anchovy produced by Seed production) was more than 10 times more expensive, leaving room for improvement in breeding methods. In addition, it was revealed that both the survival rate on board and the catch rate of skipjack were comparable to natural live bait for both cultivated and cultured live bait. Based on the above research results, it is possible to reduce fuel costs on pelagic SPLF boats by increasing the rearing water temperature by 5 to 10°C from the current 15°C and by using closed circulation rearing that reduces the water exchange rate. It has become clear that there is ample potential for significant reductions. In addition, it has been found that it is impossible to raise SPLF boats in inshore without cooling the rearing water during periods of high water temperature. It is thought that mass mortality of Japanese anchovies can be avoided by selecting fishing grounds that avoid temperate zones. Furthermore, by establishing production bases for farmed Japanese anchovies in the Pacific Ocean region of the Tohoku region to the Joban Sea area, it will be possible to revitalize the region by supporting reconstruction efforts, etc. It is also expected to contribute to improving the management of the SPLF.第 1 章 序論
カツオは，日本人にとって欠くことのできない重要魚種のひとつであり，漁獲方法のひとつに一本釣り漁法がある。その漁法では，活餌としてカタクチイワシが必要不可欠であり，船上での安全飼育が航海中に求められている。業界では，カツオの来遊不安定，魚価低迷のほか，燃油代の高騰，活餌不足など厳しい経営状態から脱却することが急務となっている。本論文は，かつお一本釣り漁業におけるコスト削減方策のひとつとして，操業に必要不可欠な活餌であるカタクチイワシの効率的な確保方法について，筆者が取り組んだ研究成果をとりまとめたものである。第 2 章では，カタクチイワシの高温側水温耐性と水温別低酸素耐性を，第 3 章では，カタクチイワシのアンモニア耐性を，第 4 章では，50 日間にわたる給餌飼育と無給餌飼育を，第 5 章では，人工カタクチイワシの生産と有効性を検証した。そして，最後の第 6 章では，船上における安全に飼育する方法を遠洋漁業と近海漁業に分けて示し，養成・養殖カタクチイワシの生産について整理し，今後の生産体制の可能性について議論した。
第 2 章 飼育下におけるカタクチイワシの高温側水温耐性と水温別低酸素耐性に関する研究
カタクチイワシは，かつお一本釣り漁業で使う活餌として重要である。本種の船上飼育時には水温を低く維持しなければならず，大きな燃油経費がかかるため，経費削減の方法が求められている。そのため，船上で安全にカタクチイワシを飼育できる条件の解明が必要である。
そこで，本種の高温側水温耐性と低酸素耐性について検討した。その結果，24 時間後，48 時間後の高温側半数個体致死温度は，28.5°C および 27.3°C であった。また，カタクチイワシが狂奔し始める溶存酸素濃度は，15～30°Cの範囲で 1.12～2.36 mg/L（酸素飽和度 13.9～35.1 %）であった。以上により，漁業現場では現行の 15°C から 5～10°C 上げてカタクチイワシを安全に飼育することが可能であり，経費削減につながる期待が高まった。同時に，溶存酸素量は 5 mg/L 以上で飼育することが安全であることも明らかになった。
第 3 章 カタクチイワシのアンモニア耐性-かつお一本釣り漁業におけるコスト削減のために
カタクチイワシは，かつお一本釣り漁業で活餌として使用されることから，一航海 4～50 日の間，漁船内で飼育されながら漁場まで運ばれる。カタクチイワシから排泄されるアンモニアは航海中の生存に影響を与える可能性があるため，漁業者は経験的に 175～500 %/時の割合で飼育水を換水し，カタクチイワシを健康な状態に維持している。より効率的かつ費用対効果の高い輸送方法を開発するために，カタクチイワシのアンモニア耐性と，収容密度と換水が生存に及ぼす影響を評価した。その結果，カタクチイワシの 24 時間および 48 時間半数致死非解離アンモニア態窒素濃度（95%信頼区間）は，15°C で0.770 (0.751～0.790) mg/L，0.706 (0.661～0.750) mg/L，25°C で 0.634 (0.466～0.802) mg/L，0.450 (0.379～0.521)mg/L と判明した。25°C での無換水飼育では非解離アンモニア態窒素濃度は致死レベルまで上昇し，収容密度に依存しつつ死亡する個体が急激に発生したが，12 時間おきに飼育水の 1 / 3 を換水すれば非解離アンモニア態窒素濃度は非致死レベルに維持することができた。以上の結果により，漁船における経験的に推定されたカタクチイワシの飼育時の換水率を低減できる可能性が示された。
第 4 章 飼育下におけるカタクチイワシの安全飼育指標に基づいた模擬長期飼育試験
第 2 章と第 3 章で得られた知見は，短期間かつ無給餌条件下の結果であり，急性的な環境応答を評価したものである。そのため，20°C と 25°C の水温で遠洋漁業での航海日数 50 日間の給餌条件下で，カタクチイワシの飼育が可能となるかを明らかにする目的で試験を実施したところ，50 日後の生残率は 91 %と 81 %となった。また，第 2 章と第 3 章で実施した試験はいずれも無給餌条件下のため，供試魚の死亡要因に餓死が含まれている可能性がある。それを排除する目的で 20°C と 25°C で飢餓耐性試験を実施したところ，死亡魚が急増し始める日数はそれぞれ 23 日後，14 日後となり，短期間での試験時の死亡要因に餓死は含まれないことが明らかになった。
第 5 章 かつお一本釣り漁業における養成および養殖カタクチイワシの餌料（活餌）としての可能性
近年，出漁前に積み込むカタクチイワシが安定供給されないことで，活餌価格の高騰や出漁が遅れることによるコストが発生している。これらを解消する目的でシラスを捕獲・畜養した養成活餌と，人工的に採卵・種苗生産した養殖活餌の 2 通りの方法で，カタクチイワシの生産コストと船上における有効性明らかにする目的で試験を実施した。天然活餌と比較した生産コストは，養成活餌はほぼ同等との結果が得られたが，シラスの漁獲自体が不安定であり実用面においては厳しいと考えられた。一方，養殖活餌は 10 倍以上のコスト高となったものの，飼育方法を改善することで実現性は十分にあると考えられた。また，船上における生残率およびカツオの釣獲率については，天然活餌と比較し養成・養殖活餌ともに遜色がないことが明らかになった。
第 6 章 総合考察
遠洋かつお一本釣り漁船では，現状の飼育水温 15°C より 5～10°C 昇温させることや，換水率を下げられる閉鎖循環式システムを用いた飼育を行うことで，現状よりも燃油経費を大幅に削減できる可能性が十分にあることが明らかになった。また，近海かつお一本釣り漁船では，高水温時期に飼育水を冷却せずにカタクチイワシを飼育することは不可能であることが判明したため，25°C 以下の海水を用いた断続換水飼育の実施や，高水温帯を避けた漁場選択により，カタクチイワシの大量斃死を避けられるものと考えられた。さらに，東北地方～常磐海域における太平洋側地域に，養殖カタクチイワシ等の生産基地を創設することで，復興支援等による地域活性化を図りつつ，かつお一本釣り漁業の経営改善に寄与することが期待できる。東京海洋大学審査学位論文departmental bulletin pape
Characterization of the dye complexes in triacid staining solutions
Full text linkTriacid staining solution (neutral mixture) contains dye complex. Here, we speculate on the structure and characteristics of the dye complex in various triacid staining solutions. It was inferred that the dye complexes in the Ehrlich (methyl green + 2 acid fuchsin, methyl green + 2 orange G, methyl green + acid fuchsin + orange G), Romanowsky (eosin + methylene blue), and Pappenheim (eosin + methylene azure) triacid stains behave as acidic dyes, and that the dye complexes do not dissociate against weakly acidophilic objects, resulting in staining with a complex color (purple). Therefore, it can be said that the objects to which the dye complexes bind without dissociation do not need to be basophilic. When the stained material is highly acidophilic or basic, the dye complex dissociates, and the acidophilic object is stained by the acidic dye and the basiophilic object by the basic dye. The dissociation of dye complexes depends on the degree of acidophilicity and basophilicity of the stained material, and the dissociation depends on the types of dye composing the dye complexes. The dye complex in a triacid stain can be defined as a purple acidic dye in which the bonds between the acidic and basic dyes in the complex can be broken, depending on the acidophilic and basophilic strength of the object.編集：水産大学校departmental bulletin pape
Combined effects of salinity and turbidity on the gaping behavior, clearance rate, survival rate and glycogen content of blood cockle Tegillarca granosa (Linnaeus, 1758)
Full text linkBlood cockle Tegillarca granosa, a popular commercial bivalve species in south-east Asia, China and South Korea usually inhabits shallow mudflats in the intertidal zone. Due to the recent unpredictable climate patterns and increase of prolonged heavy rain conditions, bivalves inhabiting mudflats would be exposed to extreme hyposaline and turbid waters which would have an effect on their physiological conditions. The possible influences of such extreme conditions were tested in the laboratory using a 2 x 4 experimental design, where 24 specimens of T. granosa were exposed to different salinities (10, 30 psu) and turbidities (0, 100, 200, 300 mg/l) with 3 replicates over a 2-week period. Results indicated that T. granosa experienced stress to some extent but was quite tolerable against hyposaline and turbid conditions within the 2-week period. That is, specimens exposed to lower salinity and higher turbidities recorded decrease in clearance rates with delay in the initiation of gaping activity, which were considered as light signs of stress. Despite signs of stress, exposed individuals recorded minimal effect on glycogen content and a high survival rate was obtained. Overall, T. granosa is likely to tolerate hyposaline and turbid water sufficiently during the limited 2-week experimental period, showing only a slight stress response.journal articl
Drifting seaweed clumps as possible early life habitats for demersal fishes
Full text linkIn this study, I investigated the seasonal occurrences of juvenile fishes that are associated with drifting seaweed in the surface waters around the Japanese archipelago. I also estimated the possible contribution of drifting seaweed to the early life history of demersal fishes as habitats. Approximately 130 species of juvenile fishes associated with drifting seaweed have been reported to be found in the waters surrounding the Japanese archipelago north of Kyushu. The fish fauna varied by the location of sea area, however, except for the yellowtail juveniles, demersal fishes are more common and abundant than pelagic fishes in each sea area. Therefore, I proposed to classify juvenile fishes that are associated with drifting seaweed into “essential residents” and “opportunistic residents” based on whether it is essential for them to accompany drifting seaweed during a certain period of their early life history. In addition, I proposed the division of “opportunistic resident” into “active opportunistic resident” and “passive opportunistic resident”. Furthermore, I suppose that the development of “essential resident” and “active opportunistic resident” drifting seaweed was related to the reduction in mortality rate during and around primary metamorphosis due to the extension of the pelagic life period.日本列島周辺海域の表層を漂う流れ藻に随伴する稚魚・幼魚の出現状況を整理し，底魚類の初期生活史における流れ藻の役割について検討した。対象海域全体では約130種の稚魚・幼魚が確認され，海域によって魚類相は異なるが各海域ともブリ稚魚を除くと底魚類が多く出現する。生活史において流れ藻への随伴が必須か否かに着目し，流れ藻に随伴する稚魚・幼魚の生活型を「必須居住者」と「機会居住者」に区分し，後者を「受動的機会居住者」と「能動的機会居住者」へ細分することを提案した。また，「必須居住者」と「能動的機会居住者」の流れ藻への稚魚の随伴様式は，浮遊期間の延長による一次的変態時の減耗率軽減に関連していると想定した。ファイル名末尾に”_abs_j”のファイルは和文要旨journal articl
