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Spatial comparison of environmental DNA metabarcoding and traditional egg/larval surveys for pelagic fishes in the spawning grounds of the western Japanese waters
Full text linkPelagic fish represent a major proportion of global fisheries, but traditional fisheries survey and monitoring tools are time-consuming. We have compared the results of environmental DNA (eDNA) metabarcoding with those of traditional egg/larval surveys using oblique tow BONGO nets and vertical tow North Pacific Standard (NORPAC) nets for six pelagic fishes in the spawning grounds of the western Japanese waters to examine the effectiveness of eDNA surveys. The detection of 52 species by eDNA was considered to be reasonable based on their natural distribution. The results using the BONGO net, which had the largest filtration volume, indicated a wider presence for six fishes than the results using eDNA metabarcoding and the NORPAC net. eDNA detection results for round herring Etrumeus micropus, Japanese sardine Sardinops melanostictus, and Japanese anchovy Engraulis japonicus were more strongly correlated with observation results for the NORPAC net than those for the BONGO net. In contrast, no correlations were observed between eDNA and two net surveys for Japanese jack mackerel Trachurus japonicus and mackerel (both Scomber japonicus and Scomber australasicus). The results indicate the effectiveness of eDNA surveys for understanding spatial distribution, especially for round herring, sardine, and anchovy during their spawning. As there were several presence results only by eDNA, this method potentially complements traditional surveys.journal articl
Evidence for sult1st6y as a Major Candidate Sex-Determining Gene in Pacific Bluefin Tuna
Full text linkIntroduction: The Y chromosome-linked gene sult1st6y (a homolog of the estrogen sulfotransferase gene) has recently been identified in Thunnus, a genus characterized by an XX/XY sex determination system. This study examined whether sult1st6y is a sex-determining gene in bluefin tuna (Thunnus orientalis). Methods: The expression of sult1st6y was examined using polymerase chain reaction analyses and in situ hybridization. Sult1st6y expression in masculinized XX testes produced by aromatase inhibitor administration and the expression profile of the sult1st6y mutant, which was produced using CRISPR/Cas9, were examined. Results:Sult1st6y was specifically expressed in XY gonads during sex differentiation. The onset of sult1st6y expression preceded that of other genes promoting sex differentiation. Sult1st6y expression was not detected in masculinized XX testes, indicating that gonads can differentiate into testes without sult1st6y if estrogens are depleted. The Sult1st6y mutant XY gonad showed a gene expression pattern similar to that of wild-type XX gonads. Conclusion: Our results collectively suggest that sult1st6y is at the top of the molecular cascade that regulates gonadal sex differentiation. Sult1st6y may trigger testicular differentiation by deactivating estrogens, although its biochemical activity should be examined. This study provides evidence that sult1st6y is a major candidate sex-determining gene in tuna.journal articl
Characteristics of Suspended Particulate Matter, Benthic Environmental Factors, and Their Relationship to Bivalves
Full text linkBivalves are of great ecological and economic importance across coastal zones around the globe. Their distribution and abundance are affected by various benthic environmental factors, including suspended particulate matter (SPM). The relationship between bivalves and SPM has been studied in various contexts but not recently. Thus, the authors conducted a literature review of SPM found in the marine environment, its characteristics (particle size and density), and how the surrounding benthic environmental factors (salinity, light availability, and current velocity) influence its characteristics. Certain areas were found to lack or require further research, such as on the characteristics of microplastics and the mechanism behind the positive influence of PIM in bivalve diet components not yet discovered. Over the past decades, coastal environments have undergone huge development and change that has affected the SPM components and conditions in coastal marine environments, justifying updated research. The need for this and other information will influence future research, as summarized at the end of the article.journal articl
Preliminary study of oxygen consumption and resistance for hypoxia in captivity of coral trout grouper Plectropomus leopardus
Full text linkWe investigated the oxygen consumption and resistance for hypoxia in captivity of coral trout grouper Plectropomus leopardus. The fish with an average bodyweight 3 g consumed 515, 667 and 654 mg/kg/h of oxygen at water temperature 25, 27 and 30℃, respectively. On the other hand, one with an average bodyweights 5 g consumed 468 and 804 mg/kg/h at 25 and 30℃. The former groups recorded a decrease in oxygen consumption rate from 5 mg/L. The latter groups recorded from 4 mg/L. In a water temperature ranges from 25 to 30℃, 3 g f ish began to die at dissolved oxygen levels of 0.99 to 1.06 mg/L (oxygen saturation of 15.4 to 16.0%), while at 0.73 to 1.15 mg/L (oxygen saturation of 11.0 to 18.8%), 5 g fish groups began to die. This is a significant result and gives a scientific impact on hypoxia for coral trout grouper aquaculture.スジアラは種苗生産が確立され，次のステージである養殖技術の開発が行われている。安定した養殖を行うためには，特に低酸素に対する耐性や水温別の酸素消費量についての基礎的な知見を集積する必要がある。本研究では，生産したスジアラ人工種苗を用いて水温別の酸素消費量を調査した結果，体重3 gサイズでは25℃，27℃および30℃のそれぞれで515，667および654 mg/kg/h，体重5 gサイズでは25℃および30℃のそれぞれで468および804 mg/kg/hの酸素量を消費していた。また，25～30℃の範囲において，体重3 gサイズではDOが2～5 mg/L，体重5 gサイズではDOが2～4 mg/Lになった時点から，それぞれ酸素消費速度の平均値が減少することが確認された。さらに，最初に死亡が確認されたDOおよび酸素飽和度は，体重3 gサイズでは25～27℃の範囲でDOは0.99～1.06 mg/L (酸素飽和度15.4～16.0％) ，体重5 gサイズでは25～30℃の範囲でDOは0.73～1.15 mg/L (酸素飽和度11.0～18.8％) であった。以上の結果から，スジアラ養殖に必要な基礎的知見である水温別の酸素消費量および低酸素耐性を明らかにした。編集：水産大学校departmental bulletin pape
Characterization of salmon-foraging harbor seals (Phoca vitulina) in the Erimo region, Hokkaido, Japan, using finite mixture models
Full text linkThe increase in the population of harbor seals (Phoca vitulina) in the Erimo region of Hokkaido, Japan, has coincided with rising fishery conflicts, affecting salmon setnets in particular. While seal-related fishery damage has been reported, quantitative evidence of seal predation on salmon has been lacking. The present study employed a finite mixture model clustering method to analyze seal feeding patterns. This analysis revealed 13 distinct clusters, with one cluster specifically characterized by salmon predation. This cluster consisted primarily of larger individuals who obtained most of their daily energy requirements from salmon. In such an environment, seals may learn of setnet structures and fish aggregation characteristics, potentially increasing their dependence on these artificial structures. However, many seals in the population were not feeding on salmon, and the findings demonstrate that only a specific subset of the population, characterized by larger body size and older age, has developed specialized feeding strategies centered on salmon predation at setnets. This adaptation to setnet environments has significant implications for both fishery management and seal conservation in the region.journal articl
The hemolymph CO2 partial pressure and bicarbonate concentration of the acid–base balance of Mytilus coruscus under resting conditions
Full text linkWe investigated the hemolymph CO2 partial pressure (Pco2) and bicarbonate concentration ([HCO3 – ]) of the acid–base balance of Mytilus coruscus under resting conditions. Hemolymph collected from the adductor muscle was subjected to the following measurements. Mean values for hemolymph pH and total CO2 concentration for this state between 18°C and 23°C were 7.568-7.601 and 1.54-1.59 mM/L, respectively. Hemolymph Pco2 and [HCO3 – ] were calculated using the hemolymph pKapp estimated using the relational expression with temperature. Hemolymph Pco2 and [HCO3 – ] were 1.77-1.83 torr and 1.47-1.50 mM/L at 18°C and 23°C. To verify Pco2 and [HCO3 – ], the values were calculated using pKapp obtained by in vitro method (tonometry). Despite the different determination methods, no statistical difference in the obtained values of Pco2 and [HCO3 – ] were observed. Non-bicarbonate buffer values (ꞵNB), which were calculated using the slope of the relational expression between pH and [HCO3 – ] in hemolymph, were 0.42 slykes at 18°C, and 0.54 slykes at 23°C. The hemolymph ꞵNB of M. coruscus was in the range of other bivalves, and the hemolymph buffer capacity of the non-bicarbonate buffer system would reflect the Mitilid species.我々は，安静状態におけるイガイMytilus coruscus のヘモリンパ液の酸塩基平衡を調べた。水温18°Cでのヘモリンパ液 pH は7.601±0.023（平均値±標準偏差）， 全炭酸含量（Tco2）は1.59±0.06 mM/Lを示した。水温23°CではpH 7.568±0.031，Tco2 1.54±0.09 mM/Lを示した。ヘモリンパ液の二酸化炭素分圧（Pco2）と重炭酸イオン濃度（[HCO3–]）は，温度との関係式から推定された炭酸解離恒数（pKapp）を使用して計算された。Pco2と[HCO3–] は水温18°Cで1.77±0.07 torrと1.50±0.06 mM/L，水温23°Cで1.83±0.08 torrと1.47±0.09 mM/Lを示した。推定したpKappを使い算出したPco2を検証するため，本研究のin vitro実験で決定したpKappを用いてPco2を計算した。異なる方法で算出した2つのPco2に統計的な有意差は認められなかった。これらのことから，イガイヘモリンパ液のpKappを温度との関係式から推定することは，Pco2と[HCO3–]の算出に有効と判断された。イガイヘモリンパ液の非重炭酸緩衝価ꞵNB）は18°Cで0.42 slykes，23°Cで0.54 slykesであり，他のイガイ類の緩衝能をよく反映していた。編集：水産大学校departmental bulletin pape
