• Title/Summary/Keyword: 대륙

Search Result 981, Processing Time 0.03 seconds

Fish Community Characteristics and the Effects of Water Quality on River Health in the Anyang Stream, Korea (안양천의 어류군집 특성 및 수질이 하천건강성에 미치는 영향)

  • Jae-Woo Joo;Myeong-Hun Ko
    • Korean Journal of Environment and Ecology
    • /
    • v.38 no.2
    • /
    • pp.189-203
    • /
    • 2024
  • This study conducted a survey two times at 20 points from April to June and from August to October 2022 to characterize the fish community and reveal the health of the Anyang stream. The survey collected 3,186 individuals belonging to 5 orders, 10 families and 34 species. The dominant species was Zacco platypus (43.4%), followed by Carassius auratus (10.1%), Cyprinus carpio (7.6%), Zacco koreanus (6.2%), Pungtungia herzi (5.2%), Oryzias sinensis (5.1%), Pseudorasbora parva (4.7%), Squalidus gracilis majimae (4.4%), Rhynchocypris oxycephalus (3.5%), Hemiculter eigenmanni (3.3%), Rhodeus ocellatus (1.4%), and Chelon haematocheilus (1.0%). Among the emerged species, 5 species (14.7%), including Rhodeus uyekii, Squalidus japonicus coreanus, and Odontobutis interrupta, were endemic to Korea, and 4 species (11.8%), including Cyprinus carpio (Israeli type), Lepomis macrochirus, Micropterus salmoides, and Poecilia reticulata, were exotic. The fish community analysis showed that the dominance was higher at the upper reaches of the Anyang stream and decreased downstream, and diversity, richness, and evenness were higher in tributary than mainstream. Stream health (fish assessment index, FAI) was generally poor, as it was rated as moderate (C) at seven sites, poor (D) at eight sites, and very poor (E) at five sites. Water quality was evaluated at eight sites, and it was rated as poor (V) at two sites, slightly poor (IV) at one site, moderate (III) at four sites, and slightly good (II) at one site, indicating that the overall water quality was poor and that the water quality had a significant impact on river health and fish habitat. Moreover, it was found that many weirs without fishways were constructed in the Anyang stream and became an obstacle to fish migration. Therefore, a systematic management plan to improve water quality and add fishways is necessary to improve the stream's health and conserve stable fish habitat.

Characteristics and Implications of Sports Content Business of Big Tech Platform Companies : Focusing on Amazon.com (빅테크 플랫폼 기업의 스포츠콘텐츠 사업의 특징과 시사점 : 아마존을 중심으로)

  • Shin, Jae-hyoo
    • Journal of Venture Innovation
    • /
    • v.7 no.1
    • /
    • pp.1-15
    • /
    • 2024
  • This study aims to elucidate the characteristics of big tech platform companies' sports content business in an environment of rapid digital transformation. Specifically, this study examines the market structure of big tech platform companies with a focus on Amazon, revealing the role of sports content within this structure through an analysis of Amazon's sports marketing business and provides an outlook on the sports content business of big tech platform companies. Based on two-sided market platform business models, big tech platform companies incorporate sports content as a strategy to enhance the value of their platforms. Therefore, sports content is used as a tool to enhance the value of their platforms and to consolidate their monopoly position by maximizing profits by increasing the synergy of platform ecosystems such as infrastructure. Amazon acquires popular live sports broadcasting rights on a continental or national basis and supplies them to its platforms, which not only increases the number of new customers and purchasing effects, but also provides IT solution services to sports organizations and teams while planning and supplying various promotional contents, thus creates synergy across Amazon's platforms including its advertising business. Amazon also expands its business opportunities and increases its overall value by supplying live sports contents to Amazon Prime Video and Amazon Prime, providing technical services to various stakeholders through Amazon Web Services, and offering Amazon Marketing Cloud services for analyzing and predicting advertisers' advertising and marketing performance. This gives rise to a new paradigm in the sports marketing business in the digital era, stemming from the difference in market structure between big tech companies based on two-sided market platforms and legacy global companies based on one-sided markets. The core of this new model is a business through the development of various contents based on live sports streaming rights, and sports content marketing will become a major field of sports marketing along with traditional broadcasting rights and sponsorship. Big tech platform global companies such as Amazon, Apple, and Google have the potential to become new global sports marketing companies, and the current sports marketing and advertising companies, as well as teams and leagues, are facing both crises and opportunities.

Comparative Analysis of Freshwater Fish Species in Civilian Control Zone in South Korea: A Comparison between Direct Survey Results and Indirect Assessment via eDNA (우리나라 민간인통제구역 내 수계 어류에 대한 비교분석: 직접조사 결과와 eDNA를 통한 간접조사 결과 비교)

  • Soon-Jae Eum;Naeyoung Kim;Min-A Seol;Ji Young Kim
    • Korean Journal of Ichthyology
    • /
    • v.35 no.4
    • /
    • pp.224-235
    • /
    • 2023
  • South Korea is the only divided nation globally, marked by a military demarcation line establishing demilitarized and civilian control zones, ensuring national security. Consequently, these areas exhibit relatively minimal ecological disruption compared to other regions. However, the threat to safety persists due to the presence of unexploded ordnances and landmines, imposing significant constraints on ecological research. To address this, we conducted a comparative study utilizing eDNA analysis as a supplementary and alternative approach within three points of the "Road of Peace" - Inje, Yanggu, and Hwacheon courses, located within the civilian control zone. Direct surveys and indirect eDNA sampling were carried out in May, July, and September of 2022. Genetic material obtained from the samples underwent amplification, library preparation, MiSeq sequencing, and subsequent ASV generation for indirect analysis. These results were then compared with the findings of direct surveys. Our findings revealed the detection of eDNA for both observed species at the Yanggu-1 point, and for two out of four species at Yanggu-2. Hwacheon-1 displayed the detection of eDNA for one out of one observed species, whereas Hwacheon-2 yielded seven out of twelve, Hwacheon-3 showed four out of six, and all one observed species at Hwacheon-4 exhibited eDNA detection. Consequently, approximately 69% of the fish species identified through direct surveys were confirmed by indirect eDNA analysis. It is necessary to verify if certain fish species, such as the continental trout and catfish, have genetic information registered in the NCBI database. Additionally, it is believed that further marker development research utilizing different genetic sequences is essential. Given the limitations imposed by the hazardous nature of the surveyed civilian control zone, eDNA analysis proves to be a suitable supplement for fish research in the area.

Estimate of Particulate Organic Carbon Export Flux Using $^{234}Th/^{238}U$ Disequilibrium in the Southwestern East Sea During Summer (동해 서남해역에서 여름철 $^{234}Th/^{238}U$ 비평형을 이용한 입자상 유기탄소 침강플럭스 추정)

  • Kim, Dong-Seon;Choi, Man-Sik;Oh, Hae-Young;Kim, Kyung Hee;Noh, Jae-Hoon
    • The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
    • /
    • v.14 no.1
    • /
    • pp.1-9
    • /
    • 2009
  • Export fluxes of particulate organic carbon were estimated for the first time by using $^{234}Th/^{238}U$ disequilibrium in the southwestern East Sea during August 2007. They were calculated by multiplying POC/$^{234}Th_p$ ratios of sinking particles (larger than 0.7 ${\mu}m$) obtained from 150-200 m water depths to $^{234}Th$ fluxes that were estimated by integrating $^{234}Th/^{238}U$ disequilibrium from surface to 100 m water depth. Export fluxes ranged from 14 to 505 mg C $m^{-2}$ $day^{-1}$, with the highest value at station A2 and the lowest value at station D4. Primary production was well correlated with export flux, indicating that it was a major factor controlling export flux. Export flux in the East Sea was generally higher than those estimated in the open ocean and similar to or somewhat higher than those in the continental marginal seas. Export flux/primary production (EF/PP) ratios varied from 0.29 to 0.62, with an average of 0.43 and were somewhat higher in the basin area than in the coastal area. EF/PP ratio in the East Sea was rather similar to those estimated in the North Sea and Chukchi Sea, but much higher than those in the Labrador Sea, Barents Sea, and Gulf of Lions. Therefore, the East Sea is one of the major areas where a large amount of organic carbon produced in the euphotic zone sinks into the deep layer below 200 m water depth.

The historical study on the Ukrainian territorial conflicts: Focusing on the Crimean War and the German-Soviet War (우크라이나 영토분쟁에 관한 사(史)적 연구: 크림전쟁과 독소전쟁의 사례를 중심으로)

  • Eunchae Lee;Ikhyun Jang
    • Analyses & Alternatives
    • /
    • v.8 no.2
    • /
    • pp.65-86
    • /
    • 2024
  • This study delves into the geopolitical tensions surrounding Ukraine throughout modern European history, aiming to shed light on its significance in geopolitical discourse. Since the 19th century, European powers, particularly the Anglo-Saxons and Germans, have formulated distinct geopolitical strategies concerning the Eurasian continent, with Ukraine at its focal point. The Crimean War and the German-Soviet War serve as key events to analyze these powers' geopolitical ambitions and interests. The British Empire, driven by its doctrine of thwarting land powers with sea power, intervened in the Crimean War against Russia. Its objective was to disrupt Russian dominance over Ukraine, thereby hindering Russian expansion into the Black Sea and Central Europe. On the other hand, the Third Reich of Germany, fixated on creating a European sphere exclusive from Anglo-Saxon sea powers and the Russian land power, initiated the German-Soviet War. This move aimed to secure a vast territory, including Ukraine, to facilitate expansion into the Caucasus and establish a buffer zone against the Soviet Union. Three key insights emerge from this analysis. Firstly, the absence of a dominant power rooted in Ukraine since the fall of the Principality of Kiev made geopolitical clashes inevitable. Secondly, these clashes ultimately result in a hollow victory for all involved parties, signifying the high costs and minimal gains of such confrontations. Lastly, the root cause of these clashes lies in the discord between exclusive geopolitical visions that fail to accommodate sustainable coexistence among diverse geopolitical spheres. In essence, the study underscores Ukraine's pivotal role in shaping European geopolitics and highlights the recurring clashes driven by competing visions of dominance and control over its territory. From the Crimean War to the German-Soviet War, the struggle for influence over Ukraine reflects broader geopolitical dynamics and the pursuit of strategic advantage by major powers. Ultimately, the study emphasizes the enduring significance of Ukraine in European geopolitics and the complexities inherent in managing its geopolitical tensions.

Possibility of Establishing an International Court of Air and Space Law (국제항공우주재판소의 설립 가능성)

  • Kim, Doo-Hwan
    • The Korean Journal of Air & Space Law and Policy
    • /
    • v.24 no.2
    • /
    • pp.139-161
    • /
    • 2009
  • The idea of establishing an International Court of Air and Space Law (hereinafter referred to ICASL) is only my academic and practical opinion as first proposal in the global community. The establishment of the International Court of Air and Space Law can promote the speed and promote fairness of the trial in air and space law cases. The creation of an ICASL would lead to strengthening of the international cooperation deemed essential by the global community towards joint settlement in the transnational air and space cases, claims and would act as a catalyst for the efforts and solution on aircraft, satellite and space shuttle's accidents and cases and all manpower, information, trial and lawsuit to be centrally managed in an independent fashion to the benefit of global community. The aircraft, satellite and spacecraft's accidents attributes to the particular and different features between the road, railway and maritime's accidents. These aircraft, satellite and spacecraft's accidents have incurred many disputes between the victims and the air and space carriers in deciding on the limited or unlimited liability for compensation and the appraisal of damages caused by the aircraft's accidents, terror attack, satellite, space shuttle's accidents and space debris. This International Court of Air and Space Law could hear any claim growing out of both international air and space crash accidents and transnational accidents in which plaintiffs and defendants are from different nations. This alternative would eliminate the lack of uniformity of decisions under the air and space conventions, protocols and agreements. In addition, national courts would no longer have to apply their own choice of law analysis in choosing the applicable liability limits or un-limit for cases that do not fall under the air and space system. Thus, creation of an International Court of Air and Space Law would eliminate any disparity of damage awards among similarly situated passengers and shippers in nonmembers of air and space conventions, protocols, agreements and cases. Furthermore, I would like to explain the main items of the abovementioned Draft for the Convention or Statute of the International Court of Air and Space Law framed in comparison with the Statute of the International Court of Justice, the Statue of the International Tribunal for the Law of the Sea and the Statute of the International Criminal Court. First of all, in order to create the International Court of Air and Space Law, it is necessary for us to legislate a Draft for the Convention on the Establishment of the International Court of Air and Space Law. This Draft for the Convention must include the elected method of judges, term, duty and competence of judge, chambers, jurisdiction, hearing and judgment of the ICASL. The members of the Court shall be elected by the General Assembly and Council of the ICAO and by the General Assembly and Legal Committee of the UNCOPUOS from a list of persons nominated by the national groups in the six continent (the North American, South American, African, Oceania and Asian Continent) and two international organization such as ICAO and UNCOPUOS. The members of the Court shall be elected for nine years and may be re-elected as one time. However, I would like to propose a creation an International Court of Air and Space Law in extending jurisdiction to the International Court of Justice at the Hague to in order to decide the air and space convention‘s cases. My personal opinion is that if an International Court on Air and Space Law will be created in future, it will be settled quickly and reasonably the difficulty and complicated disputes, cases or lawsuit between the wrongdoer and victims and the injured person caused by aircraft, satellite, spacecraft's accidents or hijacker and terrorists etc. on account of deciding the standard of judgment by judges of that’s court. It is indeed a great necessary and desirable for us to make a new Draft for the Convention on a creation of the International Court of Air and Space Law to handle international air and space crash litigation. I shall propose to make a new brief Draft for the Convention on the Creation of an International Court of Air and Space Law in the near future.

  • PDF

Future Changes in Global Terrestrial Carbon Cycle under RCP Scenarios (RCP 시나리오에 따른 미래 전지구 육상탄소순환 변화 전망)

  • Lee, Cheol;Boo, Kyung-On;Hong, Jinkyu;Seong, Hyunmin;Heo, Tae-kyung;Seol, Kyung-Hee;Lee, Johan;Cho, ChunHo
    • Atmosphere
    • /
    • v.24 no.3
    • /
    • pp.303-315
    • /
    • 2014
  • Terrestrial ecosystem plays the important role as carbon sink in the global carbon cycle. Understanding of interactions of terrestrial carbon cycle with climate is important for better prediction of future climate change. In this paper, terrestrial carbon cycle is investigated by Hadley Centre Global Environmental Model, version 2, Carbon Cycle (HadGEM2-CC) that considers vegetation dynamics and an interactive carbon cycle with climate. The simulation for future projection is based on the three (8.5/4.5/2.6) representative concentration pathways (RCPs) from 2006 to 2100 and compared with historical land carbon uptake from 1979 to 2005. Projected changes in ecological features such as production, respiration, net ecosystem exchange and climate condition show similar pattern in three RCPs, while the response amplitude in each RCPs are different. For all RCP scenarios, temperature and precipitation increase with rising of the atmospheric $CO_2$. Such climate conditions are favorable for vegetation growth and extension, causing future increase of terrestrial carbon uptakes in all RCPs. At the end of 21st century, the global average of gross and net primary productions and respiration increase in all RCPs and terrestrial ecosystem remains as carbon sink. This enhancement of land $CO_2$ uptake is attributed by the vegetated area expansion, increasing LAI, and early onset of growing season. After mid-21st century, temperature rising leads to excessive increase of soil respiration than net primary production and thus the terrestrial carbon uptake begins to fall since that time. Regionally the NEE average value of East-Asia ($90^{\circ}E-140^{\circ}E$, $20^{\circ}N{\sim}60^{\circ}N$) area is bigger than that of the same latitude band. In the end-$21^{st}$ the NEE mean values in East-Asia area are $-2.09PgC\;yr^{-1}$, $-1.12PgC\;yr^{-1}$, $-0.47PgC\;yr^{-1}$ and zonal mean NEEs of the same latitude region are $-1.12PgC\;yr^{-1}$, $-0.55PgC\;yr^{-1}$, $-0.17PgC\;yr^{-1}$ for RCP 8.5, 4.5, 2.6.

Mineralogy and Mineral-chemistry of REE Minerals Occurring at Mountain Eorae, Chungju (충주 어래산 일대에서 산출하는 희토류 광물의 광물학적 및 광물화학적 특성)

  • You, Byoung-Woon;Lee, Gill Jae;Koh, Sang Mo
    • Economic and Environmental Geology
    • /
    • v.45 no.6
    • /
    • pp.643-659
    • /
    • 2012
  • The Chungju Fe-REE deposit is located in the Kyemyeongsan Formation of the Ogcheon Group. The Kyemyeongsan Formation includes meta-volcanic rocks and pegmatite hosted REE deposit which show different kind of REE-containing minerals. The meta-volcanic rocks hosted REE deposits' main REE minerals are allanite, zircon, apatite, and sphene, whereas the pegmatite hosted REE deposits is mainly composed of fergusonite, and karnasurtite, zircon, thorite. The meta-volcanic rock hosted major REE mineral is allanite as the form of aggregation and contains 23.89-29.19 wt% TREO (Total Rare Earth Oxide), 4.71-9.92 wt% $La_2O_3$, 11.30-14.33 wt% $Ce_2O_3$, 0.11-0.29 wt% $Y_2O_3$, 0.15-0.94 wt% $ThO_2$, as a formula of (Ca, Y, REE, Th)$_{2.095}$(Mg, Al, Ti, Mn, $Fe^{3+})_{2.770}(SiO_4)_{2.975}(OH)$. Accompanying REE in a coupled substitution for $Ca^{2+}$ (M1 site) and $Al^{3+}-Fe^{2+}$ (M2 site) leads to a large chemical variety. Due to the allanite's high contents of Fe, it belongs to Ferrialanite. The pegmatite hosted deposit's domi-nant REE mineral is fergusonite as prismatic or subhedral grains associated with zircon, fluorite and karnasurtite. Geochemical composition of the fergusonite($YNbO_4$) suggests substitution of Y-REE and Y-Th in A-site, and Nb-Ta-Ti in B-site, furthermore the proportion of $Y_2O_3$ and $Nb_2O_5$ is oddly 1:1.5 comparing to the ideal ratio 1:1 and Nb is higher than Y, also A-site Y actively substitutes with REE. Karnasurtite in pegmatite variously ranges 9.16-22.88 wt% $Ce_2O_3$, 2.15-9.16 wt% and $La_2O_3$, 0.44-10.8 wt% $ThO_2$, as a calculated formula (Y, REE, Th, K, Na, Ca)$_{1.478}(Ti, Nb)_{1.304}$(Mg, Al, Mn, $Fe^{3+})_{0.988}$(Si, P)$_{1.431}O_7(OH)_4{\cdot}3H_2O$. Firstly the 870-860 Ma is the initial age of the supercontinent Rhodinia dispersal and subsequent A-1 type volcanism, which contains Fe, REE, and HFS(High Field Strength elements; Nb, Zr, Y etc.) elements in Fe-rich meta-volcanic rocks dominant Kyemyeongsan Formation, might mineralized allanite. Another synthesis is that regional metamorphism at late Paleozoic 300-280 Ma(Cho et al., 2002) might cause allanite mineralization. Also pegmatite REE mineralization highly related to the granite intrusion over the Chungju area in Jurassic(190 Ma; Koh et al., 2012). Otherwise above all, A-1 type volcanism at the same time of the Kyemyeongsan Formation development, regional metamorphism and pegmatite, might have caused REE mineralization. Although REE ore bodies display a close spatial association, each ore bodies display temporal distinction, different mineral assemblage and environment of ore formation.

A Study on Garden Design Principles in "Sakuteiki(作庭記)" - Focused on the "Fungsu Theory"(風水論) - (「사쿠테이키(作庭記)」의 작정원리 연구 - 풍수론(風水論)을 중심으로 -)

  • Kim, Seung-Yoon
    • Journal of the Korean Institute of Landscape Architecture
    • /
    • v.41 no.6
    • /
    • pp.1-19
    • /
    • 2013
  • This study tries to review 'Sakuteiki(作庭記)', the Book of Garden Making, compiled at the end of the 11th Century during the Heian Period of Japan, from the East-Asian perspective. 'Sakuteiki' is a Garden Theory Book, the oldest in the world as well as in Asia, and it contains the traditional knowledge of Japanese ancient garden culture, which originated from the continent(Korea and China). Traditional knowledge related to East-Asian garden culture reviewed in this paper is "Fungsu Theory"(風水, Asian traditional ecology: Fengshui in Chinese; Fusui in Japanese), stemmed from the culture to seek sound and blessed places to live in. Viewed from modern landscape architecture, the Fungsu Theory corresponds to ecology(science). The Fungsu Theory was established around the Han Dynasty of China together with the Yinyangwuxing(陰陽五行) Theory and widely used for making human residences including gardens. It was transmitted to Japan via Korea as well as through direct transaction between Japan and China. This study reinterprets garden design principles represented in Sakuteiki, which were selected in 5 key words according to the Fungsu Theory. The 5 key words for the Fungsu Theory are "the place in harmony of four guardian gods(四神相應地)", "planting trees in the four cardinal directions", "flow of Chi(氣)", "curved line and asymmetry", and "mountain is the king, water is the people". Garden design principles of "the place in harmony of four guardian gods(四神相應地)" and "planting trees in the four cardinal directions" are corresponding to "Myeongdang-ron(明堂論, Theory of propitious site)". The place in harmony of four guardian gods mentioned in Sakuteiki is a landform surrounded by the flow of water to the east, the great path to the west, the pond to the south, and the hill to the north. And the Theory originated from Zhaijing(宅經, Classic of dwelling Sites) of China. According to this principle, the city was planned and as a miniature model, the residence of the aristocrat during the Heian period was made. At the residence the location of the garden surrounded by the four gods(the flow of water, the great path, the pond, and the hill) is the Myeongdang(明堂, the propitious site: Mingtang in Chinese; Meido in Japanese). Sakuteiki explains how to substitute for the four gods by planting trees in the four cardinal directions when they were not given by nature. This way of planting originated from Zhaijing(宅經) and also goes back to Qiminyaoshu (齊民要術), compiled in the 6th Century of China. In this way of planting, the number of trees suggested in Sakuteiki is related to Hetu(河圖) and Luoshu(洛書), which are iconography of Yi(易), the philosophy of change, in ancient China. Such way of planting corresponds to that of Yongdoseo(龍圖墅, the villa based on the principle of Hetu) presented in Sanrimgyeongje (山林經濟), an encyclopedia on agriculture and living in the 17th Century of Korea. And garden design principles of "the flow of Chi(氣)", "curved line and asymmetry" is connected to "Saenggi Theory(生氣論, Theory of vitality)". Sakuteiki explains the right flow of Chi(氣) through the proper flow and the reverse flow of the garden stream and also suggests the curved line of the garden stream, asymmetric arrangement of bridges and stones in the garden, and indented shape of pond edges, which are ways of accumulating Chi(氣) and therefore lead to "Saenggi Theory" of the Fungsu Theory. The last design principle, "mountain is the king, water is the people", is related to "Hyeongguk Theory(形局論, Theory of form)" of the Fungsu Theory. Sakuteiki explains the meaning of garden through a metaphor, which views mountain as king, water as the people, and stones as king's retainers. It compares the situation in which the king governs the people with the help of his retainers to the ecological phenomena in which mountain(earth) controls water with the help of stones. This principle befits "Hyeongguk Theory(形局論, Theory of form)" of the Fungsu Theory which explains landform on the analogy of social systems, people, animals and things. As above, major garden design principles represented in Sakuteiki can be interpreted in the context of the Fungsu Theory, the traditional knowledge system in East Asia. Therefore, we can find the significance of Sakuteiki in that the wisdom of ancient garden culture in East-Asia was integrated in it, although it described the knowhow of a specific garden style in a specific period of Japan.

Malacological Studies on Parafossarulus manchouricus(Gastropoda: Prosobranchia) in Korea (한국산(韓國産) 왜우렁(Parafossarulus manchouricus)의 패류학적(貝類學的) 연구(硏究))

  • Chung, Pyung-Rim
    • The Korean Journal of Malacology
    • /
    • v.1 no.1
    • /
    • pp.24-50
    • /
    • 1985
  • Five different populations of Parafossarulus manchouricus (Chongpyung, Chinju and Kunsan, Korea; and Japan and Taiwan), a population of Bitbynia (Gabbia) misella (Gongju, Korea) and two different populations of Bithynta tentaculata (Michigan, U.S.A. and Bodensee, Germany) were compared in regard to eff-laying characteristics, morphology, chromosome cytology, natural infections of parasites and ecology of habitats. A satisfactory culture method was devised for laboratory rearing of the snails. Tropical fish food (Terra SML) and powdered green leaves (Ceralife) were used as the main food sources for the snails. Benthic diatoms such as Navicula and Gomphonema from the periphyton were also essential for satisfactory growth, especially for the baby snails. The aquaria were stabilized with small stones from a local stream. Young P. manchouricus snails grew to adult size in about 54 days after hatching. They laid eggs 150-156 days after hatching. The whole cycle (birth to egg-laying) took approximately 5 months. The three species of bithyniid snails are iteroparous and lay eggs once a year. There were no major morphological differences in the shells of genera or subgenera studied here. They did exhibit the following rather minor differences. The shell of Parafossarulus has spirally raised ridges, and its apex is usually eroded; the other two genera lack these characteristics. The shell of B. (Gabbia) misella is small, nor exceeding 7.5 mm in length, while the shells of the other two species are larger, being more than 10 mm in length. Scanning electron microscopy (SEM) of the protoconch of P. manchouricus reveals nearly smooth sculpture with small, low, spiral wrinkles. This sculpture is quite different from that of the Hydrobiidae, a family to which the bithyniids are frequently assigned. Scanning electron microscopy of the radulae of the three bithyniid species showed that their radular morphologies are very similar, but there are some small differences, which may be species-specific. There were some statistical differences in shell heights between the Korean and the other populations of P. manchouricus, and between this species and the other two bithyniids as well. The shell differences between the several populations of Korean P. manchouricus may be related to environment. Edtails of the chromosome cycle of these bithyniid snails are similar to those reported for other snails. No specific differences were observed in the chromosome cycle between the various species and populations of snails employed in this study. Reporred for the first time in molluscs are two darkly stained "nucleolar organizers" during pachyterne stages of meiosis. Two different chromosome numbers were observed in the three bithyniid species: n=17 in B. tentaculata and P. manchouricus, and n=18 in B. (G.) misella. no sex chromosomes or supernumerary chromosomes were seen. There were no morphological differences in karyotypes of three Korean strains of P. manchouricus. The infection rates of cercariae of Clonorchis sinensis in Chinju and Kunsan strains of P. manchouricus were 0.14% and 1.25%, respectively. However, Clonorchis cercariae were found in Chongpyung strain of P. manchouriceu and Gongju strain of B. (G.) misella. The habitats of P. manchouricus around Jinyang Lake were relatively clean without any heavy pollution of aquatic microorganisms and organic materials during the period of this study. The levels of dissolved oxygen (D.O.) and biochemical oxygen demand (B.O.D.) of the water specimens sampled from the study areas ranged from 6.0 to 9.6 ppm and from 0.4 to 1.6 ppm, respectively. Eight metalic constituents from the water samples were also assayed, and all metalic ions detercted were remarkably low below the legal criteria. However, calcium ion in the water samples from the habitats of P. manchouricus was considerably higher than others.

  • PDF