Freshwater environments serve as crucial habitats for diverse microorganisms, playing essential roles alongside plants and animals within the ecosystem. Bacteria in these environments are particularly important for maintaining ecosystem functions. Among them, members of the phylum Pseudomonadota are known to be involved in processes such as nitrogen fixation, ammonia oxidation, and biofilm formation. Pseudomonadota comprises six classes: Acidithiobacillia, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Hydrogenophilia, and Zetaproteobacteria. This study reports 43 previously unrecorded species belonging to the phylum Pseudomonadota. They were isolated from various freshwater habitats in Republic of Korea. These strains were isolated and cultured using nine different standard media, with classification based on Gram staining, cell morphology, and biochemical characteristics. Species identity was determined using 16S rRNA gene sequencing, with a similarity threshold of 98.7% for designation as unreported species. Phylogenetic analysis revealed that these 43 strains were distributed across three classes, 13 orders, 28 families, and 39 genera. This research emphasizes microbial diversity in freshwater ecosystems and provides valuable insights into ecological roles and potential novel functions of unreported bacterial species in Korea.

As part of the 2024 research initiative, “Investigation and Discovery of Prokaryotes in Freshwater Systems,” samples were collected from diverse freshwater habitats, including both water and soil environments. Approximately 2,000 bacterial strains were isolated as single colonies and identified through 16S rRNA gene sequence analysis. Among these, 38 strains shared ≥98.7% 16S rRNA gene sequence similarities with those of known bacterial species not previously reported in Korea. These strains were thus categorized as newly recorded bacterial species in Korea. These 38 bacterial strains displayed significant phylogenetic diversities, spanning 2 phyla, 4 classes, 15 orders, 24 families, and 34 genera. These unrecorded species were classified into the following classes: Actinomycetia (with genera including Microcella, Conyzicola, Curtobacterium, Leucobacter, Microbacterium, Frigoribacterium, Lysinibacter, Streptomyces, Nonomuraea, Actinocorallia, Ruania, and Actinoplanes), Alphaproteobacteria (Paracoccus, Youngimonas, Loktanella, Corticibacterium, Neorhizobium, Onobrychidicola, Ferranicluibacter, Aureimonas, Asticcacaulis, and Novosphingobium), Betaproteobacteria (Rhodoferax, Rugamonas, and Cupriavidus), and Gammaproteobacteria (Rheinheimera, Shewanella, Kosakonia, Leclercia, Hafnia, Yersinia, Pseudomonas, Lysobacter, and Acinetobacter ). Further characterization included assessment of Gram reaction, colony and cell morphology, biochemical properties, and phylogenetic relationships. This report presents detailed phylogenetic and phenotypic characteristics of these bacterial species.

During an investigation of indigenous prokaryotic species in the Republic of Korea, 17 bacterial strains belonging to the phylum Bacteroidota and 4 strains belonging to the phylum Bacillota were isolated from freshwater environments. These isolated bacterial strains formed a robust phylogenetic clade with type strains of the closest related bacterial species, with 16S rRNA gene sequences sharing similarities of higher than 98.7%. To date, there have been no official report of these 21 isolates in the Republic of Korea. At the genus level, these unreported species were affiliated with Mucilaginibacter and Pedobacter of class Sphingobacteriia, Flavobacterium and Gillisia of class Flavobacteriia, Hymenobacter of class Cytophagia, and Paenibacillus and Planococcus of class Bacilli. These species were further examined by performing Gram staining, analyzing their colonies and cell morphologies, and determining their basic biochemical characteristics and phylogenetic positions. Detailed descriptions of the 21 previously unreported species are provided.

Microalgae are efficient fatty acid producers owing to their high photosynthetic activities. They can act as sources of biofuel, feed, and various bioactive compounds. This study aimed to determine optimal culture conditions, including culture medium, temperature, and light intensity, to enhance the biomass and fatty acid content of the indigenous freshwater microalga, Tetradesmus obliquus. Evaluation using a high-throughput photobioreactor revealed that the optimal culture temperature and light intensity were 25°C and 300 μmol m-2 s-1, respectively. Additionally, we optimized components (N, P, and Mg) of the BG-11 medium to enhance the microalgal biomass. Modified BG-11 medium increased the T. obliquus biomass by 37% compared to the standard BG-11 medium. Subsequently, the culture medium was replaced with N- and P-depleted media to determine the abiotic stress factor that could increase the cellular fatty acid content. Notably, fatty acid content was significantly increased from 8.5% up to 14.6% on day 7 of culture in N-deficient (N-P+ and N-P-) media. Sequential optimization effectively increased the biomass by 83% and fatty acid content by >76% in T. obliquus. Our optimization method can be used to enhance the biomass and fatty acid contents of various other microalgae.

Biodiversity encompasses species diversity, which includes species richness and species evenness. High species diversity is known to contribute to community stability and the potential for maintaining healthy ecosystem functioning. However, the most commonly used species diversity indices have some limitations, as they require species-specific abundance data for each community. In contrast, phylogenetic diversity measures the evolutionary distances between species within a community, reflecting ecological and/or evolutionary divergences and niche differences, without requiring abundance data. This study assessed biodiversity by calculating phylogenetic diversity indices for freshwater fishes (19 species) and aquatic insects (49 species) at three sites within Seoraksan and Odaesan National Parks. The aquatic insects studied belong to the EPT group (Ephemeroptera, Plecoptera, and Trichoptera), which are widely used as bioindicators of aquatic ecosystems. Two mitochondrial DNA genes were used as molecular markers: COI and cyt b for fish, and COI and 16S rRNA for the EPT - group. Overall, Odaesan National Park exhibited higher phylogenetic diversity in both fishes and aquatic insects compared to Seoraksan National Park, although this difference was not statistically significant. The highest phylogenetic and species diversity were observed for fish at the OD2 site (Woljeong District) and for the EPT group at the OD1 (Gyebangsan) and SA2 (Jangsudae) sites. Correlation analysis revealed that phylogenetic diversity indices were more positively associated with species richness than species diversity indices. This study serves as a pilot project for establishing standardized methods for assessing biodiversity in national park habitats using phylogenetic diversity. It also aims to inform various policies, such as the development of biodiversity assessment systems and the prioritization of protected areas within national parks.

Fish require movement for feeding, spawning, growth, and evading predators, making swimming ability a critical factor in their survival. Swimming speed in fish are generally classified into sustained, prolonged, and burst speed. This study assessed the swimming capabilities of native benthic freshwater fish and provided data to inform the design and construction of fishways. Three fish species were examined: Pseudobagrus fulvidraco (family Bagridae), Tridentiger brevispinis and Rhinogobius brunneus (family Gobiidae). Measurements of total length, standard length, body weight, and body height were collected for each species, and swimming ability was evaluated using a swimming tunnel apparatus. Swimming ability was determined by measuring burst speed to calculate the critical swimming speed (Ucrit) and the relative swimming speed (TL s-1). The mean critical swimming speeds were 0.73±0.15 m s-1 for P. fulvidraco, 0.75±0.1 m s-1 for T. brevispinis, and 1.34±0.12 m s-1 for R. brunneus. Additionally, a significant correlation was found between swimming ability and total length, indicating that swimming capabilities may vary based on body type and behavior. These findings contribute essential insights into the swimming abilities of native freshwater fish, offering valuable data for improving fishway design. Further research is suggested to evaluate the swimming capabilities of a broader range of freshwater fish species to enhance fishway efficiency.

Freshwater environments are rich ecosystems that support diverse microbial communities, including members of the phylum Actinomycetota critical for nutrient cycling, organic matter decomposition, and water quality maintenance. Actinomycetota known to produce numerous bioactive secondary metabolites are valuable in biotechnology, medicine, and agriculture. Despite their significance, the diversity and distribution of Actinomycetota in freshwater habitats, especially in the Republic of Korea, are underexplored. This study aimed to report the isolation and characterization of 22 previously unrecorded bacterial species of Actinomycetota from various freshwater environments in Korea. Using standard dilution plating techniques on six different culture media, 22 bacterial strains were isolated, incubated, and characterized based on colony and cellular morphologies, Gram staining, and biochemical properties. Genomic DNA was extracted and the 16S rRNA gene was sequenced to determine species identity using the EzBioCloud service with a cutoff of 98.7% sequence similarity for classification as unreported species. These strains were phylogenetically diverse, belonging to two classes, ten orders, and eighteen genera. This study enhances our understanding of bacterial diversity in freshwater ecosystems and underscores the importance of exploring microbial diversity in underexplored habitats, potentially leading to discovery of novel bioactive compounds. Findings of this study contribute valuable insights into ecological roles and biotechnological potential of Actinomycetota in freshwater environments.

Diatoms, which are reported to have over 18,000 species worldwide and approximately 2,400 species in Korea, can be found in various environments including freshwater, seawater, and wetlands. They are particularly valuable for understanding global environmental changes throughout history due to their ability to maintain their shape for extended periods of time. Instead of collecting floating diatoms using nets, low-layer substrates such as gravel and leaves, as well as sedimentary surface layers, were gathered in order to identify attached diatom species. This is because attached diatoms demonstrate higher species diversity compared to floating diatoms. In this study, seven previously unrecorded diatoms were discovered in various domestic freshwater environments. Two species were found in reservoirs (Eunotia yanomami, Gomphonella pseudookunoi), two in parasitic cones (Eunotia carverenensis, Luticola minor), two in rivers (Cavinula maculata and Prestauroneis integra), and one (Surirella brebissonii var. kuetzingii) in a lagoon. The shapes, structures, and morphological characteristics of each diatom were identified using electron microscopy.

Zooplankton biomass is essential for understanding the quantitative structure of lake food webs and for the functional assessment of biotic interactions. In this study, we aimed to propose a biomass (dry weight) estimation method using the body length of cyclopoid copepods. These copepods play an important role as omnivores in lake zooplankton communities and contribute significantly to biomass. We validated several previously proposed estimation equations against direct measurements and compared the suitability of prosomal length versus total length of copepods to suggest a more appropriate estimation equation. After comparing the regression analysis results of various candidate equations with the actual values measured on a microbalance-using the coefficient of variation, mean absolute error, and coefficient of determination-it was determined that the Total Length-DW exponential regression equation [W=0.7775×e2.0183L; W (μg), L (mm)] could be used to calculate biomass with higher accuracy. However, considering practical issues such as the morphological similarity between species and genera of copepods and the limitations of classifying copepodid stages, we derived a general regression equation for the pooled copepod community rather than a species-specific regression equation.

In ecosystems within limited resources, interspecific competition is inevitable, often leading to the competitive exclusion of inferior species. This study aims to provide foundational information for the conservation and restoration management of Microphysogobio rapidus by evaluating species’ ecological response to biological factors within its habitat. To understand this relationship, we collected food web organisms from site where M. rapidus coexist with Microphysogobio yaluensis, a specie ecologically similar to M. rapidus, and evaluated the trophic levels (TL), isotopic niche space (INS), and the overlap of INS among fishes within the habitat using stable isotope analysis. Our analysis revealed that the M. rapidus exhibited a higher TL than M. yaluensis, with TL of 2.6 and 2.4, respectively. M. yaluensis exhibited a broad INS, significantly influencing the feeding characteristics of most fish. Conversely, M. rapidus showed a narrow INS and asymmetric feeding relationships with other species, in habitats with high competition levels. This feeding characteristics of M. rapidus indicate that the increase in competitors sharing the similar resources lead to a decrease in available resources and, consequently, is expected to result in a decrease in their density.

Captive breeding and reintroduction are crucial strategies for conserving endangered species populations. However, fish raised in predator-free environments, show a lack of recognition of predationrelated stimuli such as chemical and visual signals. It is critical to recognize chemical signals from injured conspecifics, also known as alarm signals, and the order or shape of predators to indicate the spread of predation risk in the habitat. We conducted a laboratory experiment to determine and adjust the optimal exposure period to induce appropriate anti-predator behavior response to different types of stimuli (Chemical, Visual and Chemical+Visual) for the endangered species Microphysogobio rapidus. Our results demonstrate that predator avoidance behavior varies depending on the types of stimuli and the duration of predation risk exposure. First, the results showed captive-breed M. rapidus show lack of response against conspecific alarm signal (Chemical cue) before the predation risk exposure period and tend to increase response over predation risk exposure time. Second, response to predator (visual cue) tend to peak at 48 hours cumulative exposure, but show dramatic decrease after 72 hours cumulative exposure. Finally, response to the mixed cue (Chemical+visual) tend to peak prior to the predation risk exposure period and show reduced response during subsequent exposure periods. This experiment confirms the lack of responsiveness to conspecific alarm signals in captive-bred M. rapidus and the need for an optimal nature behavior enhancement program prior to release of endangered species. Furthermore, responsiveness to predator visual signal peak at 48 hours cumulative exposure, suggest an optimal predation risk exposure period of up to 48 hours. Key words: predator cognition, captive breeding, chemical signal, visual signal, endangered

To determine the cause of the population decline in Gobiobotia naktongensis, substrate preference and burying behaviour were investigated in this study. In general, the species was shown to prefer a substrate size of 1 mm or less, depending on the flow. In addition, the burying depth varied according to the size of the fish and increased with a decrease in water temperature. Our findings showed that the main cause of the population reduction was the physical changes in the substrate structure due to the dams or barrages construction. Notably, the accumulation of silt and mud in the substrate upon the formation of an upstream lentic water region for structural construction and bed armouring caused by scouring and reduced downstream inflow of fine sediment were deterministic in the fish habitat changes, causing problems in burying. As sand substrate structure is critical for the survival and inhabitation of psammophilous species, efficient strategies should be developed with proper habitat management to reduce the anthropogenic damage

큰징거미새우(Macrobrachium rosenbergii)는 양식 시설 내에서 체색 불량 및 갑각 약화와 같은 문제로 경제적 손실을 겪고 있다. 이 종은 동물성 원료 기반의 사료로 양식되지만, 야생에서는 식물체 비중이 높은 detritus를 주로 섭취한다. 새우가 야생에서 섭취한 식물체는 기본 영양소 뿐만 아니라 체색의 재료인 카로티노이드의 공급원이기도 하다. 개나리(Forsythia koreana)는 우리나라에 널리 분포하는 꽃나무로 잎에는 황색 당근에 버금가는 양의 카로티노이드가 함유 되어 있다. 본 연구에서는 큰징거미새우에게 개나리 잎을 공급하여 체색 및 건강도에 미치는 효과를 조사하였다. 실험사료는 「배합사료 100%(대조구), CON」, 「배합사료 80%+개나리 잎 분말 20%, FP」, 「배합사료 80%+가공하지 않은 개나리 잎 20%, FL」의 세 가지였으며, 각 조건 의 사료를 평균 체중 1.1 ± 0.2 g의 어린 새우들에게 10주간 공급하였다. 실험 결과, 체색의 경 우, CON의 새우들은 일관적으로 투명한 상아색을 띠었으나, FP와 FL 새우의 경우 사육일의 경과에 따라 푸른색을 거쳐 암갈색으로 변화하였다. 생존과 성장은 CON과 FP 또는 FL 사이에 유의한 차이가 없었다. 간췌장을 조직학적으로 비교한 결과, hepatopancreatic tubule의 구성 세포 중 B cell의 vacuole 크기가 CON에 비해 FP과 FL에서 훨씬 컸다. B cell의 vacuole은 영 양소의 흡수 및 소화의 역할을 하며, 개나리 잎의 공급이 큰징거미새우의 건강에 긍정적으로 작용했을 가능성을 시사한다. 이상의 결과는 큰징거미새우의 양식에 개나리 잎을 활용하면 성장 저해 없이 체색의 개선 및 건강도의 향상을 기대할 수 있음을 보여준다.

남강댐 하류역에 위치한 사천만, 진주만, 강진만에서 가화천 방류에 따른 담수 배제의 분배 특성을 평가하기 위하여 입자추적 수치실험을 실험하였다. 가화천을 통해 3개의 방류조건(무방류, 강우시 방류, 홍수시 방류)에서 입자 1000개를 투여하여 노량수도, 대방수 도, 창선해협으로 빠져나가는 입자의 수를 비교하였다. 가화천을 통한 방류량이 늘어날수록 노량수도로의 입자 분배율이 증가하고, 대방 수도로의 분배율이 감소하는 것을 확인할 수 있었다. 즉, 평소에는 가화천 하류에 위치한 물질의 약 95%가 대방수도를 통해 빠져나가다 가, 강우에 의해 남강댐의 방류량이 증가하면서 노량수도로의 분배율이 증가하며, 홍수시에는 노량수도로의 입자 분배율이 45.5% 까지 증가하는 것을 확인할 수 있었다.

This study investigated unrecorded freshwater bacterial species in Korea. Water and sediment samples were collected from the Nakdong River basin from 2020-2022. Bacterial isolates obtained through the conventional culture method with commercial media were subjected to 16S rRNA gene sequencing to identify unrecorded bacterial species. Results of 16S rRNA gene sequencing of the bacterial isolates revealed that a total of 44 bacterial isolates shared 16S rRNA gene sequence similarities of more than 98.65%, with validly published bacterial species not reported in Korea yet. These isolates were phylogenetically assigned to 4 phyla, 7 classes, 21 orders, 33 families, and 42 genera. A total of 2, 6, 12, and 24 species belonged to phyla Bacillota, Bacteroidota, Actinomycetota, and Pseudomonadota, respectively. Here, we provide details of these 44 unrecorded bacterial species, including Gram staining, colony and cellular morphologies, biochemical properties, and phylogenetic position.

Freshwater jellyfish, a type of jellyfish exclusively found in freshwater, has a limited number of species but is found globally. However, their ecology and causes of occurrence are largely unknown. Therefore, understanding the distribution of polyps, which produce the larvae of freshwater jellyfish, can provide important data for comprehending their ecology. This study aims to explore the COI gene of freshwater jellyfish using environmental DNA from the microbial film in the Miho River system. Among the 12 survey points in the Miho River watershed, genetic material of freshwater jellyfish was detected in 8 points, mainly located upstream near reservoirs. These genetic materials were identified as genes of the well-known freshwater jellyfish species, Craspedacusta sowerbii. Notably, the C. sowerbii genes found in the Miho River watershed survey points were closely related to a species previously discovered in Italy. Consequently, utilizing environmental DNA to explore the genetic traces of freshwater jellyfish enables rapid screening of areas with a high likelihood of freshwater jellyfish occurrence. This approach is deemed to provide crucial information for understanding the distribution and ecology of freshwater jellyfish in Korea.

The aquarium pet trade is a source of potentially invasive crayfish species, which can be subsequently intentionally or unintentionally introduced into new environments. There were 34 species of freshwater crayfish imported into Korea for ornamental purposes. Starting with 1 species in 2008, it shows a trend of continuous increase every year with the maximum of 25 species in 2020. The number of freshwater crayfish imported into Korea for ornamental purposes was 1,172,159, with an annual average of 78,144 being imported. The population also recorded a record high in 2017 with a 38% increase in population imports compared to the previous year. Among the 34 pet crayfish imported into Korea, four species classified as high-risk and managed in the US and Europe were American crayfish (Procambarus clarkii), Cherax quadricarinatus, Cherax cainii, and Cherax destructor. In addition to American crayfish (P. clarkii), 3 types of high-risk invasive crayfish are designated as legally managed species by conducting an ecological risk assessment, raising awareness among importers, retailers and consumers through awareness-raising education on freshwater crayfish, and measures for route management such as species identification and improvement of labeling methods are needed.

Microphysogobio rapidus is designated as endangered species class I by Ministry of Environment, and its distribution and population have been gradually declining, and it is now limited to the Nam River and some tributary streams of the Nakdong River Watershed. For the restoration of this highly endangered species, it is important to identify the causes of the decline and establish appropriate restoration plans. However, due to lack of basic data and ecological research, most steps are stagnant. Therefore, in this study, we identified the differences in the physical, biological, and sociological habitats between current and past distributed sites through field surveys and literature reviews. As a result of the field survey, there were differences in conductivity between the current and past distributed sites, and fish communities were also showed differences. The literature data also showed that the physico-chemical values of the past distributed sites were generally unfavorable, which generated negative consequences on biological factors. In particular, the effects of urbanization were found to be a major factor affecting the habitat of M. rapidus. Habitat stabilization is crucial for the recovery of this endangered species. However, in the past distributed sites, disturbances such as stream development and weir construction have altered streams physico-chemically and result in changes of M. rapidus. Therefore, a comprehensive plan that considers both stream connectivity and water quality is needed to manage and restore the habitat of M. rapidus.