Carassius Cuvieri Research Articles

Study on sperm cryopreservation of hybrid fish derived from Carassius cuvieri (♀) × Carassius auratus red var (♂)

Cryopreservation of sperm is an effective method for conserving germplasm resources in fish genetic breeding. The high-quality hybrid fish (WR) derived from white crucian carp (Carassius cuvieri, WCC, ♀) and red crucian carp (C. auratus red var., RCC, ♂), possesses valuable traits such as high survival rates, strong resistance, and rapid growth, representing an important germplasm resources of crucian carp. This study compared the effects of different antifreeze solutions on sperm viability among three varieties (WR, WCC, and RCC) and examined changes in enzyme activity, fertilization rates, and hatching rates after cryopreservation, aiming to enhance the cryogenic sperm cryopreservation technique in hybrid fish and investigate the mechanisms underlying spermatozoa damage caused by cryopreservation. The results showed that the antifreeze combination of D14 with 15 % dimethyl sulfoxide (DMSO) had the best effect in preserving the sperm of WR and WCC, while D20 with 10 % DMSO was the optimal combination for RCC sperm. After ultra-low temperature preservation, the longevity, fertilization, and hatching rates of frozen sperm were significantly lower (P < 0.05) compared to fresh sperm. The enzyme activities of superoxide dismutase (SOD), lactate dehydrogenase (LDH), and creatine kinase (CK) were significantly decreased (P < 0.05) in spermatozoa, whereas they showed a significant increase (P < 0.05) in sperm plasma. Succinate dehydrogenase (SDH) activity was significantly reduced (P < 0.05) in frozen spermatozoa of RCC compared to fresh spermatozoa, and exhibited lower activity in frozen spermatozoa of WCC and WR. Additionally, SDH activity was significantly elevated (P < 0.05) in frozen sperm plasma, and glutathione reductase (GR) activity was significantly lower (P < 0.05) in both frozen sperm plasma and spermatozoa across all three species. The study demonstrated that cryopreservation had a significant effect on the enzyme activities of spermatozoa and sperm plasma in all three species. These findings provide important technical support for the conservation of high-quality fish germplasm resources, particularly for novel varieties resulting from distant hybridization in fish.

Fish IL-26 collaborates with IL-10R2 and IL-20R1 to enhance gut mucosal barrier during the antibacterial innate immunity

IL-26 is a cytokine that is crucial for the maintenance and function of the gut mucosal barrier. IL-26 signaling pathway relies on a heterodimeric receptor complex, which is composed of two distinct subunits, IL-10R2 and IL-20R1. However, there are no reports on the antibacterial immunity of IL-26 and its receptors in fish. For this purpose, in this study we identified IL-26 and its receptors IL-10R2 and IL-20R1 in Carassius cuvieri × Carassius auratus red var. (named WR-IL-26, WR-IL10R2 and WR-IL20R1, respectively). Phylogenetic analysis confirmed the conservation of these genes, with shared structural motifs similar to those found in higher vertebrates. Upon exposure to Aeromonas hydrophila, a common fish pathogen, there was a significant upregulation of WR-IL-26, WR-IL10R2 and WR-IL20R1 in the gut, indicating a potential role in the immune response to infection. A co-immunoprecipitation assay revealed that WR-IL-26 formed complexes with WR-IL10R2 and WR-IL20R1. In vivo experiments demonstrated that administration of WR-IL-26 activated the JAK1-STAT3 signaling pathway and protected the gut mucosa barrier from A. hydrophila infection. Conversely, silencing WR-IL10R2 and WR-IL20R1 via RNA interference significantly attenuated the activation of WR-IL-26-mediated JAK1-STAT3 pathway. These results provided new insights into the role of IL-26 and its receptors in the gut mucosa barrier and could offer novel therapeutic strategies for managing bacterial infections in aquaculture.

Population genetic characteristics of two crucian carp varieties derived from distant hybridization

The Hefang crucian carp (HFJ) derived from Carassius cuvieri (♀) × C. auratus red var. (♂) and the crucian carp-like homodiploid fish (NCRC) derived from Cyprinus carpio (♀) × Megalobrama amblycephala (♂) are important germplasm resources of crucian carp. To investigate the population characteristics and reveal the current genetic situations of these hybrid varieties, we sequenced one nuclear molecular marker transferrin (Tf) among six Carassius populations, which included two hybrid varieties (HFJ and NCRC), one laboratory variety (red crucian carp, RCC) and three wild populations. A total of 166 distinct Tf alleles (A1∼A166) were identified, with sequence lengths ranging from 1145 bp to 1244 bp. Unexpectedly, the nucleotide diversity of Tf alleles in cultured populations (HFJ, NCRC, and RCC) exceeded that of wild populations. The phylogenetic reconstruction analysis results showed that HFJ and C. cuvieri were closely related, but they could not be separated from C. auratus. Besides, while most Tf alleles of NCRC and other Carassius populations were intermixed in five clades, two Tf alleles, together with Cy. carpio, formed a distinct monophyletic clade. Moreover, network and genetic structure analyses failed to distinguish between wild and cultured populations. Although AMOVA analysis based on Tf alleles indicated genetic differentiation among all six populations, the majority of the genetic variation (92.00 %) was observed within populations. Furthermore, the population dynamics analysis suggested that these populations have maintained relative stability in recent history. Therefore, the elevated nucleotide diversity of Tf alleles in cultured populations, the ambiguous population structure, and the limited genetic divergence among the six Carassius populations highlighted the hybrid genetic characteristics of HFJ and NCRC. These findings, based on Tf alleles, differ from the results obtained using mitochondrial gene markers, providing an alternative perspective for germplasm evaluation of hybrid varieties and crucian carp breeding.

Probiotic characterization of a novel Bacillus cereus strain fkW8-1-2 isolated from intestine of white crucian carp (Carassius cuvieri)

Microbial infection can pose a great threat to health of farmed fish. This study aimed to investigate the probiotic characteristics of Bacillus cereus strain fkW8-1-2 isolated from intestine of WCC and its anti-biofilm activity against pathogenic bacteria. The strain fkW8-1-2 showed a high resistance to low pH, bile salt and lysozyme during long-term incubation. The strain fkW8-1-2 displayed a gradual increase of cell surface hydrophobicity with various forms of hydrocarbons. The strain fkW8-1-2 showed the remarkable autoaggregation and coaggregation activity with A. hydrophila L3-3 and E. tarda 1l-4. The culture medium (CM) and cell-free supernatants (CFS) of strain fkW8-1-2 at 48 h cultivation could attenuate biofilm formation of A. hydrophila and E. tarda with the maximum inhibition rates. In addition, the intact cells of strain fkW8-1-2 exhibited the strong antioxidant activity for DPPH removal and superoxide anion clearance. These results indicated that strain fkW8-1-2 possessing probiotic characteristics can pose a protective role in health of farmed fish.

Tumor necrosis factor α1 decreases mucosal immune and antioxidant response in the midgut of hybrid fish (white crucian carp ♀ × red crucian carp ♂).

Tumor necrosis factor α1 (TNFα) is a pleiotropic cytokine involved in immune regulation and cellular homeostasis, but the crucial role of TNFα in fish gut remained unclear. The current study aimed to evaluate the immunoregulatory function of TNFα1 on gut barrier in a novel hybrid fish (WR), which was produced by crossing white crucian carp (Carassius cuvieri, ♀) with red crucian carp (Carassius auratus red var, ♂). In this study, WR-tnfα1 sequence was identified, and a high-level expression was detected in the intestine. Elevated levels of WR-tnfα1 expressions were detected in immune-related tissues and cultured fish cells on stimulation. The appearance of vacuolization and submucosal rupture was observed in TNFα1-treated midgut of WR, along with elevated levels of goblet cell atrophy, whereas no significant changes were detected in most expressions of tight-junction genes and mucin genes. In contrast, WR receiving gut perfusion with WR-TNFα1 showed a remarkable decrease in antioxidant status in midgut, whereas the expression levels of apoptotic genes and redox responsive genes increased sharply. These results suggested that TNFα1 could exhibit a detrimental effect on antioxidant defense and immune regulation in the midgut of WR.

Comparative analysis of nutrients in muscle and ovary between an improved fish and its parents

In previous studies, an allodiploid lineage (WR-F1-F5) was established by the distant hybridization of white crucian carp (Carassius cuvieri, WCC, ♀) and red crucian carp (Carassius auratus red var., RCC, ♂), an allodiploid fish (WR-II) was produced by WR-F1 (♀) × WCC (♂). In this study, the nutrients in the muscle and ovary of WR-II and its parents (WCC, RCC, and WR) were investigated, including protein, fat, amino acid, docosahexaenoic acid (DHA), moisture, and ash. The results showed that the protein content of WR-II in muscle and ovary (17.90 % and 25.60 % respectively) was higher than that of WR, and was significantly higher than that of WCC and RCC (p < 0.05). The fat content of WR-II in muscle and ovary (4.30 % and 5.31 % respectively) was higher than that of WR and was significantly higher than that of WCC and RCC (p < 0.05), and the muscle and ovary of WR-II showed rich DHA content (0.32 % and 0.54 % respectively) than that of WCC and RCC (p < 0.05). Fifteen amino acids were detected in WR-II and its parents, the total amino acid (TAA) content of WR-II in muscle and ovary (15.49 % and 18.43 % respectively) was significantly higher than that of WCC (p < 0.05), the delicious amino acid (DAA) content of WR-II in muscle and ovary (6.56 % and 8.29 % respectively) was different degrees higher than that of WCC, RCC, and WR. The moisture and carbohydrates of WR-II in muscle and ovary were lower than those in WCC and RCC. Furthermore, protein, fat, TAA, and DAA content in the ovary were significantly higher than those in muscle (p < 0.05), showing tissue differences in all detected fish. This study indicated that WR-II had the characteristics of high protein, high fat, high DHA, high TAA, high DAA, low moisture, and low carbohydrates, which provided theoretical support for its application.

Evolutionarily conserved IL-22 participates in gut mucosal barrier through its receptors IL-22BP, IL-10R2 and IL-22RA1 during bacterial infection in teleost

IL-22 is a critical cytokine of epithelial mucosal barrier. In humans, IL-22 signals through a heteroduplex receptor consisting of IL-22R and IL-10Rβ. In fish, IL-22 and its receptors homologues have been cloned in a number of species, however, no studies have been reported how the receptors are involved in IL-22 transduction. For this purpose, in this study we identified IL-22 and its soluble receptor IL-22BP and transmembrane receptors IL-22RA1 and IL-10R2 in Carassius cuvieri × Carassius auratus red var. (named WR-IL-22, WR-IL-22BP, WR-IL10R2 and WR-IL22RA1, respectively). WR-IL-22, WR-IL-22BP, WR-IL10R2 and WR-IL22RA1 were relatively conserved in the evolutionary process, sharing the same conserved domains as their higher vertebrate homologues. When the fish were infected with the Aeromonas hydrophila, the expression of WR-IL-22, WR-IL-22BP, WR-IL10R2 and WR-IL22RA1 were significantly induced in the gut. The co-IP assay showed that WR-IL-22 not only interacted with WR-IL-22BP, but also with WR-IL10R2 and WR-IL22RA1. When introduced in vivo, WR-IL-22 activated the JAK1-STAT3 axis and protected the gut mucosa from A. hydrophila infection. However, overexpression of WR-IL-22BP or knockdown of transmembrane receptors WR-IL10R2 and WR-IL22RA1 significantly inhibited the activation of WR-IL-22-mediated JAK1-STAT3 axis and promoted bacterial colonization in the gut. These results provided new insights into the role of IL-22 and its receptors in the gut mucosa barrier and immune response in teleost.

WR-PTXF, a novel short pentraxin, protects gut mucosal barrier and enhances the antibacterial activity in Carassius cuvieri × Carassius auratus red var.

The pentraxin family is an evolutionarily conserved group that plays an important role in innate immunity. C-reactive protein (CRP) and serum amyloid P component (SAP) are classical members of the short pentraxins and are known to be the major acute phase proteins. In this work, we have cloned a novel pentraxin fusion protein, WR-PTXF, from Carassius cuvieri × Carassius auratus red var. In fish, the biological function of PTXF is essentially unknown. For this purpose, we report the identification and analysis of WR-PTXF and elucidate its role in the antibacterial innate immunity. WR-PTXF contains 224 amino acids and shares 79.8% and 23.0% sequence identities with crucian carp CRP and SAP, respectively. Blast analysis shows that WR-PTXF and goldfish PTXF had the highest similarity (97.3%). WR-PTXF is expressed in multiple tissues and is upregulated by Aeromonas hydrophila infection. WR-PTXF contains a short pentraxin domain and recombinant WR-PTXF protein (rWR-PTXF) can bind the A. hydrophila in a concentration-dependent manner. Further, rWR-PTXF displays apparent bacteriostatic activity against A. hydrophila in vitro by enhancing the uptake of the bound bacteria by host phagocytes. When introduced in vivo, rWR-PTXF not only protects the gut mucosa but also limits the colonization of A. hydrophila in systemic immune organs. Consistently, knockdown of WR-PTXF significantly promotes bacterial dissemination in the tissues of host. These results indicate that WR-PTXF is a classic pattern recognition molecule that exerts a protective effect against bacterial infection.

Study of biological characteristics of an improved Japanese white crucian carp lineage derived from Carassius cuvieri (♀) × Megalobrama amblycephala (♂)

Based on the formation of fertile allotetraploid fish (4nJB, 4n = 148) derived from female Carassius cuvieri (JCC, 2n = 100) × male Megalobrama amblycephala (BSB, 2n = 48), an improved Japanese white crucian carp (IJCC) was obtained by mating female 4nJB and male 4nJB, and thus far, the population of IJCC has reached the fifth generations (F1–F5). The purpose of the present study was to comparatively investigate the biological characteristics of the IJCC lineage (F1–F5) and their original female parent JCC. The results of DNA content and chromosome numbers showed that the IJCC lineage was diploid with 100 chromosomes. For morphological characteristics, it appears that IJCC-F1 has smaller head and a higher body width than that of JCC, and some countable traits as well as the ratio of measurable traits were significantly different (P < 0.05) between these two fish. With the passing of generations, the appearance of the IJCC lineage has been stable. Regarding reproductive characteristics, the fecundity, sperm volume, sperm density, fertilization rate and hatching rate were not significantly different (P > 0.05) between the JCC and IJCC lineages, indicating that the reproductive capacity of the IJCC lineage was similar to that of the JCC. Furthermore, the growth performance showed that the average weight of IJCC-F1 and IJCC-F5 was significantly greater (P < 0.05) than that of JCC both at 6 months and 1 year of age. The good fertility of the IJCC lineage ensures the multigeneration utilization of its advantage, and the IJCC lineage has significant value in aquatic applications.

Evolutionarily conserved IL-20 enhances the response of JAK1/STAT3 axis in Carassius cuvieri × Carassius auratus red var

The IL-20 cytokine family, which includes only IL-20, IL-22 and IL-26 in teleost, has a wide range of biological functions and is essential for epithelial integrity and innate host defense. IL-22 and IL-26 are the most intensively studied cytokine within this family; however, the immunological function of IL-20 in fish is essentially unknown. In this study, we examined the expression and function of an IL-20 homologue (WR-IL20) from White crucian carp (Carassius cuvieri, WCC, female) × Red crucian carp (Carassius auratus red var., RCC, male). WR-IL20 and its parents, WCC-IL20 and RCC-IL20, were both composed of 177 residues with high identities among them. Additionally, gene structure, functional domain, tertiary structure, multiple sequence alignment, and phylogeny analysis showed a conserved status between WR-IL20, WCC-IL20 and RCC-IL20. WR-IL20, WCC-IL20 and RCC-IL20 were mainly expressed in the head kidney and were upregulated by Aeromonas hydrophila infection in vivo. Furthermore, recombinant WR-IL20 protein (rWR-IL20) induced increased transcript levels of c-Myc, cyclin D, Bcl-2, JAK1, TYK2 and STAT3 in head kidney lymphocytes in vitro. These results provide a new perspective for understanding the origin, evolution and function of IL-20 in teleost.

Alteration of synergistic immune response in gut-liver axis of white crucian carp (Carassius cuvieri) after gut infection with Aeromonas hydrophila.

Aeromonas hydrophila can pose a great threat to the survival of farmed fish. In current study, we investigated the pathological characteristics and immune response in gut-liver axis of white crucian carp (WCC) upon gut infection. WCC anally intubated with A. hydrophila exerted a tissue deformation in damaged midgut with elevated levels of goblet cells along with a significant decrease in tight junction proteins and villi length-to-width ratios. In addition, immune-related gene expressions and antioxidant properties increased dramatically in gut-liver axis of WCC following gut infection with A. hydrophila. These results highlighted the immune modulation and redox alteration in gut-liver axis of WCC in response to gut infection.

Fish Diversity and Ichthyofauna of Areas Adjacent to the Demilitarized Zone in South Korea

The Korean Demilitarized Zone (DMZ) was established in 1953 during the cessation of the Korean War, which divided the Korean Peninsula into North and South Korea. The DMZ is a representative biodiversity resource because it limits human activities. The current status of faunal diversity in adjacent areas of the DMZ was investigated in five regions at 91 sites from 2015 to 2019. A total of 19,562 individuals were collected and identified, including 81 species, 19 families, and 11 orders. Zacco koreanus was the most abundant fish species (relative abundance of 21.9%), while other key species were Zacco platypus (18.2%), Rhynchocypris oxycephalus (5.2%), Rhynchocypris steindachneri (4.9%), and Pungtungia herzi (3.7%). Notably, twenty-nige endemic and seven Red Data Book species were recorded, and three exotic species, Carassius cuvieri, Micropterus salmoides, and Lepomis macrochirus were found at five sites. Human activities and disturbances were found at 34.0% of all sampling sites, and the highest disturbance factors were river dredging and agricultural use (seven sites), sewage (five sites), and fisheries and development (two sites). We recommend that the governments of South and North Korea collaboratively manage the DMZ to protect ecological diversity and maintain its status as a symbol of peace.

Redescription of &lt;i&gt;Argulus mongolianus&lt;/i&gt; (Crustacea: Branchiura: Argulidae), an Ectoparasite of Freshwater Fishes in East Asia, with Its First Record from Japan

Both adult females and males of Argulus mongolianus Tokioka, 1939 were collected from the buccal cavity wall and body surface of freshwater fishes in Lake Izunuma and Lake Uchinuma, Miyagi Prefecture, northen Honshu, Japan. The original description of the species was insufficient, based on a single female from Inner Mongolia, China, and no further description has been made to date. Thus, this paper redescribes A. mongolianus based on the newly-collected specimens, including the first description of the male. This represents the first record of A. mongolianus from Japan. The infected fishes were largemouth bass, Micropterus salmoides (Lacepède, 1802), common carp, Cyprinus carpio Linnaeus, 1758, Japanese white crucian carp, Carassius cuvieri Temminck and Schlegel, 1846, and silver crucian carp, Carassius sp. The three species other than common carp are new host records for A. mongolianus. This parasite was most probably introduced with an unspecified freshwater fish from China into Japan.

Species-specific debromination of BDE99 in teleost fish: The relationship between debromination ability and bioaccumulation patterns of PBDEs

Polybrominated diphenyl ethers (PBDEs) are known to be broken down by debromination reactions in the natural environment, such as by photolysis, microbial and metabolic processes. Although species-specific debromination of PBDEs by fish has also been reported, it has only rarely been studied from the phylogenetic perspective. The objective of this study is to reveal the factors affecting species-specific debromination through validation between the bioaccumulation of PBDEs in muscle tissue and the ability to debrominate BDE99. As environmental observations, PBDE concentrations in muscle tissues were analyzed in 25 wild fish (Cyprinidae, Gobiidae and others). As in vitro experiments, debromination experiments were conducted using the hepatic microsomes of 21 fish species. Significant amounts of BDE99 were detected in almost none of the Cyprinidae. A relatively higher debromination ability was confirmed in the Cyprinidae in in vitro experiments. The Cyprinidae thus appears to be a family with high debromination ability. BDE99 has been detected in some goby species but not others. This pattern was also seen in in vitro experiments, suggesting that debromination ability is not consistent within the Gobiidae. In further quantitative comparisons, kinetic parameters such as Km and vmax were determined for selected fish species. The common carp (Cyprinus carpio) and the Japanese crucian carp (Carassius cuvieri), both Cyprinidae, showed higher vmax values, whereas vmax values among three Gobiidae diverged widely. A comparison of field observations and in vitro experiments, revealed the bioaccumulation ratio of BDE99 to be affected by the BDE99 debromination ability of each fish species. This is the first report on classification of BDE99 accumulation ratio by debromination ability and a phylogenetic species comparison based on kinetic parameters for debromination reactions of PBDEs by fish.

琵琶湖・早崎内湖干拓地外の造成ヨシ帯におけるゲンゴロウブナ（コイ科フナ属）の産卵： 産着卵のDNA 種判別にもとづく確認

琵琶湖・早崎内湖干拓地外の造成ヨシ帯におけるゲンゴロウブナ（コイ科フナ属）の産卵： 産着卵のDNA 種判別にもとづく確認

A new type of triploid fish derived from the diploid hybrid crucian carp (♀) × autotetraploid fish (♂)

Based on the allodiploid lineage (WR, 2n ​= ​100, F1–F5) of white crucian carp (Carassius cuvieri, WCC, 2n ​= ​100) (♀) ​× ​red crucian carp (Carassius auratus red var., RCC, 2n ​= ​100) (♂) and the diploid hybrid fish (WR-II, 2n ​= ​100) derived from WR-F1 (♀) ​× ​WCC (♂), in this research, we obtain a new type of triploid fish (WR-III) by the distant hybridization of WR-II (♀) and autotetraploid fish (4nAU, 4n ​= ​200) (♂). We investigate the morphological traits, chromosomal numbers, DNA content, growth rates and 5S rDNA in the WR-III. The results show that the WR-III is triploid fish with 150 chromosomes and they have no barbel and have a gray body color. All the measurable traits of WR-III show hybrid characteristics; and there is a significant difference in the body length/body height between WR-III and 4nAU, which indicating that WR-III has a smaller head and higher body compared with 4nAU; furthermore, the WR-III has a fast growth rate, the average body weights of eight months old WR-III is 487g. The 5s rDNA of the WR-III inherits the 5s rDNA of its parents and has some mutant bases or chimeric sequences, which revealed heredity, variability and heterozygosity in WR-III. The successful production of this triploid fish is of great significance in fish genetic breeding.

Underwater video and still‐image dataset of fishes and other aquatic animals in Lake Biwa, Japan, observed via carp‐mounted video loggers

AbstractThis is the first large dataset of underwater videos from which species occurrence and behavioral records of aquatic organisms were identified in Lake Biwa, the largest lake in Japan. We compiled 109 videos and 122 still‐images of fishes, diving birds and shrimps. The images were cropped from videos taken underwater with animal‐borne video cameras which were mounted on the backs of common carp (Cyprinus carpio). The attribute of each image and its occurrence of organisms were formatted according to the Darwin Core Archive which was developed by the Biodiversity Information Standards (TDWG), and the dataset is available via the Global Biodiversity Information Facility. Our dataset includes records of 10 species, 4 genera, 2 families and 1 infraorder which includes mostly fishes, several birds and a crustacean. The fish records include a threatened endemic fish, the “gengorou‐buna” crucian carp (Carassius cuvieri), and two alien fishes, largemouth bass (Micropterus salmoides) and bluegill sunfish (Lepomis macrochirus). We confirmed several types of intraspecific and interspecific relationships between video‐mounted carp and other organisms; for example, most video‐mounted carp frequently approached or chased conspecifics upon encountering, which sometimes led to two carp feeding side by side. At least three avian species also appeared in the dataset: Eurasian coot (Fulica atra), little grebe (Tachybaptus ruficollis), great crested grebe (Podiceps cristatus), but there was no apparent interaction between carp and these birds. Our underwater videos reveal and highlight the rich biodiversity of the lake today, providing clear evidence for behavior of aquatic organisms under natural conditions.The complete data set for this abstract published in the Data Paper section of the journal is available in electronic format in MetaCat in JaLTER at http://db.cger.nies.go.jp/JaLTER/metacat/metacat/ERDP-2020-18.1/jalter-en.

Assessment of fish biodiversity in four Korean rivers using environmental DNA metabarcoding.

Environmental DNA (eDNA) metabarcoding is a cost-effective novel approach to estimate biodiversity in an ecosystem. In this study, the MiFish pipeline was employed to test if the system methodology is sufficiently reliable to estimate fish biodiversity in Korean rivers. A total of 125 unique haplotypes and 73 species were identified at the species level from 16 water samples collected from a single survey in four Korean rivers (Hyeongsan, Taehwa, Seomjin, and Nakdong). Among the four rivers, the highest species richness was recorded in the Seomjin River (52 species), followed by the Taehwa (42 species) and Hyeongsan (40 species) rivers. The Nakdong River (26 species) presented the lowest species richness and number of endemic species, presumably due to its metropolitan location and anthropogenic impacts, such as dams or weirs. We were also able to detect that five exotic species (Carassius cuvieri, Cyprinus carpio, Cyprinus megalophthalmus, Lepomis macrochirus, and Micropterus salmoides) are widely distributed in all surveyed rivers, a situation that might be problematic in terms of conservation. Our findings indicate that the eDNA metabarcoding technique is one of the most cost-effective scientific tools available for the management and conservation of the freshwater fish resources available in Korea. However, the low number of 12S sequences of endemic species in the database and low resolution of the MiFish region for differentiating several taxa should be upgraded for their wide use.

A hybrid lineage derived from hybridization of Carassius cuvieri and Carassius auratus red var. and a new type of improved fish obtained by back-crossing

Hybridization is an important technique and is widely used in fish genetic breeding; this technique prevents variety degeneration and improves variety. In this research, we obtained a hybrid lineage (WR-F1-F4) by interspecific hybridization derived from female white crucian carp (Carassius cuvieri, WCC) and male red crucian carp (Carassius auratus red var., RCC), and a new type of improved fish (WR-II) was obtained by back-crossing between the female hybrid (WR-F1) and the male WCC. We investigated the morphological traits, chromosomal numbers, DNA content, gonadal development, sperm shape and 5S rDNA in the hybrid lineage and WR-II. The results showed that all the assessed morphological traits were not significantly different between the progenies of the hybrid lineage and their original parents, but the WR-II showed smaller head and higher body compared with its original parents; the hybrid lineage and WR-II were diploid with 100 chromosomes; all the tested males and females of the hybrid lineage and WR-II had normal gonadal development and produced mature sperm and egg, respectively; the 5S rDNA of the hybrid lineage and WR-II inherited the characteristics of their parents and had some mutant bases or chimeric sequences, which revealed heredity, variability and heterozygosity in the hybrid progenies; finally, the 5S rDNA of the hybrid lineage could be highly inherited from the second generation (WR-F2) to the next generations. This study will be beneficial for the establishment and application of hybrid lineages in genetic breeding.

Impact of human activities on changes of ichthyofauna in Dongjin River of Korea in the past 30 years

ABSTRACTIchthyofauna and fish community were investigated at 17 representative stations of the Dongjin River drainage system from spring to fall in 2014. The survey resulted in a list of 53 species belonging to 14 families structured into 4 distinctive parts along the river: uppermost-stream, upper-stream, mid-stream, and lower-stream. Comparison of species lists with 30-year interval exhibited significant decreases in peripheral freshwater fishes, Acheilognathinae, endemic, and indigeneity species, but increases in exotic, epipelagic, and lentic species. Moreover, in the estuary of the Dongjin River drainage system, peripheral freshwater fish species were replaced by pure freshwater fish species due to the Saemangeum sea-wall project. In the upper region of the river, introduced eight alien species from Seomjin River via water diversion tunnels. In the mid-lower region, the construction of floodgates and numerous small weirs caused expansion of lentic water areas, facilitating the spread of problematic exotic species such as Micropterus salmoides, Lepomis macrochirus, and Carassius cuvieri. Also, water deterioration in this region resulted in an increase of tolerant species and a decrease of sensitive and endemic species. Our results suggest that a recovery strategy for a healthy ecosystem in the Dongjin River drainage system should reflect this compartmentalized cause and effect on the changes of icthyofauna.