• Korean Journal of Fisheries and Aquatic Sciences
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• v.43 no.5
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• pp.462-473
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• 2010

Inductions of hybrids and reciprocal hybrids between Oryzias dancena and O. javanicus (ODJ and OJD) were conducted and backcross hybrids between female O. dancena and male ODJ were also produced for biological and cytogenetic analysis. Embryonic development of ODJ and OJD were compared with those of their parents. Developmental time was fastest in O. dancena and ODJ, followed by O. javanicus and OJD. Oryzias dancena hatched 11 days (d) after fertilization, ODJ at 13 d, O. javanicus at 14 d and OJD at 15 d. The abnormality of external morphology rate in ODJ was 10.6%; however, OJD showed a high degree of abnormality, over 90%. The proportion of males was 90.0% and 31.3% for ODJ and OJD, respectively. Cytogenetic analysis was conducted to obtain basic information for genetic identification of O. dancena, O. javanicus and their hybrids. The karyotypes of all experimental groups showed 2n=48 chromosomes and the fundamental number (FN) was 48. The first pair carried secondary constrictions near the centromeric regions. Erythrocyte area and volume were $9.8\;{\pm}\;0.5\;{\mu}m^2$ and $18.2\;{\pm}\;1.0\;{\mu}m^3$, respectively, for O. dancena, $8.3\;{\pm}\;0.5\;{\mu}m^2$ and $15.8\;{\pm}\;1.5\;{\mu}m^3$ in O. javanicus, and $18.3\;{\pm}\;0.5\;{\mu}m^2$ and $15.7\;{\pm}\;1.3\;{\mu}m^3$ in ODJ. Erythrocyte area and volume in ODJ were similar to those of O. javanicus. In backcross hybrids between female O. dancena and male ODJ, all embryos failed to develop and died in the late gastrula stage.

• Fisheries and Aquatic Sciences
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• v.15 no.4
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• pp.317-324
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• 2012

We characterized the cytoskeletal beta-actin (${\beta}$-ACT) gene (actb) and its 5'-upstream regulatory region in the Javanese ricefish Oryzias javanicus. The gene and protein structures were deduced from amino acid sequences of the actb gene and conserved in the teleost lineage. The O. javanicus actb gene has common transcription factor binding motifs in its regulatory region found in teleostean orthologues. Following quantitative reverse transcription-PCR, actb gene transcripts were detected in all tissues examined; however, the basal expression levels were different. During early development, O. javanicus actb mRNA levels showed a gradual increase and peaked between late somitogenesis and the heartbeat stage. Microinjection of O. javanicus embryos with the actb gene promoter-driven red fluorescent protein (RFP) gene reporter vector showed a ubiquitous distribution of RFP signals, although most exhibited a mosaic pattern of transgene expression. A small number of microinjected embryos displayed a wide distribution of RFP signals over their entire body, which resembled the expression pattern of endogenous actb. Data from this study provide a basis to develop a transgenic system with ubiquitous expression of foreign genes in O. javanicus.

• Fisheries and Aquatic Sciences
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• v.15 no.4
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• pp.325-335
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• 2012

The present study characterized the fast skeletal myosin light chain-2 gene (mlc2f) in the euryhaline Javanese ricefish (Oryzias javanicus: Beloniformes). Coding nucleotide and deduced amino acid sequences of Javanese ricefish mlc2f were well conserved in the vertebrate lineage. Javanese ricefish mlc2f showed a typical seven-exon structure, and its promoter exhibited transcription factor binding motifs common to most muscle-specific genes. However, Javanese ricefish mlc2f also displayed tandem duplications of intronic sequences in both intron 1 and intron 3. Based on quantitative reverse transcription-polymerase chain reaction, the mlc2f transcripts were highly predominant in skeletal muscles of adults and were differentially modulated during embryonic development. Microinjection of the mlc2f promoter-driven red fluorescent protein (RFP) reporter construct successfully exhibited heterologous expression of the fluorescent reporter, primarily in muscular areas of hatchlings, although the distribution pattern of RFP signals was not uniform due to the mosaic nature of the introduced transgene. Data from this study indicate that the Javanese ricefish mlc2f gene has undergone "intra-intronic" duplication events in a species-specific manner and that the mlc2f regulator may also be useful in heterologous expression assays of the skeletal muscles of this species.

• Molecular & Cellular Toxicology
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• v.4 no.4
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• pp.293-299
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• 2008

To screen the differentially expressed genes in cadmuim-exposed marine medaka fish (Oryzias javanicus), a candidate marine test fish for ecological toxicity, the differential display polymerase chain reaction (DD-PCR) was carried out, since the genome-wide gene expression data are not available in this fish species yet. A total of 35 clones were isolated from cadmium-exposed fish and their nucleotide sequences were analyzed. The differentially expressed gene candidates were categorized to response to stimulus (3); ion binding (3); DNA binding (1); protein binding (6); carbohydrate binding (1); metabolic process (4); biological regulation (3); cellular process (2); protein synthesis (2); catalytic activity (2); sense of sight (1); immune (1); neurohormone (1); signaling activity (1); electron carrier activity (1) and others (3). For real-time quantitative RT-PCR, we selected catalase, glucose-6-phosphate dehydrogenase, heat shock protein 70, and metallothionein and confirmed that cadmium exposure enhanced induction of these four genes.

• Journal of Marine Life Science
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• v.6 no.1
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• pp.31-37
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• 2021

Larvae from the marine medaka fish Oryzias javanicus were exposed with polystyrene microplastics (MPs) for 24 h. Exposure to waterborne fluorescent MPs showed clear ingestion and egestion in feces. Under constant MPs, the concentration of dissolved oxygen significantly decreased in 24 h compared to the control. Significant intracellular reactive oxygen species and malondialdehyde contents were detected in larvae, indicating oxidative stress and lipid peroxidation. Significant elevations in mRNA expressions of heat shock protein 70 and antioxidant defense system genes (glutathione reductase, glutathione peroxidase, catalase, and superoxide dismutase) were measured with increases in enzymatic activity of oxidative stress-related proteins. Taken together, the alterations to the molecular and biochemical components suggested that waterborne MPs had an oxidative stress effect on marine medaka larvae.

• Journal of Marine Life Science
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• v.9 no.1
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• pp.33-40
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• 2024

To understand the detrimental effects of triclosan on Java medaka (Oryzias javanicus) embryos, fertilized embryos were exposed to different concentrations (1, 10, 50, 100, 200, 400, 600, 800, and 1,000 ㎍ l^-1) of triclosan until hatching. Then, we examined the survival rate and developmental parameters as well as alterations in antioxidant constituents and DNA damage markers. The results showed dose-dependent mortality, hatching delays, and developmental abnormalities in the embryos. Additionally, there were significant increases in oxidative stress parameters and antioxidant responses, along with elevated DNA damage. These findings suggest that sublethal concentrations of triclosan induce toxic effects through oxidative stress on Java medaka embryos, as evidenced by changes in in vivo parameters and biochemical constituents.

• Fisheries and Aquatic Sciences
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• v.14 no.2
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• pp.93-104
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• 2011

Two hepcidin paralogs (ojhamp1 and ojhamp2) were isolated and characterized from a euryhaline Javanese ricefish (Oryzias javanicus: Beloniformes). The ojhamp1 cDNA encoded 90 or 91 amino acids (aa) of a typical HAMP1 preproprotein. This preproprotein is believed to cleave and yield the 66 or 67 aa-proprotein, followed by the 26 aa-mature peptide, composed of 8 conserved cysteine residues and the QSHL amino terminal motif. The ojhamp2 cDNA encoded 89 aa of HAMP2 preproprotein, cleaved to yield a 65 aa proprotein, and subsequently the 25 aa-mature peptide. The mature OJHAMP1 possessed a cationic isoelectric point (pI), whereas OJHAMP2 had an anionic charge. At the genomic level, both ojhamp1 and ojhamp2 share a conserved tripartite structure (three exons interrupted by two introns) with other vertebrate hepcidin genes. However, the ojhamp1 was shown to exist as two distinct mRNA species, encoding 90 or 91 aa, due to alternative splicing at the junction site between intron I and exon II. Both ojhamp1 and ojhamp2 transcripts were detected in a wide range of tissue types with varying levels of basal expression, although the highest expression was observed in the liver for both isoforms. Transcriptional response to bacterial challenge using Edwardsiella tarda showed that ojhamp1 was moderately upregulated in the liver but remained unchanged in the kidney. However, the ojhamp2 was significantly suppressed in both the kidney and liver, suggesting a potential diversification between the two paralogs.

• Molecular & Cellular Toxicology
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• v.5 no.4
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• pp.283-290
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• 2009

Differential gene expression profiling was performed in the hepatic tissue of marine medaka fish (Oryzias javanicus) after exposure to benzo[a]pyrene (BaP), a polycyclic aromatic hydrocarbon (PAH), by heterologous hybridization using a medaka cDNA microarray. Thirty-eight differentially expressed candidate genes, of which 23 were induced and 15 repressed (P<0.01), were identified and found to be associated with cell cycle, development, endocrine/reproduction, immune, metabolism, nucleic acid/protein binding, signal transduction, or non-categorized. The presumptive physiological changes induced by BaP exposure were identified after considering the biological function of each gene candidate. The results obtained in this study will allow future studies to assess the molecular mechanisms of BaP toxicity and the development of a systems biology approach to the stress biology of organic chemicals.

• Journal of fish pathology
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• v.24 no.2
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• pp.131-139
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• 2011

Bisphenol A (BPA) is mainly used in the production of epoxy resins and polycarbonate plastics, which is a known endocrine disruptor and acutely toxic to aquatic organisms. In this study, estrogenic effect of BPA was investigated on hybrid between Oryzias dancena and O. javanicus (ODJ). ODJ were exposed to BPA of various concentrations (eg. 2.5 mg/L, 5.0 mg/L and 10.0 mg/L) for 56 days. The growth rate, abnormality and the ratio of female and male were observed in test group and control group. As a result, the growth was $14.7{\pm}2.0$ mm in total length (TL) in 2.5 mg/L, $13.7{\pm}2.5$ mm in 5.0 mg/L, $12.8{\pm}2.5$ mm in 10.0 mg/L in test group while it was $18.0{\pm}1.2$ mm in TL in control group which was not treated with bisphenol A. The result showed that the growth decreased as the concentration of BPA increased. The abnormality rate was 13.6% in control group, 65.4% in 2.5 mg/L, 81.3% in 5.0 mg/L and 98.1 % in 10.0 mg/L which showed increase in abnormality as an increase of BPA concentration. As a result of analyzing ratio of sex in the test group and control group, 6.0% was examined to be interspecific in controls, 76.9% in 2.5 mg/L and 100.0% in 5.0 mg/L and 10.0 mg/L. In conclusion, these results suggest that BPA has estrogenic effect on ODJ.

• Journal of Marine Life Science
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• v.7 no.2
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• pp.94-101
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• 2022

In this study, the marine medaka Oryzias javanicus was exposed to two concentrations of non-toxin-producing red tide dinoflagellate C. polykrikoides (1,000 and 2,000 cells ml^-1) for 96 h, and the time-course biochemical responses of antioxidant and immunity parameters were analyzed in the liver tissue. Significant ichthyotoxicity with increasing cell concentrations of C. polykrikoides and exposure period was observed for 96 h. Opercular respiratory rate was lowered in marine medaka exposed to 2,000 cells ml^-1 of C. polykrikoides. Intracellular malondialdehyde (MDA) content significantly elevated in response to both cell concentrations. In the case of glutathione (GSH) content, the levels were significantly elevated by 1,000 cells ml^-1 of C. polykrikoides, but the contents significantly depleted upon exposure to 2,000 cells ml^-1 of C. polykrikoides. Similarly, enzymatic activities of catalase (CAT) and superoxide dismutase (SOD) were increased by 1,000 cells ml^-1 of C. polykrikoides, whereas their activities were lowered by 2,000 cells ml^-1 of C. polykrikoides. Analysis of the two immunity parameters, alternative complement pathway and lysozyme, showed significantly lowered activities in 2,000 cells ml^-1 of C. polykrikoides-exposed liver tissue. These biochemical effects of C. polykrikoides on marine medaka would be helpful for understanding its acute effects in marine fish.