• Environmental Mutagens and Carcinogens
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• v.16 no.1
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• pp.30-34
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• 1996

This study was performed to examine the availability of using medaka (Oryzias latipes) in teratological test. Medaka embryos were collected within 2 hours post-fertilization and cultured in petri dishes containing buffered saline until hatching. The embryos were treated with 0.56 mg/l chlorpyrifos-methyl and 10 mM methyl methanesulfonate at 20 stages (about 35 hours post-fertilization). Eleven developmental features were selected and observed from 33 stages (about 9 days post-fertilization). Scoring system was developed and applicated for the measurement of potential teratological effects by the test compound. Chlorpyrifos-methyl did not induce teratological effect in medaka embryos. However, we found teratological test using medaka embryo reduced the cost, labors, period and space of experiment significantly compared with teratological study using rodents. Above findings strongly suggest that medaka embryo can be used as a lab animal model for teratogenicity test instead of rodents.

• Development and Reproduction
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• v.22 no.2
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• pp.183-192
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• 2018

The morphometric truss characteristics and classical dimensions of the marine medaka, Oryzias dancena, that might distinguish diploid and triploid fish were examined. Significant differences in all the classical and truss dimensions of the diploid and triploid fish were observed in both sexes (p<0.01). All the dimensions of the triploid fish were greater than those of the diploid fish. The triploid marine medaka shows sexual dimorphism in these characters, and the sexual dimorphism of the triploid marine medaka is similar to that of the diploid marine medaka. Thus, when their classical dimension and truss dimension was measured, the growth of triploid marine medaka is faster than that of the diploid fish, and it displays clear sexual dimorphism, with male fish having longer dorsal and anal fins than female fish.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.7 no.1
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• pp.58-65
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• 2007

Behavioral sequences of the medaka (Oryzias latipes) were continuously investigated through an automatic image recognition system in response to medaka treated with the insecticide and medaka not treated with the insecticide, diazinon (0.1 mg/l) during a 1 hour period. The observation of behavior through the movement tracking program showed many patterns of the medaka. After much observation, behavioral patterns were divided into four basic patterns: active-smooth, active-shaking, inactive-smooth, and inactive-shaking. The "smooth" and "shaking" patterns were shown as normal movement behavior. However, the "shaking" pattern was more frequently observed than the "smooth" pattern in medaka specimens that were treated with insecticide. Each pattern was classified using classification methods after the feature choice. It provides a natural way to incorporate prior knowledge from human experts in fish behavior and contains the information in a logical expression tree. The main focus of this study was. to determine whether the decision tree could be useful for interpreting and classifying behavior patterns of the medaka.

• Fisheries and Aquatic Sciences
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• v.13 no.3
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• pp.224-230
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• 2010

Growth hormone (GH) is known as one of the main osmoregulators in euryhaline teleosts during seawater (SW) adaptation. Many of the physiological actions of GH are mediated through insulin-like growth factor-I (IGF-I), and the GH/IGF-I axis is associated with osmoregulation of fish during SW acclimation. However, little information is available on the response of fish IGF-II to hyperosmotic stress. Here we present the first cloned IGF-I and IGF-II cDNAs of marine medaka, Oryzias dancena, and an analysis of the molecular characteristics of the genes. The marine medaka IGF-I cDNA is 1,340 bp long with a 257-bp 5' untranslated region (UTR), a 528 bp 3' UTR, and a 555-bp open reading frame (ORF) encoding a propeptide of 184 amino acid (aa) residues. The full-length marine medaka IGF-II cDNA consists of a 639 bp ORF encoding 212 aa, a 109 bp 5' UTR, and a 416 bp 3' UTR. Homology comparison of the deduced aa sequences with other IGF-Is and IGF-IIs showed that these genes in marine medaka shared high structural homology with orthologs from other teleost as well as mammalian species, suggesting high conservation of IGFs throughout vertebrates. The IGF-I mRNA level increased following transfer of marine medaka from freshwater (FW) to SW, and the expression level was higher than that of the control group, which was maintained in FW. This significantly elevated IGF-I level was maintained throughout the experiment (14 days), suggesting that in marine medaka, IGF-I is deeply involved in the adaptation to abrupt salinity change. In contrast to IGF-I, the increased level of marine medaka IGF-II mRNA was only maintained for a short period, and quickly returned a level similar to that of the control group, suggesting that marine medaka IGF-II might be a gene that responds to acute stress or one that produces a supplemental protein to assist with the osmoregulatory function of IGF-I during an early phase of salinity change.

• Proceedings of the Korea Society of Environmental Toocicology Conference
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• 2001.05a
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• pp.121-121
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• 2001

Studies were carried out to compare the bioconcentrations of TCDD and PCB 126 in different sizes of Japanese medaka, and to examine the whole body elimination kinetics of TCDD and PCB 126 in juvenile Japanese medaka. For bioconcentration studies, different sizes of fry and juvenile medaka were exposed statically to varying doses of waterborne TCDD and PCB 126 for 96 hours. (omitted)

• Journal of Life Science
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• v.23 no.3
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• pp.333-340
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• 2013

This study was performed to determine whether stem bark extract containing saponin of Albizzia julibrissin in the diet influences gonadal maturation and spawning in medaka (Oryzias latipes). The crude extraction containing saponin (HaBC) was partially purified from n-BuOH extraction of A. julibrissin stem bark by Diaion HP-20, Silica gel and Sephadex LH-20 chromatographies. We fed diets supplemented with HaBC to medaka. We then studied the effects of the HaBC supplement on the suppression of gonadal maturation and spawning in female medaka that were reared in aquaria with recirculation systems. In the experiment with immature female medaka, the periods of initiation of gonadal maturation and spawning were delayed in the fish that were fed diets supplemented with at least HaBC 20 mg/g-feed. In the experiment with mature female medaka, the fish that were fed diets supplemented with at least HaBC 20 mg/g-feed had lower GSIs than the control diet group did. The results showed that the growth of the immature medaka was not correlated with the amount of supplementation of HaBC in the diet. However, the condition factors (CF) in the medaka that were fed diets supplemented with at least HaBC 20 mg/g-feed were higher than in the medaka fed on the control diet. We concluded that extracts containing saponin from the stem bark of A. julibrissin have the potential to inhibit gonadal maturation in female medaka, but they did not act as growth stimulation. Further studies are required to determine the mechanism of the action.

• Korean Journal of Environmental Biology
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• v.38 no.1
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• pp.137-145
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• 2020

The sectioned-body morphometric characteristics of the diploid and triploid marine medaka, Oryzias dancena, of both sexes were examined to collect basic data on the significant differences between the diploid and triploid fish. Significant differences between the diploid and triploid fish in both sexes were observed in the body circumference anterior to the base of the pelvic fin, the body circumference anterior to the base of the anal fin, the body circumference anterior to the base of the dorsal fin, the area anterior to the base of the pelvic fin, the area anterior to the base of the anal fin, the area anterior to the base of the dorsal fin, the total height anterior to the base of the pelvic fin, the total height anterior to the base of the anal fin, the height anterior to the base of the pelvic fin, the height anterior to the base of the anal fin, the width anterior to the base of the anal fin, the belly thickness II anterior to the base of the anal fin, section shape 2-1, and section shape 4-1 (p<0.05). These measurements were greater in the triploid marine medaka of both sexes than those in the diploid marine medaka of both sexes, and they were also greater in the male diploid and triploid marine medaka than those in the corresponding female fish. Therefore, the sectioned-body morphometric dimensions were greater in the triploid males than those in the triploid females and the diploid fish in this study.

• Korean Journal of Environmental Biology
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• v.38 no.2
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• pp.323-331
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• 2020

The method of natural spawning is very passive and inconvenient for the study of developmental engineering in marine medaka, Oryzias dancena. The optimum concentration of human chorionic gonadotropin (HCG) and carp pituitary extract (CPE) for ovulation and spawning, and the injection time for the artificial spawning of marine medaka were analyzed in this study. The success rate, survival rate, and hatching rate were highest with 100IU HCG kg^-1 BW and 5mg CPE L^-1 in both male and female marine medaka (p<0.05). After obtaining unfertilized eggs and sperm by the injection of HCG and CPE into the broodstock of marine medaka, artificial fertilization could be successfully achieved any time fertilized eggs are needed in this species. This result should be useful for developing a study program for marine medaka as an experimental animal.

• Molecules and Cells
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• v.20 no.1
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• pp.151-156
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• 2005

The phylogeny and geography of the medaka (Oryzias latipes) populations of Korea were investigated by analyzing sequence data for the mitochondrial control region. From the 41 haplotypes including 25 Korean haplotypes detected in 64 Korean specimens and data for the Japanese and Chinese populations, phylogenetic and nested clade analyses were executed to examine the phylogeny of haplogroups and the relation of the genetic architecture of the haplotypes to the historical geography of the Korean medaka fish. The analyses suggest that there are two very distinct lineages of Korean medaka, and that these result from reproductive isolation mechanisms due to geographic barriers. The southeastern lineage has experienced recent range expansion to the western region. The northwestern lineage, sister to Chinese populations, showed evidence of internal range expansion with shared haplotypes.

• Environmental Analysis Health and Toxicology
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• v.20 no.2 s.49
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• pp.187-194
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• 2005

Octachlorostyrene (OCS) is a primarily concerning chemical in many countries because of its persistent and bioaccumulative properties in the environment. OCS is not commercially manufactured or used but it may be produced during incineration or chemical synthetic processes involving chlorinated compounds. There are several reports that OCS was found in the waters, sediments, fish, mussels, and also in human tissues. However, systematic studies on the OCS toxicities are scarce in literature. In this study, we tried to get the gene expression data using medaka DNA chip to identify biomarkers of OCS exposure. Medaka (Oryzias latipes.) was exposed to OCS 1 ppm for 2 days and 10 days, respectively. Total RNA was extracted and purified by guanidine thiocyanate method and the Cy3- and Cy5-labelled cDNAs produced by reverse trancription of the RNA were hybridized to medaka microarray. As results, eighty five genes were found to be down-or up regulated by OCS. Some of the genes were listed and confirmed by real-time PCR.