• Journal of Environmental Health Sciences
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• v.33 no.3
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• pp.207-210
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• 2007

The study was designed to determine the estrogenic effect of some penicillins on endocrine function in adult Japanese medaka (Oryzias latipes). Vitellogenin (Vtg) produced in male fish has been used for a biomarker to study endocrine disrupters. $17\beta-estradiol\;(E_2)$ was used a positive control that was induced Vtg in male fish. Result of total protein qantification and ELISA for female and male fish were exposed to $17\beta-estradiol$ 10ng/ml for $3\sim5$ days. As a result, male fish exposed to amoxicillin respectively appeared 0.75, 0.23, 8.21 and $9.36\%_{\circ}$ of 1, 10, 100 and 1000 ppm respectively, that value was elevated compared with control male fish. Male fish exposed to ampicillin respectively appeared 1.85, 4.68, 0.85 and $39.59\%_{\circ}$ of 1, 10, 100 and 1000 ppm respectively, that value was elevated compared with control male fish. This study is one of the first reports suggesting potential endocrine disruption of some penicillins in aquatic ecosystem. These results suggest that vitellogenin and estrogen receptor induction patterns alter in male medaka treated with selected estrogenic compounds, and that these results may be useful molecular biomarkers for screening estrogenic EDCs (endocrine-disrupting chemicals) in the shortest possible time.

• Korean Journal of Ichthyology
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• v.24 no.3
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• pp.220-226
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• 2012

The aim of this study is to observe the reproductive behavior of the marine medaka, Oryzias dancena, and determine the factors of reproductive behavior to provide useful information for improving their artificial reproduction techniques. The reproductive behavior of the marine medaka was observed in laboratory aquaria. Once the experiment began, all of the males chased the females. The males attempted to stimulate the urogenital openings of the females. While chasing a female, a large male would bite a relatively small male's anus. Larger males expelled smaller males with biting, and the defeated males were barred from the female. After the other males were expelled, the remaining male approached and drew alongside the female. The male's dorsal and anal fins covered the female's body. Spawning began after complete covering took place. Spawning of males and females occurred simultaneously. The loadings for 2 factors were calculated. The calculation was restricted to 2 factors because these 2 factors explained about 81% of the total common variance (P<0.05) and the following factors possessed no practical significance. Two movements (biting, expelling) had high positive values for factor one. This factor related a male's defensive behavior to courtship behavior and spawning, and explained 23.1% of the total common variance (P<0.05). The second factor had high positive values for chasing, rejection, covering, and parallel swimming. This factor related a male's courtship behavior and female's defensive behavior to spawning, and explained 59.7% of the total common variance (P<0.05). This research provided basic biological data for the conservation of this species and useful information for improving their artificial reproduction techniques.

• Environmental Analysis Health and Toxicology
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• v.23 no.3
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• pp.221-230
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• 2008

Chlorpyrifos (CPF) is a widely used organophosphate insecticide. Japanese medaka, Oryzias latipes was selected to investigate the effects of chlorpyrifos on survival rate, hatching rate, reproductivity and histopathological changes. Adult fish were exposed to CPF at concentrations of 20, 40, 80 and $160{\mu}g/L$, and the test duration was 4 weeks. An experiment with eggs was also performed under CPF exposure continued for 7 days covering from the fecundation to end-hatching stages. Survival rate of the adult medaka decreased in CPF $80{\mu}g/L$ and $160{\mu}g/L$ treatment groups compared with control, solvent control, $20{\mu}g/L$ or $40{\mu}g/L$L treatment group. Spontaneous start of feeding significantly decreased compared with the control (p < 0.01) when exposed to CPF at above 40 $\mu g/L$. Total spawning decreased by the 20 or $40{\mu}g/L$ CPF treatment compared with the control or solvent control in the test with eggs obtained from untreated adult medaka, and abnormal eggs increased in those CPF-treated groups. There were certain adverse effects at above $40{\mu}g/L$ determined from liver and gonad histological examinations. The results indicate that CPF has insignificant toxic effects in Japanese medaka at less than $20{\mu}g/L$ in long term exposure.

• Korean Journal of Ichthyology
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• v.22 no.1
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• pp.9-16
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• 2010

Osmoregulatory capabilities of a euryhaline medaka, Oryzias dancena (Beloniformes; Teleostei), was examined with a particular emphasis on adult and larval viability during direct salinity changes. O. dancena adults were highly capable for hyper-osmoregulation as well as hypo-osmoregulation, as evidenced by no adverse effect on their viability during the direct transfer either from complete freshwater ($0^{\circ}/_{\circ\circ}$) to $40^{\circ}/_{\circ\circ}$ salinity, or from $70^{\circ}/_{\circ\circ}$ to $0^{\circ}/_{\circ\circ}$. Furthermore, the phased increase of external salinity with acclimation periods allowed them to survive at a salinity as high as $75^{\circ}/_{\circ\circ}$. However, tolerant capability to acute salinity increase in early larval stage was much less than in adult stage, based on the finding that the tolerance range of salinity increase was only $15^{\circ}/_{\circ\circ}$ from freshwater, indicating that the hyper-osmoregulation system might not be fully developed in the early larval stage. On the contrary, the hypoosmoregulation system could be more solidified in O. dancena larvae, as evidenced by their good survival even after direct transfer from $45^{\circ}/_{\circ\circ}$ to $0^{\circ}/_{\circ\circ}$. Knowledge achieved in this study could form the basis for a wide scope of researches including ecotoxicogenomics and geneexpression assay using this model species.

• Korean Journal of Ichthyology
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• v.22 no.1
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• pp.25-33
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• 2010

Effects of different salinity levels on spawning performance, embryonic development and early viability of a euryhaline medaka species, Oryzias dancena, were examined. O. dancena were able to spawn eggs in a wide range of salinity from 0 to 70$^{\circ}/_{\circ\circ}$, however, the spawning frequency was lowered in complete freshwater (0$^{\circ}/_{\circ\circ}$) and in highly salted water (70$^{\circ}/_{\circ\circ}$). Fertilization success was negatively affected when the environmental salinity was higher than the salt concentration found in normal seawater. Embryonic viability and hatching success were also inversely related with the salinity levels. Typical abnormality was observed in developing embryos incubated at high salinities (30, 45 and 60$^{\circ}/_{\circ\circ}$). In addition, the time to hatch was significantly delayed with increasing salinities: peak hatching occurred at 12~14 days post fertilization (dpf) in freshwater and at least at 17 to 18 dpf in 60$^{\circ}/_{\circ\circ}$. Mean survival rates of the hatched larvae up to 7 days post hatching (dph) were at least 97% in salinity levels ranging from 0 to 30$^{\circ}/_{\circ\circ}$. However, larvae reared in 45 and 60$^{\circ}/_{\circ\circ}$ experienced significant mortality, especially in the early phase, resulting in only 75% and 64% survival rates up to 7 dph, respectively.

• Korean Journal of Environmental Biology
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• v.37 no.4
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• pp.735-740
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• 2019

The aim of this study was to conduct a comparative analysis of the diploid and induced triploid cell cycles in marine medaka, Oryzias dancena, tissues. The mean fraction of cells in the G₁, S, and G₂+M phases was 85.5%, 7.6%, and 6.9%, respectively, in the tail fin tissues of diploid fish and 91.2%, 3.6%, and 5.2%, respectively, in those of induced triploid fish. The mean fraction of cells in the G₁, S, and G₂+M phases were 78.4%, 10.6%, and 11.0%, respectively, in the liver tissues of diploid fish; 86.2%, 5.9%, and 7.9%, respectively, in those of induced triploid; 79.3%, 9.4%, and 11.3%, respectively, in the gill tissues of diploid fish; and 85.7%, 5.4%, and 8.9%, respectively, in the induced triploid fish. The differences among the tissues were statistically significant within both the diploid and induced triploid fish (p<0.05). Mitosis was more active in each tissue of the diploid fish than in the corresponding tissues of the induced triploid fish and mitosis was more active in the liver and gill tissues than in the tail fin tissues in both the diploid and induced triploid marine medaka.

• 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.

• Journal of fish pathology
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• v.26 no.3
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• pp.283-287
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• 2013

The susceptibility of marine medaka, Oryzias dancena to fish pathogenic viruses (infectious pancreatic necrosis virus (IPNV), viral hemorrhagic septicemia virus (VHSV), hirame rhabdovirus (HIRRV), infectious hematopoietic necrosis virus (IHNV), and lymphocystis disease virus (LCDV)) was investigated. The cumulative mortalities of fish immersed with IPNV (experimental condition: $15^{\circ}C$ sea water (SW)), VHSV ($15^{\circ}C$ SW), HIRRV ($15^{\circ}C$ fresh water (FW)) were 30%, 40% and 60%, respectively. In the fish immersed with IPNV ($15^{\circ}C$ FW, $18^{\circ}C$ FW and SW), VHSV ($15^{\circ}C$ FW, $18^{\circ}C$ FW and SW), HIRRV ($15^{\circ}C$ SW), IHNV ($15^{\circ}C$ FW and SW), LCDV ($15^{\circ}C$ FW and SW, $18^{\circ}C$ FW and SW), and mock-challenged group, mortality rate was less than 10%. IPNV, VHSV and HIRRV were re-isolated from the dead fish. These results suggest that marine medaka is susceptible to IPNV, VHSV and HIRRV, although their susceptibility depends on the environmental conditions.

• Proceedings of the Korea Society of Environmental Toocicology Conference
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• 1997.12a
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• pp.114-114
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• 1997

• Molecular & Cellular Toxicology
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• v.3 no.sup4
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• pp.33.2-33.2
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• 2007