Java Medaka Research Articles

Negligible additive effect of environmental concentrations of fragmented polyethylene terephthalate microplastics on the growth and reproductive performance of Java medaka exposed to 17β-estradiol and bisphenol A

To investigate whether environmental concentrations of fragmented polyethylene terephthalate (PET) microplastics (MPs) have additional or combined effects on endocrine-disrupting activity, Java medaka (Oryzias javanicus) were exposed to 17β-estradiol (E2; 5, 10, 50, and 100 ng L−1), bisphenol A (BPA; 5, 10, 50, and 100 µg L−1), and E2 and BPA combined with PET MPs (1 and 100 particles L−1) for 200 days. The growth parameters, such as body length and weight, were significantly decreased by the highest concentrations of E2 and BPA. A significant reduction in egg production was observed in female fish exposed to BPA, with an additive toxic effect of PET MPs. A female-biased sex ratio was observed in fish exposed to both chemicals. Exposure to E2 significantly increased the hepatosomatic index (HSI) in both sexes, while no significant effect was observed in the gonadosomatic index (GSI). Exposure to BPA significantly increased the HSI in female fish and decreased the GSI in both sexes of fish. An additive effect of PET MPs was observed on the GSI value of female exposed to BPA. Significant elevations in vitellogenin (VTG) levels were observed in both sexes due to exposure to E2 and BPA. Additive effects of PET MPs were observed on VTG levels in males exposed to E2 and BPA. Taken together, even long-term treatment with PET MPs induced only a negligible additive effect on the endocrine-disrupting activity in Java medaka at environmentally relevant concentrations.

Detrimental effects of hull-cleaning wastewater on embryo development via oxidative stress induction in the Java medaka Oryzias javanicus

Detrimental effects of hull-cleaning wastewater on embryo development via oxidative stress induction in the Java medaka Oryzias javanicus

First application of one‐class support vector machine algorithms for detecting abnormal behavior of marine medaka Oryzias javanicus exposed to the harmful alga Karenia mikimotoi

AbstractIt is empirically known that fish exposed to harmful algal blooms (HABs) exhibit abnormal behavior. This might serve as a method for early detection of HABs. There has been no report of the detection of behavioral abnormalities of fish exposed to harmful algae using machine learning. In this study, the behavior of Oryzias javanicus (Java medaka) exposed in a stepwise manner to the HAB species Karenia mikimotoi at densities of 0 cells mL−1 (control), 1 × 103 cells mL−1 (nonlethal), and 5 × 103 cells mL−1 (sublethal) was recorded for 30 min at each cell density using two digital cameras connected to a software that tracked behavioral metrics of fish. The level of anomaly in the behavior of Java medaka was then analyzed using one‐class support vector machines (OC‐SVM) to determine whether the behavioral changes could be considered abnormal. The results revealed abnormal swimming behavior evidenced by an increase of swimming speed, a decrease of shoaling behavior, and a greater depth of swimming in Java medaka exposed especially to the sublethal K. mikimotoi density. The medaka exposed to K. mikimotoi also displayed physical deformities of their gills that were thought to have caused their abnormal behavior. This supposition was confirmed by further analysis using OC‐SVM because the behavior of groups exposed to nonlethal and sublethal densities of K. mikimotoi were considered abnormal compared with that of the control groups. The results of this study show the possibility of using this system for early and real‐time detection of HABs.

Combined effect of anthracene and polyethylene microplastics on swimming speed and cytochrome P4501A monooxygenase expression of Java medaka (Oryzias javanicus).

Microplastics have been detected in a variety of aquatic ecosystems, and the combined effect of microplastics and chemical pollutants has become a matter of increasing concern. We conducted a 12-d co-exposure test of anthracene and spherical or fragmented polyethylene microplastics (size 200 µm) on Java medaka (Oryzias javanicus). The accumulation of anthracene in Java medaka muscle reached a plateau on day 5 in all anthracene exposure groups, and no significant differences were detected among the groups (ANT, 20.4 ± 5.5; ANT + SPPE-MP, 24.7 ± 2.7; ANT + FRPE-MP, 24.6 ± 4.7 µg/g). However, co-exposure to anthracene and spherical or fragmented polyethylene microplastics increased the duration of slow swimming in a swimming behavior test (control, 4.1 ± 1.4; ANT, 5.2 ± 2.8; ANT + SPPE-MP, 12.4 ± 3.7; ANT + FRPE-MP, 17.4 ± 5.1 min/30 min), and co-exposure to anthracene and fragmented polyethylene microplastics induced higher cytochrome P4501A monooxygenase (CYP1A) expression in Java medaka livers than the other anthracene exposure groups (ANT, 189 ± 74; ANT + SPPE-MP, 203 ± 75; ANT + FRPE-MP 272 ± 36% of control). Polyethylene microplastics appear to be weak vectors of anthracene at the size tested (200 µm), and the effect of shape (spherical or fragmented) on the vector effect was small. However, the presence of polyethylene microplastics could affect the swimming behavior and CYP1A expression in Java medaka.

Size effect of polystyrene microplastics on the accumulation of anthracene for Java medaka (Oryzias javanicus)

Pollution by microplastics in aquatic ecosystems is a worldwide problem, and the role of microplastics as vectors of pollutants has been a concern. Although small microplastics are thought to have a greater effect than large microplastics as vectors of pollutants, the impact of the size of microplastics on their ability to serve as vectors of pollutants has not been quantified. In this study, we conducted the 14-day experiment (7 days of exposure and 7 days of depuration) with polystyrene microplastics (2-μm or 10-μm diameter) and anthracene. On the last day of the exposure period, the concentration of anthracene in the muscle of Java medaka exposed to both anthracene and 2-μm polystyrene microplastics was the highest (47.4 ± 15.2 μg/g-muscle) of any group, followed by the group exposed to both anthracene and 10-μm polystyrene microplastics (23.0 ± 4.2 μg/g-muscle) and the group exposed to only anthracene (11.2 ± 2.2 μg/g-muscle). These results demonstrated that the size of microplastics was a critical determinant of their ability to serve as vectors of anthracene. The concentrations of anthracene and fine microplastics in the environment are sufficiently low that the effect of microplastics as vectors of anthracene may be observed only under experimental conditions that are unlikely to occur in the present environment. However, because pollution by plastics is expected to become more serious in the future, careful thought and proactive action will be needed to ensure that the impact of microplastics as vectors of pollutants does not become demonstrable under future environmental conditions.

Bioaccumulation and reproductive effects of fluorescent microplastics in medaka fish

This study was performed to elucidate the uptake and bioaccumulation of polystyrene microplastics (PS-MPs) in Japanese medaka (freshwater fish) and Java medaka (marine fish), and to assess its impacts on the survival, reproduction, and gene expression of Japanese medaka. Both species were exposed to 2-μm fluorescent PS-MPs (107 beads/L) for 3 weeks. The bioaccumulation factor of PS-MPs for Java medaka was calculated at about 4 × 102, higher than that for Japanese medaka (about 1 × 102). The exposure had no significant effects on the survival and reproduction of Japanese medaka. The mRNA sequencing analysis showed that the expression of a few genes involved in the cell adhesion, xenobiotic metabolic process, brain development, and other functions in medaka intestines significantly changed after exposure. These results suggest that virgin PS-MPs can potentially accumulate in medaka intestines, but has limited toxicity to Japanese medaka at the concentration up to 107 beads/L.

The genome of the Java medaka (Oryzias javanicus): Potential for its use in marine molecular ecotoxicology

The Java medaka (Oryzias javanicus) is distributed in tropical brackish water and is considered as an ecotoxicological experimental organism for assessing diverse pollutions and global climate change effects in the ocean. In this study, we sequenced and assembled the genome of O. javanicus using the Oxford Nanopore technique and anchored the scaffolds to the 24 genetic linkage map of a sister species Oryzias melastigma. The assembled genome consisted of 773 scaffolds including 24 LG-based scaffolds, and the estimated genome length was 846.3 Mb (N50 = 19.3 Mb), containing 24,498 genes. As detoxification processes are crucial in aquatic organisms, antioxidant-related genes including glutathione S-transferases, superoxide dismutase, catalase, and glutathione peroxidase were identified in this study. In the genome of O. javanicus, a total of 21 GSTs, 4 SODs, 1 CAT, and 7 GPxs were identified and showed high similarities between sister species O. melastigma and Oryzias latipes. In addition, despite having 8 classes of cytosolic GSTs family, medaka showed no presence of GST pi and sigma classes, which are predominantly found in carp and salmon, but not in neoteleostei. This study adds another set to genome-library of Oryzias spp. and is a useful resource for better understanding of the molecular ecotoxicology.

Genome Sequence of the Euryhaline Javafish Medaka, Oryzias javanicus: A Small Aquarium Fish Model for Studies on Adaptation to Salinity.

The genus Oryzias consists of 35 medaka-fish species each exhibiting various ecological, morphological and physiological peculiarities and adaptations. Beyond of being a comprehensive phylogenetic group for studying intra-genus evolution of several traits like sex determination, behavior, morphology or adaptation through comparative genomic approaches, all medaka species share many advantages of experimental model organisms including small size and short generation time, transparent embryos and genome editing tools for reverse and forward genetic studies. The Java medaka, Oryzias javanicus, is one of the two species of medaka perfectly adapted for living in brackish/sea-waters. Being an important component of the mangrove ecosystem, O. javanicus is also used as a valuable marine test-fish for ecotoxicology studies. Here, we sequenced and assembled the whole genome of O. javanicus, and anticipate this resource will be catalytic for a wide range of comparative genomic, phylogenetic and functional studies. Complementary sequencing approaches including long-read technology and data integration with a genetic map allowed the final assembly of 908 Mbp of the O. javanicus genome. Further analyses estimate that the O. javanicus genome contains 33% of repeat sequences and has a heterozygosity of 0.96%. The achieved draft assembly contains 525 scaffolds with a total length of 809.7 Mbp, a N50 of 6,3 Mbp and a L50 of 37 scaffolds. We identified 21454 predicted transcripts for a total transcriptome size of 57, 146, 583 bps. We provide here a high-quality chromosome scale draft genome assembly of the euryhaline Javafish medaka (321 scaffolds anchored on 24 chromosomes (representing 97.7% of the total bases)), and give emphasis on the evolutionary adaptation to salinity.

Toxicity Assessment of Sediments Collected from Hiroshima Bay, Japan, Using Java Medaka Embryos

The effects of chemicals in sediments in coastal areas on environmental organisms are almost unknown, although a number of investigations on the distribution of pollutants in these sediments were performed, often resulting in the detection of chemical residues with high concentrations. In this study, toxicities of sediments collected from 11 locations in Hiroshima Bay, Japan, was assessed using embryos of Java medaka, Oryzias javanicus. The embryos were placed on sediments containing a little pore water without adding overlying water. The results showed that as high as 37% of the embryos exposed to sediments collected near Hatsukaichi City died. Additionally, the mortality was 33% at a site distant slightly from an industrial area in Otake City. Delayed hatching was observed at six locations. Thus, the certain effects of exposure to sediments collected from the bay in the embryos were observed, and the authors concluded that these effects are most likely to have been caused by chemicals in the sediments.

PRELIMINARY STUDY OF LARVAL DEVELOPMENT Oryzias javanicus IN INDONESIA

Java medaka Oryzias javanicus potentially developed as test organism, represents the coastal region because it has a high adaptability in freshwater, brackishwater and marine environments. Utilization of it as a test organism has some obstacles such as lack of number of test organisms with same size or age. The fulfillment of number can be solved if the test organism is cultivated exclusively in the laboratory. This study was a preliminary study to get information about suitable salinity for spawning and hatching. Parameter observed were spawning ability in 0 and 20 ppt and hatching rate of egg among 0. 15 and 30 ppt and development of larval fish in 0 ppt. Result indicated that the fish was be able to spawn in 0 and 20 ppt. Eggs were hatched within 9 days in 30 ppt, faster than in freshwater and 15 ppt. In general, O. javanicus was be able to spawn either in freshwater or seawater, but there are differences in the behavior of fish in the laying of egg. Fish will carried their eggs in the abdomen in freshwater, while 20 ppt salinity fish tends to release the eggs. O. javanicus be able to live and lay eggs on freshwater and seawater. Selection of salinity is adjusted to test requirement in egg phase, pascalarva or adult. In general, breeding of fish easier and faster done in fresh water while hatching eggs take place more quickly in high salinity.Keywords: Indonesia, Java Medaka, Oryzias javanicus, test organism

PRELIMINARY STUDY OF LARVAL DEVELOPMENT Oryzias javanicus IN INDONESIA

<p><em>Java medaka </em><em><span style="text-decoration: underline;">Oryzias</span> <span style="text-decoration: underline;">javanicus</span> potentially developed as test organism, represents the coastal region because it has a high adaptability in freshwater, brackishwater and marine environments. Utilization of it as a test organism has some obstacles such as lack of number of test organisms with same size or age. The fulfillment of number can be solved if the test organism is cultivated exclusively in the laboratory. This study was a preliminary study to get information about suitable salinity for spawning and hatching. Parameter observed were spawning ability in 0 and 20 ppt and hatching rate of egg among 0. 15 and 30 ppt and development of larval fish in 0 ppt. Result indicated that the fish was be able to spawn in 0 and 20 ppt. Eggs were hatched within 9 days in 30 ppt, faster than in freshwater and 15 ppt. In general, O. javanicus was be able to spawn either in freshwater or seawater, but there are differences in the behavior of fish in the laying of egg. Fish will carried their eggs in the abdomen in freshwater, while 20 ppt salinity fish tends to release the eggs. O. javanicus be able to live and lay eggs on freshwater and seawater. Selection of salinity is adjusted to test requirement in egg phase, pascalarva or adult. In general, breeding of fish easier and faster done in fresh water while hatching eggs take place more quickly in high salinity.</em></p><p><em><br /></em></p><p><strong><em>Keywords: </em></strong><em>Indonesia, Java Medaka, <span style="text-decoration: underline;">Oryzias</span> <span style="text-decoration: underline;">javanicus</span>, test organism</em><strong><em></em></strong></p>

Effect of glyphosate-based herbicide on early life stages of Java medaka (Oryzias javanicus): A potential tropical test fish

Glyphosate is globally a widely used herbicide, yet there is little information on their toxicity to marine fishes. Java medaka, a small tropical fish native to coastal areas in several Southeast Asian countries, is viewed as a suitable candidate for toxicity test and thus was used for this study. Java medaka adults were cultured in the laboratory and the fertilized eggs of the F2 generation were exposed to different concentrations of glyphosate-based herbicide (100, 200, 300, 400 and 500ppm) until they hatched. The survival and hatching rates of the embryos, changes in the heart rate and morphological impairments were recorded. Generally, survival and hatching percentage decreased as glyphosate concentration increased. Absence of pectoral fin(s) and cornea, permanently bent tail, irregular shaped abdomen, and cell disruption in the fin, head and abdomen are among the common teratogenic effects observed. Furthermore, risk factor also increased with the increased in glyphosate concentrations.

English

The acute toxicity of Zn on Java medaka (Oryzias javanicus) fish was studied. To obtain the results, the experiments were carried out in 3-liter aquariums (15 to 20 fish for each aquarium) with static condition based on O.E.C.D method with 5 treatments, and 1 blank in two repetitions. During the experiment, water physico-chemical factors were pH = 7.7 to 7.9, salinity = 19.3 to 19.7 p.p.t, temperature = 29.1 to 30.8°C and conductivity = 13.54 to 13.94 ms. On the basis of obtained results, the LC50-96 h for Zn were determined at 9.75 (9.65 - 9.85) mg/l for juveniles and 14.32 (13.94 - 14.70) mg/l for adults, respectively. Also, the maximum allowable concentration (MAC) values for Zn on Oryzias javanicus juveniles and adults were determined at 0.97 mg/l for juveniles and 1.43 mg/l for adults. These results will be helpful for future ecotoxicology study based on heavy metals pollution in estuary areas.   Key words: Ecotoxicology, Oryzias javanicus, maximum allowable concentration (MAC), juveniles, adults.

Expression profiling of liver in Java medaka fish exposed to 17β-estradiol

Java medaka (Oryzias javanicus) cDNA array was constructed and the microarray platform was used to compare the hepatic expression profiles of Java medaka fish exposed to 17β-estradiol with those of unexposed controls. Data analysis demonstrated that the expression profiles were strongly affected by 17β-estradiol exposure, with 655 genes up- or downregulated after 24 h, and 633 genes after 48 h. The differentially expressed genes were analyzed to determine the effects of 17β-estradiol exposure on the liver tissue and were classified into five functional categories: information storage and processing, cellular processes and signaling, metabolism, general function prediction only, and function unknown. Genes whose expression was upregulated more than 10-fold were predominantly associated with energy production/conversion and reproduction, and 30% of the genes whose expression was downregulated more than 10-fold were associated with carbohydrate transport and metabolism. The observed differences in the expression profiles of 7 genes (encoding apolipoprotein B, cytochrome P450 1A, glucose-6-phosphate dehydrogenase, glutamate dehydrogenase 1b, vitellogenin, selenoprotein M, and transferrin) were confirmed by quantitative RT-PCR, and their transcriptional changes in the livers of Java medaka induced by exposure to 10, 100, and 1,000 μg/L 17β-estradiol were investigated. These results should allow the development of biomarkers for the identification of 17β-estradiol contamination in the environment and provide molecular biological information on the effects of endocrine-disrupting chemical exposure on marine animals.

Effect of mercury and cadmium on early life stages of Java medaka (Oryzias javanicus): A potential tropical test fish

Several organisms have been used as indicators, bio-monitoring agents or test organisms in ecotoxicological studies. A close relative of the well established Japanese medaka, the Java medaka (Oryzias javanicus), has the potential to be a test organism. The fish is native to the estuaries of the Malaysian Peninsula, Thailand, Indonesia and Singapore. In this study, newly fertilised eggs were exposed to different concentrations of Cd and Hg. Observations were done on the development of the embryos. Exposure to low levels of Cd and Hg (0.01–0.05ppm) resulted in several developmental disorders that led to death. Exposure to ⩾1.0ppm Cd resulted in immediate developmental arrest. The embryos of Java medaka showed tolerance to a certain extent when exposed to ⩾1.0ppm Hg compared to Cd. Based on the sensitivity of the embryos, Java medaka is a suitable test organism for ecotoxicology in the tropical region.

Java medaka: A proposed new marine test fish for ecotoxicology

Java medaka (Oryzias javanicus), which is distributed in estuarine waters of East to Southeast Asia, is proposed here for consideration as a new marine test fish. Semi-static acute toxicity tests were conducted at 26 degrees C for 1 week, 2 weeks, and 1 month old Java-medaka exposed to 4-chlorophenol and zinc, and 2 weeks olds exposed to potassium dichromate (hexavalent chromium) and sodium hypochlorite (residue chlorine). Ninety-six hours LC50s of 4-chlorophenol, zinc, hexavalent chromium, and residue chlorine were from 3.0 to 4.1, from 12.4 to 14.7, 7.4, and 0.05 mg/L, respectively. There were no large differences in sensitivity for 4-chlorophenol and zinc among the three growth stages. Compared with other fish species, these LC50s were relatively low suggesting that Java medaka has relatively high sensitivity to chemicals. This fish is quite easy to keep in the laboratory, with low mortalities at early stages and it takes about 3 months to mature from hatching, suggesting that this fish can be used not only for short-term toxicity tests but also for early life stage toxicity tests. From these results, Java-medaka is highly recommended as a marine test fish for ecotoxicity tests.

Comparative study of bioconcentration and EROD activity induction in the Japanese flounder, red sea bream, and Java medaka exposed to polycyclic aromatic hydrocarbons

Japanese flounder (Paralichthys olivaceus), red sea bream (Pagrus major), and Java medaka (Oryzias javanicus) were exposed to water borne polycyclic aromatic hydrocarbons (PAHs) for 10 days to compare PAH bioconcentration and P450 enzyme induction by ethoxyresorufin-O-deethylase (EROD) activity for use in oil spill biomonitoring in Asian waters. Target exposure concentration for phenanthrene, pyrene, and chrysene were 30 microg/L each, while benzo[a]pyrene was 3.0 microg/L. Phenanthrene and pyrene were accumulated in the flounder and red sea bream; chrysene was found only in the livers of the red sea bream, while Java medaka accumulated the high molecular weight benzo[a]pyrene along with the other PAHs. Total PAH concentrations increased with duration of exposure in the red sea bream from 184+/-37 ng/g wet weight (w.w.) in day 2 to 572+/-72 ng/g (w.w.) in day 10; It, however, decreased in the other two species. Among the three fish species, Java medaka had the highest initial total PAH concentration of 388+/-62 ng/g (w.w.); this was, however, reduced to the lowest final concentration of 52.3+/-3 ng/g (w.w.). It also had the highest EROD activity of 4.2+/-2.8 n mol/min/mg protein compared to the lowest of 0.11+/-0.03 n mol/min/mg protein in the Japanese flounder. Java medaka with high EROD activity induction and bioaccumulation of all PAHs will be suitable for PAH biomonitoring in Asian waters. Due to its high PAH bioconcentration red sea bream is also recommended for consideration for biomonitoring and PAH chronic toxicity tests.

Effects of estrone on full life cycle of Java medaka (Oryzias javanicus), a new marine test fish

Estrone is a natural estrogen detected in sewage treatment works effluents and in estuarine waters. However, there is little information on the effects of estrone on marine fish. This study investigated the effects of estrone on reproduction of the estuarine fish, Java medaka (Oryzias javanicus). Java medaka were exposed to concentrations of 39, 198, 484, 1,188, and 3,701 ng/L of estrone from embryonic stages up to adult stages for 239 d after hatching. The fertility and egg numbers of Java medaka exposed to 1,188 and 3,701 ng/L were significantly lower than that of control. The hepatic vitellogenin concentrations in male Java medaka exposed to estrone greater than 484 ng/L were significantly higher than that of control. Oocytes in testis (testis-ova) were not detected in the males in any of the exposure groups. The lowest-observed-effect concentration and no-observed-effect concentration for Java medaka were 484 and 198 ng/L of estrone. These results suggest that in relatively low estrone concentrations, 39 and 198 ng/L, Java medaka will not be affected by exposure to estrone.