Table 3: Utilization of O.  melastigma as a research model for toxicological studies.

Responsive toToxicological research aboutAge of fishExposure concentration and timeMain worksMain conclusionsReferences

Organic chemicals
WAFsCYP1A-involved detoxification mechanism3-week-old fish and adults 2.5, 5, 10, 20, 40, 60, 80, and 100% WAF for 24 h; 5% for 6, 12, 24, 48, 72, and 96 h Transcript profiling of whole omCyp genes, enzyme activity and steroid hormones assay, omCyp1a mRNA expression in different tissues during different developmental stages, and effects of β-NF, BaP, and WAF on expression of omCyp1a WAF induced CYP-involved detoxification mechanism but reduced steroidogenic metabolism; omCyp1a would be associated with the initiation of the cellular defense systems.[25, 33]
PBDE-47Immune-modulatory effectsThree-month-old290 and 580 ng/day from 2 dpf to hatchingCorrelation between BDE-47 body burden and complement gene expression (RT-PCR) in different gendersGenes studied were gender dependent (males > females); BDE-47 is not biotransformed in marine medaka.[29]
Maternal transfer2- and 3-month-old μg/day for 21 daysAccumulation of PBDE 47 in 2-month-old fish and maternal transfer of PBDE 47 from adult female medaka to eggsPBDE 47 transfer is associated with lipid mobilization during egg production.[42]
PFOSMitochondrial dysfunctionEmbryos0.25 and 1 mg/L from 2 dpf to 6 dpfSequence the RNA mixtures using Solexa/Illumina RNA-Seq at various developmental stages and after various types of exposure, and DGE and qRT-PCR analysis for relative gene expressionThe mitochondrial dysfunction appears to be involved in multiple toxicological effects of PFOS on O.  melastigma embryos.[27]
Precocious hatching Embryos1, 4, and 16 mg/L from 2 dpf to hatchingRecord the time for hatching, hatching rate and mortality of fry hatched within a week, and hatching enzymatic activity and RT-PCR analysis for gene expressionPFOS induced the hatching enzyme, leading to the precocious hatching of embryos and the decrease of larvae survival.[10]
Endocrine-disruptive effectEmbryos1, 4, and 16 mg/L for 2 dpf, 4 dpf, and 10 dpf, respectivelyThe mortality and malformation rates, the transcriptional responses of the ER, AHR, and PPAR pathways to PFOS by RT-PCR, and quantification of PFOS in exposure solutions and medaka embryos PFOS has estrogenic activity and endocrine-disruptive properties and could elicit gene responses in a stage-specific manner.[28]
Cardiac toxicityEmbryos1, 4, and 16 mg/L for from 2 dpf to hatchingCardiac morphology, heart rates and the SV-BA distance of the heart was measured; RT-PCR analysis of gene expression profiles was conducted.PFOS affected the development and function of the heart in the marine medaka embryos.[23]
ImmunotoxicityEmbryos0, 1, 4, and 16 mg/L from 2 dpf to hatchingPFOS body burden, survival rates, and growth parameters of fish larvae during 17 dph, liver histological examination, and gene expression in fish larvae after LPS exposure for 12 h at 27 dphThe immunosuppression effects caused by PFOS could lead to functional dysfunction or weakness of the immune system in the fish larvae.[26]
BPACardiac toxicity Embryos200 μg/L for 2 dpf-incubationHeart beat rate, SV-BA distance of embryos, body length and width, histology, and BPA-induced inflammation-related genes and heart-related genesBPA induced cardiac toxicity of the O.  melastigma embryos.[31]
PAHs (ANF, Pyr, Phe, and BaP)Developmental malformations EmbryosDifferent PAHs for 18 daysDeformity assessment, heart rate, heart elongation, hatch rate, and EROD and Caspase-3/7 activity assays of embryos exposed to PAHs with or without 100 μg/L ANFInhibition of CYP1A, EROD, and Caspase-3/7 activities can be used as indicator in the ecological early warning and PAHs detection.[43, 44]
Estrogen (E2, EE2, NP, and BPA)Estrogenic pollutantsSexually matureE2, EE2 (1, 10, 100, and 500 ng/L); NP, BPA (1, 10, 100, and 200 μg/L) for 7 daysE2-inducible choriogenins expression in embryos and yolk-sac larvae by end-point PCR; effects of EE2, BPA, and NP, respectively, on omChgh and omChgl expression by RT-PCRThe rapid inducibility (within 24 h) of omChgh by E2 during early developmental stages was found to be more estrogen sensitive than omChgl. [34]
BenzotriazoleReproductive effect3-month-old0.01, 0.1, and 1 mg/L for 4 and 35 daysBenzotriazole can induce Vtg and Cyp19a gene expression but inhibits the Cy1a1 gene expression (qPCR analysis).Benzotriazole had adverse potential on the endocrine system.[45]

Inorganic chemicals
DWNTs Ecotoxicity data of DWNTs48 h posthatching10, 50, and 100 mg/L for 14 daysMortality and total length of medaka fish larvae over 14 days exposed to different concentrations of stirred and sonicated double-walled carbon nanotubes. So-DWNTs are more toxic than st-DWNTs; the dispersion method and size of aggregations should be considered in DWNT toxicity testing.[46]
nZnOSublethal toxicities<24 h4 and 40 mg/L ZnO for 96 hStress responses in fish after acute exposure (SDS-PAGE) nZnO did not display the same toxicity as ZnO towards the fish.[40]
HgCl2Hepatotoxicity and neurotoxicityWeighing 0.5 ± 0.05 g1000 μg/L for 8 h; 1 or 10 μg/L for 60 dProtein expression profile in liver and brain exposed to HgCl2 (MALDI-TOF/TOF MS) and mercury accumulation and damaged liver ultrastructure in medakaHg hepatotoxicity might involve oxidative stress, cytoskeleton impairment, and a dysfunction in metabolism.[37, 38]
Cd2+, Hg2+, Cr6+, and Pb2+Toxic effects of heavy metalsEmbryos and larvae96 h and 14 dThe mortality, heart beat rate, and malformation rates The fish species has relatively high sensitivity to heavy metal stress.[47]

Detrimental organisms
Vibrio parahaemolyticus Immunotoxicity5-month old6 × 105 cfu/fish for 6 h, 24 h and 48 hqPCR analysis of the complement genes in liver; age-, tissue-, and gender-differences in the expression of hepcidin; hepcidin expression in hepatocyte by ISHO.  melastigma can serve as a model to understand the basic biological processes related to immune function.[30, 48]
K. brevis: PbTx-1Neurotoxicity Adult0, 6, 8, 10, 12, 16 and 18 μg/L for 24 h; 6 μg/L for 2 daysAlgal toxicity (toxic symptoms, 24 hour mortality, 1/LT50) and its supernatant, MeOH and TCM extracts of O.  melastigma; changes in protein profiles in medaka gill and brain exposed to PbTx-1K. brevis-induced hypoventilation response in medaka; the down-regulation of several proteins involved in cell protection.[36, 49]
C. marina Ichthyotoxins of C.  marina 4–8 months-old10,000 cells/mL for 0, 24, 48 and 60 hAlgal cell density, growth rate, their toxicity (toxic symptoms, 24-hour mortality, 1/LT50) and its supernatant, MeOH and TCM extracts to O.  melastigma Fish susceptibility to C.  marina is related to its growth rate, but not to cell density; C. marina developed the hyperventilation response of the fish.[49, 50]

Environmental stress
HypoxiaHypoxia-responsive4-week old adult1.8 ± 0.2 mg O2/L for 3 months; 12 weeks 1.8 mg O2/L for 24, 48 and 96 hAdult male fish were processed for ISH and IHC; volume density indices of omTERT mRNA and protein, PCNA and TUNEL signals in liver hepatocytes after chronic exposure to hypoxia; expression of Tert, Hif  1α, Epo, Lepr, and Ho in tissues by RT-PCRHypoxia upregulates omTERT expression via omHIFhif-1 in liver and testis and the omLepR omLEPR expression demonstrated its independent control in endocrine and peripheral tissues.[16, 22, 24]
Ichthyotoxins of C.  marina 4–8 months old7 mg/L, 6.0  mg/L and 1  mg/L DO for 60 hOxygen consumption rate, threshold lethal DO and correlation between body weight and survival time of marine medaka inside the sealed syringeFish susceptibility to C. marina is related to the susceptibility of the fish to hypoxia.[50]
SalinityOsmoregulatory mechanism2.50 ± 0.30 cmSW (35 ), BW (15 ), FW (0) for Three weeks or 1 monthPlasma osmolality, MWC, Na+/Cl concentration, time course, NKCC1a-like protein expression, NKA activity, NKA-IR cell activity, NKA α-subunit mRNA and protein expression in gills in response to hypoosmotic challenge; salinity effects on multiple Fxyd mRNA and FXYD11 protein abundance; co-immunoprecipitation of NKA with FXYD11 and the localization of Fxyd11 mRNA in gill sections in freshwater-acclimated marine medakaThe expression pattern of branchial Fxyd11 was similar to that of Nkaα in the O.  latipes, but non-correlated expression patterns were observed in the O.  melastigma at both the mRNA and protein levels; the lowest NKA activities were found in the environments with salinities similar to their natural habitats.[5, 7, 32]
Ichthyotoxins of C. marina 4–8 months old70 seawater and natural seawater. The LT50 of marine medaka at different ages (4–8 months-old) exposed to 70 hypersalinity (70 -SW) Fish susceptibility to C. marina is not related to its tolerance to hypersalinity stress.[50]

Notes: days postfertilization (dpf); days posthatching (dph); sinus venosus-bulbus arteriosus (SV-BA); lipopolysaccharides (LPS); β-naphthoflavone (β-NF); benzo[a]pyrene (BaP); phenanthrene (Phe); pyrene (Pyr); methanol (MeOH); chloroform (TCM); quantitative polymerase chain reaction (qPCR).