Transcriptomic Profiles of Male Thai Ricefish (Oryzias minutillus) after Encountering Two Related Species of Males (Oryzias latipes or Oryzias woworae).

<b>Background and Objective:</b> The Thai ricefish (<i>Oryzias minutillus</i>) is the smallest <i>Oryzias</i> spp. and is important in the trophic structure of freshwater ecological systems. However, interactions with related species via gene expression profiles are unknown in this species. Here, this study reports on the first attempt to investigate the transcriptome profiles of male Thai ricefish induced by the males of two <i>Oryzias</i>. Japanese ricefish (<i>O. latipes</i>) and Daisy's ricefish (<i>O. woworae</i>, a remarkably colourful <i>Oryzias</i>) were used in the experiments. <b>Materials and Methods:</b> <i>Oryzias minutillus</i> was put in the presence of <i>O. latipes</i> (as group 1) or <i>O. woworae</i> (as group 2) for 7 days in aquaria divided by a transparent partition wall. Thai ricefish faced the same species as control group. Fish in each group were measured the distance between fish individuals of <i>O. minutillus</i> to <i>O. latipes</i> or <i>O. woworae</i>. One-way ANOVA with <i>post hoc</i> Tukey's test was used to analyse the significant differences among groups. <i>Oryzias minutillus</i> from groups 1 and 2 on day 7 were subjected to RNA-sequencing analysis via next-generation sequencing. <b>Results:</b> Long-distance encounters of fish appeared in group 2 on day 7, but there were no significant differences between fish distances. Among the differentially expressed genes, the up-and downregulated genes were more highly expressed in group 2 than in group 1. According to gene ontology term enrichment analysis, genes downregulated in the "locomotion" pathway were detected in group 1 but not in group 2. Conversely, downregulation of "pigmentation" and "reproductive process" was detected only in group 2. <b>Conclusion:</b> These results suggested that the different patterns of gene expression in <i>O. minutillus</i> may be affected by the presence of <i>O. latipes</i> and <i>O. woworae</i>.