Increasing salinity levels in marine and estuarine ecosystems greatly influence developmental, physiological and molecular activities of inhabiting fauna. Marine medaka (Oryzias melastigma), a euryhaline research model, has extraordinary abilities to survive in a wide range of aquatic salinity. To elucidate how marine medaka copes with salinity differences, the responses of Oryzias melastigma after being transferred to different salt concentrations [0 practical salinity units (psu), 15 psu, 30 psu (control), 45 psu] were studied at developmental, histochemical and transcriptome levels in the gill and liver tissues. A greater number of gills differentially expressed genes (DEG) under 0 psu (609) than 15 psu (157) and 45 psu (312), indicating transcriptomic adjustments in gills were more sensitive to the extreme hypotonic environment. A greater number of livers DEGs were observed in 45 psu (1,664) than 0 psu (87) and L15 psu (512), suggesting that liver was more susceptible to hypertonic environment. Further functional analyses of DEGs showed that gills have a more immediate response, mainly in adjusting ion balance, immune and signal transduction. In contrast, DEGs in livers were involved in protein synthesis and processing. We also identified common DEGs in both gill and liver and found they were mostly involved in osmotic regulation of amino sugar and nucleotide sugar metabolism and steroid biosynthesis. Additionally, salinity stresses showed no significant effects on most developmental and histochemical parameters except increased heartbeat with increasing salinity and decreased glycogen after transferred from stable conditions (30 psu) to other salinity environments. These findings suggested that salinity-stress induced changes in gene expressions could reduce the effects on developmental and histochemical parameters. Overall, this study provides a useful resource for understanding the molecular mechanisms of fish responses to salinity stresses.

海洋和河口生态系统中盐度的增加极大地影响了栖息动物的发育、生理和分子活动。海洋青鳉（Oryzias melastigma）是一种广盐研究模型，具有在广泛的水生盐度范围内生存的非凡能力。为了阐明海洋青鳉如何应对盐度差异，Oryzias melastigma的反应在转移到不同的盐浓度 [0 实际盐度单位 (psu)、15 psu、30 psu (对照)、45 psu] 后，在鳃和肝脏组织的发育、组织化学和转录组水平进行了研究。在 0 psu (609) 下，鳃差异表达基因 (DEG) 的数量比 15 psu (157) 和 45 psu (312) 更多，表明鳃中的转录组调整对极端低渗环境更敏感。在 45 psu (1,664) 中观察到比 0 psu (87) 和 L15 psu (512) 更多的肝脏 DEG，表明肝脏更容易受到高渗环境的影响。DEGs的进一步功能分析表明，鳃有更直接的反应，主要是在调节离子平衡、免疫和信号转导方面。相比之下，肝脏中的 DEG 参与蛋白质合成和加工。我们还在鳃和肝脏中发现了常见的 DEG，发现它们主要参与氨基糖和核苷酸糖代谢和类固醇生物合成的渗透调节。此外，盐分胁迫对大多数发育和组织化学参数没有显着影响，除了随着盐分增加心跳增加和从稳定条件（30 psu）转移到其他盐分环境后糖原减少。这些发现表明，盐分胁迫诱导的基因表达变化可以减少对发育和组织化学参数的影响。总体而言，这项研究为了解鱼类对盐分胁迫的反应的分子机制提供了有用的资源。