Effects of CO2-driven ocean acidification on early life stages of marine medaka (Oryzias melastigma)

The potential effects of elevated CO2 level and reduced carbonate saturation state in marine environment on fishes and other non-calcified organisms are still poorly known. In present study, we investigated the effects of ocean acidification on embryogenesis and organogenesis of newly hatched larvae of marine medaka (Oryzias melastigma) after 21 d exposure of eggs to different artificially acidified seawater (pH 7.6 and 7.2, respectively), and compared with those in control group (pH 8.2). Results showed that CO2-driven seawater acidification (pH 7.6 and 7.2) had no detectable effect on hatching time, hatching rate, and heart rate of embryos. However, the deformity rate of larvae in pH 7.2 treatment was significantly higher than that in control treatment. The left and right sagitta areas did not differ significantly from each other in each treatment. However, the mean sagitta area of larvae in pH 7.6 treatment was significantly smaller than that in the control (p = 0.024). These results suggest that although marine medaka might be more tolerant of elevated CO2 than some other fishes, the effect of elevated CO2 level on the calcification of otolith is likely to be the most susceptibly physiological process of pH regulation in early life stage of marine medaka.

海洋环境中二氧化碳浓度升高与碳酸盐饱和度降低对鱼类及其他非钙化生物的潜在影响，目前仍鲜为人知。本研究以海洋青鳉（Oryzias melastigma）为研究对象，将其鱼卵暴露于不同人工酸化海水（pH分别为7.6、7.2）中21天，探究海洋酸化对其胚胎发生与器官发生的影响，并与对照组（pH 8.2）进行对比。研究结果显示，二氧化碳驱动的海水酸化（pH 7.6和7.2）未对胚胎的孵化时长、孵化率及心率产生可检测到的显著影响。然而，pH 7.2处理组仔鱼的畸形率显著高于对照组。各处理组内仔鱼的左右矢耳石（sagitta）面积均无显著差异，但pH 7.6处理组仔鱼的平均矢耳石面积显著小于对照组（p=0.024）。上述结果表明，尽管海洋青鳉对二氧化碳浓度升高的耐受性可能优于部分其他鱼类，但二氧化碳浓度升高对耳石（otolith）钙化的影响，大概率是海洋青鳉早期生活阶段中对pH调控最为敏感的生理过程。