海洋酸化对青鳉鱼(Oryzias melastigma)耳石形态和成分的影响

海洋酸化导致海水中碳酸钙（CaCO₃）的饱和度下降，对海洋钙化生物影响较大。某些鱼类，如海水青鳉鱼（Oryzias melastigma）内耳中具有钙质的耳石，可能对海洋酸化敏感。海洋酸化对幼鱼耳石发育影响已有报道，但成鱼耳石的形态和化学组成是否受到影响的研究较少。本文模拟未来100~300 a的近岸海域可能的酸化水平，研究其对海水青鳉鱼成鱼耳石形态及主要元素成分的影响。研究发现，在高浓度CO₂（980 ppm、2900 ppm和4850 ppm）的酸化水体中养殖青鳉鱼成鱼45 d，青鳉鱼体长和体重与对照组差异不显著，内耳中矢耳石、星耳石和微耳石的形状，包括耳石表面积和圆趋近率，没有受到酸化的影响。然而，随着水体中CO₂浓度升高，矢耳石的重量则呈现下降的趋势，其中2900 ppm和4850 ppm高浓度组矢耳石重量显著低于对照组。在2900 ppm酸化处理组中，左右耳石不对称性趋势明显。而且，酸化处理组中，实验鱼耳石中C元素相对含量显著低于对照组。高浓度CO₂酸化海水对青鳉鱼成鱼的耳石形态和成分的影响，可能干扰其听觉，并对捕食、防御敌害等听觉相关行为造成影响。

Effect of ocean acidification on the otolith shape and composition in marine Medaka (Oryzias melastigma)

Ocean acidification will decrease the saturation state of calcium carbonate and negatively affect a range of calcareous taxa.Some fishes, such as marine medaka Oryzias melastigma, produce otolith structures that are mainly composed of aragonitic CaCO₃, which may be sensitive to elevated levels of pCO₂.It has been particularly concerned that ocean acidification impacts on the development of otolith in fish embryos and larvae.Nevertheless, the effects of ocean acidification on calcification of otolith in adult fish have few reports.In this study, the potential effects of an increasing CO₂ on the morphology and composition of the otoliths were investigated in mature medaka.Four-month old individuals were raised during 45 days under four CO₂ concentration conditions (450 ppm, 980 ppm, 2900 ppm and 4850 ppm) that are predicted to occur over the next 100 to 300 years.Medaka exhibited somatic growth resilience to all treatments.There are three pairs of otolith in medaka's inner ears.They are sagittae, asteriscus and lapillus, respectively.The shape of otolith (including surface area and roundness) was not affected by ocean acidification.However, the weight of sagittae decreased with the increase of CO₂ concentration.In 2900 ppm and 4850 ppm treatment groups, the weight of sagittae was significantly lower than that in the control group.There were obvious asymmetry in otolith surface area and otolith roundness between left and right sagittae of medaka reared in 2900 ppm treatment groups.In higher CO₂ treatment groups, the relative content of C in sagittae was significantly higher than that in control group.The changes of otoliths due to elevated CO₂ concentration could have consequence on auditory sense and relating behaviors, such as predation, avoidance of predators.