Effects of elevated CO2 on early life history development of the yellowtail kingfish, Seriola lalandi, a large pelagic fish

An increasing number of studies have examined the effects of elevated carbon dioxide (CO2) and ocean acidification on marine fish, yet little is known about the effects on large pelagic fish. We tested the effects of elevated CO2 on the early life history development and behaviour of yellowtail kingfish, Seriola lalandi. Eggs and larvae were reared in current day control (450 µatm) and two elevated CO2 treatments for a total of 6 d, from 12 h post-fertilization until 3 d post-hatching (dph). Elevated CO2 treatments matched projections for the open ocean by the year 2100 under RCP 8.5 (880 µatm CO2) and a higher level (1700 µatm CO2) relevant to upwelling zones where pelagic fish often spawn. There was no effect of elevated CO2 on survival to hatching or 3 dph. Oil globule diameter decreased with an increasing CO2 level, indicating potential effects of elevated CO2 on energy utilization of newly hatched larvae, but other morphometric traits did not differ among treatments. Contrary to expectations, there were no effects of elevated CO2 on larval behaviour. Activity level, startle response, and phototaxis did not differ among treatments. Our results contrast with findings for reef fish, where a wide range of sensory and behavioural effects have been reported. We hypothesize that the absence of behavioural effects in 3 dph yellowtail kingfish is due to the early developmental state of newly hatched pelagic fish. Behavioural effects of high CO2 may not occur until larvae commence branchial acid-base regulation when the gills develop; however, further studies are required to test this hypothesis. Our results suggest that the early stages of kingfish development are tolerant to rising CO2 levels in the ocean.

已有越来越多的研究探讨了二氧化碳（CO₂）升高与海洋酸化对海水鱼类的影响，但目前针对大型远洋鱼类（pelagic fish）的相关影响仍知之甚少。本研究以黄尾鰤（Seriola lalandi）为研究对象，检验了二氧化碳升高对其早期生活史发育与行为的影响。实验将鱼卵与仔鱼分别置于当前环境对照组（450 µatm）与两个高二氧化碳处理组中培育，培育周期为受精后12小时至孵化后3日龄（dph），总时长6天。其中，高二氧化碳处理组分别匹配了2100年开放海域在典型浓度路径（Representative Concentration Pathway, RCP）8.5下的二氧化碳浓度预测值（880 µatm CO₂），以及与远洋鱼类常见产卵的上升流区相关的更高浓度水平（1700 µatm CO₂）。

二氧化碳升高对仔鱼的孵化存活率及3日龄存活率均无显著影响。油球直径随二氧化碳浓度升高而呈减小趋势，提示高二氧化碳可能对初孵仔鱼的能量利用存在潜在影响，但其余形态学性状在各组间无显著差异。与预期相悖的是，高二氧化碳并未对仔鱼行为产生显著影响：各组仔鱼的活动水平、惊跳反应与趋光性均无显著差异。

本研究结果与礁区鱼类的相关研究结论存在显著差异，后者已有大量研究报道了二氧化碳升高对其感官与行为的广泛影响。我们提出假说：3日龄黄尾鰤未出现行为响应变化，可能是由于初孵远洋鱼类仍处于早期发育阶段。高二氧化碳的行为影响可能仅在仔鱼鳃发育并开始进行鳃酸碱调节时才会显现，但该假说仍需后续实验验证。本研究结果表明，黄尾鰤的早期发育阶段对海洋中不断升高的二氧化碳浓度具有耐受性。