Land and Food Systems, University of British Columbia, 2357 Main Mall, Vancouver, BC V6T 1Z4, Canada.
Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, BC V6T 1Z4, Canada.
Sci Total Environ. 2024 Dec 10;955:177185. doi: 10.1016/j.scitotenv.2024.177185. Epub 2024 Oct 23.
Anadromous salmon populations are declining in the Pacific Northwest, with high mortality during the transition from fresh- to seawater as smolts, a stage particularly vulnerable to adverse environmental conditions. This study seeks to explore the impacts of warming and ocean acidification on the transition of life in freshwater to life at sea in Chinook salmon smolts. In a fully factorial experiment, we transitioned Chinook salmon from fresh- to seawater at current and future conditions of temperature (13 °C and 16 °C, respectively) and ocean acidification (400 and 1400 atm CO), including a fluctuating CO treatment (between control and high CO) that may be more representative of natural environmental conditions associated with upwelling and tidal cycling. We hypothesized that constant elevated CO levels would impair smoltification success immediately following seawater transfer, but that fluctuating conditions would be even more physiologically challenging. We predicted that elevated temperatures would exacerbate these effects. To test this, we measured plasma ion concentrations, gill Na/K-ATPase (NKA) isoform mRNA and protein expression, as well as condition indices in freshwater and following 1, 3, 6, and 18 days in seawater at the respective treatments. We confirmed the existence of gill freshwater and seawater isoforms of NKA (α1a and α1b, respectively) in Chinook salmon for the first time, and found an upregulation of both isoforms in the fluctuating CO treatment but a reduction of the number of NKA α1b cells 3-days post seawater transfer at 13 °C. At 16 °C, NKA α1b was upregulated in high CO levels, with an elevated hematocrit indicating fish were likely stressed. Taken together, plasma ions, gill NKA and condition indices revealed a complex response to interacting warming and acidification during the first few days in seawater, however there were no longer-term adverse physiological responses. Thus, Chinook salmon appear to be relatively resilient to near-future climate change.
太平洋西北地区溯河洄游的鲑鱼数量正在减少，其幼鱼在从淡水过渡到海水的过程中死亡率很高，这一阶段特别容易受到不利环境条件的影响。本研究旨在探讨变暖与海洋酸化对奇努克鲑鱼幼鱼从淡水向海水过渡过程中的影响。在一个完全因子实验中，我们将奇努克鲑鱼从淡水转移到当前和未来的温度（分别为 13°C 和 16°C）和海洋酸化（400 和 1400 个大气压 CO2）条件下，并包括一个波动的 CO2 处理（在对照和高 CO2 之间），该处理可能更能代表与上升流和潮汐循环相关的自然环境条件。我们假设，持续升高的 CO2 水平会立即损害幼鱼化过程的成功，但波动的条件会更具生理挑战性。我们预测，高温会加剧这些影响。为了验证这一点，我们在淡水和各自处理的海水转移后 1、3、6 和 18 天测量了血浆离子浓度、鳃 Na/K-ATP 酶（NKA）同工型 mRNA 和蛋白质表达以及条件指数。我们首次在奇努克鲑鱼中证实了鳃具有淡水和海水同工型的 NKA（分别为α1a 和α1b），并发现波动的 CO2 处理中两种同工型都上调，但在 13°C 时，海水转移后 3 天，NKAα1b 细胞数量减少。在 16°C 时，高 CO2 水平上调了 NKAα1b，较高的红细胞比容表明鱼类可能处于应激状态。总之，血浆离子、鳃 NKA 和条件指数揭示了在进入海水的最初几天中，变暖与酸化相互作用的复杂反应，但没有出现长期的不良生理反应。因此，奇努克鲑鱼似乎对近期气候变化具有相对的适应能力。
