An Investigation of CO2-Induced Behavioural Changes in Freshwater Fish

由于人为工业活动，大气中的二氧化碳(CO2)水平不断上升；18世纪时为每百万人280二氧化碳，目前已上升至400ppm。据预测，到2100年，二氧化碳水平将进一步增加到约1000ppm。大气中的二氧化碳溶解在海洋、湖泊和河流中，与水反应形成碳酸氢根离子以及使水酸化的质子。二氧化碳还可以跨细胞膜移动，降低细胞内的pH值，增加细胞内的碳酸氢盐水平。二氧化碳、pH和碳酸氢盐水平的变化可能会对酶和细胞功能产生巨大影响。在海洋生物中，海洋酸化改变了浮游植物和无脊椎动物的钙化过程，改变了行为的侧化，改变了鱼类的嗅觉能力，并损害了鱼类的学习能力。我们也有证据表明，暴露在高二氧化碳(~1100ppm)下的海鱼会增加焦虑。这一机制至少部分是由于GABAA受体功能的改变，因为高二氧化碳导致氯离子的平衡电位发生变化。然而，到目前为止，还没有研究过二氧化碳增加对淡水鱼的影响。这项研究的主要目的是研究二氧化碳增加对鱼类行为的影响，二氧化碳增加会导致淡水变得更加酸性(酸化)。具体地说，我们将研究个人(焦虑、记忆、运动)和群体(学校/浅滩)行为的变化，并探索各种药物激动剂和拮抗剂所涉及的神经机制。我们还将研究淡水酸化引起的GABAA受体分布的特定大脑变化。另一个目标是研究淡水酸化的长期，以阐明对高二氧化碳水平的任何适应。斑马鱼被选为实验模式生物，是因为有可能通过基因操作来表征所涉及的细胞机制。与气候变化有关的恐惧和焦虑的研究是新的，还没有任何其他研究小组进行过。到目前为止，还没有关于水酸化对淡水鱼行为影响的其他研究。由于鱼类是生态系统的重要组成部分，也是人类的主要食物来源，它们存在的任何变化都可能对人类种群至关重要。因此，无论结果如何，这项研究的结果都将是重要的。

The levels of carbon dioxide (CO2) in the atmosphere are continually rising due to anthropogenic industrial activity; they were 280 per million (ppm) in the 18th century and have currently risen to 400 ppm. CO2 levels are predicted to further increase to ~1000 ppm by the year 2100. Atmospheric CO2 dissolves in the ocean, lakes and rivers, reacting with water to form bicarbonate ions as well as protons that acidify the water. CO2 can also move across cell membranes, lowering pH and increasing bicarbonate levels inside cells. Changes in CO2, pH, and bicarbonate levels can potentially have a great effect on enzyme and cell functions. In marine organisms ocean acidification alters calcification processes in phytoplankton and invertebrates, and shifts behavioural lateralization, alters olfactory ability, and impairs learning in fish. We also have evidence that marine fish exposed to high CO2 (~1100 ppm) have increased anxiety. The mechanism is at least in part due to altered GABAA receptor functioning because of a shift in the equilibrium potential for Cl- caused by high CO2. However, to date there have been no studies examining the affect of increased CO2 on freshwater fish. The main objective of this study is to examine the effects of increased CO2, which causes freshwater to become more acidic (acidification), on fish behaviour. Specifically, we will examine changes in individual (anxiety, memory, locomotion) and group (schooling/shoaling) behaviour and explore the neuronal mechanisms involved with various pharmacological agonists and antagonists. We will also investigate specific brain changes in GABAA receptor distribution due to freshwater acidification. Another objective is to examine long durations of freshwater acidification to elucidate any adaptation to high CO2 levels. Zebrafish were chosen as the experimental model organism because of the possibility for genetic manipulations to characterize the cellular mechanisms involved. The study of fear and anxiety in relation to climate change is novel and has not been performed by any other research group. To date, there have been no other studies on the effects of water acidification on freshwater fish behaviour. Since fish are an essential part of the ecosystem and a major food source for humans, any alteration in their existence could be crucial for human populations. Therefore, results from this study will be significant regardless of the outcome.