Hypoxia adaptation in fish of the Amazon: a never-ending task

Abstract

In addition to seasonal long-term changes in dissolved oxygen and carbon dioxide, water bodies of the Amazon present periodic short-term episodes of hypoxia and even anoxia. To preserve gas exchange and acid base balance, fish of the Amazon have developed multiple adaptive solutions which occur at all biological levels. These solutions are thought to represent adaptive convergence rather than phylogenetic relatedness. Fish of the Amazon exposed to different experimental conditions adjust, for example, several parameters to improve oxygen transfer from the gas-exchange site to the tissues. These parameters include morphological changes such as the development of the lower lip in Colossoma, changes in ventilation rates, changes in circulatory parameters, increased circulating red blood cells, decreased levels of intraerythrocytic phosphates, and adjustments of intraerythrocytic pH (pHi). These adjustments that allow fish to survive both short- and long-term hypoxia occur in different degrees in different fi...