EXTENDED ABSTRACT ONLY – DO NOT CITE

In hypoxia-intolerant temperate fish such as the rainbow trout, exposure to severe environmental hypoxia results in a large elevation of circulating catecholamines (Reid et al., 1998). In general, these hormones serve to increase the transfer of oxygen across the gills and the transport of oxygen, in the blood, to actively metabolising tissues. During environmental hypoxia, catecholamines are mobilised into the blood when the arterial oxygen content decreases by approximately 50 % (Perry and Reid, 1994). Furthermore, the concentration of plasma catecholamines can reach over 500 nmol l-1 in this species. This study examined whether hypoxia-tolerant neotropical fish also release catecholamines during hypoxia and whether the levels are comparable to those observed in the rainbow trout. Three species were studied: 1. Jeju, 1 Hoplerythrinus unitaeniatus (a facultative air breather). 2. Traira, Hoplias malabaricus (an obligate air breather) and 3. Pacu, Piaractus mesopotamicus (a species that performs aquatic surface respiration)