Sea surface temperatures are increasing and ocean pH is decreasing as a result of additional carbon dioxide in the atmosphere. In the tropics, considerable attention has focused on the impacts that global warming and ocean acidification have on coral communities. Much less is known about the likely impacts of these threats to reef fish communities. Although temperatures are projected to increase less in tropical seas than in temperate seas, tropical species may be sensitive to small increases in temperature because they have evolved in a thermally stable environment. The likely effects of ocean acidification on marine fishes are almost completely unknown. In this seminar I present results for a series of experiments designed to test the effects of elevated temperature and reduced pH on the physiological condition, life history traits, and behaviour of reef fishes. Small increases in average summer temperature affected aerobic capacity, growth, body condition and reproductive output of adults. Growth and development of larvae was not disadvantaged by conditions simulating ocean acidification. However, larval sensory ability was substantially impaired at moderate levels of acidification. These results indicate that climate change will have significant consequences for reef fish communities.