LAUSR

The effects of increased levels of carbon dioxide (CO2 ) on the Earth's temperature have been known since the end of the 19th century. It was long believed that the oceans' buffering capacity would counteract any effects of dissolved CO2 in marine environments, but during recent decades, many studies have reported detrimental effects of ocean acidification on aquatic organisms. The most prominent effects can be found within the field of behavioural ecology, for example complete reversal of predator avoidance behaviour in CO2 -exposed coral reef fish. Some of the studies have been very influential, receiving hundreds of citations over recent years. The results have also been conveyed to policymakers and publicized in prominent media outlets for the general public. Those extreme effects of ocean acidification on fish behaviour have, however, spurred controversy given that more than a century of research suggests that there are few or no negative effects of elevated CO2 on fish physiology. This is due to sophisticated acid-base regulatory mechanisms that should enable their resilience to near-future increases in CO2 . In addition, an extreme 'decline effect' has recently been shown in the literature regarding ocean acidification and fish behaviour, and independent research groups have been unable to replicate some of the most profound effects. Here, I present a brief historical overview on the effects of elevated CO2 and ocean acidification on fishes. This historical recap is warranted because earlier work, prior to a recent (approximately 10 year) explosion in interest, is often overlooked in today's ocean acidification studies, despite its value to the field. Based on historical data and the current knowledge status, I suggest future strategies with the aim to improve research rigour and clarify our understanding of the effects of ocean acidification on fishes. This article is protected by copyright. All rights reserved.