Fax +41 61 306 12 34 E-Mail karger@karger.ch www.karger.com Citation Classics Brain Behav Evol 2012;79:215–217 DOI: 10.1159/000338719 Fish Hearing: New Perspectives from Two ‘Senior’ Bioacousticians 1 Richard R. Fay a Arthur N. Popper b a Marine Biological Laboratory, Woods Hole, Mass., and b Department of Biology and Center for Comparative and Evolutionary Biology of Hearing, University of Maryland, College Park, Md., USA acoustics to a ‘real world’ issue [e.g. Slab- bekoorn et al., 2010; Popper and Hawkins, 2012]. Moreover, this ‘translational’ issue causes us to stretch what we know about fish hearing and leads us to focus on old and new questions that can help us better mitigate issues resulting from exposing animals to man-made sounds. In the following sections, we consider a few of the issues that we think are most important 20 years after our 1993 paper. In each case, we provide our sense of the role for each issue in understanding the newer issue of the effects of man-made sounds on fishes. Particle Motion versus Pressure for Sound Detection Fishes have, in the past, been often clas- sified as ‘hearing specialists’ or ‘hearing generalists’ based, to a large degree, on their hearing range and sensitivity. It is now generally accepted, however, that fishes fall on a broad continuum with re- spect to particle motion sensitivity versus pressure sensitivity [Popper and Fay, 2011]. The elasmobranchs and flatfishes (and many other species) fall at one end of the continuum in having no swim bladder or equivalent, and they are therefore likely to be purely motion sensitive. At the other Our 1993 paper was written 20 years after our 1973 review [Popper and Fay, 1973] that critically examined our knowl- edge of fish hearing up to that time. Our goal in 1993 was to examine the field 20 years after our first paper, see where ad- vances had taken place and provide our thoughts as to future research in the field. It is now almost 40 years since our first review (and our first paper together 2 ). We are not going to review the literature in this essay [see the papers in Webb et al., 2008], but we will look back briefly at a few issues that particularly interest us. We do this in the context of a new perspective of fish bioacoustics that has arisen in the past 20 years and that will, in our view, shape the future of the field. This context is the increasing societal and scientific concerns about the effects of the substantial increas- es in man-made (or anthropogenic) sounds on fishes (as well as on marine mammals, aquatic turtles and invertebrates). This perspective enables us to apply what we have learned about fish hearing and bio- Published online: June 18, 2012 Richard R. Fay Marine Biological Laboratory Woods Hole, MA 02543 (USA) Tel. +1 508-568-6469 E-Mail rfay  @  luc.edu © 2012 S. Karger AG, Basel 0006–8977/12/0794–0215$38.00/0 Accessible online at: www.karger.com/bbe end of the continuum, primarily detecting pressure, are the Otophysi (goldfish, cat- fish and relatives) that have Weberian os- sicles connecting the swim bladder to the ears. Most other fishes fall somewhere in between with an unknown ratio of dual sensitivities to pressure and particle mo- tion. Beyond developing the concept of a hearing continuum, we also argued that fishes cannot be placed on this continuum on the basis of anatomy alone [Popper and Fay, 2011]. Instead, to place fishes on a con- tinuum of the relative importance of pres- sure versus particle motion in individual species, we need to have functional exper- iments that reveal fish hearing sensitivity in terms of both pressure and particle mo- tion. To do this, it is imperative that a single, reasonably priced, readily available and ‘off-the-shelf’ system for simultaneously measuring both pressure and particle mo- tion be developed, and that this be accom- panied by broadly acceptable standards for its use and interpretation. Such a device would make both lab tank and field studies on hearing much more interpretable and would render moot many of the issues re- lated to ‘near’ and ‘far’ fields that have in- hibited workers since the 1960s. Moreover, to understand man-made sound sources and how they affect fishes, it will be critical The classic paper discussed in this essay: Popper AN, Fay RR (1993): Sound detection and processing by fish: critical review and major re- search questions. Brain Behav Evol 41:14–38. 1  We dedicate this paper to our friend, col- league and mentor Prof. William N. Tavolga, in honor of his 90th birthday. 2  For those who might be curious, this is our 25th paper together. We have also co-edited 50 books (and counting!) and organized several in- ternational meetings together. 