Audiograms of intact walking catfish ( Clarias batrachus ) (open circles), catfish with encapsulated bladders, and catfish with free bladders. The data for the latter two groups were re-plotted by the means thresholds of each investigated species published previously. Eight species of catfish with encapsulated bladders in solid squares: superscripted two, Corydoras paleatus from the study of Ladich 1999; superscripted three, Ancistrus ranunculus, Corydoras sodalis, Dianema urostriatum, Hemiodontichthys acipenserinus, Hypoptopoma thoracatum from the study of Lechner and Ladich 2008; superscripted four, Otocinclus affinis from the study of Botta 2009; superscripted eight, Corydoras aeneus from the study of Lechner and Ladich 2011. Sixteen species with free bladders in reversed triangles: superscripted one, Arius felis from the study of Tavolga 1982; superscripted two, Platydoras armatulus from the study of Ladich 1999; superscripted three, Ariopsis seemanni, Batrochoglanis raninus, Malapterurus beninensis, Synodontis schoutedeni, Trachelyopterichthys taeniatus from the study of Lechner and Ladich 2008; superscripted five, Ictalurus punctatus from the study of Wyoscki et al. 2009; superscripted six, Synodontis schoutedeni from the study of Lechner et al. 2010; superscripted seven, Lophiobagrus cyclurus from the study of Lechner et al. 2011; superscripted eight, Silurus glanis from the study of Lechner and Ladich 2011; superscripted nine, Acanthodoras spinosissimus, Agamyxis pectinifrons, Amblydoras affinis, Hemidoras morrisi, Megalodoras uranoscopus, Oxydoras niger from the study of Zebedin and Ladich 2013. Data at the frequencies below 300 kHz are not shown.