Size matters: diversity in swimbladders and Weberian ossicles affects hearing in catfishes

Abstract

SUMMARYOtophysine fish possess Weberian ossicles, which connect the swimbladder to the inner ear and improve hearing ability. There is a high diversity in the morphology of the swimbladder and Weberian apparatus in catfishes, which might affect hearing. We have examined these structures in representatives of six families with large, single bladders (Ariidae, Auchenipteridae, Heptapteridae, Malapteruridae, Mochokidae, Pseudopimelodidae) and five subfamilies from two families (Callichthyidae, Loricariidae) having small, paired, encapsulated bladders. We tested their hearing abilities utilizing the non-invasive auditory evoked potential recording technique. Species with single, non-encapsulated, free airbladders possess one, three or four ossicles, whereas species with encapsulated bladders possess one or two. The relative sizes of the bladders and ossicles were significantly smaller in the latter group. All species were able to detect sound stimuli between 50·Hz and 5·kHz. Interspecific differences in hearing sensitivity varied at most by 24·dB below 1·kHz, whilst this variation increased to more than 50·dB at higher frequencies. Catfishes with free bladders had lower thresholds above 1·kHz than those having encapsulated ones. The relative lengths of swimbladders and of ossicular chains were correlated with hearing sensitivity above 1 and 2·kHz, respectively. The number of ossicles affected hearing at 4 and 5·kHz. These results indicate that larger bladders and ossicles as well as higher ossicle numbers improve hearing ability at higher frequencies in catfishes. We furthermore assume that the tiny bladders have minimized their hydrostatic function but were not completely lost because of their auditory function.

Diversity in Fish Auditory Systems: One of the Riddles of Sensory Biology

“…Otophysans do not exhibit a standard morphology of swim bladders and Weberian ossicles as illustrated by von Frisch and Stetter (1932) (Figure 13A) but a large diversity, especially in siluriforms (Chranilov, 1927(Chranilov, , 1929Alexander, 1962Alexander, , 1964Chardon, 1968;Lechner and Ladich, 2008). Members of numerous catfish families have large unpaired and free swim bladders and one up to four ossicles.…”

“…These tiny bladders are surrounded by bony capsules formed by the skull and anterior vertebrae (Chranilov, 1929). The small size of these bladders indicates that they no longer function as buoyancy organs but were most likely retained for hearing purposes (Lechner and Ladich, 2008).…”

“…Ladich (1999) observed that members of the families Pimelodidae and Doradidae are more sensitive to sound than a member of the family Callichthyidae with reduced bladders. In order to determine whether this is a common difference between these two catfish groups, Lechner and Ladich (2008) investigated swim bladders, Weberian ossicles and hearing sensitivities in eleven species from eight different catfish families. Representatives of the Ariidae, Pseudopimelodidae, Malapteruridae, Heptapteridae, Mochokidae, and Auchenipteridae possess large, unpaired and free swim bladders and 1-4 ossicles, whereas members of the Loricariidae and Callichthyidae have significantly smaller swim bladders (3-5 vs. 8-13% of fish length), just 1-2 ossicles and thus a significantly shorter ossicular chain.…”

“…Mean auditory thresholds of six species having large bladders and of all five species having tiny paired bladders revealed significant differences in hearing sensitivity between both groups between 1 and 5 kHz but not at lower frequencies ( Figure 13D). Moreover, a longer ossicular chain and more ossicles resulted in better hearing at 3 to 5 kHz (for details see Lechner and Ladich, 2008;Ladich, 2016).…”

Phylogenetic relationships of the South American Doradoidea (Ostariophysi: Siluriformes)

“…35b,d,f;Arratia, 1987;Lechner & Ladich, 2008). However, in the species of the Auchenipteridae and Doradidae, the transformator process of the tripus is straight and firmly attached to the gas bladder (Figs.…”