Walter Lechner

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

SUMMARY Otophysine 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.

Ontogenetic Development of Weberian Ossicles and Hearing Abilities in the African Bullhead Catfish

Background The Weberian apparatus of otophysine fishes facilitates sound transmission from the swimbladder to the inner ear to increase hearing sensitivity. It has been of great interest to biologists since the 19th century. No studies, however, are available on the development of the Weberian ossicles and its effect on the development of hearing in catfishes. Methodology/Principal Findings We investigated the development of the Weberian apparatus and auditory sensitivity in the catfish Lophiobagrus cyclurus. Specimens from 11.3 mm to 85.5 mm in standard length were studied. Morphology was assessed using sectioning, histology, and X-ray computed tomography, along with 3D reconstruction. Hearing thresholds were measured utilizing the auditory evoked potentials recording technique. Weberian ossicles and interossicular ligaments were fully developed in all stages investigated except in the smallest size group. In the smallest catfish, the intercalarium and the interossicular ligaments were still missing and the tripus was not yet fully developed. Smallest juveniles revealed lowest auditory sensitivity and were unable to detect frequencies higher than 2 or 3 kHz; sensitivity increased in larger specimens by up to 40 dB, and frequency detection up to 6 kHz. In the size groups capable of perceiving frequencies up to 6 kHz, larger individuals had better hearing abilities at low frequencies (0.05–2 kHz), whereas smaller individuals showed better hearing at the highest frequencies (4–6 kHz). Conclusions/Significance Our data indicate that the ability of otophysine fish to detect sounds at low levels and high frequencies largely depends on the development of the Weberian apparatus. A significant increase in auditory sensitivity was observed as soon as all Weberian ossicles and interossicular ligaments are present and the chain for transmitting sounds from the swimbladder to the inner ear is complete. This contrasts with findings in another otophysine, the zebrafish, where no threshold changes have been observed.

How do albino fish hear

Pigmentation disorders such as albinism are occasionally associated with hearing impairments in mammals. Therefore, we wanted to investigate whether such a phenomenon also exists in non-mammalian vertebrates. We measured the hearing abilities of normally pigmented and albinotic specimens of two catfish species, the European wels Silurus glanis (Siluridae) and the South American bronze catfish Corydoras aeneus (Callichthyidae). The non-invasive auditory evoked potential (AEP) recording technique was utilized to determine hearing thresholds at 10 frequencies from 0.05 to 5 kHz. Neither auditory sensitivity nor shape of AEP waveforms differed between normally pigmented and albinotic specimens at any frequency tested in both species. Silurus glanis and C. aeneus showed the best hearing between 0.3 and 1 kHz; the lowest thresholds were 78.4 dB at 0.5 kHz in S. glanis (pigmented), 75 dB at 1 kHz in S. glanis (albinotic), 77.6 dB at 0.5 kHz in C. aeneus (pigmented) and 76.9 dB at 1 kHz in C. aeneus (albinotic). This study indicates no association between albinism and hearing ability. Perhaps because of the lack of melanin in the fish inner ear, hearing in fishes is less likely to be affected by albinism than in mammals.

Chapter 19 – Wildlife Attractions: Zoos and Aquariums

Abstract From time immemorial, humans have been fascinated by wildlife and interacted with animals. Besides using animal-derived products, they started keeping living animals already many centuries BC for economical and recreational reasons. Over the time and ancient menageries, this led to the modern zoos and aquariums of today and to aquariums and terrariums of hobbyists at their private homes. Nowadays several thousands of public zoos and aquariums exist in all countries, and they fulfill roles in education, research, preservation, and recreation. In modern times, the habit of keeping animals in captivity is discussed ambivalently, due to ethic and animal welfare reasons. Nevertheless, hundreds of millions of people worldwide visit public zoos and aquariums every year, and they are the first places for modern urban residents to get in contact with wild animals. So their importance from the ethnozoological view is indisputable.

Young Squeaker Catfish Can Already Talk and Listen to Their Conspecifics

Numerous fish species are able to produce sounds and communicate acoustically. Nevertheless, hearing and sound production in fishes is poorly understood and the ontogenetic development of acoustic communication has only been studied in a few species. So far the yellow marbled squeaker catfish Synodontis schoutedeni is the only species that has been shown to be able to communicate acoustically across generations at all postlarval stages of development. In two further fish species the smallest size groups were not yet able to detect sounds of equal conspecifics. Increasing body size in S. schoutedeni correlates with increasing hearing sensitivity for lower frequencies, decreasing hearing sensitivity at higher frequencies, increasing sound pressure level and duration of stridulation sounds, and decreases in stridulation sound dominant frequency. The excellent hearing sensitivities of S. schoutedeni, which are characteristic for Otophysi (fish with a Weberian apparatus), is probably the reason for their ability to communicate acoustically in early stages of development.

Ontogenetic development of hearing and sound communication in catfishes.

Catfish possess a high diversity in accessory hearing structures, hearing sensitivities, and sound‐generating mechanisms. Nevertheless, the ontogeny of their hearing and sound communication remains unknown. We investigated the development of Weberian ossicles and hearing sensitivity in the African bullhead catfish from postlarval stages up to adults and also examined the ontogenetic development of hearing and sound production in the yellow marbled squeaker catfish. In the smallest bullhead catfishes, the Weberian ossicles and interossicular ligaments are not fully developed. They are unable to detect sounds at low levels and high frequencies. In later stages of both species tested, hearing sensitivity increases with size at low frequencies and decreases at high frequencies. In the squeakers, the duration of stridulation sounds, sound pressure level, and pulse period increase, whereas the dominant frequency decreases with size. The most sensitive frequencies correlate with the dominant frequencies of strid...