Читать книгу Clinical Guide to Fish Medicine - Группа авторов - Страница 23

The acoustic organs provide information on acoustical stimuli, gravitational forces, and linear and angular accelerations of the head. Fish make use of a labyrinth that includes semicircular canals, ampullae of the inner ear, and otoliths or otoconia (discussed in more detail under auditory anatomy of elasmobranchs) (Hoar et al. 1983). Otoliths are calcified stones that overlay sensory epithelium and are surrounded by endolymph, which facilitates their movement for sound perception and equilibrium (Roberts and Ellis 2012). In most ray‐finned fish, there is a single otolith in each otic chamber, but there may be several. Otoliths can be used to age and identify bony fish. Pathology of the inner ear can lead to loss of equilibrium.

The swim bladder and other gas cavities can conduct sound using bones known as the Weberian apparatus (or ossicles) in several species, e.g. carp (Cyprinus carpio), bowfin (Amia calva), and tetras (Characidae) (Schulz‐Mirbach et al. 2012). Fish that show a direct or indirect connection from the swim bladder to the perilymphatic system of the inner ear can perceive higher frequency sounds (e.g. up to 4000 Hz in carp and catfish, Cyprinidae and Ictaluridae) than those without (up to 520 Hz in cod, Gadiformes) (Roberts and Ellis 2012).

There are three methods of sound production: stridulatory (teeth, fins, spines, and bones), hydrodynamic (swimming movements), and muscle vibrations around the swim bladder (Hoar et al. 1983).

From a clinical perspective, it is difficult to evaluate these structures. Swim bladders and otoliths can be identified on radiography, computed tomography, or MRI (Figure A1.7). Animals with swim bladder disease may show reduced functional hearing. In catfish, swim bladder damage decreased the hearing frequency range (Kleerekoper and Roggenkamp 1959).