Gas Secretion and Absorption
| Schellert and Popper (1992)
have documented the evolution of the particular connections between the
swimbladder and inner ear in various types of fish. This connection
is called an otophysic connection (Crawford
& Huang 1999). In some cases, as in Carassius,
the connection is a collection of tiny bones from the inner ear (Weberian
ossicles) to the anterior end of the swimbladder. In other cases,
as in Notopterus, the swimbladder itself is extended so it directly
links with the inner ear (Coombs
& Popper 1982a). In either form, this connection enhances the hearing
capabilities of the fish. These fish (i.e. Myripristis) are
now able to detect much higher and lower frequencies of sound than those
without the connection (Coombs
& Popper 1982b).
In other species of fish (some are found in the genus Chaetodon), there might be a laterophysic connection, where there is a relationship between the lateral line and the swimbladder. The lateral line on its own detects physical changes outside its body such as nearby fish or swimming obstacles; but when connected with the swimbladder, the lateral line may now have pressure-detecting abilities as well (Webb 1998).
Oftentimes, the swimbladder is also able to produce or amplify sounds as a way of communicating with other fish for breeding and defensive purposes (Jones 1957). In mormyrid fish (African electric fish), the males have a significantly larger swimbladder muscle than the females suggesting that the males use their swimbladder to produce sounds to facilitate their search for a mate (Crawford & Huang 1992). When internal mechanisms in close proximity to the swimbladder, such as pharyngeal teeth, make sounds, the bladder can act as a resonator. Other ways for the swimbladder to produce sounds is through the escaping of gases from the pneumatic duct (Jones 1957) or through the vibration of their swimbladder wall with a specialized drumming muscle (Crawford & Huang 1999).
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