Croaking mechanism of Sciaenidae
In the Sciaenidae, a family of fish, a trait shared by all members is the ability to croak. However the pitch and use of croaking varies species to species. The croaking ability is a distinguishing characteristic of Sciaenidae The croaking mechanism is used by males as a mating call in some of the species in Sciaenidae. These muscles are allowed to atrophy when not in the mating season. In other species in Sciaenidae, most notably the Atlantic Croaker, the croaking mechanism is present in both genders and remains active year round. These species are theorized to use croaking for communication purposes such as announcing hazards and location when in turbid water.
The croaking mechanism
In Sciaenidae the swim bladder is vibrated by special muscles to produce their croaking sound. These muscles are called sonic muscle fibers, and run horizontally along the fish's body on both sides around the swim bladder and are connected to a central tendon which surrounds the swim bladder ventrally. These sonic muscle fibers are contracted against the swim bladder to produce the croaking sound that Drum and Croakers are most known for. The swim bladder of species in Sciaenidae, is used as a resonating chamber. The large swim bladder is more expansive and branched than species outside of Sciaenidae, which aids in croaking. In some species of Sciaenidae the sonic muscle fibers are only present in males. These muscles strengthen during mating season and weaken the remaining time, causing the croaking mechanism to be inactive.
Croaking in communication
In all Sciaenidae croaking is used as a mating call. In some species croaking is used for communication aside from attracting mates. For those species that have year round croaking ability it is theorized that the croaks serve as a low-aggression warning during group feeding as well as to communicate location in turbid waters. In Sciaenidae that lack the ability to croak year round, croaking is usually restricted to males for attracting mates. A disadvantage to the croaking ability is that it allows Bottlenose dolphin to easily locate large groups of Croaker and Drum as they broadcast their position, indicating large amounts of food for the dolphins.
- Froese, Rainer, and Daniel Pauly, eds. (2010). "Sciaenidae" in FishBase. august 2010 version.
- Ramcharitar, John; Gannon, Damon; Popper, Arthur (May 16, 2006), "BIoacoustics of Fishes of the Family Sciaenidae", Transactions of the American Fisheries Society 135 (5): 1, doi:10.1577/T05-207.1
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