Dermogenys
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 Dermogenys sumatrana, pregnant female about 5 cm long
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The freshwater and brackish water halfbeaks of the genus Dermogenys are widely distributed in South and South East Asia from India to Indonesia. They are all viviparous, producing small clutches of up to 30 fry that closely resemble the adults except that they are much smaller, around 10 to 15 mm in length. Adult Dermogenys are typically around 60-70 mm in length, with females being slightly larger than males. Males tend to be more brightly coloured and are well known for being aggressive towards one another. The Wrestling halfbeak is a species of Dermogenys, Dermogenys pusilla, that is widely used in Asia as fighting animals upon which wagers are placed (see Siamese fighting fish). Both sexes have lower mandibles that are much longer than the upper one, and from this comes the "halfbeak" name.
Dermogenys feed extensively on small insects, either in the form of aquatic larvae or as flying insects that have fallen onto the surface of the water. They are important predators on insects such as mosquitoes and so play a role in controlling malaria.
See the article on halfbeaks for details on the maintenance of these fish in home aquaria.
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[edit] Reproduction
Dermogenys are livebearing fish that practise internal fertilisation. The male is equipped with a gonopodium-like anal fin known as an andropodium that delivers sperm into the female. The gestation period is about one month. The exact mode of reproduction ranges from ovoviviparity through to viviparity (see section on reproduction in the halfbeak article). About ten embryos are developed at any one time, but at birth these are fairly large (around 10 mm) compared with other fish of this size (adult Dermogenys are around 4-7 cm in length, depending on the species).
[edit] See also
[edit] Further reading
- Scott, Peter (1997): Livebearing Fishes, Tetra Press, ISBN 1-56465-193-2
