Madagascan rainbows redescribed

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Two species of Madagascan rainbowfish have been redescribed by scientists.

Paul Loiselle of the New York Aquarium and Damaris Rodriguez of the American Museum of Natural History redescribed Bedotia geayi and B. madagascariensis as part of their study on the newly discovered Bedotia leucopteron.

Although the fish are perhaps the two best known members of the Bedotia genus, the original descriptions were not detailed enough to allow the fish to be told apart easily.

Loiselle and Rodriguez examined new material to allow them to redescribe the two species and have just published their findings in the journal Zootaxa, along with their description of B. leucopteron.

The two fish differ in colour, the length of the head, snout, anal fin, caudal peduncle and base of the second dorsal fin, as well as meristically in their second dorsal and anal fin ray counts.

Bedotia madagascariensisB. madagascariensis is the species kept by aquarists who mistakenly believe it to be geayi, and is a member of the Bedotia group in which two longitudinal stripes are displayed.

Loiselle and Rodriguz said that it typically only shows a single longitudinal stripe, while B. geayi normally has two:

"A narrow dark stripe extends from the tip of the snout to the angle of the operculum. Here it becomes a midlateral stripe two scale rows deep that extends from the margin of the operculum to the caudal peduncle and in a more diffuse form, extends onto the caudal fin for about half its length.

"The midlateral stripe is sometimes interrupted along its posterior third. The lower dark lateral stripe is usually only evident in recently preserved material."

The species is considered "shade dependent" and does not occur in bright, open water. The original specimens of B. madagascariensis sold in shops today are descendents of fish collected in Ambila-Lemaitso on the shore of Lake Anjanaborona.

Bedotia geayiUnlike B. madagascariensis, B. geayi, which is not commonly seen in the aquarium trade, has two longitudinal stripes that are usually apparent in live specimens.

Live males normally have red margins to the anal and dorsal fin, a red tail and a large red spot on their chin.

It can be told apart from madagascariensis by its greater number of anal fin rays (17-19 in geayi, versus 14-17 in madagascariensis); its shorter caudal peduncle (13.9-17.7% versus 16.1-20.4%); longer second dorsal fin base (16.9-21.4% versus 15.9-18.7%); shorter head (22-29.8% versus 27-31%) and shorter snout (7.1-10.1% versus 8.0-10.2%).

The species is found in small streams in shady forest cover and occurs at altitudes of 300-650m above sea level.

Loiselle PV and D Rodriguez (2007) - A new species of Bedotia (Teleostei: Atherinomorpha: Bedotiidae) from the Rianila drainage of Eastern Madagascar, with redescriptions of Bedotia madagascariensis and Bedotia geayi. Zootaxa, 1520: 1-18.