| Onilahy River | |
|---|---|
 Onilahy River estuary | |
 Map of the Onilahy River watershed | |
| Location | |
| Country | Madagascar |
| region | Atsimo-Andrefana, Anosy |
| Cities | Mandrofify, Ambolofoty |
| Physical characteristics | |
| Source | |
| • location | near Betroka |
| Mouth | Bay of Saint-Augustin |
• location | Saint Augustin, Mozambique Channel |
• elevation | 0m |
| Length | 525 km (326 mi) |
| Basin size | 31,600 km2 (12,200 sq mi)[1] |
| Discharge | |
| • location | Near mouth |
| • average | (Period: 1971–2000)183 m3/s (6,500 cu ft/s)[2] |
| Basin features | |
| Protection status | |
| Official name | Zones humides de l'Onilahy |
| Designated | 22 May 2017 |
| Reference no. | 2304[3] |
Onilahy is a river in Atsimo-Andrefana and Anosy (Toliara Province), southern Madagascar. It flows down from the hills near Betroka to the Mozambique Channel. It empties at St. Augustin (23°34′00″S 43°45′00″E / 23.5666667°S 43.75°E), and into the Bay of Saint-Augustin.
Two species of cichlids are endemic to the river basin, but Ptychochromis onilahy is probably already extinct[4] and the remaining range of Ptychochromoides betsileanus covers less than 10 square kilometres (3.9 sq mi).[5][6]
- ^ Onilahy
- ^ "Madagascar".
- ^ "Zones humides de l'Onilahy". Ramsar Sites Information Service. Retrieved 25 April 2018.
- ^ Stiassny, M., and Sparks, J. S. (2006). Phylogeny and Taxonomic Revision of the Endemic Malagasy Genus Ptychochromis (Teleostei: Cichlidae), with the Description of Five New Species and a Diagnosis for Katria, New Genus. American Museum Novitates 3535.
- ^ Ravelomanana, T.; Sparks, J.S. (2020). "Ptychochromoides betsileanus". IUCN Red List of Threatened Species. 2020: e.T18832A177066640. doi:10.2305/IUCN.UK.2020-3.RLTS.T18832A177066640.en. Retrieved 12 November 2021.
- ^ Walaszczyk, I.; Marcinowski, R.; Praszkier, T.; Dembicz, K.; Bieńkowska, M. (August 2004). "Biogeographical and stratigraphical significance of the latest Turonian and Early Coniacian inoceramid/ammonite succession of the Manasoa section on the Onilahy River, south-west Madagascar". Cretaceous Research. 25 (4): 543–576. doi:10.1016/j.cretres.2004.05.001. ISSN 0195-6671.