Madagascar Freshwater

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Zombitse National Park Wetland with forest in background, Vohibasia, Madagascar.
© WWF / Olivier LANGRAND

About the Area

Madagascar has one of the most distinctive freshwater ecosystems in the world with many endemic species. The island has an elevated plateau from which short, swift rivers flow over a narrow strip of land as they descend to the Indian Ocean to the east.

To the west, long rivers flow down from the central plateaus across sedimentary beds into the Mozambique Channel. Due to climatic variability throughout the island, the freshwater systems of the east side of the island contrast greatly with those of the west, although they all experience seasonal flooding and high discharges.

Malagasy freshwater fishes are "living fossils" and belong to the most primitive of catfish, herrings, cychlids, killies, silversides and their allied species.
Size:
590,000 sq. km (230,000 sq. miles)

Habitat type:
Small Rivers

Geographic Location:
Madagascar, an island off the southeast coast of Africa

Conservation Status:
Critical/Endangered
Local Species
High level of endemism: 8 of Madagascar’s 25 amphidromous and all of its 101 known freshwater fishes are endemic at the species level. Madagascar has large numbers of endemic fish, aquatic mammals, reptiles, amphibians, gastropods, crustaceans, and although poorly studied - aquatic insects.

The majority of the endemic freshwater fishes of Madagascar are from the Herring (Clupeidae), Sea catfish (Ariidae), Bedotiid (Bedotiidae), Sleeper (Eleotridae), Rivuline (Aplocheilidae), Goby (Gobiidae), and Cichlid (Cichlidae) families. Examples of these fishes are Chonophorus macrorhynchus, Teramulus kienerie, and Rheocles alaotrensis.

Other important endemic species include the aquatic tenrec (Limnogale mergulus) - from a family of insectivorous mammals, the rare turtle - Eretmochelys madagascariensis, a large aquatic lizard (Scelotes astrolabi), a rich community of endemic decapod crustaceans, including 6 species of Parastacid crayfishes (Astacoides spp.), and many endemic frogs.

In addition, at least 20 species of Atyid shrimps (Caridina spp.), 3 species of Palaemonid shrimps (Machrobrachium spp.), and 9 species of Patamonid crabs, inhabit the island's rivers and streams. All 6 genera of freshwater crabs found in Madagascar are endemic.

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/ ©: WWF-Canon / Helena TELKÄNRANTA
Cichlids (Cichlidae).
© WWF-Canon / Helena TELKÄNRANTA

Featured species

Aquatic tenrec (Limnogale mergulus)

The aquatic or web-footed tenrec Limnogale mergulus is a semi-aquatic lipotyphlan known only from stream habitats of eastern Madagascar. It is a small tenrec, and the only one that lives in the water. The hind feet are webbed, and the tail flattened (to aid swimming). The pelage is dense and soft (no spines), the upperparts and head being brownish (with red and black guard hairs poking through).

The diet of Limnogale consists mainly of larval and adult aquatic insects, larval anurans and crayfishes. It is strictly nocturnal and remains in streamside burrows during daylight hours. It sleeps in burrows beside a stream. Breeding takes place between December and January. Litter size is around 3.

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Threats
The freshwater fishes of Madagascar are considered the island's most endangered vertebrates. Habitat degradation, siltation, temperature increases due to deforestation, agriculture, overfishing, and exotic species are considered the main causes of species decline. Introduced fish species have already replaced many native species in inland lakes and streams.

The loss of forest cover profoundly alters the basic hydrological regime of rivers, changing them from persistent to intermittent. The extirpation of their freshwater fish fauna inevitably follows.

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WWF’s work

Toliara Coral Reef Conservation
The Southwestern coast of Madagascar supports the third largest coral reef system in the world. The Toliara reefs have high fish diversity, and support an important artisanal fishery. St. Augustin Bay, near Toliara, Madagascar.

The project is about to create multi-use marine protected areas on the Toliara reef system to conserve its wide variety of marine and coastal habitats. The project is a direct response to this local plea to restore wise management and conservation to this globally important ecosystem. It aims to establish the first marine park designed to conserve its spectacular biodiversity.

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Photos and graphics © WWF or used with permission. Text available under a Creative Commons licence.