The island of Madagascar, situated in the Indian Ocean some 360 km from mainland Africa, is world-renowned as a biodiversity hotspot. While perhaps less well known than most of its terrestrial faunas, Madagascar’s endemic fishes represent some of the most endangered vertebrates on the island. It was long thought that the freshwater fish fauna was well described and while most of the species were recognized as being endemic to the island, often with extremely localized distributions, overall the fauna was considered to be relatively small. However, collecting and revisional work undertaken over the past twenty years has uncovered much-undescribed biodiversity and new species descriptions continue to appear regularly in the scientific literature. Based on a revised number of island species, and considering the surface area of the island, the old idea that Madagascar’s fish fauna is depauperate is no longer tenable. In fact by some estimates the island actually harbors more fish species than would be predicted given its size.
On the negative side very few pristine freshwater habitats remain and most are moderately to highly degraded, with many now dominated by exotic species. Three main factors account for the dire state of Madagascar’s ichthyofauna; the degradation of aquatic habitats following deforestation and agricultural clearing, exotic species, and overfishing. Additionally, the often extremely limited distributional range of many of the island’s endemics renders these fishes extremely vulnerable, particularly given the accelerating rate of human encroachment and lack of protected areas incorporating aquatic habitats. As noted by Spark’s and Stiassny (2005:70) “Although it may already be too late to save all but a remnant of Madagascar’s unique freshwater ichthyofaunas, it is our hope that the situation in Madagascar will serve as a warning and underscore the importance of early protection of vulnerable island freshwater ecosystems.”
With a surface of around 589,800 square kilometers, Madagascar is the world’s fourth largest island, and has been isolated from other Gondwanan landmasses probably for the past 80 million years. Shaped not unlike a huge left foot, the island is bisected by a massive central high plateau with an extensive sedimentary plain to the west, xeric spiny desert to the south, and a steep eastern escarpment descending rapidly to a narrow coastal plain. From a freshwater perspective five ecoregions partition the island – the eastern highland and lowland rivers, the western basins, the northwestern rivers and lakes, and the arid southern region. These regions differ greatly in community composition and harbor varying numbers of endemic species.
The eastern rivers empty into the Indian Ocean, and typically are short and clear watered with many rapids and falls in the upper reaches. The eastern slopes occupy about 25% of the island area and flow through the remnants of what was once continuous forest cover (over 90% of Madagascar’s original forests are thought to have been destroyed since humans reached the island), onto the coastal plain where an interconnected series of man-made canals and natural lakes forms the Panagalanes – one of the longest canals in the world. Western Madagascar is much drier than the east and its rivers are typically slow flowing, shallow and turbid and harbor considerably fewer endemic species than those of the east. The rivers and numerous floodplain lakes of the northwest form a separate and distinct ecoregion that is home to a rich endemic cichlid fauna, and most notably diverse in species of the genus Paretroplus – the sister of the south Asian cichlids of the genus Etroplus.
A precise estimate of the number of fish species on the island is difficult to make, mainly due to the high discovery rates and numerous undescribed species known to taxonomists and fish hobbyists. However, it is probably fair to say that somewhere in the range of 135 to 150 native fish species inhabit the island (this number would increase steeply if exotic species were included in the tally), and most of those species are endemic. In all, these species are distributed in 21 families and 56 genera. The 5 families with the most species (a number of which are awaiting formal scientific description) are Cichlidae (27), Bedotiidae (25), Gobiidae (24), Eleotridae (13), and Aplocheilidae (6). While endemism is extremely high for the island’s species, at the higher taxonomic levels the degree is muted with only two endemic families (the anchariid catfishes, and the bedotiid rainbowfishes) and 13 endemic genera.
Many of the Madagascan species are thought to represent the sister group to the remainder of their lineage – that is to say they occupy a position at the base of their family trees and as such represent a major resource for evolutionary studies. But while the fishes of the island are of undisputed interest it has often been pointed out that those missing from the fauna are of almost equal interest. For example, given its Gondwanan origin the fact that the island lacks all representation of many of the families found on Africa and India, such as anabantids, bagrids, channids, clariids, mastacembelids, notopterids and schilbeids is puzzling. Many explanations have been proposed, but consensus has yet to be reached and the fishes of this extraordinary island continue to fascinate.
According to an IUCN assessment of Madagascan freshwater fishes made in 2004, over half of the species (54%) are Endangered and 4% are already Extinct. Furthermore, 28% of the species are Data Deficient and only 14% of the island’s species are Least Concerned or Not Threatened.
The main threats to the Madagascar fishes are identified as:
• Deforestation of associated catchments. This activity has led to increased sedimentation of river habitats, particularly spawning beds, erosion of riverbanks leading to alterations in water flow, and loss of nutrient input.
• Introduced exotic fish species. A large number of non-native freshwater fish species have been introduced for fishery and aquaculture purposes, or as escapees from home aquariums. These species often present a major threat to the endemic species through predation and competition for resources.
• Conversion of wetland habitats for farming, particularly for rice fields. A number of taxa (e.g. Pantanodon spp.) are dependent upon wetland habitats, such as marshlands. The loss of these habitats has had a clearly negative impact on these taxa.
Ongoing efforts of a number of international NGOs, in-country conservation groups and individuals over the past decade have resulted in a number of positive outcomes regarding the island’s endemic fishes. Below is a short review of some ongoing efforts:
Nosivolo River: The Durrell Foundation together with Conservation International are working to improve the condition of the Nosivolo River (home to a large number of Madagascar’s eastern coastal endemics) through improving local people’s quality of life (health, education, alternative livelihoods) to reduce the impact of human activity on the Nosivolo. The Nosivolo River is home to 19 native species, 4 of which are endemic with some confined to just a short stretch of the river. Working with residents of the Marolambo region local fishermen have imposed a complete fishing ban during the breeding season of two of the river’s endemic cichlids, Katria katria and Oxylapia polli. They have also agreed to ban the use of small-mesh gill nets that catch pre-reproductive individuals of those species. Other actions include a campaign to persuade landowners to establish riparian buffer zones along the Nosivolo to reduce erosion and siltation of the river and fish breeding sites.
Farihy Tseny Lake: This small lake in the Sophia River basin of northwestern Madagascar supports the last remaining population of Paretroplus menarambo (until recently thought extinct in the wild), as well as two other endangered Paretroplus species and the endemic freshwater clupeid, Sauvagella robusta. The Malagasy conservation NGO, Tany Maeva, is working together with Toronto and Denver Zoos on community-based efforts to preserve the lake. The goal of this effort is to have Farihy Tseny declared closed to outside fishers and to have its exploitation sustainably regulated by local stakeholders.
Reintroduction of Paratilapia into Lake Fulgence: A decade ago, the Wildlife Conservation Society, the Madagascar Faunal Interest Group, and a consortium of aquarium hobbyists undertook the re-introduction of Paratilapia sp./Fony to Lake Fulgence, an impoundment on the grounds of the Parc Zoologique d’Ivoloina, located just to the north of Toamasina, Madagascar’s main seaport. This formerly abundant species had disappeared from the park as a result of over-exploitation and poor water management. Despite a number of set-backs, by 2007 it was evident that at least a few of the 120-odd repatriated fish had survived and bred. The necessity of draining the lake in order to effect dam repairs provided an opportunity to evaluate how well this effort had succeeded. A total of 2,350 individuals representing six distinct size classes were moved to smaller holding ponds during the course of this project. Half were subsequently returned to the lake, with the remainder divided between the park’s abandoned fish ponds. While Paratilapia sp./Fony is not in any immediate danger of extinction, this exercise has proven of extreme value. It demonstrates that re-introduction of an extirpated fish species is possible and in so doing offers captive breeding programs a viable end point.
Benstead, J.P., DeRham, P.H., Gattolliat, J.-L., Gibbon, F.-M., Loiselle, P.V., Sartori, M., Sparks, J.S. and Stiassny, M.L.J. 2003. Conserving Madagascar’s freshwater biodiversity. Bioscience 53(11): 1101-1111. Available here
IUCN. 2004. Red list assessment of Madagascar freshwater fishes. Unpublished report. Available here
Sparks, J.S. and Stiassny, M.L.J. 2003. Introduction to the Freshwater Fishes. Chapter 9. In: The Natural History of Madagascar. S. M. Goodman and J. P. Benstead (eds), Chicago University Press, pp. 849-863.
Sparks, J.S. and Stiassny, M.L.J. 2005. Madagascar’s Freshwater Fishes: An imperiled treasure. In: Thieme et al. (eds). Freshwater ecoregions of Africa: A conservation assessment. Island Press, Washington, DC,USA, 62-70 pp.
Madagascar Conservation and Development – electronic, open-access, peer-reviewed, multi-disciplinary journal
Madagascar Wildlife Conservation
Madagascar’s Endangered Fishes
Mongabay.com – Freshwater fish of Madagascar
Melanie Stiassny is the Axelrod Research Curator in the Department of Ichthyology at the American Museum of Natural History (AMNH), a Professor in the museum’s Richard Gilder Graduate School and an Adjunct Professor at Columbia University and at City College where she has active graduate and undergraduate teaching programmes. Before coming to the AMNH she was an Assistant Professor of Biology at Harvard University. Her PhD is from the University of London and she spent three years as a Royal Society Postdoctoral Fellow in the Netherlands before joining the faculty at Harvard University.
Melanie’s research focuses broadly on issues in freshwater biodiversity documentation, systematics, bioinformatics, and increasingly seeks to integrate these into conservation planning and sustainable resource management. In addition to being Lead Curator for the AMNH’s Milstein Family Hall of Ocean Life, Dr Stiassny is a scientific advisor to various scientific and conservation organizations including the World Wildlife Fund for Nature, Conservation International, the World Resources Institute, the International Foundation for Science and is a member of the National Geographic Society’s Conservation Trust. Dr Stiassny has authored numerous scientific papers, books, and articles and is a popular lecturer and participant in museum travel and educational outreach programs.