Katrana (Rheocles alaotrensis)

GenusRheocles (1)
SizeLength: up to 14 cm (2)

Classified as Vulnerable (VU) on the IUCN Red List (1).

The katrana is one of a family of small, colourful fish, the Bedotiidae or Madagascan rainbowfish, which inhabit the waters of Madagascar. This species is one of the largest in the family, with an attractive yellow, pink and brown body (3). Male and female katranas can be distinguished by the colour of their fins; while the male’s fins are bright red, those of the female have a pale rose colouration (4).

Endemic to Madagascar, the katrana is found in Lake Alaotra, the largest lake on the island, as well as the Maningory and Rianila river systems and tributaries of the Betsiboka River (1) (2) (4).

This freshwater species inhabits small rivers and streams that are clean, silt-free and well oxygenated, often with over-hanging vegetation (5), as well as the open waters of Lake Alaotra (4).

The katrana is a schooling fish (5), which feeds primarily on insects that have fallen into the water from the surrounding vegetation, as well as aquatic insect larvae (6).

The eggs of the katrana are adhesive and attach to the stream banks and vegetation, preventing them from being swept away to unfavourable habitats. After spawning, the katrana leaves its eggs unguarded (7) (8). The eggs hatch in 10 to 14 days, and the resulting fry (young fish) are capable of swimming and feeding as soon as they hatch (9).

This small, colourful fish is threatened by an increase in human activities in the areas surrounding its habitat. Large-scale slash-and-burn deforestation, such as that occurring around Lake Alaotra (10), results in soil erosion and run-off into the surrounding rivers and streams. The increased silt suspended in the water disrupts water flow, smothers fish eggs, and generally creates an unfavourable environment (6).

There is also an active fishery for this species in Lake Alaotra (4). Heavy fishing pressure has resulted in the katranas in the lake having a much smaller average length than that of populations inhabiting rivers (9).

Invasive fish species, introduced by humans to increase fishery productivity, are an ever-increasing problem to the native fishes of Madagascar. It is not known how precisely these species displace the native fishes, but it is suspected a mix of predation and competition is responsible (6).

Although there are currently no specific conservation measures in place for the katrana in its natural environment, Denver Zoo is working on a captive breeding programme (11) and there are several broad-spectrum projects working on wetland preservation in the region (12). While this species is currently doing much better than previously expected, like the other species in its family the katrana is still under considerable threat (1).

To find out more about the endangered fish of Madagascar see:

Authenticated (17/08/10) by Dr. Paul V. Loiselle, Curator of Freshwater Fishes, New York Aquarium.

  1. IUCN Red List (April, 2010)
  2. Maugé, L.A. (1986) Atherinidae. In: Daget, J., Gosse, J.P. and Thys van den Audenaerde, D.F.E. (Eds.) Check-list of the Freshwater Fishes of Africa. Volume 2. ORSTOM, Paris and MRAC, Tervuren.
  3. Stiassny, M.L.J. (1990) Notes on the anatomy and relationships of the Bedotiid fishes of Madagascar: with a taxonomic revision of the genus Rheocles (Atherinomorpha, Bedotiidae). American Museum Novitates, 2979: 1-33.
  4. Kiener, A. (1963) Poissons, Pêche et Pisciculture à Madagascar. Centre Technique Forestier Tropical, Nogent-sur-Marne.
  5. Loiselle, P.V. and Stiassny, M.L.J. (2003) Rheocles, Malagasy rainbowfish, Aona. In: Goodman, S.M. and Benstead, J.P. (Eds.) The Natural History of Madagascar. University of Chicago Press, Chicago.
  6. Reinthal, P.J., Riseng, K.J. and Sparks, J.S. (2003) Water management issues in Madagascar: biodiversity, conservation and deforestation. In: Crisman, T.L., Chapman, L.J., Chapman, C.A. and Kaufman, L.S. (Eds.) Conservation, Ecology and Management of African Fresh Waters. University Press of Florida, Florida.
  7. Breder, C.M. and Rosen, D.E. (1966) Modes of Reproduction in Fishes. Natural History Press, New York.
  8. Saunders, A. (March, 2010) Pers. comm.
  9. Loiselle, P.V. (August, 2010) Pers. comm.
  10. Mutschler, T. (2003) Lac Alaotra. In: Goodman, S.M. and Benstead, J.P. (Eds.) The Natural History of Madagascar. University of Chicago Press, Chicago.
  11. Denver Zoo (April, 2010)
  12. Andrianandrasana, H.T., Randriamahefasoa, J., Durbin, J., Lewis, R.E. and Ratsimbazafy, J.H. (2005) Participatory ecological monitoring of the Alaotra wetlands in Madagascar. Biodiversityand Conservation, 14: 2757-2774.