Boeseman's rainbowfish  (Melanotaenia boesemani)

Classified as Endangered (EN) on the IUCN Red List (1).

Like other rainbowfish, Boeseman’s rainbowfish is a small, freshwater fish with a rather compressed body, large scales, and, as the name suggests, bright colouration (3). The colour pattern of the male Boeseman’s rainbowfish is unusual in that the head and front half of the body are a bright blue-grey, sometimes almost blackish, while the fins and rear half of the body are a contrasting vivid orange-red. Between these two areas are alternating light and dark vertical bars (2) (4) (5). Boeseman’s rainbowfish has two dorsal fins, both of which have a white outer margin, and the second of which is long and, unlike the first, lacks spines (3) (5). The anal fin is also long (3). In contrast to the male, the female Boeseman’s rainbowfish is much less brightly coloured, and has shorter and less elaborate dorsal fins (2) (3) (4) (5).

Boeseman’s rainbowfish is found only in the Ayamaru Lakes region of the Vogelkop Peninsula, Irian Jaya, Indonesia, where it mainly occurs in Lake Ayamaru, Lake Hain and Lake Aytinjo, as well as in a few surrounding tributaries (1) (2) (4) (5) (6).

Boeseman’s rainbowfish inhabits freshwater lakes and streams, the largest lake being around 7 kilometres long and 2 kilometres wide, and situated about 250 metres above sea level (1) (2). The lakes are reported to have clear water and abundant vegetation, but to support relatively few fish, most of which appear to use the shallow margins of the lakes, where prey is more abundant (2) (5).

Very little information is available on the biology of Boeseman’s rainbowfish. In general, rainbowfish are schooling fishes, and eat a variety of foods, including algae, aquatic insects and small crustaceans. Spawning may occur year-round or be stimulated by the rainy season, and the eggs are laid amongst aquatic vegetation (3). In captivity, the female Boeseman’s rainbowfish is reported to lay up to 20 eggs a day, and the eggs may hatch after about two weeks, depending on the water temperature (5).

The habitat of Boeseman’s rainbowfish may regularly undergo wide fluctuations in water level, but these are believed to have become more severe in recent years (1). The introduction of non-native fish to the lakes, as a food source and for malaria control, as well as the local use of poisons in fishing, may also be affecting this species, although the current impacts on the population are unknown (2). By far the biggest threat to Boeseman’s rainbowfish, however, is from the overharvesting of individuals for the international aquarium fish trade. The beautiful colours of this species, particularly the males, have made it perhaps the most popular rainbowfish in the trade, with an estimated one million individuals captured from the wild each year (1) (2) (3) (5).

The Indonesian government are reported to have restricted the trade in Boeseman’s rainbowfish (5), but it is likely that careful controls in trade and further research into the species will be needed before its conservation status can be better known and its populations more effectively protected.

View information on this species at the UNEP World Conservation Monitoring Centre.

To find out more about Boeseman’s rainbowfish see:

• FishBase:
  http://www.fishbase.org
• Home of the Rainbowfish: Melanotaenia boesemani:
  http://members.optushome.com.au/rainbowfishes/Boesemani.htm