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Melanotaenia lacustris

Melanotaenia lacustris
Blue Rainbow
The Lake Kutubu Rainbowfish was scientifically described by Munro in 1964. Its scientific name is Melanotaenia lacustris. The species was collected by Patrol Officer T. Terrell in 1955. It would then take until 1983 before the species was collected again, this time by Gerald R. Allen, Barry Crockford and John Paska.
The Lake Kutubu Rainbowfish can reach a length of at least 12 cm. The body colourations varies from brilliant turquoise blue to more greenish shades on the upper half of the body, while the lower half is white. The back can sometimes have a golden shine. 

The Lake Kutubu Rainbowfish lives in central Papua New Guinea. It has only been found in Lake Kutubu and the connected Soro River. Lake Kutubu is the second-largest lake in Papua New Guinea and situated in the Southern Highlands. (It drains into the Kikori River.) Unlike most other lakes in the country, Lake Kutubu has formed in a depression in the rugged interior mountains. This mountainous region is located at an elevation of 800 meters 
The water in the Lake Kutubu Rainbowfish habitat is clear and the lake gets majority of its water from underground sources. The surrounding environment consists of limestone and the water in the lake is really alkaline. The lake has a rich underwater plant life. About every second year, a massive upwelling of really dark water from the bottom of the lake occurs, a phenomenon known as “the turning of the water”. This water is oxygen-deficient and causes massive fish death during a few days.