Glossolepis incisus - [Male & Female] - photo© Neil Armstrong

Glossolepis incisus

Weber, 1908
Salmon-Red Rainbowfish

Species Summary
Female Glossolepis incisus have a yellowish olive body colour with a golden iridescence to the scales, and clear fins. The males on the other hand are brilliant, the entire body and fins are a bright salmon-red colour. Some of the scales have a silvery sheen, which creates a most unusual effect over the red background colour. Young fish are all rather dull in colour, being an overall olive greenish colour with a trace of silvery sheen. However, once the fish reach a length of 4 to 5 cm the males begin to colour up. Once the colour change begins to occur it progresses quite rapidly. By the time the fish are 7 to 8 cm long the males should have their full intense red colouration. Males are typically deeper bodied than females and have a high rounded back which gives them the appearance of having a relatively small head and disproportionately large eyes. Males may reach a maximum size of 15 cm, but females are usually less than 12 cm.

Distribution & Habitat
Glossolepis incisus are found only in Lake Sentani. Lake Sentani is located some 10 kilometres west of Jayapura at the NE extremity of West Papua. It is an irregularly shaped lake with approximate dimensions of 28 km (E-W) by 19 km (N-S) and a surface area of 104 km². Its blue-green waters are dotted with at least 16 small islands, and it is surrounded by hillsides in the south and the Cyclops Mountains in the north, which separate the lake from the Pacific Ocean. Lake Sentani is by far the largest of the West Papuan lakes and has a catchment area of about 600 km². About 35 small rivers flow into the lake, and there is one natural outlet in the south-eastern tip, via the Jafuri and Tami rivers to the Pacific Ocean near the Papua New Guinea border. The lake is divided into three main sections with recorded depths of 7 to 52 metres. According to surveys in 1970-71, 1984 and 1987 the lake is thermally unstratified, with surface temperatures of 29-32°C and pH 6.2-6.8. Rainbowfishes are generally found around the margins of the lake. Large numbers are found congregating around submerged aquatic vegetation, fallen tree branches etc.

Glossolepis incisus was originally collected from Lake Sentani during the 1899-1900 Siboga Expedition to the Dutch East Indies (West Papua). The discovery and collection of rainbowfishes in remote places in New Guinea has always been very difficult and it wasn't until 1973 before live specimens of this species were collected. In 1973, A. Werner, Jr. of Munich, and E. Frech of Memmingen, Germany collected live specimens during a collecting trip to Java, Celebes, and West Papua. They took a number of colourful fishes back to Europe, including Glossolepis incisus. Werner and Frech are also credited with the introduction of another beautiful and appealing rainbowfish to the aquarium hobby - Iriatherina werneri.

Glossolepis incisus - photo© Hristo Hristov

Weber M. (1907). Süsswasserfische von Neu-Guinea ein Beitrag zur Frage nach dem früheren Zusammenhang von Neu-Guinea und Australien. In: Nova Guinea. Résultats de l'expédition scientifique Néerlandaise à la Nouvelle-Guinée. Süsswasserfische Neu-Guinea 201-267.

Adrian R. Tappin
Updated August, 2015

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