An exceptionally colourful new species of rivulid killifish has been described from the waters of the Guyana shield in South America.
Rivulus mahdiaensis has just been described by Suijker and Collier of the University of Tulsa in the latest issue of the systematics journal Zootaxa. The species was discovered in a small creek which feeds into the Potaro River near Mahdia in central Guyana in the north east of South America.
The species is very brightly coloured with a silver-white to metallic-blue base colour overlayed with numerous narrow longitudinal red stripes. The greatly elongated dorsal and anal fin are red with yellow and blue squiggles, while the lyre-shaped caudal fin has long extensions and is a gaudy combination of red, blue and yellow.
Suijker and Collier report that females of Rivulus mahdiaensis differ from most other members of the Rivulus genus in the presence of a dark, narrow longitudinal band on their flanks.
Suijker and Collier also studied the chromosomes of the fish and believe that R. mahdiaensis has a unique karyotype 2n=38 among members of the Rivulus group. The fish is believed to be a member of a monophyletic group of Rivulus which includes several other small species found in the Guyana shield and nearby areas in the north east of South America.
The species is believed to have been introduced into the aquarium hobby under the name Rivulus sp. "Mahdia".
For more information on the new species see the paper: Suijker WH and GE Collier (2006) - Rivulus mahdiaensis, a new killifish from central Guyana (Cyprinodontiformes: Rivulidae). Zootaxa 1246: 1-13 (2006).