Aethiomastacembelus sp. "Rosette"

Aethiomastacembelus sp. "Rosette" is the name given by Ad Konings to this beautiful spiny eel, which was first observed and photographed at Mbenji Island, Malawi, an isolated island far from shore in the southern quarter of the lake. This spiny eel has occasionally been exported to the aquarium trade. Konings has since observed this form at additional localities, including along the east coast of the lake in Malawi, at Mbowe Island, and at Minos Reef on the Mozambique coast (Konings, in litt., 8 November 1999). The above photograph of it is published in the large T.F.H. book by Konings (1990: 473 fig. 4; discussed on p. 476), and is reproduced here with his kind permission. A video of several individuals of the "rosette" in the aquarium is available here (by MalawiCarsten).
No museum specimens seem to have been collected, making it impossible to determine with confidence if "Rosette" represesents an undescribed species (as Konings originally supposed), or is merely a local color variant of A. shiranus. "Rosette" does appear distinctive, with a dark brown ground color and orange markings that include broken longitudinal stripes on the head and, on the body, 3-4 longitudinal rows of orange markings that vary from small spots and clusters of spots to irregular ellipses (the "rosettes"). It is certainly tempting to believe that a second spiny eel has finally been discovered in L. Malawi. It is listed as a distinct species (Mastacembelus sp. rosette) in the checklist of Snoeks (2004b).
However, the coloration of African mastacembelids is notoriously variable. For example, the only spiny eel found in Lake Victoria, now called Aethiomastacembelus frenatus (or occasionally Caecomastacembelus frenatus), has no fewer than five distinct color patterns (Greenwood, 1966: 122-3). (See an illustration of one of its appearances here.) Its brown ground color "varies from a dark chocolate (almost black in some cases) to a bright, orange-brown." There may be numerous white spots on the body, or there may be white marbling but no spots. Darker blotches at the base of the dorsal fin may be present or absent. The anal fin may or may not have large white reticulations; and so on. Thus, conclusions about mastacembelid species based only on coloration — even striking differences — can be misleading. We will have to await the capture, preservation, and examination of a series of specimens of A. sp. "Rosette," including detailed morphological examination and comparison with a series of A. shiranus, before we know if this represents an additional species.

The Cichlid Fishes of Lake Malawi, Africa: MalawiCichlids.com