A morphological study on species of African Mormyrus (Teleostei: Mormyridae) and their electric organ discharges

Abstract

Five species of Mormyrus Linné 1758, three from West Africa and one each from East and southern Africa, were compared morphologically, and their electric organ discharges (EODs) recorded in the field. The five species were morphologically well differentiated in terms of principal components analysis and discriminant analysis, with syntopical M. rume Valenciennes 1846 and M. subundulatus Roberts 1989 very close to but distinct from one another. Half the variation in the dataset was captured by PC1 alone, being mainly loaded by caudal peduncle depth and length, anal fin length, length of snout, pre-anal length, and dorsal fin ray count and length, in that order. Allopatric samples of M. lacerda Castelnau 1861 from the Upper Zambezi/Kwando system and Cunene River, Namibia, showed some differentiation regarded as infrasubspecific, similar to that of the M. rume samples from the Bandama River compared to those of the Comoé River, both in Côte d’Ivoire. The EODs, normalised to 25 °C, varied in average duration from 362 μs in the monopolar pulses of M. tenuirostris Peters 1882 sampled in Kenya, to 6 675 μs in the biphasic waveform pulses of M. lacerda, the waveform also displayed by all other Mormyrus species. The EOD of M. hasselquistii Valenciennes 1846 was so strong the fish was painful to handle. The EOD pulse duration of M. rume differed significantly between the sexes, being on average 1 334 μs (SE 106) in females and 2 008 μs (SE 195) in males.

Keywords: allopatric populations, body shape, intra-generic variation, intraspecific variation

African Journal of Aquatic Science 2013, 38(1): 1–19