Karyotype of the african weakly electric fish, <i>Gymnarchus niloticus</i> (Osteoglosiformes: Gymnarchidae) from Oluwa River, Nigeria

Abstract

Bonytongue fishes of the order Osteoglossiformes provide an interesting clade for evolutionary study considering their wide distribution and their basal position in the general Teleostei phylogeny. Lack of adequate information on the cytogenetics of this group of fishes has been a limiting factor to the understanding of karyotype evolution of the clade. In this study, karyotype of Gymnarchus niloticus, the only species in the family Gymnarchidae collected from Oluwa River was investigated in order to increase the knowledge of karyotype pattern in the family. Metaphase chromosomes were obtained from the anterior portion of the kidney after injecting the fish intraperitoneally with 0.05% colchicine. Slide preparation followed the conventional Giemsa staining technique while digital images of the chromosomes were processed using Mirosoft Excel and Photoshop. The result revealed a karyotype of 2n = 54 (26m+14sm+14sta) which was significantly different in chromosome number and in chromosome macrostructure from the karyotype of 2n = 34 (34m/sm) reported for G. niloticus from Lekki Lagoon. The wide difference in chromosome number and in chromosome structure observed in G. niloticus from these two locations is not a common occurrence among closely related fish species. These two karyotypes therefore raise a question of the possibility of another species in the family Gymnarchidae.

Keywords: Cytogenetics, Chromosomes, Bonytongues, Osteglossomorpha