The Ecological Differentiation of Two Closely Resembling Haplochromis Species From Lake Victoria (H. Iris and H. Hiatus ; Pisces, Cichlidae)

Abstract

In external appearance and in standard taxonomic analysis Haplochromis iris and H. hiatus, are closely resembling species, which morphologically mainly differ in the live col- ours of sexually active males (Plate I) and, with marginal overlap, in the number of gill-lamellae, the size of the swimbladder and fat content. Ecologically the two species demonstrate (again with overlap) differences in bathymetric distribution, breeding periods, relative contributions of their (otherwise same) food items and in nematode infection. The relation between these ecological differences and the relation between ecological and morphological differences is analysed. The results corroborate the biological validity of the species rank, which hitherto was based on morphology only. The data and their interpretation lead to a discussion on bathymetric segregation as a speciation mode for lacustrine cichlids. Finally the possible role of trophic polymorphs in the radiation of Lake Victoria haplochromines is considered.