The largely endemic cichlid species flocks of the East African Great Lakes are among the prime examples for explosive speciation and adaptive radiation. Speciation rates differ among cichlid lineages, and the propensity to radiate has been linked to intrinsic and extrinsic factors such as sexual selection and ecological opportunity. Remarkably, only one cichlid tribe—the Boulengerochromini—comprises just a single species, Boulengerochromis microlepis, a predominantly piscivorous endemic of Lake Tanganyika and the world’s largest cichlid. While the lineage diverged from its closest relatives at the onset of the Lake Tanganyika radiation >8 MYA, mitochondrial control region sequences collected in this study dated the most recent common ancestor of B. microlepis to ~60–110 KYA. There was no evidence of phylogeographic structure in the lake-wide sample. Patterns of genetic diversity and demographic analyses were consistent with slow and steady population growth throughout the reconstructed timescale. Additionally, the shallow divergence within the species may be related to a possibly large variance in reproductive success in this highly fecund species. Trophic niche space restriction by sympatric piscivores, lack of geographic structure, low potential for sexual selection arising from the monogamous mating system and extinction may have contributed to keeping the lineage monotypic.

Lake Victoria holds a young but species‐rich assemblage of cichlid fishes, which form a monophyletic assemblage with additional species from surrounding water bodies, termed the Lake Victoria superflock. Lake Victoria is surrounded by smaller lakes that are somewhat disconnected from the main lake. Lake Kanyaboli is such a small lake, having markedly reduced species diversity, in part comprised of Lake Victoria species and endemics. Here, we studied the modern haplochromine component of the cichlid fauna, represented by Lipochromis maxillaris, Astatotilapia nubila, Xystichromis phytophagus and Astatotilapia sp. ‘Bigeye’, as well as a number of unidentified modern haplochromine specimens. We used landmark‐based geometric morphometrics to study the degree of morphological divergence among those young entities. Twenty landmarks and 14 interlandmark distances were used for shape analysis. Multivariate analysis revealed significant differences between all four species, but principal component analysis and canonical variate analysis did not clearly discriminate between A. nubila and X. phytophagus, demonstrating great overall morphological similarity despite clear dietary differences. Besides coloration there was sexual dimorphism in body proportions, so that only male individuals were analysed further. In all four species, the observed similarities and differences in body shape conform to the type of ecological specialization of the fish. Most unidentified specimens overlapped the range of A. nubila and X. phytophagus, while the assignment test based on the canonical variate analysis suggested 70% of the three overlapping entities as separate units. To test their reproductive distinctness and to demonstrate potential hybridization, nuclear genetic data are needed.

The study was carried out to determine the effect of different inclusion levels of pawpaw seeds powder (PSP) on the proximate composition, growth and histological structure of Nile tilapia gonads.  Nile tilapia were treated with pawpaw seeds powder at four levels at 0 g, 4 g, 8 g and 12 g PSP/kg feed for 60 days. The proximate composition of the carcass of the  Nile tilapia showed that the 8 g PSP/kg feed treatment group had the highest values (mean ± SE) of Crude protein  and ash (53.97 ± 0.094 and 20.05 ± 0.35) respectively. The highest body weight gain and specific growth rate was achieved at the 8 g PSP/kg treatment level but this treatment level showed the lowest feed conversion ratio. Histology of gonads of Nile tilapia treated with different levels of PSP revealed that ovaries and testes of 0 g PSP/kg feed were normal. Ovaries of the 4 g PSP/kg feed had degenerative stromas while testes had scanty spermatozoa. At 8 g PSP/kg feed, the ovaries showed increased atretic follicles and testes had degeneration of spermatozoa.Treatment with 12 g PSP/kg feed resulted in severe atretic follicles of the ovaries and deformation of seminiferous tubules and erosion of spermatozoa of the testes. The results of this study showed that pawpaw seeds powder can be used to control the breeding of Nile tilapia in production units.