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Grasscutter (Thryonomys swinderianus) is a large-body old world rodent found in sub-Saharan Africa. The body size and the unique taste of the meat of this major crop pest have made it a target of intense hunting and a potential consideration as a micro-livestock. However, there is insufficient knowledge on the genetic diversity of its populations across African Guinean forests. Herein, we investigated the genetic diversity, population structures and evolutionary history of seven Nigerian wild grasscutter populations together with individuals from Cameroon, Republic of Benin, and Ghana, using five mitochondrial fragments, including D-loop and cytochrome b (CYTB). D-loop haplotype diversity ranged from 0.571 (± 0.149) in Republic of Benin to 0.921 (± 0.013) in Ghana. Within Nigeria, the haplotype diversity ranged from 0.659 (± 0.059) in Cross River to 0.837 (± 0.075) in Ondo subpopulation. The fixation index (FST), haplotype frequency distribution and analysis of molecular variance revealed varying levels of population structures across populations. No significant signature of population contraction was detected in the grasscutter populations. Evolutionary analyses of CYTB suggests that South African population might have diverged from other populations about 6.1 (2.6–10.18, 95% CI) MYA. Taken together, this study reveals the population status and evolutionary history of grasscutter populations in the region.

Cichlids are among the economically important which serve as a source of food for people ‎around the world. A deep understanding of the population structure and genetic diversity of ‎cichlids are vital for initiation of conservation policies and sustainable aquaculture. There is ‎paucity of information on the patterns of genetic variations among and within cichlids in ‎North-central Nigeria. This study, therefore, investigated population genetic structure of ‎Coptodon zillii, Oreochromis niloticus, and Hemichromis fasciatus collected from different ‎freshwater bodies in North-central Nigeria. Genomic DNA was extracted, and five highly ‎polymorphic RAPD primers were used for RAPD-PCR amplification and genotyping of the ‎fish. Genetic polymorphism within and between the three tilapia species were examined. ‎Percentages of polymorphism loci, pairwise population matrix, analysis of molecular variance ‎‎(AMOVA), and genetic distances of cichlid populations were determined using standard ‎methods, and dendrograms were constructed using an un-weighted pair group method of ‎arithmetic mean (UPGMA). Overall, percentages of estimated molecular variance within and ‎among C. zillii, H. fasciatus and O. niloticus populations were 5% and 95%; 4% and 96% and ‎‎13% and 87%, respectively. Our results suggest that the three cichlids have close evolutionary ‎relationship and there were no distinct genetic differences on the basis on sampling locations. ‎C. zillii and H. fasciatus are more genetically closer than O. niloticus. This study concludes that ‎RAPD is useful in studying the population genetic structure of cichlids. This study therefore ‎recommends conservation of genetic pool of cichlid species through proper maintenance and ‎restoration of polluted habitat to guarantee sustainable fishery production. However, markers ‎such as microsatellite DNA can be assayed in further studies for better results‎.

Heavy metals environmental pollution has become a global menace requiring constant biomonitoring and concerted efforts towards its reduction. There are reports of heavy metals pollution of Usuma River, Gwagwalada, Federal Capital Territory, Nigeria. However, information on the direct and indirect health impacts of such pollution on inhabiting fish and on their human consumers are non-existent, especially in Oreochromis mossambicus. The analyses of the physicochemical parameters of Usuma River water, fish heavy metals, histopathological changes, and health risks were performed according to standard procedures. The physicochemical characteristics of the Usuma River water were within acceptable ranges. The Pb bioaccumulation at 2.5100 ± 0.42 mg/kg was significantly (p < 0.05) higher than the values recorded for Cd at 0.4267 ± 0.16 mg/kg and zinc at 0.6027 ± 0.02 mg/kg. Nevertheless, Pb and Cd bioaccumulated more than their recommended permissible levels. Human health risks assessment revealed no immediate carcinogenic risk at a target rate of between 1.2690 × 10 -5 - 2.3530 × 10 -5 . The current heavy metals' concentration posed no long-term non-carcinogenic risk at a hazard index of less than one. This is because the target rate figure above 1.0 × 10 -3 and the hazard index figure above one signifies great health risks. The recorded gills and hepatic cellular changes did not affect organ functionalities as their obtained degree of tissue change figures were all below 10 based on the protocol. Although there was a positive strong correlation between the water temperature and its biochemical oxygen demand as well as between the water dissolved oxygen content and gill cellular changes, a negative strong correlation existed between the water pH and its electrical conductivity and total dissolved solids. The findings highlighted the progressing volatility of heavy metals pollution dynamics within the study area that could pose great human health risks, if unchecked., Competing Interests: Declarations Ethical approval The University of Abuja Ethics Committee on Animal Use (UAECAU) approved the work with Reference no.: UAECAU/2021/004. Competing interests The authors declare no competing interests., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

The fast-growing discharge of effluents of engineered nanomaterials (ENM) and heavy metals in freshwater ecosystems raises concern in recent times. This study investigated the effects of the co-exposure between nanoparticles (TiO 2 NPs) and lead (Pb) in a simplified freshwater food web model, including zooplankton (copepods sp.) and Clarias gariepinus on bioaccumulation and antioxidant activity. We carried out a chronic (28 days) semi-static bioassay by feeding individually fish with zooplankton exposed to TiO 2 NPs (0.09 and 0.20 μM), Pb (0.01 and 0.04 μM), and their binary mixtures. The binary mixtures caused a significant (p < 0.05) decrease in malondialdehyde (1.64-2.01-fold), catalase (3.18-3.89-fold), glutathione reductase (1.37-1.46-fold), and glutathione peroxidase (1.19-1.89-fold) levels. Lead accumulated in the tissues had bioaccumulation factor between 0.40 and 1.42 in binary mixture. These results indicate that chronic exposure of TiO 2 NPs could influence the BAF of Pb, neurotoxicity, changes of antioxidant enzymes, and retardation of food uptake. These findings raise concerns regarding the fate of higher trophic levels in polluted freshwater ecosystems with a binary mixture of engineer nanomaterials and heavy metals.