Doctoral Degrees (Animal Sciences)

Permanent URI for this collection

https://scholar.sun.ac.za/handle/10019.1/526

Browse

Browsing Doctoral Degrees (Animal Sciences) by Subject "Aquatic biodiversity conservation -- Africa -- Malawi"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Genetics studies of cichlid Oreochromis shiranus towards sustainable aquaculture and fisheries management in Malawi
    (2020-12) Sanudi, Thomson Joseph; Roodt-Wilding, Rouvay; Rhode, Clint; Brink, Danie; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Science.
    ENGLISH ABSTRACT: Oreochromis shiranus is an economically important fish species in Malawi, but levels of harvest from the wild have declined due to overexploitation and habitat degradation. There is an urgent need to devise strategies for sustainable utilization of this species. The aim of this study was to understand the reproductive behaviour, geographic distribution, genetic diversity, population structure, past demographic fluctuations and association of quantitative trait loci (QTL) with traits of economic importance which are prerequisites for the design and implementation of these strategies. A random sample of 306 live fish, collected across the main water bodies in Malawi, were reared in one pond to reproduce an F1 generation in random families. This study observed that mate selection and competition among the females for males and mating sites resulted in only a few females (42%) and males (27%) contributing to the F1 generation. However, there was no statistically significant variation in genetic diversity between the broodstock and the F1 generation, because of the large genetic base and participation of broodstock from all the sampled locations. The study concluded that due to limited gene flow, O. shiranus populations in the wild in Malawi were structured according to and within water basins. There was evidence of population bottlenecks in the wild, which corresponded to small effective population sizes (Ne = 104). The population bottlenecks did not result in low genetic diversity and inbreeding depression due to isolate breaking. Finally, the association of some QTLs for body weight in Oreochromis spp. suggest considerable evolutionary conservation and synteny within the genus. The observed levels of genetic diversity and Ne across the main water bodies in Malawi are adequate to increase Ne and mitigate against future bottlenecks if closed fishing seasons and fishing net mesh size are enforced. Restocking programmes may not be necessary at the moment unless in the event of complete desiccation. During restocking, it is therefore recommended that, to ensure genetic diversity, broodstock for stock enhancement should be randomly sampled from the different populations within the water body. In aquaculture, where interest is to increase production of large fish, these findings will greatly inform management and breeding programmes to ensure genetic diversity and increase selection efficiency by using QTLs. Although it was not possible to determine the ideal number of individuals that should be included as founder population for selective breeding programmes, this study recommends that a wide genetic base is required to ensure genetic diversity. The results of this study are useful in conservation management of the species in the wild and the establishment of genetic improvement programs in aquaculture.