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Title: Behavioural and molecular genetic studies of Oreochromis species and their hybrid
Author: Goodyear, N. M.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 1998
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The tilapiine cichlids of the genus Oreochromis are an increasingly important component of aquaculture in many countries. Aquaculture in Malawi is expanding rapidly and its importance may increase if local cichlid fisheries continue to decline. There is concern that sympatric species (O. shiranus and O. karongae) are hybridizing in farm ponds. The ease with which Oreochromis species hybridize is of much concern to the maintenance of their biological diversity. Mate choice and courtship behaviour were investigated in the allopatric species O. mossambicus and O. spilurus, and their hybrid. Pure-bred females largely mated assortatively and behaved differently to conspecific and heterospecific males. Females mated with heterospecifies if conspecific males were not available. Hybrid females showed a preference for O. mossambicus. Differences in behaviour largely predicted mate choice in pure-bred fish. O. karongae is one of three species belonging to the unique Oreochromis (Nyasalapia) species flock of Lake Malawi ('chambo'). The incidence of hybridization in farm ponds was examined using allozyme, RAPD and morphological analysis. Markers that distinguished between O. shiranus and chambo were found with both molecular genetic techniques. Markers for each chambo species were not detected. O. shiranus and chambo were discriminated using eight morphometric variables. Chambo species were discriminated using morphometrics, meristics and colouration. Hybrids of O. shiranus and chambo were detected in all ponds sampled from three sites in Malawi. No F1 hybrids were detected and introgression was common. Discrepancies in fish identification illustrates the merits of using several techniques when identifying post-F1 hybrids. Morphological analysis was least effective in identifying hybrids. The implications of hybridization and possible escapes into the wild are discussed in relation to the impacts on aquaculture and on the unique cichlid species endemic to Lake Malawi. Recommendations for the management of Oreochromis in aquaculture are considered in relation to ecological and socioeconomic issues. Processes that maintain reproductive isolation between Oreochromis species are discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available