Morphometric Variations in Sarotherodon melanotheron (Pisces: Cichlidae) from Brackish and Fresh Water Habitats in South-western Nigeria

  • Omoniyi I
  • Agbon A
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Abstract

A comparative racial study of Sarotherodon melanotheron (Ruppell) from brackish and fresh water habitats both in south-western Nigeria using morphometric and meristic characters to determine variations showed that they were phenotypically separable populations of the same species. The results revealed significant differences (P < 0.05) in body depth, caudal peduncle depth, number of gill rakers and scales on the lateral line which were suggested to have occurred as a result of difference in the temperature, salinity and substratum in the two water bodies. The results also implied that fresh water broodstock could be preferable to the brackish population for breeding programmes. Introduction Sarotherodon melanotheron (Ruppell) is a cichlid that occurs commonly in West Africa and supports a major fishery in the lagoons. This status earns it the common name 'West African lagoon tilapia' (Eyeson, 1979). Pauly (1976) had earlier mentioned the species as a possible candidate for aquaculture. Aspects of its biology and fishery in brackish water of coastal lagoons and estuaries along West Africa have been reported (Fagade & Olaniyan, 1974; Pauly, 1976; Eyeson, 1979, Trewavas, 1982; and Ugwumba, 1988). However, in Nigeria specimens of S. melanotheron were found to have escaped during a high flood of 31 August 1980 from an experimental pond into a small fresh water reservoir in Ibadan, where they have since successfully established themselves. This is Awba reservoir within the University of Ibadan. It is now even suspected that the species may have spread downstream and probably into adjoining fresh water bodies. At this reservoir, Ugwumba & Adebisi (1992), and Ugwumba & Ugwumba (1993) provided information on its food and feeding ecology and biology, respectively. Oyekanmi (2000) studied some morphometric features of the species in relation to limnology of the reservoir. Ugwumba (2002) also reported the diurnal feeding intensity and gut pH of the species from Awba reservoir. For this species to have established and thrived well in a fresh water environment for over two decades, there is the need to assess its stock. The aim of this paper is, therefore, to report on a racial study of S. melanotheron using morphometric and meristic characters to determine variations between the Awba reservoir and Lagos lagoon populations in view of possible ecological changes. This study will provide additional information on the species for its farming programme in Nigerian fresh waters. Materials and methods Study areas The study sites are the Awba reservoir in Ibadan and the Lagos lagoon along the coast of Nigeria. Awba reservoir, formed in 1964, is located within the University of Ibadan which lies on latitude 7º 26 and longitude 3º 53É. The reservoir, with a surface area of about 6 ha and a maximum depth of 5.5 m, is located at an altitude of 185 m above sea level and about 140 km from the coast of Nigeria. The bottom of Awba reservoir was essentially mud with clayey sand in some parts.

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Authors

  • I T Omoniyi

  • A O Agbon

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