Production of Lines of Growth Enhanced Transgenic Tilapia (Oreochromis Niloticus) Expressing a Novel Piscine Growth Hormone Gene

Abstract

Since the first introduction of novel genes in fish (Maclean and Talwar, 1984; Zhu et al., 1985), a wide range of fish species have been used in transgenic research either for commercial or academic purposes. For commercial exploitation this technology has been applied in several commercially important fish species to improve desirable genetic traits such as growth (Rokkones et al., 1989; Zhang et al., 1990; Brem et al., 1988; Penman et al., 1990; Gross et al., 1992), cold tolerance (Fletcher et al., 1988), or disease resistance (Anderson et al., 1996) for aquaculture development. Most of these gene transfer experiment have concentrated on growth enhancement using regulatory sequences and coding sequences of distantly related species (Rokkones et al., 1989; Penman et al., 1990; Brem et al., 1988; Zhang et al., 1990). Although successful gene transfer in these fish was observed in only a few cases has germline transmission and expression of transgenes in progeny been convincingly demonstrated (see reviews by Maclean and Rahman, 1994; Gong and Hew, 1995). In studies where the regulatory sequences used were of mammalian origin, low or nil expression was observed (Guyomard et al., 1989; Alam et al., 1996). In other studies, enhanced growth was observed in transgenic carp (Zhang et al., 1990) and in tilapia (Martinez et al., 1996) when growth hormone sequences were driven by a viral promoter. However, the main objective of the production of transgenic fish with GH gene is to generate novel strain of growth enhanced fish which could subsequently be used in aquaculture. It is, therefore, important that the gene constructs used for producing trans-genic fish be of fish origin, and not from mammalian or viral origin. Moreover, it was also observed that regulatory sequences from fish are found to be more effective than those of mammalian origin in respect to expression of transgenes (Alam et al., 1996) in fish.