CHARACTERIZATION OF TRANSGENIC TILAPIA LINES WITH DIFFERENT ECTOPIC EXPRESSION OF TILAPIA GROWTH-HORMONE

The transfer of growth hormone (GH) genes has opened new possibilities for the manipulation of growth in economically important fish species . However, the ectopic GH levels to optimize growth acceleration in fi sh, and specially in tilapia, are not known and must he determined exp erimentally. The tilapia GH (tiGH) cDNA was used Co construct chimeric genes expressing different levels of tiGH in vitro and in vivo. These constructs were used to generate four lines of transgenic tilapia by microinjection into one-cell embryos. Different patterns and levels of ectopic expression of tiGH and IGF were detected in organs of transge nic tilapia by RNA or protein analysis. The two lines with lower ectop ic tiGH mRNA levels were tile only ones showing growth acceleration, s uggesting that the expression of ectopic tiGH promoted growth only al low expression levels, The effect of higher ectopic tiGH levels resemb led the physiologic situation of low condition factor and permitted us to postulate a model for growth acceleration in transgenic tilapia ex pressing ectopic tiGH.