Mendelian transmission, transgene dosage and growth phenotype in transgenic tilapia (Oreochromis hornorum) showing ectopic expression of homologous growth hormone

Abstract Gene transfer has offered a new tool for the development of improved fish strains for aquaculture. However, characterization is required before these strains can be introduced into national aquaculture programs. Transgenic tilapia ( O. hornorum urolepis ) were produced by the microinjection into early embryos of a transgene containing the tilapia growth hormone (tiGH) cDNA under the regulatory sequences derived from the human cytomegolovirus (CMV). A male containing 1 copy/cell of the transgene was selected to establish a transgenic tilapia line. The transgene was transmitted to F 1 –F 4 generations in a Mendelian fashion. Previous studies showed ectopic, low level expression of tiGH in brain, heart, gonad, liver and muscle cells of transgenic tilapia. Biochemical analyses indicated lower levels of cholesterol, free alanine and aspartic acid in the muscle of transgenic animals. Four month old transgenic homozygous (F 2 +/+ ) and heterozygous (F 2 −/+ ) tilapia and non-transgenic siblings ( N TRANSGENICS =14; N CONTROLS =11; N F2 −/+ =8; N F2 +/+ =6) were studied for 3 months grown communally in the same pond. Transgenic (F 2 −/+ +F 2 +/+ ), F 2 −/+ , and F 2 +/+ progeny were larger than non-transgenic siblings at P =0.009, P =0.005 and P =0.07 (Student t -test), respectively, suggesting a transgene-dosage effect. These results indicate stable germ line transformation in this fast-growing transgenic tilapia line.