A recombinant plasmid containing the Rous sarcoma virus-long terminal repeat (RSV-LTR) promoter linked to rainbow trout (Salmo gairdneri) growth hormone (GH) cDNA was microinjected into fertilized carp eggs. Genomic DNA extracted from pectoral fin of individual presumptive transgenic fish was analyzed by dot blot and Southern blot hybridization, using the RSV-LTR and/or the GH cDNA sequences as probes. Out of 365 presumptive transgenic fish analyzed, 20 individuals were found to contain pRSV-rtGH-cDNA sequence in the genomic DNA. Expression of the trout GH polypeptide was detected by immunobinding assay in the red blood cells of nine transgenic fish tested. The level of expression, however, varied among the transgenics and could not be correlated with exogenous DNA copy number. Although there was considerable variation in the sizes of the transgenic fish, those microinjected during the one-cell stage were (P less than 0.05) 22% larger, on the average, than their sibling controls. A randomly selected fraction of the progeny derived from crosses between transgenic males and non-transgenic females inherited the foreign DNA. These transgenic progeny grew faster (P less than 0.05) than their non-transgenic siblings.

Hybrid and parental backcross experiments were performed using olive flounder, Paralichthys olivaceus, summer flounder, Paralichthys dentatus, and their female F1 hybrids to examine hybrid fitness in the backcross. Fertilization rate, hatching rate, and combined fitness measure (CFM, product of fertilization rate and hatching rate) were detected and the results showed that the CFM of hybrid and backcross generations was reduced significantly compared to pure olive flounder crosses. Genomic inheritance from parents to backcross progeny was also detected by amplified fragment length polymorphism (AFLP). Almost all AFLP bands observed in parents were presented in backcross progeny (backcross1, 218/227; backcross2, 265/282), although 9 and 17 parental bands were missing in backcross1 and backcross2, respectively. Novel bands (absent in parents) also occurred in progeny at the frequencies of 5.63% (13/231) in backcross1 and 3.28% (9/274) in backcross2. Additionally, 27.40 and 31.18% of AFLP markers deviated from expected Mendelian ratio in backcross1 and backcross2, respectively. The present study suggests that genetic incompatibilities may exist between olive flounder and summer flounder. Furthermore, possible implications of segregation distortion for reduced hybrid fitness in backcross generations are discussed.