Effects of family and promoter on growth performance of ccGH cDNA transgenic channel catfish, Ictalurus punctatus, grown in a trough culture system

Constructs bearing growth hormone (GH) cDNA from channel catfish, Ictalurus punctatus, driven by the ocean pout, Zoarces americanus, antifreeze protein promoter (opAFP), or by the rainbow trout, Oncorhynchus mykiss, metallothionein promoter (rtMT) were transferred to channel catfish via electroporation. Transgenic P1 individuals were mated to produce F1 individuals that exhibited enhanced growth rate. The inheritance of the transgene by the F1 generation was 10% to 36%. The mean body sizes of F1 transgenic fish were larger than their non-transgenic full-siblings (P < 0.001). Transgenic channel catfish harboring channel catfish growth hormone (ccGH) cDNA, driven by the ocean pout antifreeze protein promoter (opAFP) grew 1.41- to 1.62- fold larger than their non-transgenic full-siblings, and transgenic channel catfish possessing the channel catfish growth hormone (ccGH) cDNA, driven by the rainbow trout metallothionein promoter (rtMT) grew 1.23- to 1.78- fold larger than their non-transgenic full-siblings. However, non-transgenic full-siblings in one family of opAFP-ccGH had the same mean size as transgenic individuals of a another family, and non-transgenic full-siblings in two families of rtMT-ccGH had the same mean size as transgenic individuals of a third family that was the slowest growing family, illustrating the importance of the family effect (P < 0.001) or possibly variable insertion sites. The slowest growing family exhibited the greatest observed response to the GH transgene insertion. Condition factor was not different (P > 0.05) between transgenic and non-transgenic full-siblings except for one opAFP-ccGH family, although the observed means were smaller for four of six transgenic groups as apparently their relative length was increasing more rapidly than relative weight compared to their respective controls. Examining the data from the current experiment and that from an earlier experiment with the same genetic types, but grown to a smaller size, it appears that the two promoters gave similar results in regards to growth enhancement. The largest individuals were always in the transgenic families, and this along with the family effects suggest that gene transfer coupled with combined individual and family selection might result in larger fish than the GH transgenesis alone. The growth enhancement in the current experiment was better than previous experiments with channel catfish that used RSV-LTR-salmonid GH constructs. Assuming government approval and the same growth to food size, GH transgenic channel catfish would increase farm income by $3421/ha compared to use of non-transgenic channel catfish.