Gut morphology in growth hormone transgenic Atlantic salmon

Growth hormone transgenic Atlantic salmon Salmo salar reared at 12–13°C were F2 generation derived, using eggs from a transgenic F1 female and fertilized with milt from a non‐transgenic male. At the time of tissue sampling the transgenic salmon were growing 1·6 times faster than control salmon. Transgenic salmon tended to have more intestinal folds that were longer than those of control salmon. Consequently, the transgenic salmon had a larger digestive surface area both in the anterior intestine (surface area 1·5 times control) and in the pyloric caeca (surface area 1·2 times control). Most morphological features of the intestine and of the pyloric caeca of transgenic salmon were larger than those of control salmon; in particular, the surface area of the anterior intestine was concordant with the growth rate difference.