Gill morphometry in growth hormone transgenic Atlantic salmon

Gill tissue was sampled from salmon (Salmo salar) that were transgenic for somatotropin and from non-transgenic control salmon. The transgenics were the F2 generation produced using eggs from a transgenic F1 female and milt from a non-transgenic male. At the time when the gill tissues were sampled, the transgenic salmon were growing 2.1 times more rapidly and their oxygen uptake rate was about 1.6 times greater than in controls. The gill surface area available for respiratory exchange in the transgenics was about 1.24 times that in the controls, which did not parallel the 1.6-fold increase in oxygen uptake. The increase in gill exchange area was due largely to a relatively uniform increase in the length of each gill filament.