Cardiorespiratory modifications, and limitations, in post-smolt growth hormone transgenic Atlantic salmon Salmo salar.
In recent years, there has been a great deal of interest in how growth hormone (GH) transgenesis affects fish physiology. However, the results of these studies are often difficult to interpret because the transgenic and non-transgenic fish had very different environmental/rearing histories. This study used a stable line of size-matched GH Atlantic salmon (Salmo salar) that were reared in a shared tank with controls (at 10 degrees C, for approximately 9 months) to perform a comprehensive examination of the cardiorespiratory physiology of GH transgenic salmon, and serves as a novel test of the theory of symmorphosis. The GH transgenic salmon had a 3.6x faster growth rate, and 21 and 25% higher values for mass-specific routine and standard oxygen consumption (M(O(2))), respectively. However, there was no concurrent increase in their maximum M(O(2)), which resulted in them having an 18% lower metabolic scope and a 9% reduction in critical swimming speed. This decreased metabolic capacity/performance was surprising given that the transgenics had a 29% larger heart with an 18% greater mass-specific maximum in situ cardiac output, a 14% greater post-stress blood haemoglobin concentration, 5-10% higher red muscle and heart aerobic enzyme (citrate synthase or cytochrome oxidase) activities, and twofold higher resting and 1.7x higher post-stress, catecholamine levels. However, gill surface area was the only cardiorespiratory parameter that was not enhanced, and our data suggest that gill oxygen transfer may have been limiting. Overall, this research: (1) shows that there are significant metabolic costs associated with GH transgenesis in this line of Atlantic salmon; (2) provides the first direct evidence that cardiac function is enhanced by GH transgenesis; (3) shows that a universal upregulation of post-smolt (adult) GH transgenic salmon cardiorespiratory physiology, as suggested by symmorphosis, does not occur; and (4) supports the idea that whereas differences in arterial oxygen transport (i.e. cardiac output and blood oxygen carrying capacity) are important determinants of inter-specific differences in aerobicity, diffusion-limited processes must be enhanced to achieve substantial intra-specific improvements in metabolic and swimming performance.
Deitch
E J
EJ
Ocean Sciences Centre, Memorial University of Newfoundland, St John's, Newfoundland A1C 5S7, Canada.
Fletcher
G L
GL
Petersen
L H
LH
Costa
I A S F
IA
Shears
M A
MA
Driedzic
W R
WR
Gamperl
A K
AK
D000818:Animals; D030801:Animals, Genetically Modified / Q000502:physiology*; D002950:Citrate (si)-Synthase / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000378:metabolism; D004777:Environment; D004912:Erythrocytes / Q000737:chemistry / Q000166:cytology; D005880:Gills / Q000502:physiology*; D013006:Growth Hormone / Q000235:genetics* / Q000502:physiology; D006321:Heart / Q000033:anatomy & histology / Q000502:physiology*; D006454:Hemoglobins / Q000032:analysis; D006854:Hydrocortisone / Q000097:blood; D010101:Oxygen Consumption; D020317:Salmo salar / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D013550:Swimming / Q000502:physiology
D006454:Hemoglobins; D013006:Growth Hormone; D003576:Electron Transport Complex IV; D002950:Citrate (si)-Synthase; D006854:Hydrocortisone