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Growth hormone increases growth and dominance of wild juvenile Atlantic salmon without affecting space use


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Martin-Smith, KM, Armstrong, JD, Johnsson, JI and Bjornsson, BT 2004 , 'Growth hormone increases growth and dominance of wild juvenile Atlantic salmon without affecting space use' , Journal of Fish Biology, vol. 65, no. Supple , pp. 156-172 , doi: 10.1111/j.1095-8649.2004.00542.x.

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Growth hormone (GH) was applied to Atlantic salmon Salmo salar parr (the pre-migratory
freshwater life stage) to manipulate growth potential experimentally and to elucidate the effects
on dominance status, actual growth, exploratory activity and home range. Experiments were
conducted using seven groups of eight parr from May to September of two successive years.
The fish were tagged with passive integrated transponders (PIT tags), tested for dominance, and
then held in an enclosed section of a natural stream which was fitted with an array of PIT tag
detectors to record space use at a definition of c. 2 m. Relationships between dominance rank,
space use and growth were established over 2 weeks. The four lowest ranking fish in each group
were then given a slow-release GH implant while the other fish received a placebo. The GH
stimulated increase in fork length (LF) and mass and decrease in condition factor due to the
relatively greater increase in LF. There was, however, an interaction between GH-stimulated
increase in growth and season, with the hormone having an effect only during the early part of
the summer. Regardless of treatment, fish that moved most around their home range grew
fastest. Increased growth in GH-treated fish was associated with an increase in growth per unit
movement, not increased total movement. This suggested that GH-treated fish increased their
rate of short-distance (<2 m) foraging movements. Overall, space use, measured in terms of
home range size and time allocation throughout the range, did not vary consistently in response
to application of GH. There was a strong correlation between the weighted centre of the home
range (a measure of position within the enclosure) before and after treatment, irrespective of
whether fish were given GH or a placebo. The study shows that when density is low relative to
carrying capacity, GH stimulates increased dominance and growth in a near-natural environment
without having measurable effects on space use at a definition of c. 2 m. The results are
interpreted as suggesting that high dominance status gives no significant growth advantage in a
highly competitive situation, but increases foraging rate when food is abundant. Increased
foraging appears to result from local changes in time budgeting rather than variations in the
extent of home range and larger-scale movements within it. Thus, in areas with declining wild
Atlantic salmon populations where the habitat is unsaturated and food is abundant, introduced
domestic Atlantic salmon may be competitively superior.

Item Type: Article
Authors/Creators:Martin-Smith, KM and Armstrong, JD and Johnsson, JI and Bjornsson, BT
Keywords: Salmo salar; social status; territory
Journal or Publication Title: Journal of Fish Biology
ISSN: 0022-1112
DOI / ID Number: 10.1111/j.1095-8649.2004.00542.x
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