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Factors affecting feed intake, aggression, growth and condition around transfer to sea in Atlantic salmon (Salmo salar)


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Flood, MJ 2007 , 'Factors affecting feed intake, aggression, growth and condition around transfer to sea in Atlantic salmon (Salmo salar)', PhD thesis, University of Tasmania.

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Atlantic salmon is an anadromous species undergoing smoltification to adapt to the
seawater environment. In aquaculture despite being fully smolted when transferred from
freshwater hatcheries to sea cages, feed intake is suppressed, sometimes for long periods
of time. Farms try to ensure salmon recommence feeding rapidly to reduce loss of
condition which may lead to pinheading. The current research aimed to better define the
term pinheading and examine factors effecting feed intake, aggression, growth
performance, condition and nutritional status of fish around seawater transfer.
Pinheads and non-pinheads from a commercial farm were compared. All pinheads had
condition factors < 0.865. Pinheads had significantly (p<0.05) lower body weight, fork
length, condition factor, visceral fat ratios, dry matter, total lipid and gross energy and
significantly higher ash than non-pinheads, all indicating decreased condition. There
was no significant difference in crude protein, osmolality, or digestive ability (based on
trypsin activity).
Feeding frequency following seawater transfer was examined in fish fed eight meals per
day before transfer. One meal per day following transfer resulted in a greater initial
decrease in feed intake than four or eight and significantly increased feeding hierarchy
strength (not significant for four or eight meals) before it decreased again to pre-transfer
strength within three weeks of transfer. No differences between meal frequency
treatments were observed in growth, condition or chemical composition. In a second
experiment changing feeding frequency, whether increasing or decreasing, concurrently
with seawater transfer had little effect on post-transfer feed intake. Following seawater
transfer one meal per day fish had lower initial feed intake than eight meal fish
regardless of pre-transfer frequency.
Feeding and dominance hierarchies were examined immediately before and following
seawater transfer. Feeding ranks were stable (Kendalls coefficient of concordance) in
both freshwater and seawater but no correlation existed between mean freshwater and
seawater hierarchies. Dominance ranks were also stable in freshwater but not seawater and mean dominance hierarchies in freshwater and seawater did not correlate. Findings
suggest seawater hierarchies can not be predicted from freshwater hierarchies.
A period of feed-deprivation for the first fourteen days following seawater transfer
resulted in feed-deprived fish being significantly out-competed by non-deprived fish in
terms of feed intake, growth and final condition. Although not significant, aggression
also tended to be lower for feed-deprived fish. Further findings suggest that at higher
densities the advantage to non-deprived fish may be diminished.
Experiments show advantages of high feeding regimes immediately before and
following seawater transfer and the difficulties in predicting performance of individuals
in seawater based on their freshwater performance. They also suggests that fish that wait
too long to recommence feeding may be at some disadvantage to those recommence

Item Type: Thesis - PhD
Authors/Creators:Flood, MJ
Keywords: Atlantic salmon
Copyright Information:

Copyright 2007 the author

Additional Information:

Ch. 1. General introduction -- Ch. 2. Defining the Atlantic salmon pinhead -- Ch. 3. Manipulation of feeding frequency following transfer to sea in Atlantic salmon -- Ch. 4. The effects of changing feeding frequency simultaneously with transfer to sea in Atlantic salmon -- Ch. 5. Changes in dominance and feeding hierarchies in Atlantic salmon as a result of transfer from a freshwater to a seawater environment -- Ch. 6. Effect of feed-deprivation immediately following seawater transfer on feeding, dominance and growth of Atlantic salmon -- Ch. 7. General discussion

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