Four extruded diets differing in protein/fat concentrations,
378/389 g kg–1, 425/346 g kg–1, 480/308 g kg–1 and 524/256 g
kg–1 were tested in a digestibility trial and a growth study.
Apparent digestibility of protein and fat were not significantly
different among the diets when tested in 1-kg Atlantic salmon,
Salmo salar L., in sea water. The diets represented a range of
digestible protein to digestible energy ratios (DP/DE ratios) of
14.1, 16.4, 18.8 and 21.9 g MJ–1.
The 138-day growth study was performed with triplicate
groups of Atlantic salmon of 1.0 and 2.5 kg initial weight.
Irrespective of size; growth, feed conversion ratio (FCR),
nitrogen and energy retention were poorer in fish fed the diet with
DP/DE ratio of 14.1 g MJ–1 compared with the fish fed the other
diets. A DP/DE ratio of 16.4 g MJ–1 was sufficient to produce
maximum growth for the large fish, while the DP/DE ratio of
18.8 g MJ–1 produced the highest growth in the small fish. In the
large fish, the lowest FCR was obtained on a DP/DE ratio of 16.4
g MJ–1, while there was no clear difference in FCR within the small
fish when diets of DP/DE ratios of 16.4–21.9 g MJ–1 were fed.
The carcass-to-body ratio in the small fish decreased with
decreasing DP/DE ratios. The fish fed the diet of 21.9 g MJ–1 had
significantly lower fat and dry matter and higher protein content
than fish of similar size fed the other diets. Increased dietary lipid
content seemed to improve astaxanthin deposition in the small
fish, while the large fish showed no significant differences in
astaxanthin deposition due to dietary treatment.
This study indicates that a DP/DE ratio of 14.1 g MJ–1 in highenergy
diets for Atlantic salmon in sea water is below the optimal
DP/DE ratio for growth and feed utilization, and that the optimal
DP/DE ratio decreases with increasing fish weight. DP/DE ratios
around 19 g MJ–1 for fish weighing 1 to 2.5 kg, and 16–17 g MJ–1
for fish weighing 2.5 to 5 kg, are suggested to be optimal.
Four extruded diets differing in protein/fat concentrations,378/389 g kg–1, 425/346 g kg–1, 480/308 g kg–1 and 524/256 gkg–1 were tested in a digestibility trial and a growth study.Apparent digestibility of protein and fat were not significantlydifferent among the diets when tested in 1-kg Atlantic salmon,Salmo salar L., in sea water. The diets represented a range ofdigestible protein to digestible energy ratios (DP/DE ratios) of14.1, 16.4, 18.8 and 21.9 g MJ–1.The 138-day growth study was performed with triplicategroups of Atlantic salmon of 1.0 and 2.5 kg initial weight.Irrespective of size; growth, feed conversion ratio (FCR),nitrogen and energy retention were poorer in fish fed the diet withDP/DE ratio of 14.1 g MJ–1 compared with the fish fed the otherdiets. A DP/DE ratio of 16.4 g MJ–1 was sufficient to producemaximum growth for the large fish, while the DP/DE ratio of18.8 g MJ–1 produced the highest growth in the small fish. In thelarge fish, the lowest FCR was obtained on a DP/DE ratio of 16.4g MJ–1, while there was no clear difference in FCR within the smallfish when diets of DP/DE ratios of 16.4–21.9 g MJ–1 were fed.The carcass-to-body ratio in the small fish decreased withdecreasing DP/DE ratios. The fish fed the diet of 21.9 g MJ–1 hadsignificantly lower fat and dry matter and higher protein contentthan fish of similar size fed the other diets. Increased dietary lipidcontent seemed to improve astaxanthin deposition in the smallfish, while the large fish showed no significant differences inastaxanthin deposition due to dietary treatment.This study indicates that a DP/DE ratio of 14.1 g MJ–1 in highenergydiets for Atlantic salmon in sea water is below the optimalDP/DE ratio for growth and feed utilization, and that the optimalDP/DE ratio decreases with increasing fish weight. DP/DE ratiosaround 19 g MJ–1 for fish weighing 1 to 2.5 kg, and 16–17 g MJ–1for fish weighing 2.5 to 5 kg, are suggested to be optimal.
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