Ž .
Ž . Ž
Feed conÕersion ratio FCR s feed eaten r final biomass q biomass of dead fish y .
initial biomass Ž
. Ž
Ž . Ž Ž
..
3
. Condition factor CF s fish weight g r Fish length cm
= 100
Ž .
Ž .
Hepatosomatic index HSI s liver weightrbody weight = 100 Ž
. Retention of nitrogen s nitrogen increase in fishrnitrogen intake = 100
Ž .
Retention of energy s energy increase in fishrenergy intake = 100. 2.7. Statistics
Statistical evaluation of differences between diets was conducted using analysis of Ž
. Ž .
variance general linear model SAS Institute, 1989 . Multiple comparisons of growth,
specific growth rate, feed conversion, plasma amino acids, body composition, nutrient retention and digestibility of protein, fat, starch and energy, of amino acids absorbabil-
ity, and of enzyme activities between diets were conducted using the Duncan multiple range test, with tank mean as observation. For lipolytic and proteolytic activity,
comparisons were also carried out within each intestinal region separately. A signifi- cance level of P F 0.05 was chosen for all tests. As the variance of the amino acid
absorbabilities within each intestinal segment were fairly similar, a comparison of the
Ž absorbabilities was carried out on the basis of 95 confidence range least significant
. difference , estimated as 4 = SEM.
3. Results
3.1. Feed intake, growth and FCR Feed intake increased during the first part of the experiment, indicating that the fish
needed a certain period of acclimatisation before intake stabilised at 1.3 of BW. A pre-experimental period of acclimatisation was not included in the experiment, as it
would have affected the start weights of the fish. At the end, fish fed the MCT-diet Ž
. turned out to have eaten slightly less 6 than fish fed the other diets. No significant
Ž .
growth differences were observed among fish fed the four diets Table 3 , and all fish showed similar condition factor after the trial, approximately 1.3. Fish fed the MCT-diet
had significantly lower gutted weight percentages and higher HSI than any of the other groups. Fish fed the MCT-diet showed significantly lower FCR than fish fed the
Ž .
ALA-diet and MET-diet Table 3 . FCRs for fish fed the CYS-diet were of intermediate Ž
. magnitude, significantly different only from the ALA-diet group Table 3 .
3.2. Digestibility and absorbability Dietary inclusion of MCT improved energy digestibility by improving protein
digestibility 5 units, fat digestibility by 3 units and starch digestibility by 13 units, Ž
. Ž
. Ž
compared to the ALA-diet Table 3 . Both methionine MET-diet and cysteine CYS- .
diet improved fat digestibility significantly. Cysteine also improved starch, protein and energy digestibility significantly.
Table 3 Growth, FCR, apparent nutrient digestibility, body composition, liver index, gutted weight and nutrient
retention for Atlantic salmon fed diets mixed with alanine, methionine, cysteine or MCT for 65 days Ž
. ALA-diet
MET-diet CYS-diet
MCT-diet P value
SEM ns12 Ž .
Growth g 118.2
118.6 126.6
125.2 0.200
1.80
a a,b
b,c c
FCR 1.07
1.04 0.97
0.93 0.028
0.02 Digestibilityr absorbability
c c
b a
Starch 60
62 66
73 0.0001
1.6
c b,c
b a
Nitrogen 80
81 82
85 0.0006
0.6
b a,b
a,b a
c
Sum of amino acids 76
79 81
86 0.0039
1.4
b a
a a
Fat 91
93 92
94 0.0060
0.4
c b,c
a,b a
Energy 72
74 75
77 0.0056
0.7 Body composition
a a
a b
y1
Ž .
Fat g kg 113
111 110
85 0.0004
0.40
b b
a,b a
y1
Ž .
Protein g kg 171
173 175
177 0.0309
0.08 Condition factor
1.31 1.31
1.34 1.34
0.4554 0.01
y1
Ž .
Ash g kg 21
21 21
21 0.5900
0.01
b b
b a
HSI 2.0
1.9 2.1
2.6 0.0005
0.08
a a
a b
Ž . Gutted weight
86.1 86.1
86.5 84.2
0.0002 0.30
Nutrient retention
c c
b a
Nitrogen retention 52
55 61
66 0.0009
1.7
a a
a b
Energy retention 47
45 46
38 0.0110
1.1 Numbers are treatment means. Results from analysis of variance, where SEM is the standard error of the
mean, and the P-value is the significance level for the effect of dietary treatment. Mean values with different superscript letters are significantly different.
Ž .
Faeces were collected by stripping Austreng, 1978 .
c
Determined as sum of amino acid residues in chyme collected by dissection from the distal most parts of the intestine.
Fig. 1 illustrates the cumulative apparent total amino acid absorbability along the GI tract. The results indicate that cysteine and MCT supplementation increased absorbabil-
ity of amino acids in the distal intestinal segments. Amino acid absorption was Ž
. significantly improved for the MCT-diet compared to the ALA-diet P s 0.0039 .
Table 4 presents absorbability of all amino acids along the GI tract in the ALA-diet, whereas Fig. 2 depicts cumulative absorbability along the GI tract for four selected
amino acids: cysteine, glycine, alanine and methionine in this diet. Total amino acid absorbability, estimated as accumulated absorbability in the DI2 segment, was highest
for glutamic acid and lowest for cysteine. Cysteine absorbability was low throughout the
Ž .
intestinal tract, particularly in the pyloric region Fig. 2 . Ž
. Taurine concentrations 1 SEM in chyme dry matter from the ALA-diet group
were 1 0.6, 20 0.8, 18 1.1, 16 0.5, 11 0.1 and 7 0.6 mg g
y1
in ST, PR, MI1, MI2, DI1 and DI2, respectively.
The CYS-diet showed a higher absorbability of cysteine in all segments compared to Ž
. the ALA- and MET-diets Fig. 3 . Also MCT fat increased total apparent absorbability
Ž .
of cysteine significantly P s 0.0002 , although apparent absorbability of cysteine was
Fig. 1. Cumulative apparent absorbability of total amino acids in the GI tract of Atlantic salmon fed diets Ž
. Ž
. Ž
. Ž
. mixed with alanine ALA-diet , methionine MET-diet , cysteine CYS-diet or MCT MCT-diet . Data points
Ž .
represent the mean of three tanks. Bars indicate SEM ns 3 .
Table 4 Cumulative absorbability of individual amino acids
a
in intestinal tract
b
of Atlantic salmon fed the ALA-diet
c
PR MI1
MI2 DI1
DI2 Alanine
59.00.6 70.32.7
80.30.3 82.32.2
81.03.1 Arginine
56.00.6 67.72.6
78.70.9 80.72.8
79.0 4.6 Aspartic acid
30.72.4 49.75.3
68.00.6 71.02.6
67.34.1 Cysteine
4.74.3 23.38.7
50.30.9 57.32.3
58.03.2 Glutamic acid
57.30.9 69.72.4
81.00.6 83.72.4
82.73.9 Glycine
41.71.9 54.74.8
70.00.6 73.02.3
71.03.8 Histidine
46.30.3 60.33.7
74.00.6 76.72.4
75.04.2 Isoleucine
50.01.2 65.03.1
78.00.6 80.72.4
78.74.4 Leucine
54.30.9 67.72.4
79.30.7 81.72.4
79.34.3 Lysine
56.70.7 70.32.3
81.70.9 82.72.4
80.04.2 Methionine
55.70.3 72.32.6
80.01.0 83.02.3
81.33.8 Phenylalanine
50.70.9 64.72.8
77.00.6 78.32.7
76.73.9 Proline
53.01.2 65.71.9
75.70.3 79.02.0
76.33.7 Serine
41.01.5 55.34.7
70.00.6 73.32.3
71.04.2 Threonine
40.71.8 57.74.4
72.70.7 76.32.3
74.04.2 Tyrosine
33.31.8 54.05.5
70.70.3 73.02.6
71.34.4 Valine
49.01.0 63.03.1
76.00.6 78.72.4
77.34.3
a
Tryptophan was not analysed.
b
PR s pyloric region, the proximal region of the intestine, starting at the distal side of the pyloric sphincter and ending at the location of the distal-most caeca; MI s mid-intestine, the region distal to the pyloric region
and proximal to the increase in intestinal diameter; DI sdistal intestine, from the distal end of the mid-intestine to the anus.
c
Ž .
Results are means for tanksSEM of mean ns 3 .
Fig. 2. Cumulative apparent absorbability of methionine, alanine glycine and cysteine in Atlantic salmon fed Ž
. the ALA-diet. Data points represent the mean of three tanks. Bars indicate SEM ns 3 .
Ž .
low in the pyloric caeca Fig. 3 . Fig. 4 depicts apparent absorbability of methionine for the four diets. Total apparent methionine absorbability increased 15 in the MCT-diet,
Ž . Ž
. compared to the ALA-diet and the MET-diet P s 0.0143
Fig. 4 .
Fig. 3. Cumulative apparent absorbability of cysteine in the GI tract of Atlantic salmon fed diets mixed with Ž
. Ž
. Ž
. Ž
. alanine ALA-diet , methionine MET-diet , cysteine CYS-diet or MCT MCT-diet . Data points represent
Ž .
the mean of three tanks. Bars indicate SEM ns 3 .
Fig. 4. Cumulative apparent absorbability of methionine in the GI tract of Atlantic salmon fed diets mixed with Ž
. Ž
. Ž
. Ž
. alanine ALA-diet , methionine MET-diet , cysteine CYS-diet or MCT MCT-diet . Data points represent
Ž .
the mean of three tanks. Bars indicate SEM ns 3 .
Of all the amino acids, aspartic acid and glutamic acid were present in highest concentrations in all parts of the intestinal tracts. Concentration of total amino acids in
the chyme decreased from 256 mg g
y1
in the stomach to 114 mg g
y1
in the DI2 segment.
3.3. Body composition Body fat level was found to be significantly lower in the MCT-fed fish compared to
Ž .
the other groups Table 3 , while there were no significant differences among the ALA-diet, MET-diet and CYS-diet groups. The body nitrogen level was significantly
higher for the MCT group compared to ALA and MET groups. The CYS-diet group was intermediate of these and not significantly different from either group.
3.4. Retention of nitrogen and energy Nitrogen retention was significantly higher for the MCT-diet than for all other diets
Ž .
Table 3 . Fish fed the CYS-diet had significantly higher nitrogen retention than those fed the ALA- and MET-diets. The latter groups did not differ significantly from each
other. On the other hand, retention of energy was considerably and significantly lower in the MCT-fed groups than in all the other groups.
3.5. Enzymes and luminal pH Ž
. No difference in GI pH profile was found. Average pH 1 SEM values were
5.1 0.53, 8.3 0.40, 8.5 0.31 and 8.6 0.27 in the stomach, the pyloric, the mid-
and distal intestine, respectively. Proteolytic activity of chyme in the pyloric region was 75 higher in fish fed the MCT-diet compared to fish fed any of the other diets
Ž .
P s 0.0001 . A difference in proteolytic activity was maintained throughout the entire length of the intestine. The only exception was the proximal mid-intestinal segment
Ž . Ž
. Fig. 5. a Total proteolytic activity mmolrminrmg yttrium in five postgastric regions of Atlantic salmon
Ž .
Ž .
Ž .
Ž .
fed diets mixed with alanine ALA-diet , methionine MET-diet , cysteine CYS-diet or MCT MCT-diet . Ž
. Total proteolytic activity was measured with casein as substrate and activity is expressed as DOD
nm r10
280
Ž .
min in the TCA supernatant. Bars represent the mean of three tanks, and error bars indicate SEM ns 3 . Ž .
Ž .
Means with the same letter are not significantly different. b Lipolytic activity mmolrminrmg yttrium in Ž
. Ž
. the postgastric regions of Atlantic salmon fed diets mixed with alanine ALA-diet , methionine MET-diet ,
Ž .
Ž .
cysteine CYS-diet
or MCT MCT-diet . Activity is expressed as mmol 4-nitrophenyl myristate
Ž .
hydrolysedrmin. Bars represent the mean of three tanks, and error bars indicate SEM ns 3 .
Ž .
MI1 where the total proteolytic activity for the MET-diet approached that of the Ž
. MCT-diet Fig. 5a . A similar pattern of increased enzyme activity was seen for lipolytic
Ž .
activity, although not significant Fig. 5b . There were, however, significant correlations between both lipolytic activity measured in the pyloric region and fat digestibility
Ž
2
. r s 0.73, P s 0.006 and between proteolytic activity in the pyloric region and protein
Ž
2
. digestibility
r s 0.81, P s 0.001 . Moreover, fish fed MCT showed significantly Ž
. lower P s 0.0016 dry matter content in chyme compared to the three other diets in the
MI1 region, 16.2 and 20.6, respectively. 3.6. Plasma amino acids and taurine
Significant differences were observed among fish fed the different diets for plasma Ž
. threonine, glutamine, hydroxyproline, glycine, methionine and taurine Table 5 . Me-
thionine supplementation elevated plasma methionine significantly. In contrast, alanine supplementation did not affect plasma alanine significantly. Cysteine supplementation
caused a marked increase in plasma glycine level. This diet also increased glutamate level compared to the ALA-diet and hydroxyproline level compared to the ALA and
Ž .
MCT-diets plasma cysteine itself was not analysed . Both cysteine and methionine supplementation caused elevation of plasma taurine. Fish fed MCT fat showed lower
hydroxyproline levels than fish fed the other diets.
Table 5 Ž
. Plasma concentration of amino acids and taurine mmolr100 mol in Atlantic salmon fed diet with alanine,
methionine, cysteine or MCT supplementation
a
Ž .
ALA-diet MET-diet
CYS-diet MCT-diet
P value SEM ns60
Alanine 66
77 73
76 2.7
Arginine 17
20 19
16 0.8
Asparagine 3
2 1
0.6 Aspartic acid
4 3
3 3
0.5 Glutamic acid
36 35
40 47
1.0
b ab
a ab
Glutamine 19
23 27
34 0.046
1.7
b b
a b
Glycine 48
49 63
37 0.001
2.3 Histidine
4 4
4 3
0.2
b ab
a c
Hydroxy proline 15
19 21
11 0.0001
0.8 Isoleucine
13 15
15 16
0.7 Leucine
31 35
31 38
1.4 Lysine
14 19
15 23
2.0
b a
b b
Methionine 17
34 20
15 0.0001
1.4 Ornithine
1 1
0.2 Phenylalanine
15 17
16 16
0.5 Proline
9 11
11 9
0.6 Serine
22 21
22 18
1.7
ab a
a b
Threonine 17
21 22
15 0.007
0.9 Tryptophan
2 2
2 2
0.1 Tyrosine
8 9
10 8
0.5 Valine
42 48
46 47
1.6
b a
a b
Taurine 71
118 131
51 0.0001
5.9
a
Values with different superscript letters are significantly different.
4. Discussion
