2.3. Satistical analyses Ž
. Final weight, percent weight gain, feed conversion ratio FCR , protein efficiency
Ž .
Ž .
ratio PER , net protein utilization NPU and body composition data were analyzed for Ž
. statistical significance
P - 0.05 by analysis of variance, and individual differences between dietary treatments were determined by Duncan’s new multiple range test.
Ž .
Growth responses in terms of average weight gain in gram
to dietary protein concentrations in Experiment 1 were estimated by the polynomial regression method
Ž .
Ž .
Zeitoun et al., 1976 . The broken-line analysis technique Robbins, 1986 was used to Ž
. examine growth response mean weight gain in gram to lipid supplementation in
Experiment 2. The breakpoints of the regression equations are regarded as the most suitable levels for optimal growth.
3. Results
3.1. Experiment 1 No fish died during the growth trial. Dietary protein concentrations significantly
Ž .
Ž .
P - 0.05 affected growth of the fish Table 3 . Final fish weight, weight gain and FCR were highest or best when the protein concentrations were 44, 48 or 52. The fish
Ž .
Ž .
fed the diets with the highest 60 or lowest 36 protein concentrations showed the poorest growth and FCR among all treatments. The results of PER and NPU tended to
show a decreasing trend of efficiency with increasing dietary protein inclusion. Fish fed diets with protein concentrations 56 or higher utilized dietary protein less efficiently
Ž
. P - 0.05
than the other dietary groups. Polynomial regression analysis between
Table 3 Ž
. Ž
. Ž
. Weight gain, feed conversion ratio FCR , protein efficiency ratio PER and net protein utilization NPU of
the cobia fed diets containing graded levels of protein
1 2
3 4
Dietary protein, Weight gain,
FCR g dry PER g gainrg
NPU g body gr100 g
gr100 g feedrg gain
protein proteinrg
protein
d b
c,b a
36 187.67.9
1.550.06 1.920.08
1.540.06
c c
a,b,c a
40 238.07.9
1.310.01 1.950.02
1.570.02
a,b e,f
a a
44 267.57.3
1.180.02 2.060.03
1.600.03
a,b e,f
c,b b
48 274.010.9
1.140.02 1.86.04
1.440.03
a f
c a
52 283.42.1
1.090.01 1.830.02
1.540.02
b,c c,d
d c
56 250.411.3
1.280.04 1.490.05
1.210.04
d a
e d
60 175.51.8
1.840.03 0.940.01
0.790.01
1
Initial average body weight was approximately 33.0 g. Values are meansS.E.M. Means within a given Ž
. column with different superscripts are significantly different P - 0.05 . No fish died during the 8-week trial.
2
Ž . Ž .
FCR s feed supplied g rbody weight gain g .
3
Ž . Ž .
PER s body weight gain g rprotein fed g .
4
Ž . Ž .
NPUs body protein gain g rprotein fed g .
Table 4 Ž
.
1
Muscle proximate composition dry weight basis of the cobia fed diets containing various levels of protein Dietary protein,
Protein, gr100 g Lipid, gr100 g
Ash, gr100 g gr100 g
a,b a,b
36 82.61.6
6.61.6 6.90.3
a,b a,b
40 82.91.0
7.60.4 6.30.0
b a,b
44 79.92.9
8.20.1 6.40.5
b a
48 79.00.8
9.90.3 6.10.1
a b
52 85.80.5
3.80.9 6.70.3
a,b a,b
56 84.11.0
6.00.6 6.80.2
a b
60 86.51.6
4.51.3 7.00.6
1
Ž .
Ž .
Means S.E., ns 3 with different superscript letters are significantly different P - 0.05 .
protein concentration and weight gain of the fish indicated a weight gain peak at dietary protein concentration of 44.5. Crude protein concentrations of lateral muscle from the
cobia fed the diets containing 52 or 60 were significantly higher than those fed 44 Ž
. or 48 Table 4 . There was no difference in muscle ash concentration among dietary
groups.
3.2. Experiment 2 There was no mortality during the 8-week growth trial. Dietary lipid concentration
Ž .
Ž .
significantly P - 0.05 affected growth and feed conversion of the cobia Table 5 .
Among the seven lipid concentrations tested, 3 and 12 groups in general showed inferior growth and feed conversion. The differences among treatments became apparent
6 weeks after the feeding trial began. If data of the 12 group were excluded, there was
Table 5 Ž
. Ž
. Weight gain, feed conversion ratio FCR and protein efficiency ratio PER of the cobia fed test diets
containing graded levels of lipid in an 8-week period
1 2
3
Dietary lipid, Weight gain,
FCR g dry PER g gainrg
gr100 g gr100 g
feedrg gain protein
initial weight
b a,b
b,c
3 295.74.2
1.340.00 2.060.01
a,b b
a,b
6 318.13.4
1.270.01 2.220.01
a b
a
9 328.27.9
1.250.02 2.240.03
b a
c
12 294.79.4
1.420.06 2.000.08
a b
a,b
15 325.711.6
1.290.04 2.210.07
a b
a,b
18 327.313.7
1.280.04 2.160.07
1
Initial average body weight was approximately 41.0 g. Values are meansS.E.M. Means within a given Ž
. column with different superscripts are significantly different P - 0.05 . There was no mortality during the
growth trial.
2
Ž . Ž .
FCR s feed supplied g rbody weight gain g .
3
Ž . Ž .
PER s body weight gain g rprotein fed g .
no difference in weight gain when the dietary lipid level was higher than 6. This relationship of weight gain and dietary lipid level is best expressed by a broken-line
analysis. The breakpoint at 5.76 gave the lowest mean square error and thus was the minimum lipid level for optimal fish growth. No significant growth enhancement was
observed when the lipid levels were increased beyond the breakpoint to the highest lipid
Ž .
level tested 18 .
4. Discussion
