Ž DL and sex are fixed effects sex is considered as being naturally randomised between
. fish within each tank . Consequently, the analysed variables corresponded to Ls means
Ž .
SD of measures carried out per experimental unit, adjusted by effects of other Ž
factors. For one-way ANOVAs, the means were tested by a Newman–Keuls test fit for .
balanced design . For the split-plot ANOVAs, the Ls means were tested by a Fisher test with the contrast method. In all tests, a significance level of P - 0.05 was used.
3. Results
3.1. SurÕiÕal and growth The 12- and 18-h groups have significantly higher survival rates than the 24-h group
Ž . Ž
. P - 0.05
Table 1 . In all tanks, mortality was caused mostly by social interactions Ž
leading to high disappearance, regurgitation and enucleation rates 61 16 of total .
mortality . Ž
. Ž
. Relative RGR and specific growth rates SGR were significantly affected by DL,
with RGR and SGR averaging 620–650 and 1.7–1.8 day
y1
for both the 18- and
Table 1 Ž
Influence of the daylength on survival, growth, gonad development, and N and P budgets Ls meansSD; .
Ž .
ns 3 replicates per treatment of Eurasian perch Perca fluÕiatilis L. juveniles reared in recirculation systems Initial carcass content expressed in , FW was 15.05 for protein and 0.62 for P. Values followed by the same
Ž .
letter in a row are not significantly different P 0.05 . RMSE sRoot mean square error.
Parameters Daylengths
RMSE 12-h group
18-h group 24-h group
Ž . Sr
89.03.2 a 88.23.3 a
76.07.4 b 5.00
Ž . L
1.41.9 a 3.31.7 a
4.62.0 a 1.88
Ž . Wi g
5.20.7 a 4.90.3 a
5.40.6 a 0.56
Ž . Wf g
23.50.3 a 36.47.2 b
39.35.3 b 5.14
Ž . CVi
29.01.2 a 27.21.1 a
28.32.4 a 1.68
Ž . CVf
40.32.6 a 50.26.6 b
54.14.1 b 4.72
FE 0.800.05 a
0.740.03 a 0.740.06 a
0.05 Ž .
RGR 361.259.7 a
644.6148.4 b 628.751.7 b
97.08
y1
Ž .
SGR day 1.360.12 a
1.780.18 b 1.770.06 b
0.13 Ž .
Male Wf g 25.284.10 a
39.493.82 b 44.392.53 b
3.55 Ž .
Female Wf g 29.151.63 a
47.3314.69 b 49.578.33 b
9.8 Ž .
Male GSI 1.250.62 a
0.080.02 b 0.050.00 b
0.36 Ž .
Female GSI 0.400.04 a
0.430.04 a 0.330.04 b
0.04 Final carcass content
Ž .
Protein FW 16.70.3 a
17.40.2 b 16.60.1 a
0.22 Ž
. P FW
0.600.05 a 0.650.05 a
0.650.03 a 0.04
Retention Ž
. N of distributed
30.41.4 a 29.10.5 a
27.42.1 a 1.5
Ž .
P of distributed 49.27.8 a
49.65.8 a 49.43.2 a
5.9
Ž .
24-h groups, respectively, and significantly higher P - 0.05; Table 1 than those of the Ž
. 12-h group. From D56 onwards, a highly significant difference
P - 0.01 was also recorded between the mean body weights of the 12-h group and the 18- and 24-h groups
Ž .
Fig. 1 . No growth difference was observed between the 18- and 24-h groups. This enhancement of growth with DL increase did not significantly affect the feed efficiency
Ž0.80 0.05, 0.74 0.03, and 0.74 0.06, respectively, for the 12-, 18- and 24-h .
groups . 3.2. Weight heterogeneity, sexual growth dimorphism and gonad deÕelopment
Ž .
The analysis of the coefficient of variation in weight Fig. 2 showed a significantly Ž
. higher CV for the 24-h group at D56 P - 0.05 compared to the 12- and 18-h groups.
Ž .
At the end of the experiment Table 1 , there was a significant difference between the 12-h group and the 18- and 24-h groups. This lower weight heterogeneity in the 12-h
group, compared to that of the 18- and 24-h groups, developed from D84 onwards Ž
. P - 0.05; Fig. 2 .
The necropsy made at the end of the experiment indicated that the sex ratio was Ž
similar in all groups with a percentage of females slightly higher than males 55.0 .
6.1, 54.7 11.0, and 52.5 10.7 for the 12-, 18-, and 24-h groups, respectively . Ž
. A highly significant effect P - 0.01 of DL on the mean weight of males and females
was recorded. The mean weights of males and females from the 12-h group were Ž
. significantly lower than those of the 18- and 24-h groups Table 1 . However, for a
Ž given DL, mean weights of males and females showed no statistical difference P -
. 0.05 , regardless of treatment. At the end of the experiment, males of the 12-h group had
Ž .
a significantly higher GSI P - 0.05 compared to the males of the 18- and 24-h groups
Ž .
Fig. 1. Growth of juvenile Eurasian perch mean weightqSD; ns 3 replicates per treatment reared in Ž
. recirculation systems and submitted to three different DL 12, 18, and 24 h over 112 days. Values followed by
Ž .
different letters at a same day are significantly different P - 0.05 .
Ž .
Fig. 2. Coefficient of variation in individual weight Ls meansqSD; ns 3 replicates per treatment of juvenile Ž
. Eurasian perch reared in recirculation systems and submitted to three different DL 12, 18, and 24 h over 112
Ž .
days. Values followed by different letters at a same day are significantly different P - 0.05 .
Ž .
Table 1 . There was also an influence of DL on the female GSI with an average 24-h Ž
. group female GSI significantly lower P - 0.05 than the 12- and 18-h ones. Males of
Ž .
the 12-h group had a higher GSI than the females of the same group P - 0.05 ,
whereas it was the opposite in the 18- and 24-h groups. 3.3. Sexual steroids and thyroid hormones
The results were summed up in Table 2. For females, there was no significant DL Ž
. effect on E , T, T and T levels P 0.05 . The E levels remained low whatever the
2 3
4 2
Table 2 Ž
y1
Influence of the daylength on steroid and thyroid levels ng ml , Ls meansSD, ns 3 replicates per
. Ž
. treatment of Eurasian perch P. fluÕiatilis L. juveniles reared in recirculation systems
Ž .
In a same line, values followed by a same letter are not significantly different P 0.05 . RMSE sRoot mean square error.
Parameters 12-h group
18-h group 24-h group
RMSE Females
E 0.640.14 a
0.540.13 a 0.490.15 a
0.14
2
T 3.572.07 a
2.041.14 a 2.901.95 a
1.77 T
11.752.57 a 12.031.72 a
10.841.99 a 2.12
3
T 14.432.03 a
14.290.87 a 14.350.95 a
1.39
4
Males T
4.511.29 a 2.111.23 a
2.813.13 a 2.08
11-KT 0.810.42 a
0.310.28 a 0.390.22 a
0.32 T
12.651.83 a 14.610.55 a
11.401.15 a 1.39
3
T 15.730.31 a
14.822.09 a 14.150.79 a
1.08
4
Ž .
Fig. 3. Relationship between individual gain and N and P loss mean, ns15 fish per batch in batches of Ž
. juvenile Eurasian perch submitted to three different DL 12, 18, and 24 h . Left graph, total loss; right graph,
faecal and metabolic loss. In left graph, arrows indicate the values obtained for one of the replicate submitted to a daylength of 24 h and in which mortality rate was high.
Ž
y1
. daylength between 0.01 and 1.47 ng ml
. Average female T levels were also low, around 3 ng ml
y1
, although they reached 8 ng ml
y1
in some sampled females. For Ž
. males, there was no treatment effect on T, 11-KT, T and T levels P 0.05 .
3 4
3.4. N and P balances Ž
. Neither the protein nor the P content of the carcasses was affected by DL Table 1 .
No effect of DL on N and P retention was significant. In addition, there was no Ž
. treatment effect on N nor P loss Table 1 . An increase in standard deviation was
observed for N and P total loss when DL is increased, but this increase was not observed when considering only the faecal and metabolic losses. In fact, it can be seen in Fig. 3
that this difference in standard deviation between total loss and faecal and metabolic losses should be attributed to one 24-h replicate, in which mortality was high. From Fig.
3, it can be seen also that there is no relationship between loss and individual gain. This statement is particularly obvious when considering only the faecal and metabolic losses.
4. Discussion
