levels were measured by radioimmunoassay RIA using a commercially available kit Coat-A-Count Cortisol, DPC which has been previously validated for fish
Ainsworth et al., 1985. In the present study, the sensitivity of the assay was 0.2 m
gdl and intra- and interassay coefficient of variation was 3.2 and 6.5, respectively.
Liver total lipids Folch et al., 1957, hepatosomatic index and liver glycogen Montgomery, 1957 were also determined. Conventional techniques were used for
specific growth rate SGR, food conversion ratio FCR and condition factor determinations Papoutsoglou and Tziha, 1996. In addition, all fish of each group
were minced together, without viscera, lyophilized and used for proximate carcass analysis six replicates for each group according to Kjeldahl and Soxhlet methods.
Comparisons of means were performed by one-way analysis of variance ANOVA and Duncan’s multiple range test Sokal and Rohlf, 1995. Differences
were considered significant at P B 0.05. Where appropriate, data were log trans- formed in order to obtain homogeneity of variance. Untransformed means 9
S.E.M. are given. The data obtained for the replicate groups of each color were pooled, after testing the significance of differences between them in all parameters
examined. For the parameters not individually estimated SGR, FCR, carcass composition the duplicated mean is presented.
3. Results
Skin color adaptation to background color was completed by the end of 2 weeks in all populations. Fish from black tanks obtained deeply darkened skin color,
while fish from white tanks became distinctively pale. Carp maintained on green background held the color they initially had before transfer to the experimental
tanks grey-brownish. Not any obvious change of body color was further observed in all groups throughout the experiment.
Plasma cortisol levels in white-adapted carp 43.05 9 10.316 ngml were signifi- cantly P B 0.05 lower than those in black-adapted fish 87.69 9 10.352 ngml,
whereas in green-adapted fish 71.58 9 12.389 ngml levels did not significantly differ from those in both other counterparts Fig. 1. In addition, in white-adapted
carp, pCO
2
and pH were significantly higher and lower, respectively, compared to those observed in black- and green-adapted carp Table 1. Furthermore, black-
adapted fish exhibited the highest plasma total lipid levels, significantly different from those in both other counterparts. No significant differences were found in the
other blood parameters among the fish adapted to three colored backgrounds.
A considerable mean increase of body weight was observed in white-adapted carp 43.892, being 4.66 and 3.58 higher than that obtained from black-
39.226 and green-adapted carp 40.314, respectively Table 2. Also, white- adapted carp showed the highest specific growth rate SGR level, while the
black-adapted the lowest Fig. 2a. In addition, fish from white tanks developed the lowest food conversion ratio FCR level compared to that of fish from black and
green backgrounds Fig. 2b.
No statistically significant P \ 0.05 differences for the values of final body weight, condition factor, hepatosomatic index and liver glycogen content and no
important differences in values of the major carcass components were found among experimental fish groups Table 2. Nevertheless, black-adapted carp showed the
lowest liver total lipid levels, significantly different P B 0.05 from those observed in the other groups.
Fig. 1. Plasma cortisol levels means 9 S.E.M. after adaptation for 14 weeks on black n = 18, green n = 20 and white n = 20 backgrounds; means marked with different letter are significantly different
P B 0.05.
Table 1 Effect of background adaptation for 14 weeks on blood parameters
Background color n
White Black
n Green
n 20
88.66 9 8.209
a
Glucose mg100ml 17
70.65 9 7.191
a
86.76 9 9.561
a
16 3.44 9 0.803
a
15 pO
2
mmHg 2.52 9 0.768
a
19 14
1.94 9 0.262
a
pCO
2
mmHg 8.98 9 0.298
a
14 13.00 9 0.807
b
15 19
9.30 9 0.576
a
19 7.47 9 0.037
b
14 pH
7.36 9 0.041
a
7.54 9 0.033
b
15 19
120.28 9 1.430
a
14 124.45 9 1.038
a
15 Na
+
mmoll 121.47 9 1.277
a
2.89 9 0.266
a
13 K
+
mmoll 2.26 9 0.372
a
15 11
3.34 9 0.194
a
Cl
−
mmoll 97.00 9 1.637
a
14 102.00 9 1.195
a
15 19
99.68 9 1.311
a
18 0.262 9 0.002
a
14 Osmolality osmolKg
0.262 9 0.001
a
0.259 9 0.001
a
15 20
41.98 9 0.910
a
20 Haematocrit
42.10 9 0.978
a
41.35 9 1.470
a
20 19
132.08 9 5.164
a
20 140.59 9 5.903
a
Triglycerides mg100ml 20
148.48 9 6.410
a
Cholesterol mg100ml 126.51 9 6.451
a
20 116.77 9 5.029
a
20 131.44 9 3.936
a
20 Total lipids mg100ml
19 19
613.4 9 24.15
a
20 739.4 9 37.62
b
612.8 9 24.39
a
Means with different superscript are significantly different PB0.05. Values represent mean 9 S.E.M.
Table 2 Effect of background adaptation for 14 weeks on growth and liver parameters
Background color White
Black Green
16.715 16.487
16.699 Carcass protein w.w.
†
5.762 5.408
Carcass total lipid w.w.
†
5.841 3.114
2.953 3.000
Carcass ash w.w.
†
74.545 74.661
74.504 Carcass moisture w.w.
†
43.892 40.314
Mean increase of b.wt
†
39.226 Initial body weight g
‡
114.6 9 6.87
a
118.8 9 7.71
a
114.6 9 7.17
a
164.9 9 10.45
a
160.8 9 8.53
a
165.4 9 10.33
a
Final body weight g
‡
1.65 9 0.040
a
1.58 9 0.035
a
1.61 9 0.040
a
Condition factor
‡
1.21 9 0.081
a
Hepatosomatic index
‡
1.33 9 0.093
a
1.35 9 0.080
a
11.85 9 0.636
b
10.67 9 0.523
b
8.49 9 0.420
a
Total liver lipids w.w.
‡
1.50 9 0.231
a
1.32 9 0.196
a
1.72 9 0.246
a
Liver glycogen w.w.
‡
Means with different superscript are significantly different PB0.05.
†
Values represent duplicated means.
‡
Values represent mean 9 S.E.M. n = 20.
Fig. 2. Effect of background adaptation for 14 weeks on: a specific growth rate SGR and b food conversion ratio FCR; duplicated means.
4. Discussion
