Despite the worldwide economic importance of carp Cyprinus carpio L. culture, which is carried out by the application of all known production systems using
earth ponds, plastic or concrete tanks, net cages, recirculated water systems, there is no published information related to the physiological responses of this species
caused by different rearing background colors.
The present study has been designed to evaluate the effects of long-term adaptation to black, green and white background on growth performances and
physiological responses of scaled carp under certain experimental conditions using a recirculated water system.
2. Materials and methods
2
.
1
. Fish and experimental design Fish acclimated to laboratory conditions for 18 months were used in the
experiment. They were kept in pale-blue circular fiberglass tanks and fed twice a week ad libitum. Sixty fish with mean initial body weight of 116 g were randomly
distributed in six black, white and green cylindrical tanks of 27-l capacity, at a density of ten individuals per tank two replicate tanks for each color. The water
used water exchange rate: 5.9 times per hour was tap water drawn from the 50-ton laboratory recirculating system dechlorinated, filtered and UV-sterilized, provided
with compressed air supply and its physicochemical parameters means 9 S.E.M. were monitored daily temperature = 23.9 9 0.07°C, DO = 6.0 9 0.03 ppm, pH =
7.25 9 0.005, total ammonia = 0.24 9 0.006 ppm, NH
3
= 2.3 9 0.1 × 10
− 3
ppm, NO
2 -
= 0.02 9 0.002 ppm, Cl
-
= 60.1 9 0.53 ppm, hardness = 11.4 9 0.15°d. Con-
stant photoperiod 8L:16D was used throughout the experiment, which lasted 14 weeks. Light intensity just over the net cover of the tanks was approximately 75 – 80
lux. Fish were fed by hand a pelleted diet, once per day 1.5 of initial body weight, of the following composition: moisture 9.5, crude protein 47, crude fat
11.5, crude fiber 2, ash 11.5 and N.F.E. 18.5. Feeding level was not adjusted during the experiment to prevent possible stress responses caused by the weighing
procedures in fish.
2
.
2
. Blood sampling and analytical methods At the end of the experiment, all fish per tank were anaesthetized using
2-phenoxyethanol 0.0008 mlg per l and immobilized within 2 min. All fish groups were handled in the same way. Blood samples were taken individually from both
the heart and ventral aorta by heparinized syringes. Blood from the heart was immediately used for haematocrit determination, as well as for electrolytes Na
+
, Cl
−
and K
+
, pCO
2
and pH measurements 288-Blood Gas System, Ciba-Corning. Blood from the ventral aorta was used for plasma glucose, cholesterol, triglycerides,
total lipids enzymatic colorimetric methods, Elitech or BioMe´rieux and osmolality cryoscopic osmometer, Gonatec Osmomat 030 determinations. Plasma cortisol
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
