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 (means9S.E.M.)
were monitored daily (temperature23.990.07°C, DO6.090.03 ppm, pH
7.2590.005, total ammonia0.2490.006 ppm, NH32.390.1103 ppm,
NO2 - 0.0290.002 ppm, Cl-60.190.53 ppm, hardness11.490.15°d). Constant
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.
2.1. Fish and experimental designFish acclimated to laboratory conditions for 18 months were used in theexperiment. They were kept in pale-blue circular fiberglass tanks and fed twice aweek ad libitum. Sixty fish with mean initial body weight of 116 g were randomlydistributed in six black, white and green cylindrical tanks of 27-l capacity, at adensity of ten individuals per tank (two replicate tanks for each color). The waterused (water exchange rate: 5.9 times per hour) was tap water drawn from the 50-tonlaboratory recirculating system (dechlorinated, filtered and UV-sterilized), providedwith compressed air supply and its physicochemical parameters (means9S.E.M.)were monitored daily (temperature23.990.07°C, DO6.090.03 ppm, pH7.2590.005, total ammonia0.2490.006 ppm, NH32.390.1103 ppm,NO2 - 0.0290.002 ppm, Cl-60.190.53 ppm, hardness11.490.15°d). Constantphotoperiod (8L:16D) was used throughout the experiment, which lasted 14weeks. Light intensity just over the net cover of the tanks was approximately 75–80lux. Fish were fed by hand a pelleted diet, once per day (1.5% of initial bodyweight), of the following composition: moisture 9.5%, crude protein 47%, crude fat11.5%, crude fiber 2%, ash 11.5% and N.F.E. 18.5%. Feeding level was not adjustedduring the experiment to prevent possible stress responses caused by the weighingprocedures in fish.
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