Effects of background color on growth performances and physiological responses of scaled carp (Cyprinus carpio L.) reared in a closed circulated system

Growth performances and physiological responses of Cyprinus carpio after long-term (14 weeks) background color adaptation were investigated. Six groups of ten individuals each (initial body weight 116 g) were reared in black, green and white tanks (two replicate groups for each color). At the end of the experiment, blood (cortisol, glucose, haematocrit, cholesterol, triglycerides, total lipids, osmolality, electrolytes, pCO₂, pH), liver (total lipids, glycogen, hepatosomatic index) and growth (body weight, specific growth rate, food conversion ratio, condition factor, proximate carcass composition) parameters were determined. Plasma cortisol levels in white-adapted carp were significantly (P<0.05) lower than those in black, while in green-adapted fish did not differ significantly from those in both other counterparts. White-adapted carp showed the highest specific growth rate and the lowest food conversion ratio, whereas black-adapted fish exhibited the opposite pattern. In addition, mean (%) increase of body weight in white-adapted carp was 4.66 and 3.58% higher than that in black- and green-adapted fish, respectively. Furthermore in white-adapted carp, blood pCO₂ and pH were significantly higher and lower, respectively, than those obtained in black- and green-adapted fish. In black-adapted carp, liver total lipid levels were significantly lower, and plasma total lipid levels were significantly higher, than those in white- and green-adapted fish. No significant variations were observed in the other parameters. It is concluded that different background colors may lead to different growth performances of scaled carp depending upon rearing conditions.