Dietary copper requirement of fingerling Channa punctatus (Bloch) based on growth, feed conversion, blood parameters and whole body copper concentration

A 12-week feeding trial was conducted to estimate the dietary copper requirement of fingerling Channa punctatus. Six casein-gelatin-based test diets (450 g kg(-1) crude protein; 18.81 kJ g(-1) gross energy) with graded levels of copper as copper sulphate (3.7, 4.7, 5.7, 6.7, 7.7 and 8.7 mg copper equivalent kg(-1) diet) were formulated and fed to triplicate groups of fish (7.25 +/- 0.81 cm; 5.21 +/- 0.27 g) near to satiation. Fish fed diet with 6.7 mg kg(-1) copper had highest absolute weight gain (AWG; 51.63 g fish(-1)), protein efficiency ratio (PER; 1.42 g fish(-1)), protein gain (PG; 8.34 g fish(-1)), haemoglobin (Hb; 9.68 g dL(-1)), haematocrit (Hct; 31.18%) and RBCs (3.24 x 10(6) x mm(-3)). Feed conversion ratio (FCR) was found to be best (1.57) at above level of dietary copper. Whole body copper concentration was found to increase with the increasing levels of dietary copper. Hepatic thiobarbituric acid-reactive substances concentration was found to decrease with increasing dietary concentrations of copper up to 6.7 mg kg(-1) beyond which a reverse trend in this parameter was noted. Broken-line regression analysis of AWG, FCR and PG concentrations against varying levels of dietary copper yielded the requirement in the range of 6.66-6.78 mg kg(-1). Data generated during this study would be useful in formulating copper-balanced commercial feeds for the intensive culture of this fish.