Dietary copper requirement of juvenile yellow catfish Pelteobagrus fulvidraco

The present experiment was conducted to quantify dietary copper (Cu) requirement for juvenile yellow catfish Pelteobagrus fulvidraco. The six experimental diets were formulated to contain the graded levels of CuSO₄·5H₂O (0, 0.005, 0.01, 0.02, 0.04 and 0.08 g kg⁻¹ diet respectively) providing the actual dietary copper values of 2.14 (control), 3.24, 4.57, 7.06, 12.22 and 22.25 mg Cu kg⁻¹ diet respectively. Each diet was fed to triplicate groups of yellow catfish (initial body weight: 3.13 ± 0.09 g, means ± SD) in an indoor static rearing system for 7 weeks. Fish fed the diet containing 3.24 mg Cu kg⁻¹ diet had the highest weight gain and specific growth rate, but they were not significantly different from that of fish fed the 4.57 and 7.06 mg Cu kg⁻¹ diets (P > 0.05). The poorest feed conversion rate, the lowest protein efficiency ratio, the lowest hepatosomatic index and viscerosomatic index were observed in fish fed the diet containing the highest Cu content diet (P < 0.05). Condition factor showed no significant differences among the treatments (P > 0.05). Proximate composition of fish body was significantly affected by dietary copper level (P < 0.05). Cu contents of whole body and liver increased with dietary Cu levels (P < 0.05), but muscle Cu content remained relatively stable (P > 0.05). Analysis by the second-order regression of SGR and linear regression of whole-body Cu retention of the fish indicated that dietary Cu requirements in juvenile yellow catfish were 3.13-4.24 mg Cu kg⁻¹ diet.