Quantitative dietary zinc requirement of juvenile yellow catfish Pelteobagrus fulvidraco, and effects on hepatic intermediary metabolism and antioxidant responses

The present study was conducted to determine dietary zinc (Zn) requirement for juvenile yellow catfish Pelteobagrus fulvidraco and evaluate the effect of dietary Zn levels on growth performance, whole body mineral composition, hepatic intermediary metabolism and antioxidant responses for this fish species. The six experimental diets were formulated to contain the graded levels of ZnSO4·7H2O (0, 0.002, 0.004, 0.008, 0.016 and 0.032%, respectively), providing the actual dietary Zn values of 7.60 (control), 11.90, 16.24, 24.81, 38.75 and 76.36 mg kg−1 diet, respectively. Each diet was assigned to three replicate groups of yellow catfish (initial body weight: 6.08 ± 0.12, means ± SD) for 8 weeks. Increasing dietary Zn level up to 16.24 mg kg−1 diet increased growth performance and feed utilization, beyond which they remained nearly unchanged. Whole body lipid contents significantly declined, but whole body moisture and protein contents showed no significant differences with increasing dietary Zn levels. Whole body Zn content tended to increase with increasing dietary Zn level, whereas whole body Cu and Fe contents declined with dietary Zn addition. Hepatic succinate dehydrogenase (SDH), lactate dehydrogenase (LDH) and malic dehydrogenase (MDH) activities showed no significant differences among the treatments. However, lipoprotein lipase (LPL) and hepatic lipase (HL) activities increased with increasing dietary Zn levels. Superoxide dismutase (SOD) activity increased and malondialdehyde (MDA) level declined with increasing dietary Zn levels up to the requirement level. Hepatic catalase (CAT) activity showed no significant differences among the treatments. Analysis by the broken-line regression of specific growth rate (SGR) and protein efficiency rate (PER) indicated that dietary Zn requirements in juvenile yellow catfish were 17.12–20.86 mg kg−1 diet.