Effects of dietary iron levels on growth performance, iron metabolism and antioxidant status in spotted seabass (Lateolabrax maculatus) reared at two temperatures

The increased ambient temperature is often accompanied by the enhanced metabolic rate and oxygen consumption of fish, which affects their nutritional requirements. Currently, no information compares the iron requirements of fish species under moderate and high temperatures. This study investigated the effects of dietary iron levels on growth performance, iron metabolism, and antioxidant status in spotted seabass ( Lateolabrax maculatus ) reared at two temperatures. Six diets were formulated to contain 63, 120, 188, 316, 425, and 554 mg/kg iron, each of which was fed to two groups of juveniles reared at 27 °C (MT) and 33 °C (HT) for 56 days. The results showed that the satisfied iron requirement for spotted seabass improved growth, feed utilization, and antioxidant capacity. Furthermore, fish fed with high‑iron diets prevented iron overload by repressing intestinal iron-regulatory proteins and inducing liver hepcidin production. Iron deficiency depressed erythropoiesis and worsened HT-induced hypoxic status as supported by the significantly up-regulated hif and down-regulated vhl in the liver. Moreover, the HT compromised fish growth, feed utilization and liver hepcidin expression, while inducing lipid deposition. Compared to 27 °C, the iron demand was increased at 33 °C as more blood erythrocyte and tissue iron deposition were required by spotted seabass at HT. Based on the broken-line regression analysis of weight gain, the optimum dietary iron levels for spotted seabass reared at 27 °C and 33 °C were 178.5 and 209.0 mg/kg, respectively. • Appropriate dietary iron supplementation improved growth, feed utilization, erythropoiesis and antioxidant status of spotted seabass. • Fish fed with high-iron diets could prevent iron overload by repressing intestinal iron-regulatory proteins and inducing liver hepcidin production. • High temperature inhibited fish growth, feed utilization and liver hepcidin expression. • High temperature increased the iron demand of fish as more blood erythrocyte and tissue iron deposition were required.