Ferric citrate is half as effective as ferrous sulfate in meeting the iron requirement of juvenile tilapia, Oreochromis niloticus x O. aureus.

Two growth experiments were conducted to estimate the minimum dietary iron requirement for juvenile hybrid tilapia, Oreochromis niloticus x O. aureus. Purified diets containing 0, 10, 30, 50, 100, 150, 200 and 400 mg Fe/kg from ferric citrate (Experiment 1) and 0, 10, 30, 50, 100, 150 and 200 mg Fe/kg from ferrous sulfate (Experiment 2) were fed to tilapia (mean initial weight: 0.63 +/- 0.01 g, Experiment 1; 0.64 +/- 0.01 g, Experiment 2) for 8 wk. In Experiment 2, 150 mg Fe/kg from ferric citrate was also included for comparison. The rearing water contained 1.07 micro mol/L iron, and supplemental levels were confirmed by analysis. Each diet was fed to three replicate groups of fish. In Experiment 1, weight gain and feed efficiency (FE) were highest (P < 0.05) in fish fed the diet supplemented with 150 mg Fe/kg, followed by fish fed diets with 50, 100 and 200 mg Fe/kg and lowest in fish fed the unsupplemented control diet. Hepatic iron concentration was highest in fish fed diets supplemented with >150 mg Fe/kg, followed by fish fed the diet with 100 mg Fe/kg and lowest in fish fed diets with </=10 mg Fe/kg. Hemoglobin (Hb) and hematocrit (Hct) were higher in fish fed diets with >/=100 mg Fe/kg and mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH) were higher in fish fed diets with >/=150 mg Fe/kg than in fish fed the diet without iron supplementation. In Experiment 2, weight gain was higher in fish fed the diet with 50 mg Fe/kg than in fish fed diets with 150, 200 and </=30 mg Fe/kg. FE was higher in fish fed diets with 50 and 100 mg Fe/kg and the ferric citrate comparison diet than in fish fed diets with </=10 mg Fe/kg. Hepatic iron concentration was higher in fish fed diets with >/=50 mg Fe/kg and the ferric citrate comparison diet than fish fed diets with </=30 mg Fe/kg. Hb, Hct, MCV and MCH were higher in fish fed diets with >/=50 mg Fe/kg than in fish fed the unsupplemented control diet. Analyses by polynomial regression of weight gain and by broken-line regression of hepatic iron and blood Hb concentrations indicated that the dietary iron requirement for tilapia is approximately 150-160 mg Fe/kg and 85 mg Fe/kg with ferric citrate and ferrous sulfate as the iron source, respectively; it also appears that ferric citrate was approximately 50% as effective as ferrous sulfate in meeting the iron requirement.