Growth performance and tissue mineral content of juvenile grouper (Epinephelus coioides) fed diets supplemented with various levels of manganese

This study was conducted to investigate the effect of dietary manganese (Mn) on growth, vertebrae and whole-body Mn content of juvenile grouper, and to examine the effect of dietary Mn on copper (Cu), iron (Fe), zinc (Zn), calcium (Ca), phosphorus (P) and magnesium (Mg) content of vertebrae and whole body. Seven casein-gelatin-based diets were supplemented with 0, 5, 10, 15, 20, 50 and 1000 mg kg-1 of Mn from MnSO4 center dot H2O. Grouper with an initial weight of 12.9 +/- 0.4 g were fed to satiation with one of the seven diets for 8 weeks. Growth was not significantly affected by dietary Mn supplements. Vertebrae Mn increased from 31.7 to 118.1 mg kg-1 dry weight with dietary Mn supplement increasing from 0 to 50 mg kg-1 (y = -0.0002x3 + 0.0162x2 + 1.3903x + 26.27, R2 = 0.9561, where y is the vertebrae Mn content and x is the dietary Mn content). Whole-body Mn increased from 2.5 to 7.8 mg kg-1 wet weight with dietary Mn supplement increasing from 0 to 50 mg kg-1 (y = 0.00001x3 - 0.00107x2 + 0.11054x + 2.24615, R2 = 0.9080, where y is the whole-body Mn content and x is the dietary Mn content). Dietary Mn had no significant effect on vertebrae Fe, Ca, P and Mg content, and whole-body Cu, Zn and Mg content. However, vertebrae Zn and whole body Ca, P were highest in fish fed diet supplemented with 15 mg kg-1 of Mn. Based on this, Mn supplement of 15 mg kg-1 might be the optimum when the basal diet contained 4 mg kg-1 of Mn. Fish fed diet supplemented with 1000 mg kg-1 of Mn did not show any gross abnormality or change in feeding behaviour, but Mn contents of vertebrae and whole body were as high as 695.1 mg kg-1 dry weight and 42.5 mg kg-1 wet weight, respectively. Also, whole body Fe decreased significantly when Mn supplement was up to 1000 mg kg-1.