Dietary manganese requirement of juvenile grass carp (Ctenopharyngodon idella Val.) based on growth and tissue manganese concentration

A growth trial was conducted to estimate the optimum concentration of dietary Manganese (Mn) for grass carp (Ctenopharyngodon idella). Triplicate groups of grass carp (3.97 +/- 0.05g) were fed diets containing graded levels (4.0, 8.9, 13.8, 18.7, 23.6 and 33.3mgkg(-1)) of Mn for 8weeks. Weight gain, specific growth rate and feed efficiency were linearly increased up to the 18.7mgkg(-1) dietary Mn and then levelled off beyond this level. For body composition, lipid contents in whole body, muscle and liver decreased significantly with increasing dietary Mn level. Grass carp fed with dietary Mn levels higher than 19.7mgkg(-1) significantly decreased condition factor. Whole body, vertebrae and scales mineralization were all affected significantly by dietary Mn levels. Mn contents in whole body, vertebrae and scales were linearly increased up to the 18.7mgkg(-1) dietary Mn and then levelled off beyond this level. Contrarily, Ca and P contents seem to be inversely related to dietary Mn. However, dietary Mn levels had no significant effect on body Fe contents. Broken-line analysis indicated that 20.6mgkg(-1) dietary Mn was required for maximal tissue Mn storage, as well as satisfied for the optimal growth of juvenile grass carp.