EFFECTS OF DIETARY VITAMIN A ON GROWTH PERFORMANCE AND CALCIUM AND PHOSPHORUS CONTENTS IN BONE OF SUBADULT GRASS CARP (CTENOPHARYNGODON IDELLUS)

To determine the optimum dietary requirement of vitamin A (VA) of subadult grass carp (Ctenopharyngodon idellus), seven isoenergetic and isonitrogenous semi-purified diets were formulated to contain VA level at 89, 732, 1129, 2378, 4688, 7218 and 9802 IU/kg diet respectively, for a 12-week growth trial that was conducted in 21 net-cages located in an earth pond. The results indicated that dietary VA level significantly regulated the specific growth rate (SGR) and feed conversion ratio (FCR) of subadult grass carp (P < 0.05) with the highest SGR and the lowest FCR both in 4688 IU/kg group. Feeding rate, survival rate and hepatosomatic index were not affected by dietary VA level (P>0.05). Dietary VA level showed significant (P < 0.05) effect on serum SOD activity with the highest SOD values in 4688 IU/kg group. Serum ALP activity, MDA, calcium (Ca) and phosphorus (P) contents were not significantly (P>0.05) affected by dietary VA level. Body moisture content in 9802 IU/kg group was significantly lower. Body lipid, protein and ash contents were not affected by dietary VA level (P>0.05). The ash contents either in skull or in vertebra were significantly affected (P < 0.05) by dietary VA level. The higher Ca and P contents in skull and vertebra were both observed in 4688 and 7218 IU/kg groups (P < 0.05). Broken-line analysis for the SGR of fish suggested that the optimal dietary VA content for subadult grass carp was 3184 IU/kg diet.