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Six purified vitamin-free casein-based diets were formulated to contain six levels vitamin A at 0, 500, 1000, 2000, 4000, and 8000？IU·kg？1, respectively. Tilapias (initial mean weight: 7.73±0.03？g) were fed the diets in quadruplicate aquaria to apparent satiation twice daily for 10 weeks. No differences in mortality, weight gain, or feed efficiency ratio (FER) were observed among the groups. Liver vitamin A levels reflected dietary vitamin A levels. Immune parameters, such as hemoglobin levels, total cell count, red blood cell count, total serum protein, and serum lysozyme activity, did not vary with the dietary vitamin A levels. White blood cell counts of fish in 2000？IU·kg？1 diet groups were significantly higher than that in other diets groups. Serum complement activities of fish in 2000 and 4000？IU·kg？1 vitamin A diet groups were also higher than those in other diet groups. After the 14-d challenge test, the mortality and antibody titer were similar among the treatments. The results indicated that dietary vitamin A inclusions did not affect the immune response of Oreochromis niloticus. |
