A short note on the effects of vitamin A hypervitaminosis and hypovitaminosis on health and growth of Tilapia nilotica (Oreochromis niloticus)

A total of 120 Tilapia nilotica fingerlings were fed diets supplemented with 0, 5000, 10 000 and 40 000 IU vitamin A kg(-1) diet, respectively, at a rate of 3\% of body weight for 18 weeks. The Vitamin A unsupplemented group developed severe signs of vitamin deficiencies (restlessness, abnormal movement, blindness, exophthalmia, haemorrhages of eyes, fins and skin, per-belly syndrome, reduced mucous secretion). Growth and feed consumption were severely depressed, and the mortality rate amounted to 48\%. An addition of 5000, 10 000 and 40 000 IU vitamin A resulted in a body weight gain of 23.9, 21.6 and 13.2 g, a feed consumption of 60.2, 59.6 and 50.2 g, a feed/gain ratio of 2.5, 2.8 and 3.8 g/g and mortality rates of 7\%, 7\% and 33\%, respectively. Clinical signs ana post-mortem lesions of fingerlings with hypervitaminosis were impaired skeletal formation, especially of the vertebrae, haemorrhages of the skin, necrosis of the caudal fin and enlargement of the liver and spleen. It is concluded that 5000 IU vitamin A kg(-1) diet covers the requirement of Tilapia nilotica fingerlings, while 10 000 IU already show signs of metabolic distortion and even higher dosages cause hypervitaminosis.