Dietary vitamin supplementation decrease stress caused by high stocking density, and boosts immunological system of farmed fish. A studied was carried out to determine vitamin A requirements of Nile tilapia (Oreochromis niloticus) in an all male group (13.8 ± 1.2 g) and a mixed sex population (9.8 ± 2.3 g). Fish stocked in 100-L plastic aquaria (26.0 ± 1.0°C) were fed to near satiety, twice a day, seven days a week, during 75 days with vitamin A-free, semi-purified diets supplemented with 0; 600; 1,200; 1,800; 2,400; 3,000; 3,600; 4,200; 4,800 and 5,400 International Units (IU) of retinyl palmitate (30% vitamin A) per kg of diet in a completely randomized experimental design, factorial arrangement 2χ10 (n = 4). Deficiency signs of vitamin A were observed in fish fed 0 to 1.200 IU vitamin A kg-1 diet; moderate signs were observed in fish fed diets with 1.800 to 3.600 IU vitamin A kg-1 diet; no interactions group*level (p < 0.05) were detected. Dietary levels of vitamin A up to 5.400 IU kg-1 influenced final weight and weight gain of fish (p < 0.05), but did not influence feed consumption (p > 0.05). A group effect was observed regarding all performance variables (p < 0.0001). Quantification of hepatic retinol (HPLC) detected vitamin A only in fish fed 5.400 IU retinol kg-1 of diet, therefore characterizing that dietary retinol was used and stored. The quantity of 5.400 IU of retinol kg-1 of diet is recommended for adequate nutrition of Nile tilapia.666751756Beveridge, M.C.M., McAndrew, B.J., (2000) Tilapias: Biology and Exploitation (fish and Fisheries Series, 25), p. 505. , London: Kluwer AcademicCamargo, L.A.A., Yashuda, Y., Saad, W.A., Vitamina A em óleo de fígado de peixes brasileiros de água doce (1975) Archivos Latinoamericano De Nutrición, 25, pp. 273-281Davis, K.B., Simco, W.A., Li, M., Robinson, E., Effect of reduction of supplementary dietary vitamins on the stress response of channel catfish Ictalurus punctatus (1998) Journal of The World Aquaculture Society, 29, pp. 319-324de Silva, S.S., Anderson, T.A., (1995) Fish Nutrition In Aquaculture, p. 319. , London: Chapman & HallFontagné, S., Bazin, D., Breque, J., Vachot, C., Bernarde, C., Rouault, T., Bergot, P., Effects of dietary oxidized lipid and vitamin A on the early development and antioxidant status of Siberian sturgeon (Acipenser baeri) larvae (2006) Aquaculture, 257, pp. 400-411Goswami, U.C., Dutta, N.K., Vitamin A-deficient diet and its effects on certain haematological parameters of Heteropneustes fossilis a 3-4 dehydroretinol rich freswater fish (1991) International Journal of Vitamin Nutrition Research, 61, pp. 205-209Halver, J.E., Recent advances in vitamin nutrition and metabolism in fish (1985) Nutrition and Feeding In Fish, pp. 415-429. , In: COWEY, C.B.MACKIE, A.M.BELL, J.G., London: Academic PressHalver, J.E., The vitamins (1989) Fish Nutrition, pp. 32-109. , In: HALVER, J.E., 2 ed. San Diego. Academic PressHarikumar, P., Karati, R., Goswami, U.C., Vitamin A- deficiency and its effects on the lysosomal enzymes of fish (1996) International Journal of Vitamin Nutrition Research, 66, pp. 97-100Hemre, G.I., Deng, D.F., Wilson, R.P., Berntssen, M.H.G., Vitamin A metabolism and earlier biological responses in juvenile sunshine bass (Morone chrysops x M. saxatilis) fed graded levels of vitamin A (2004) Aquaculture, 235, pp. 645-658Hepher, B., (1988) Nutrition of Pond Fishes, p. 388. , Cambridge: Cambridge University PressHernandez, L.H.H., Techima, S., Koshio, S., Ishikawa, M., Tanaka, Y., Alam, M.S., Effects of vitamin A on growth, serum anti-bacterial activity and transaminase activities in the juvenile Japanese flounder, Paralichtys olivaceus (2007) Aquaculture, 262, pp. 444-450Hole, S.M., Taylor, K.D.A., Methods of extraction composition and stability of vitamin A and other components in dogfish (Squalus acanthias) liver oil (1996) Food Chemestry, 55, pp. 215-220Hu, C.J., Chen, S.M., Pan, C.H., Huang, C.H., Effects of dietary vitamin A or β-carotene concentrations on growth of juvenile hybrid tilapia, Oreochromis niloticus x O. aureus (2006) Aquaculture, 253, pp. 602-607Katuyama, M., Matsuno, T., Carotenoid and vitamin A, and metabolism of carotenoids, β-carotene, canthaxanthin, astaxanthin, zeaxanthin, lutein and tunaxanthin, lutein and tunaxanthin in tilapia Tilapia nilotica (1988) Comparative Biochemistry and Physiology, 90 B, pp. 131-139Kubitza, F., Cyrino, J.E.P., The effects of feed quality and feeding practices on the quality of fish: A Brazilian fish culture outlook (1999) Advances In Extrusion Technology, p. 171. , In: CHANG, Y.K.WANG, S.S. (Ed.), Lancaster: TechnomicKubitza, F., Cyrino, J.E.P., Ono, E.A., Rações comerciais para peixes no Brasil: Situação atual e perspectivas (1998) Panorama Da Aqüicultura, 8, pp. 38-49Landen Júnior, W.O., Eitenmiller, R.R., Appliccation of gel permeation chromatography and nonaqueous reverse phase chromatography to high pressure liquid chromatographic determination of retinyl palmitate and β-carotene in oil and margarine (1979) Journal of The Aoac International, 62, pp. 283-289Lowe-McConnel, R.H., (1975) Fish Communities In Tropical Freshwaters, p. 337. , London: LongmanMohamed, J.S., Sivaram, V., Roy, T.S.C., Mariam, M.P., Murugadass, S., Hussain, M.F., Dietary vitamin A requirement of juvenile greasy grouper (Epinephelus tauvina) (2003) Aquaculture, 219, pp. 693-701Moren, M., Opstad, I., Berntssen, M.H.G., Infante, J.L.Z., HAMRE, K. An optimum level of vitamin A supplements for Atlantic halibout (Hippoglossus hippoglossus, L.) juveniles (2004) Aquaculture, 235, pp. 587-599(1993) Nutrient Requirements of Fish, p. 114. , NATIONAL RESEARCH COUNCIAL - NRC, Washington, D.C.: National Academy PressOrnsrud, R., Graff, I.E., Hoie, S., Totland, G.K., Hemre, G.I., Hypervitaminosis A in first-feeding fry of the Atlantic salmon (Salmo salar, L.) (2002) Aquaculture Nutrition, 8, pp. 7-13Plumb, J.A., (1999) Health Maintenance and Principal Microbial Diseases of Cultured Fishes, p. 328. , Ames: Iowa State University PressPost, G., (1987) Textbook of Fish Health, p. 288. , Neptune City: T.F.H. PublicationsPoston, H.A., Riis, R.C., Rumsey, G.L., Ketola, H.G., The effect of supplemental dietary amino acids, minerals and vitamins on salmonids fed cataractogenic diets (1977) Cornell Veterinary, 67, pp. 472-509Roberts, R.J., (1981) Patologia De Los Peces, p. 355. , Madrid: Mundi-Prensa(1999) Carotenoides Y Preparación De Alimentos: La Retención De Los Carotenoides Provitamina a En Alimentos Preparados, Procesados Y Almacenados, p. 105. , Washington, D.C.: USAID/JSI, (OMNI Project)Saleh, G., Eleraku, W., Gropp, J.M., A short note on the effects of vitamin A hypervitaminosis on health and growth of Tilapia nilotica (Oreochromis niloticus) (1995) Journal of Applied Ichthyology, 11, pp. 382-385(2001) Sas/stat User's Guide: Statistics V.8.2, , SAS INSTITUTE, Cary: SAS InstituteSteffens, W., (1989) Principles of Fish Nutrition, p. 384. , New York: Haslted PressTacon, A.G.J., (1992) Nutritional Fish Pathology, p. 75. , Rome: FAO, (FAO Fisheries Technical Paper, 330)Taveekijaran, P., Miyazaki, T., Matsumoto, M., Arai, S., Vitamin A deficiency in cherry salmon (1994) Journal of Aquatic Animal Health, 6, pp. 251-259Thompson, I., Chouber, C., Houlihan, D.F., Secombes, C.J., The effect of dietary vitamin A and astaxanthin on the immunocompetence of rainbow trout (1995) Aquaculture, 133, pp. 91-102Toguyeni, A., Fauconneau, B., Boujard, T., Fostier, A., Kuhn, E.R., Mol, K.A., Baroiller, J.F., Feeding behavior and food utilization in tilapia, Oreochromis niloticus: Effect of sex ratio and relationship with the endocrine status (1997) Physiology Behaviour, 62, pp. 273-279