DIGESTIVE ENZYMES, IMMUNITY AND OXIDATIVE STATUS OF NILE TILAPIA (Oreochromis niloticus) REARED IN INTENSIVE CONDITIONS

High stocking density is significantly disturbing the growth and productivity of aquatic animals. Digestive enzymes, immunity and oxidative status of Nile tilapia were investigated in case of culturing in several densities. Fish (14.3 +/- 0.03 g) were stocked in 12 aquaria (70 L) at four densities of 10 (SD10), 20 (SD20), 30 (SD30) and 40 (SD40) fish per aquarium for 30 days. Fish growth, feed efficiency ratio, digestive enzyme activity and dissolved water oxygen significantly (P<0.05) decreased, while the total ammonia increased with increasing stocking density. Immunoglobulin and NBT levels decreased significantly (P<0.05) in SD40 set compared to SD20 set without no differences with the other two groups. Lysozyme activity reported the highest significant (P<0.05) values in SD10 and SD20 groups over the high stocking density group (SD40) without no difference with SD30 group. Bactericidal, phagocytic activities and phagocytic index reported significantly (P<0.05) lower values in fish reared in SD30 and SD40 groups than fish reared in SD10 and SD20 groups. Peroxidase activity also showed significantly (P<0.05) low values in SD40 and SD30 groups with the weakest activity in SD40 group. Total serum protein lowered relatively in SD30 and SD40 groups without no differences with the other groups. Furthermore, fish reared at high stocking densities resulted in significantly (P<0.05) decreased superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) activities as well as increased malonaldehyde (MDA) activity in blood of tilapia suggesting suppressed antioxidant response. In conclusion, intensive conditions depressed the growth, digestive enzyme activity, immunity and oxidative status of Nile tilapia.