PROTECTIVE EFFECT OF Ocimum gratissimum LEAF AQUEOUS EXTRACT, ANTIOXIDANT CAPACITY, IMMUNOCOMPETENCE AND DISEASE RESISTANCE OF Oreochromis niloticus FINGERLINGS AGAINST Vibrio parahaemolyticus INFECTION

This study was carried out to assess the protective effect of Ocimum gratissimum leaf aqueous extract on immunological responses, antioxidant capacity and disease resistance of Oreochromis niloticus fingerlings against Vibrio parahaemolyticus infection. Five iso-nitrogenous (30.02%) diets containing 0g (control), 2g, 4g, 8g and 16g Ocimum leaf extract (g/kg) were fed to triplicate groups of fish (initial weight 3.31±0.05g) for 90 days. After 90 days feeding trial, test fish were injected with pathogenic V. parahaemolyticus and survival rate was recorded for the next 14 days. The white blood cell (12.29±0.35×103/µl), red blood cells (3.60±0.21×103/µl), packed cell volume (27.76±0.08g/dl) and haemoglobin (7.21±0.47g/dl) were all highest in fish fed 8g/kg of Ocimum leaf extract. Following a challenge with V. parahaemolyticus, the study indicated that Ocimum leaf extract reduces the metabolic stress of infected fish compared to the control. There is a significant increase in glucose (101.00±2.89mg/dl) levels and liver enzymes ALT (74.14±2.31UI/ L) and AST (49.00±1.73UI/L) in the control group (0g/kg), whereas the opposite was true for diets supplemented with Ocimum leaf extract. Ocimum leaf extract group significantly (p< 0.05) enhanced immune parameters such as lysozyme, immunoglobulin (IgM) and Interleukine-1β (IL-1β) in the spleen, skin and kidney. After infection, the supplemented diets with Ocimum leaf extract showed significantly (p< 0.05) higher lysozyme and IgM activity in the spleen, skin, and kidney. The result of the challenge test with V. parahaemolyticus revealed that the highest (80%) percentage survival was recorded in the group fed 8- and 16 g/kg of Ocimum-supplemented diets, and the least (15%) skin lesion morbidity was observed in 8 g/kg-fed fish. This study revealed that the inclusion of O. gratissimum leaf extract in the diet of O. niloticus enhanced the biochemical parameters, immune response, and improved resistance against V. parahaemolyticus.