Evaluation of the effects of Ocimum basilicum essential oil in Nile tilapia diet: growth, biochemical, intestinal enzymes, haematology, lysozyme and antimicrobial challenges

Due to the intensification of tilapiculture, problems attributed to health of fish stocks have become more frequent. The objective of the present study was to evaluate growth, physiological responses and survival of Nile tilapia juveniles fed a diet containing the essential oil of Ocimum basilicum (EOOB) and infected by Aeromomas hydrophila. Five diets (in quadruplicates) were evaluated with increasing levels of EOOB (0.0 - control; 0.25; 0.5; 1.0 and 2.0 kg diet(-1)). On day 45, three fish from each tank were sampled and blood, intestine and liver samples were taken. On day 46, nine fish from each tank were infected with A. hydrophila followed by a 15-day period of observation. An addition of 2.0 mL EOOB in the diet improved the growth performance and increased haematological variables and activity of intestinal enzymes. Higher concentrations of EOOB in the diet reduced plasma triglycerides and glucose and hepatic glycogen and alanine aminotransferase (ALT) levels and increased plasma total proteins and ALT levels and lysozyme post-infection activity. The survival of fish after A. hydrophila infection was not influenced by the addition of EOOB in the diet. The use of 1.0 mL EOOB kg diet(-1) seems to be more suitable than 2.0 mL EOOB kg diet(-1) since the latter may be related to liver damage.