Various plant-based products are currently undergoing testing in aquaculture as growth and/or health enhancers for fish, serving as substitutes for chemicals and antibiotics that may be detrimental to animal and consumer well-being. Azadirachtin is a bioactive compound extracted from the Azadirachta indica plant, with great microbicidal and immunostimulant potential. The aim of this study was to evaluate the effects of dietary azadirachtin supplementation on the zootechnical performance and health of juvenile Nile tilapia (Oreochromis niloticus) reared in a recirculating aquaculture system. Juvenile tilapia (n = 400; mean weight 13.03 ± 0.77 g) were randomly distributed into 20 experimental units (EUs) divided into five groups with four replicates each. Over a 45-day period, four groups were given diets containing azadirachtin at concentrations of 20, 70, 120, and 170 mg kg-1, while a control (0 mg kg-1) group was fed a diet without the compound. At the end of this period, assessments were conducted on growth performance, haematoimmunological parameters, histological conditions of the liver, spleen, kidney, and intestine, as well as analyses of intestinal microbiota, hepatic antioxidant enzymatic activity, and malondialdehyde content. No significant differences were found in growth performance, whereas the inclusion of 170 mg kg-1 of azadirachtin resulted in higher antimicrobial activity of fish blood plasma against Aeromonas hydrophila and lower intestinal Streptococcus spp. counts compared to non-supplemented fish. The mean corpuscular haemoglobin concentration was significantly lower in fish from the 170 mg kg-1 treatment group than in the control group. Conversely, dietary inclusion of azadirachtin adversely affected the structure and overall health of organs, especially the kidney and liver. Malondialdehyde content in the hepatic tissue of Nile tilapia was significantly higher in fish from the 120 mg kg-1 treatment than in the 20 mg kg-1 treatment and the control group. Fish from the 120 and 170 mg kg-1 treatments showed a significant increase in superoxide dismutase activity compared to the control group. Although some beneficial effects on immunity have been observed, such as increased agglutination titre and enhanced antimicrobial activity of fish blood plasma against A. hydrophila, as well as reduced levels of Streptococcus spp. in the intestine, caution is advised when incorporating azadirachtin into the diet of juvenile O. niloticus as it may have the potential to compromise the integrity of tissues in vital organs.
Ferreira et al. (Wed,) studied this question.