Effects of dietary baobab, Adansonia digitata on growth, haemato-immunological status, antioxidant biomarkers, intestinal histomorphometry, gene expression responses, and disease resistance in Nile tilapia, Oreochromis niloticus

This study explored the influences of baobab fruit extract powder (BP) on growth, oxidant-antioxidant balance, immunity, intestinal histology, expression of growth and immune genes, and disease resistance in Nile tilapia. Fish were fed on five test diets supplied with different BP levels as BP0 (control; 0 g kg-1), BP1 (1 g kg -1), BP2 (2 g kg -1), BP3 (3 g kg -1), and BP4 (4 g kg -1) for two months. Results revealed that dietary BP improved the growth in all BP groups compared with the BP0 group, with the best values apparent in the BP4 group. However, dietary BP did not affect the whole-body chemical composition and survival rates in all groups. Serum immunity biomarkers (lysozyme, myeloperoxidase, and bactericidal activities) were enhanced in all BP groups compared to the BP0 group. Hepatic antioxidant status significantly improved, as manifested by increases in the hepatic CAT, SOD, and T-AOC and decreases in MDA concentrations in BP groups compared to the controls. Of interest, dietary BP supplementation significantly increased the expression of growth-related genes (ghr1, ghr2, igf-1, and igf-2) in the liver and immunity-associated genes (inf-gamma 1, lyz, il-1 beta, il-10, and hepcidin) in the spleen of BP-treated fish in comparison with the controls. The intestinal histological sections revealed no significant variations among all groups with normal histoarchitecture and goblet cells. After experimental infection with Aeromonas hydrophila, the survival rates (%) in the BP0, BP1, BP2, BP3, and BP4 groups were 23.33, 43.33, 56.67, 63.33, and 70.00, respectively, suggesting the positive roles of BP in increasing the fish disease resistance. To conclude, dietary BP could improve growth (particularly in the BP4), serum immunity, antioxidant capacity, and transcription of growth and immune genes in O. niloticus. In addition, the highest disease resistance was also found in the BP4 group. All in all, BP at a dose rate (4 g kg -1 diet) could be regarded as a functional feed supplement for tilapia farming.