A blend of Guava, Bitter, and Neem Leaf extracts improves haematology and resistance to co-infection of Streptococcus agalactiae and Aeromonas jandaie but not Liver health in Nile tilapia

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Given the intense interest in the use of herbal extracts to improve fish growth, fish health, and disease resistance in fish in culture systems, in this study, we examined the effects of a blend of Guava, Bitter and Neem leaf extracts (GBNL) (i.e., 1:1:1 for GL, BL, and NL respectively) at different inclusion (i.e. 0 GBNL gkg−1, 1 GBNL gkg−1, 3 GBNL gkg−1, 5 GBNL gkg−1, 7 GBNL gkg−1 and 10 GBNL gkg−1) levels on growth, haematology, immunity, liver toxicity and resistance to bacterial co-infections in Nile tilapia. After 8 weeks of feeding, Nile tilapia fed 3 GBNL gkg−1 diets showed significant effects in improving weight gain compared to those fed the control diet. GBNL fed fish showed improved health of fish by stimulating significant increases in levels of White blood cells, Red blood cells, Haemoglobin, and Haematocrit in relation to those fed the control diet. Also, the applications of deferent GBNL levels in Nile tilapia diets showed the potential to upregulate the expression of the immune-related genes heat shock protein 70, chicken type lysozymes, and Beta-defensin, with significant effects shown in fish fed 5GBNL gkg−1 diets in comparison to the control. The results also indicate that GBNL supplementation can decrease mortalities to co-infection of Streptococcus agalactiae and Aeromonas jandaie in Nile tilapia with the lowest mortalities of 13.65% and relative per cent survival of 82.57 % in fish fed 5GBNL gkg−1. Despite the potential of GBNL applications in Nile tilapia, findings of this study indicate fish fed the different concentrations of GBNL, particularly with 7 GBNL gkg−1 can promote the leaching of the liver enzymes: alanine transaminase, aspartate aminotransferase, and alkaline phosphate into the bloodstream which is suggestive of potential liver damage in Nile tilapia. Histological examinations of a cross-section of the liver tissues of fish fed GBNL showed various injuries including hydropic changes, pyknosis nuclei, erythrocytes congestion and vacuolation with the severest seen in those fed 7 GBNL gkg−1. Taking all of the above into consideration, 5GBNL gkg−1 application could improve the health and disease resistance of Nile tilapia; however, prolong use thus after 8 weeks of administration could be injurious to fish liver health.