The antibacterial activity of bitterleaf (gymnanthemum amygdalinum (delile) sch.bip.) And water hyacinth (pontederia crassipes, mart) and their effect on growth and survival of juvenile Nile tilapia (oreochromis niloticus, linnaeus 1758)

Abstract

Aquaculture, particularly the cultivation of Nile tilapia Oreochromis niloticus, plays a crucial role in global food security. However, disease outbreaks and suboptimal growth rates present significant challenges. Natural plant-based additives offer promising alternatives to synthetic antibiotics and growth promoters. The study aimed to investigate the antibacterial activity of bitter leaf, Gymnanthemum amygdalinum (Syn: Vernonia amygdalina) and water hyacinth Pontederia crassipes Mart and the effects on the growth and survival of juvenile Nile tilapia. Dry powdered leaves of G. amygdalinum and P. crassipes were used for proximate and phytochemical analyses. Fish of average weight 1.4 ± 0.3g distributed into 9 rectangular glass tanks (3 treatments) were fed for 10 weeks to assess the influence of the treated diets on the fish performance. Further, 60 fish fed on plant-treated diet for 10 weeks and 60 new but healthy Oreochromis niloticus were injected intraperitoneally with an estimated 108 cells of Aeromonas hydrophila to evaluate the prophylactic and therapeutic potential of the ground leaves of G. amygdalinum and P. crassipes. Results revealed that G. amygdalinum contained significantly higher crude protein (25.47 ± 0.33%) and carbohydrate content (43.13 ± 0.14%) than P. crassipes, which had higher fibre (26.00 ± 0.05%) and lipid content (7.50 ± 0.10%). Additionally, G. amygdalinum contained four phytochemicals including flavonoids, alkaloids, saponins, and tannins, whereas P. crassipes contained flavonoids and tannins. Growth performance trials demonstrated that Nile tilapia fed on a diet supplemented with G. amygdalinum had a higher survival rate, grew faster, and gained more body mass compared to those fed on P. crassipes and the control group. However, the diets did not yield better condition factor, linked to possible adverse effects on the fish's health. In a challenge experiment with Aeromonas hydrophila, Nile tilapia fed on G. amygdalinum as prophylaxis showed a more enhanced survival rate of 85% than the P. crassipes and the control diet. However, there was a lower survival rate of 40% in fish fed on the two plants used as chemotherapy. The findings suggest that G. amygdalinum could be a valuable ingredient in fish feed formulation due to its high protein content and antibacterial properties, contributing to better growth performance and disease resistance in juvenile Nile tilapia. Further studies are recommended to optimize the inclusion levels of G. amygdalinum in fish diets, explore alternative extraction methods for bioactive compounds, and assess the long-term health impacts on Nile tilapia.