Therapeutic effect of Bouea macrophylla Griffith in protecting Koi fish from Enterococcus faecalis infection and acute ammonia toxicity.

This study evaluates the potential of dietary supplementation with Bouea macrophylla Griffith leaf ethanolic extract (TD1 extract) as an antibiotic alternative for koi carp (Cyprinus carpio) within the One Health framework. Fish were fed diets supplemented with 0.5-1.5% TD1 extract and compared with doxycycline-treated and control groups. Disease resistance was tested by challenging fish with haemolytic Enterococcus faecalis, and protection against acute ammonia toxicity was also assessed. Fish receiving 0.5% TD1 extract or doxycycline supplementation showed approximately 60% survival after bacterial challenge, while 1% TD1 supplementation resulted in complete survival. In prevention tests, fish fed doxycycline or 1.5% TD1 extract-supplemented feed had reduced natural Vibrio infections, with survival rates of 65 and 60%, respectively, compared to 30% in controls after 10 days. Against acute ammonia exposure, fish receiving 1% TD1 extract showed no mortality, while doxycycline and control groups exhibited moderate (43%) and high (90%) mortalities, respectively. Serum glutamic pyruvate transaminase (SGPT) levels remained stable in the group of fish fed TD1 extract-supplemented feed but increased marginally in fish doxycycline-supplemented feed after ammonia exposure. These findings suggest that B. macrophylla TD1 extract is a promising and eco-friendly alternative to antibiotics. However, further long-term and large-scale studies are essential to validate safety and efficacy across diverse aquaculture species. Additionally, exploring potential synergistic effects with probiotics or immunostimulants will be important for optimizing its application in commercial aquaculture systems.