Effects of Guava (Psidium guajava) Aqueous Leaf Extract on Total Heterotrophic and Coliform Counts in Intestinal Tract of Oreochromis niloticus (Lennaues, 1758)

Antibiotic use in fish farming is increasingly restricted due to associated risks. This study examines the effects of guava (Psidium guajava) leaf extract on Oreochromis niloticus gut bacteria and body composition. This is to establish if the extract selectively reduces enteric pathogens without disrupting beneficial microbiota and the body composition, a critical growth indicator. Psidium guajava leaves were collected from the botanical garden, University of Ibadan, washed, air-dried for 3 weeks, and milled into powder form. Aqueous extracts from the powder were screened quantitatively and qualitatively using standard procedures. Five isonitrogenous diets (35% Crude protein) were formulated containing 0, 0.25, 0.50, 0.75, and 1.00% P. guajava extract. Diets were fed to triplicate groups of 300 O. niloticus (mean weight: 1.32 ± 0.04g) twice daily to satiation for 84 days. Initial and final proximate compositions of experimental fish were determined using standard methods. Total heterotrophic count and total coliform count were carried out on the aseptically removed guts. Psidium guajava extracts contained 14.6% alkaloids, 22.4% flavonoids, 36.6%, saponins while tannin was 18.3 %. Total heterotrophic count and Total coliform count (1.92 x 104 cfu/g and 1.40 x 104 cfu/g, respectively) were significantly higher (P<0.05) in the gut of fish fed the control diet compared to those fed 0.5% extract and above. High protein was observed in fish fed with testes diet. This study has revealed the ability of extracts from guava leaf to reduce pathogenic bacteria in the gut of Oreochromis niloticus and improve protein deposition in the flesh. Keywords: Pathogen, Fish Phytochemicals, Intestinal microbes