Pathogenicity of Aeromonas hydrophila associated with seed production in Clarias gariepinus

Abstract

Aeromonas hydrophila causes haemorrhagic septicaemia in fish. Its role in hatchery propagation of Clarias gariepinus is not well elucidated, thus necessitating the investigation. Pathogenicity test was conducted using β- haemolytic Aeromonas hydrophila on Clarias gariepinus seeds in Petri-dishes. Aeromonas hydrophila (109, 1010 and 1011 cfu/ml) effect on fertilized eggs (200), day-old larvae (720) and fry (240) exposed by bath for 20 minutes (eggs), and 15, 30 and 60 minutes (larvae and fry) were determined. The larvae and fry were fed artemia ad-libitum, and observed for seven and four days respectively. Eighty fingerlings were orally challenged with similar Aeromonas hydrophila doses, monitored for clinical signs (30 days) and bacterial isolation determined. Data were analysed using standard tests at α0.05. Hatchability significantly improved with increasing bacterial dose. Larval mortality significantly increased from 0.33±0.33 (pre-fed) to 4.33±0.67 (post-fed) on first-exogenous feeding. Aeromonas hydrophila significantly reduced post-fed larval mortality to 1.33±0.44 (1011cfu/ml) and 2.00±0.41 (60-minutes exposure), and insignificantly reduced fry mortality from 1.83±0.31 to 0.83±0.48 (1010 cfu/ml) and 0.83±0.31 (60-minutes exposure). Challenged fingerlings showed no clinical sign throughout the period. Aeromonas hydrophila was isolated from fingerlings’ gut and liver. Studied Aeromonas hydrophila was non-pathogenic, enhanced the seeds’ health and is a prospective gut stabilizer.