Effect of spatio‐temporal variables, host fish species and on‐farm biosecurity measures on the prevalence of potentially pathogenic Aeromonas species in freshwater fish farms.

Abstract

Aims: To determine the prevalence of Aeromonas species in freshwater fish farms, factors affecting their prevalence and virulence factors associated with each species.

Methods and results: In a cross-sectional study from 128 farms in four districts of Uttar Pradesh, India, 11 species of Aeromonas were identified by gyrB sequencing including the first report of Aeromonas crassostreae from fish. Four species of Aeromonas were more prevalent (MP) in fish farms, A. veronii bv. sobria (50.0%) was the highest, followed by A. caviae (18.8%), A. veronii bv. veronii (11.7%) and A. dhakensis (7.0%). The less prevalent (LP) species were A. hydrophila, A. media, A. jandaei, A. allosaccharophila, A. salmonicida, A. crassostreae and A. taiwanensis. Spatial variation in the prevalence of Aeromonas species was observed. Dominance of biovar sobria ranged from 33.3 to 68.6%, notably lesser in farms with on-farm biosecurity measures. The prevalence of biovar veronii was significantly associated with pangas fish, rainy season and farms with on-farm biosecurity measures. The prevalence of LP species was significantly higher in mrigal fish and winter season. Multiple virulence factors (>6) were detected in 70.2% of the Aeromonas species. Significant association of β-hemolysin, DNase, slime production, act, ahh1, aexT and lip was observed with different species of Aeromonas. Moreover, 75.8% of Aeromonas species possessed one or more enterotoxins genes (act/alt/ast).