Commensal and Pathogenic Bacteria Associated with Farmed Rainbow Trout (Oncorhynchus mykiss Walbum) and Aquaculture Environment

Abstract

The bacterial microflora associated with farmed rainbow trout (Oncorhynchus mykiss Walbaum) and its aquaculture environment was characterized. The counts of commensal, indicator and pathogenic bacteria were determined and bacterial colonies were characterized. The mean mesophilic counts were 4.5 log CFU g -1 and 7.6 log CFU g -1 in skin with muscle and intestine respectively. Significantly high densities of faecal coliform, E. coli and Enterococci was detected in pond sediment, fish intestine and feed when compared to pond water and trout tissues. A total of 110 randomly selected isolates from TSA were identified and characterized. Of the mesophiles, 70–75% were aerobic Gram-negative bacteria, both motile and non-motile, and members of the Enterobacteriaceae family. The skin microflora of trout was dominated by Gram-negative aerobic rods belonging to Enterobacteriaceae, Aeromonadaceae, Pseudomonas/ Shewanella, Moraxella, Acinetobacter and Flavobacterium. Psychrotrophic bacterial isolates of the genera Pseudomonas, Morganella, Hafnia were identified in trout. Pathogenic bacteria such as Clostridium botulinum, Yersinia enterocolitica could not be detected. However, Aeromonas hydrophila, A. veronii biovar sobria, A. veronii biovar veronii were prevalent in farmed trout. Presence of bacterial pathogens in the trout farm envisages a strict hygienic handling and processing of fish from such culture systems for ensuring public health safety.