Quantitative and qualitative study of the bacterial flora of farmed freshwater prawn (Macrobrachium rosenbergii) larvae

Quantitative and qualitative studies of the bacterial flora of farmed freshwater prawn (Macrobrachium rosenbergii) larvae in Saudi Arabia were performed, and isolates identified where possible. Physico‐chemical characteristics, bacterial counts, and the nature of the bacterial flora of larvae rearing tank water, sediment, tank wall surfaces, larval surface, supplied water, and feed were investigated. Bacterial counts ranged from 2.1 ± 1.3 × 10⁵ to 2.2 ± 0.8 × 10⁷ colony forming units (CFU) ml^?1 in tank water; 4.4 ± 0.9 × 10⁷ to 8.3 ± 1.7 ×10⁹ CFU g^?1 in tank sediment; 8.6 ± 1.0 × 10² to 9.8 ±0.7 × 10⁴ CFU cm^?2 on the tank wall surface; 1.3 ± 1.1 × 10⁴ to 7.7 ± 1.6 × 10⁶ CFU per larva surface, 7.9 ± 1.2 × 10⁵ to 5.0 ± 1.5 × 10⁷ CFU g^?1 in washed larval tissue slurries, 9.1 ± 0.7 × 10³ CFU ml^?1 in supplied water, and 2.4 ± 1.9 ×10¹⁰ CFU g^?1 in mixed feed. Fourteen bacterial genera were identified, including Chryseomonas sp., Vibrio spp., Cellulomonas sp., Aeromonas hydrophila, and Pasteurella sp. The tank water and sediment had similar bacteria to those on the prawn larvae. Chryseomonas sp., Cellulomonas sp. and Vibrio sp. were the most dominant species (prevalence >10%) in tank water; Chryseomonas sp., Pseudomonas alcaligenes and Shewanella putrefaciens in the sediment; Ps. alcaligenes and Cellulomonas sp. on the tank wall surface; Chryseomonas sp., and Cellulomonas sp. on the larval surface; and Chryseomonas sp., Vibrio vulnificus, Sh. putrefaciens and V. alginolyticus in the washed larval tissue slurries (prevalence 10%). Pseudomonas alcaligenes, Moraxella sp., Serratia liquefaciens, Gordona sp. and Burkholderia glumae were absent in larvae but identified in the culture water, tank sediment, and tank wall surface. Pseudomonas sp., Chryseomonas sp., Pasteurella sp. and V. alginolyticus were the prevalent bacteria (>12%) in supplied water. The feed contained V. alginolyticus, A. hydrophila and Cellulomonas sp. as the dominant bacteria (>13%). In the culture water and larvae samples, 83% of the feed and supplied water bacteria were identified.