Abstract:
Culture-based fisheries of Giant Freshwater Prawn (GFP), Macrobrachium rosenbergii have
been introduced in Sri Lankan reservoirs, making economically important component in the
inland fishery. Hitherto, microbial studies associated with GFP in reservoirs have not been
reported. Present study is of utmost importance since it is a novel study conducted in the Sri
Lankan context to ascertain the total bacteria and total Vibrio associated with larvae, post larvae
and adults of M. rosenbergii and investigate the antibiotic sensitivity of these associated bacteria.
Five larvae and post larvae samples containing 30 individuals in each were collected from 10
different tanks in freshwater prawn breeding centre, Kahandamodara whilst the sample of adult
M. rosenbergii were collected from five reservoirs; Ridiyagama, Bandagiriya, Urusita wewa,
Handapanagala wewa and, Muthukandiya wewa. All the samples were homogenized separately.
To determine the total bacteria count (TBC) and total vibrio count (TVC), samples were
inoculated on Standard plate count agar plates and Thiosulfate Citrate Bile Sugar (TCBS) plates,
respectively by spread plate method. TBC and TVC were expressed as Colony Forming Unit/mL
(CFU/mL). Kirby-Bauer disk diffusion method was used to examine the antibiotic sensitivity of
the bacteria associated with different life stages of M. rosenbergii against Ampicillin (10μg),
Ciprofloxacin (30μg) and Tetracycline (30μg). Mean no of total bacteria count associated with
larvae, post larvae and adult were 2.96±2.4x108 CFU/mL, 2.64±5.90x1011 CFU/mL and,
1.05±2.30x1011 CFU/mL, respectively. The mean no of total bacteria associated with post larvae
and adult of M. rosenbergii were significantly higher (p<0.05) than that of in the larvae. Mean
no of total Vibrio count of post larvae (3.62±2.00x104 CFU/mL) were significantly lower
(p<0.05) than that of larvae (4.13±3.54x106 CFU/mL) and adult (4.31±3.11x106 CFU/mL).
Bacteria associated with all the stages of M. rosenbergii showed resistance to Ampicillin whilst
they were sensitive to Ciprofloxacin and Tetracycline. Present study warrants comprehensive
studies on antibiotic sensitivity of all larval stages (12) of M. rosenbergii.
