Abundance of Vibrio sp. Isolated from Macrobrachium rosenbergii in Seven Reservoirs of Hambanthota and Monaragala Districts, Sri Lanka.

Abstract

Vibrios, essential natural microflora of Macrobrachium rosenbergii, are a pivotal aspect to explore because regulating Vibrio growth significantly impacts the overall production of M. rosenbergii, as Vibrios are opportunistic pathogens that cause detrimental diseases in the species. The present study investigates the abundance of Vibrio sp. associated with M. rosenbergii captured from seven selected dry zone reservoirs in Sri Lanka. Samples of M. rosenbergii were collected from Bandagiriya Wewa, Mahagal Wewa, Ridiyagama Wewa, and Weerawila Wewa in the Hambanthota district, as well as Handapanagala Wewa, Muthukandiya Wewa, and Urusita Wewa in the Monaragala district, from fish landing sites in each reservoir and stored in sterilised polythene bags. The prawn samples were then homogenised and inoculated onto Thiosulphate Citrate Bile Sugar plates using the spread plate method. After incubation, the grown colonies were counted manually and expressed as CFU/g of prawn. The resulting colonies were subjected to a set of biochemical tests to confirm their identity as Vibrios. The abundance of Vibrio sp. associated with M. rosenbergii from the seven reservoirs was compared using the Kruskal-Wallis Pairwise comparison test. All isolated colonies were confirmed as Vibrio sp. based on the biochemical test results. The mean total number of Vibrio sp. isolated from Muthukandiya Wewa (8.19 ± 0.84 log CFU/g of prawn) was significantly higher than that from Bandagiriya Wewa (7.03 ± 0.74 log CFU/g of prawn), Handapanagala Wewa (6.92 ± 0.55 log CFU/g of prawn), and Urusita Wewa (6.85 ± 0.35 log CFU/g of prawn). This study concludes that M. rosenbergii cultured in the Muthukandiya reservoir contains the highest number of Vibrio sp. Further research on the regulation of growth factors for Vibrios is recommended to elucidate the variations in their abundance in these reservoirs.