Variations in Physicochemical Parameters of Water and Abundance of Vibrios Associated with Giant Freshwater Prawn (Macrobrachium rosenbergii) in Selected Reservoirs of Sri Lanka

Abstract

Exhaustive scrutiny of Vibrios, one of the preeminent autochthonous microbes in the Giant Freshwater Prawn, GFP (Macrobrachium rosenbergii), is pivotal, as they can profoundly influence the production of GFP. This study aimed to enumerate Vibrio populations isolated from GFP and examine their relationship with the physicochemical properties of seven reservoirs in Sri Lanka. GFP samples were collected, homogenized, and plated using the spread plate technique on Thiosulfate Citrate Bile Salt (TCBS) agar to isolate Vibrio spp. In-situ measurements of water parameters temperature, pH, conductivity, dissolved oxygen (DO), and Secchi disk depth were taken from each reservoir. Chlorophyll-a and organic matter contents were analyzed in the laboratory. To identify significant variations, Kruskal-Wallis pairwise comparisons were used to compare Vibrio abundance and water parameters across reservoirs. Regression analyses assessed the relationships between Vibrio abundance and environmental factors. Results showed significant differences in Vibrio sp. abundance among reservoirs. The highest mean Vibrio count was observed in GFP from Muthukandiya Wewa (8.19±0.74 log CFU g⁻¹), significantly exceeding counts from Bandagiriya, Handapanagala, and Urusita reservoirs. Among the water quality variables, only pH in Urusita Wewa showed a significant positive correlation (r = 0.740, p = 0.006) with Vibrio abundance.The study infers that the abundance of Vibrios is high in Muthukandiya Wewa. Furthermore, the abundance of Vibrios in Urusita Wewa is regulated by reservoir pH. An assiduous and perpetual analysis of Vibrio abundance and factors of lasting repercussions on its abundance helps facilitate mitigation measures to control Vibrios.