Introduction
Numerous investigations have highlighted frequent large-scale die-offs in olive flounder (Paralichthys olivaceus ), largely linked to a variety of infectious agents. Key contributors to these episodes include Miamiensis species , which trigger scuticociliatosis ; Streptococcus species , known for causing streptococcosis ; viral hemorrhagic septicemia virus (VHSV), an easily transmissible viral invader; Vibrio strains , which bring about vibriosis; Tenacibaculum bacteria, implicated in gliding motility disorders; the protozoan Cryptocaryon irritans , which causes marine white spot illness (MWSD); and Edwardsiella bacteria, the source of edwardsiellosis. These organisms pose serious risks to fish farming operations, underlining the need for robust diagnostic systems and intervention measures to curtail disease progression and avoid substantial financial setbacks in the sector.
Materials and methods
To explore the relationship between bacterial levels, water temperature, and extreme weather at aquaculture sites, a two-year field survey was carried out in Jeollanam -do and Jeju-do , Korea. This study evaluated how environmental and climate variables affect bacterial growth in fish farms. Based on continuous monitoring data, a novel water purification system (TSS-PRS) was developed and installed at a site in Jeollanam -do to test its real-world effectiveness in managing water quality. After deployment, both raw and treated water, along with cultured fish, were analyzed to determine the system’s ability to reduce microbial contamination. Detection and quantification of ten critical pathogens were conducted using DNA extraction and real-time PCR techniques to ensure precise microbial assessment.
Results
In untreated water, bacterial levels rose sharply in Jeollanam -do between July 12 and July 30, 2024—from 10.9×10³ to 5.15×104 BQV mL–1—coinciding with severe weather on July 16, including a peak temperature of 30 ℃, 64 mm of rainfall, and wind speeds of up to 8.5 m s–1 (Fig. 6e). This surge is likely linked to these meteorological extremes. In contrast, treated water showed a steadier pattern, with bacterial activity ranging from 3.00×103 to 7.68×103 BQV mL–1 over the same period. Even during subsequent weather events—such as 45.4 mm of rain on September 21, 26.7 mm on October 22, and winds of 7.9 m s–1 on November 26—bacterial levels in both treated and untreated samples stayed below 0.4×103 BQV mL–1, indicating minimal impact.