Abstract
Regular monitoring of laboratory zebrafish health status is crucial for ensuring both animal welfare and scientific validity in aquatic research. While zebrafish usage in research has increased substantially due to their biological advantages and experimental benefits, including high fecundity and vertebrate similarity, systematic health monitoring remains uncommon in South Korean facilities. This study presents a comprehensive assessment of zebrafish colony health monitoring practices in South Korea, combining comparative survey data from 2018 and 2024 with microbiologic and environmental analyses of 11 facilities. Our survey revealed a trend: despite facility scale expansion (proportion of the large-scale facilities with >200 tanks increasing from 41.7% to 54.5%) and universal adoption of recirculation systems, monitoring efforts have declined. The percentage of facilities without active monitoring increased from 50.0% in 2018% to 81.8% in 2024, while awareness of monitoring necessity decreased from 91.7% to 72.7%. To investigate these issues, we conducted analyses across 11 facilities (6 research institutes and 5 local suppliers). The analysis encompassed multiple parameters: 1) detection of key infectious agents (Mycobacterium spp., Aeromonas hydrophila, Flavobacterium columnare, Pseudocapillaria tomentosa, Pseudoloma neurophilia, Pseudomonas aeruginosa) in sump tank biofilm, zebrafish specimens, and feed samples; and 2) evaluation of water chemistry parameters (pH, nitrate concentration, conductivity) in tank water. Our findings revealed that Mycobacterium spp. were present in biofilm samples from all facilities and in >80% of fish samples from research facilities. Aeromonas hydrophila was detected across all sample types. Both Mycobacterium spp. and A. hydrophila are opportunistic pathogens that necessitate careful consideration in long-term zebrafish experiments. Furthermore, evaluation of water quality analyses indicated widespread deviations from acceptable parameters, particularly in nitrate levels and pH values. Our results underscore the need for implementing standardized monitoring protocols and enhanced water system management to safeguard research integrity, animal health, and occupational safety in zebrafish facilities.