Plastisphere Promotes Gill-Rot Disease: A Retrospective Study on a Sudden Fish Mortality Incident

Plastisphere is a hotspot for some potential pathogens. Herein, a sudden incident of gill-rot disease in the Haihe River, China, is speculated to be related to the effects of the plastisphere. Significantly higher levels of microplastics (MPs) were present in the gills of dying carps identified with gill-rot disease, while <i>Flavobacterium columnare</i> was identified as the main pathogenic microorganism. A six-week simulated exposure experiment was conducted to further confirm the relationship among MPs, <i>Flavobacterium columnare</i> and the pathogens of gill-rot disease. At an exposure concentration reflecting environmental abundance, all four MPs─PET and PLA in fiber and granule forms─were found to promote <i>F. columnare</i>-driven gill tissue damage, pathogen enrichment in the gills, and pathogenic metabolism. Compared to granular and nonbiodegradable PET MPs, fibrous PLA, which exhibited higher retention in the gills and greater microbial affinity, resulted in the highest disease incidence. For the first time, the risk of respiratory infectious diseases in aquatic animals caused by the plastisphere on MPs was presented and demonstrated.