Analyzing the Interaction between and Bacteria under Different Physicochemical Conditions When Infecting Guppy Using the eDNA Method.

In the aquaculture system of ornamental fish, the interaction between bacterial microbiota and ciliate protozoa can prevent or promote disease outbreaks, and different physicochemical conditions will affect the relationships between them. We investigated the interaction between bacterial microbiota and the parasite when infecting (guppy) under different physicochemical conditions. The abundance of in water, the relative abundance of bacterial species, and histopathological observation were studied or monitored using environmental DNA (eDNA) extraction technology, the qPCR method, and 16s rRNA sequencing, respectively. The morphological identification and phylogenetic analysis of were carried out. The infected guppy tissue was also stained by the hematoxylin and eosin methods. The results showed: (1) the bacterial communities of water samples were mainly composed of species assigned to Proteobacteria and Bacteroidetes, and and Puniceicoccaceae were positively correlated with fish mortality, abundance, and temperature. (2) and universalis with different correlations between ciliates appeared in different treatment groups, the result of which proved that environmental factors affected the interaction between bacteria and . (3) Lower temperatures and a higher pH were more beneficial for preventing disease outbreaks.