Prevalence of Aeromonas hydrophila and Pseudomonas fluorescens and factors influencing them in different freshwater fish ponds

Real-time quantitative PCR (qPCR) was performed to elucidate the abundance of Aeromonas hydrophila and Pseudomonas fluorescens, which are among the most widespread fish pathogens in ponds. Both pathogens have three different breeding patterns, namely, (a) gibel carp (Carassius auratus gibelio), (b) yellow catfish (Pelteobagrus fulvidraco), and (c) black carp (Mylopharyngodon piceus), over a production season. Results revealed that pond sediments have significantly higher bacterial levels of A. hydrophila and P. fluorescens (10^5 –10^6 copies µl-1 DNA) than pond water (10^3 –10^4 copies µl^-1 DNA). In addition, independent regression models revealed that environmental variables influence the levels of pathogenic bacteria. The occurrence of A. hydrophila and P. fluorescens were significantly positively correlated to dissolved oxygen and water temperature, respectively. On the contrary, both pathogens were negatively correlated to total nitrogen. In this study, the prevalence of pathogenic bacteria and their relationships with physicochemical factors in different pond environments were investigated for the first time through a molecular method. Furthermore, although we did not include fish diseases occurring during the production season, our results can provide useful theoretical information for fish breeding especially with regard to the prevention of related bacterial diseases.