The aquaculture industry faces frequent disease outbreaks due to issues such as high stocking density and environmental deterioration. Pathogenic bacteria have a rapid infection rate and high mortality rate. Once an outbreak occurs，it can cause serious economic harm to the aquaculture sector.

Edwardsiella tarda

is a highly harmful pathogenic bacterium in aquaculture. Rapid and efficient field detection methods can effectively prevent and control disease outbreaks. Rolling circle amplification（RCA） with lateral flow strip（LFS） technology，using latex microspheres as labels waw combined to establish a novel RCA-LFS method for detecting

E. tarda

. This method has three steps in total. First，a conservative sequence of the unique gene of

gyrb

of this bacterium was used to designe

d the padlock probe and corresponding primer pair，and the Taq DNA ligase was used to circularize the single-stranded padlock probe. Then exonuclease Ⅰ was used to digest the uncircled single-stranded nucleic acid，and the circled padlock probe was rolling circle amplified by Bst DNA polymerase and primers. Finally the LFS was directly inserted into the amplification product solution for visual result reading just need to wait 15 min. The optimized RCA conditions was determined to be as follows：locking probe concentration，500 pmol/L；amplification temperature，61 ℃；and amplification time，50 min. The positive results showed a striking blue band on LFS detection line while a red band on quality control line. The negative results showed nothing on LFS detection line while a red band on quality control line. The RCA-LFS assay was specific，displaying no cross-reactivity with other common pathogenic bacteria. The detection limit for

E. tarda

genomic DNA was 50 ng/mL. Compared to the polymerase chain reaction（PCR） amplification，the reaction condition of RCA was stable. A large number of nucleic acid amplification could be completed without thermal circulation meter. Therefore，RCA was a kind of field detection method more suitable than PCR. Compared with common colloidal gold markers，latex microspheres were stable and colorful，and it was possible to achieve simultaneous detection of multiple bacteria through color changes alone. In addition，the established RCA-LFS simplified the operational steps by eliminating the need to detect probe hybridization；instead，it directly used LFS for detection after rolling circle amplification. The RCA-LFS method was used to detect samples of infected

Anguilla japonica

with

E. tarda

. We could get

E. tarda

positive result from sample DNA in liver，intestine，muscle，kidney and gill. The results were consistent with those obtained from conventional gel electrophoresis. This method was simpler，faster，and easier for result interpret

ation. RCA-LFS significantly promoted field detection of pathogenic bacteria.