Streptococcus spp. and Photobacterium spp. are the most important pathogenic bacterium that causes several freshwater and marine fish disease, including sea bass, sole, yellow tail, gilt-head sea bream and turbot both in natural environments and in aquacultures. At last, it resulting in economic losses worldwide. The current detection methods as RT-qPCR , multiplex PCR assay and LAMP for those pathogenic bacterium are not well suited for direct field testing because they involve complicated, time-consuming operations. Rapid diagnosis of fish is essential for a proper management and effective control of outbreaks in farmed fish. In this study, we combined isothermal recombinase polymerase amplification (RPA) with a lateral flow (LF) strip to rapidly and reliably detect S. iniae, S. agalactiae, P. bacterium subsp. damselae and P. bacterium subsp. piscicida. This assay could be used to detect those pathogenic bacterium within 20 min, including DNA amplification with RPA for 15 min at 37 °C and visualization of the amplicons by LF strips for 5 min. Experiments confirmed a detection limit as low as 0.1 to 15 ng of DNA in pure cultures. Furthermore, RPA-LF exhibited no cross-reactions with pathogens. RPA-LF can be used as a sensitive and rapid detection technique for Eleutheronema tetradactylum, we will use rapid diagnosis to avoid seriously outbreaks in Eleutheronema tetradactylum by those panthogens under larve stage.