Vibrio harveyi is an opportunistic pathogen in seawater and can cause severe vibriosis. It is prevalent in hatcheries worldwide and can lead to severe economic losses. Therefore, there is an urgent need to develop a rapid detection method for monitoring this pathogen. In this study, to increase the detection sensitivity of our assay with monoclonal antibodies (Mabs) against V. harveyi, the conditions of the dot blot assay were optimized, and enhanced chemiluminescent (ECL) substrate replaced the traditional tetramethylbenzidine (TMB) substrate. Based on the optimization results, an ECL-based novel dot blot assay was developed for the rapid and sensitive detection of V. harveyi. Compared with the traditional dot blot assay, the incubation time was shortened from 8 to 2 h. The limit of detection (LOD) for V. harveyi was 2 × 105 CFU per ml (103 CFU per spot) in pure bacterial suspension, which was 50-fold more sensitive than the traditional dot blot assay (1 × 107 CFU per ml). Furthermore, when compared with indirect ELISA, the dot blot assay showed approximately 1000-fold higher sensitivity (CFU/CFU). After the test sample was pre-enriched in turbot homogenates for 6 h before the dot blot analysis, the LOD for V. harveyi was 10 CFU per ml.