Abstract: To explore the pathogens causing the mortality of the lined seahorses（Hippocampus erectus）in some fish farms located in Tianjin, the predominant bacteria Par-1 was isolated from the dying seahorses' liver pancreas. Through multiple methods, including morphological observation, physicochemical characteristics test, and 16S rRNA analysis, the results showed that Par-1 was a gram-negative bacterium with short and curved shape, and it could ferment glucose without gas. 16S rRNA gene of Par-1 amplified by PCR was a 1 418 bp gene fragment, and the analysis on the phylogenetic tree showed that Par-1 was most closely related to Vibrio parahaemolyticus, with sequence homology reached to 99%-100%, so Par-1 was identified as Vibrio parahaemolyticus. The median lethal dose（LD₅₀）was 5.01×10⁶ CFU/mL by challenge. The antibiotic sensitivity analysis showed that the strain was sensitive to 22 kinds of anti-bacteria drugs including imipenem, meropenem, cefotaxime, azithromycin, norfloxacin, streptomycin and tetracycline, etc. The results will provide reference for the control of bacterial disease from the lined seahorses.

Key words: lined seahorse, Vibrio parahaemolyticus, physicochemical characteristics, antibiotic sensitivity