Abstract: Skin ulcer epidemic is a serious disease of cultured groupers （Epinephelus coioides）prevalent recently in Tianjin, China. During the past three years, epidemiologic investigations have been carried out in the grouper culture factory. The infected or moribund fish exhibited gross skin ulcers on body surface and tumefied liver, blanched intestine in anatomic symptoms. Neither parasites was examined on skin ulcers, gill filaments or other organs by microscope, nor was virus particles observed under an electron microscope. However, seven pathogenic bacteria were isolated and purified from ulcers and internal organs. They were identified by morphological and physiological characteristics as well as housekeeping genes amplification. Among the seven pathogenic bacteria strains, five strains belonged to genus Vibrio harveyi, which was isolated every year, one strain belonged to genus Aeromonas salmonicida, and the other one belonged to genus Vibrio fluvialis. The researches show that V. harveyi is the major pathogen, A. salmonicida and V. fluvialis are other infective pathogens of skin ulcer occurred in cultured groupers in Tianjin, China. The results will lay better foundation for preventing outbreak and prevalence of skin ulcer epidemic in cultured groupers.

Key words: Epinephelus coioides, skin ulcer, bacterial identification, Aeromonas salmonicida, Vibrio harveyi, Vibrio fluvialis