A bacterial infection was spread in the Broomtail wrasse (Cheilinus lunulatus) during winter 2019 in a marine aquarium without a heating system while salinity diluted with tap water. The infected fish became lethargic, pale gills, change to excessive black colouration. Internally, the kidney was swollen and had granulomatous lesions, that showed the presence of bacterial colonies and necrotic phagocytes, and accumulations of macrophages. The isolated strain was gram-negative rods with rounded ends bacteria, psychrophilic, and non-pigmented bacteria in BHI, colored yellow in TCBS. Partial 16S rRNA sequences demonstrated high sequence homology with Janthinobacterium sp. and to J. lividum. The strain showed high resistance to all the studied antibiotics and low sensitivity to chloramphenicol.