A Case of Mycobacteriosis in Cultured Japanese Seabass (Lateolabrax japonicus) in Southern China

Japanese seabass (Lateolabrax japonicus) is an important species of cultured marine fish with high economic value in China. Nevertheless, from May to November 2019, mass mortality among occurred Zhuhai City, Guangdong Province Approximately 0.2–0.5% was recorded daily, and the cumulative up 30% during this disease outbreak. In study, clinical signs pathological characteristics diseased were investigated. Furthermore, pathogenicity antibiotic sensitivity identified pathogenic bacteria analyzed. The infected showed uncoordinated swimming; anorexia; pigment changes; a number 1–5 mm grayish-white nodules liver, spleen, kidney tissues also found. A bacterial strain, which designated as ZHLJ2019, isolated fish. To ensure that ZHLJ2019 isolate causative agent, Koch postulate trial performed. Healthy by intraperitoneal injection 5 × 104, 105 106 CFU/fish, mortalities within 42 days 75%, 90%, 100%, respectively. colony had traditional morphological biochemical similar Mycobacterium marinum. Phylogenetic molecular analyses 16S rRNA, rpoB, hsp65, erp, ITS genes confirmed strain M. granulomatous inflammation internal organs naturally experimentally consistent classic features mycobacteriosis. Drug susceptibility 11 antibiotics determined broth dilution method vitro. minimum inhibitory concentrations (MICs) minocycline, rifampicin, ethambutol, isoniazid, streptomycin, doxycycline hydrochloride, kanamycin sulfate, levofloxacin, roxithromycin, prothionamide against 4, 2, 8, 16, 8 μg/mL, results study suggest marinum causal agent responsible for morbidity intensive brackish water dirt ponds southern