Isolation and Identification of Mycobacterium marinum Associated with Splenic and Renal Granuloma Disease of Cultured Turbot (Scophthalmus maximus)

Abstract:

With the highest annual production among flatfish, turbot (Scophthalmus maximus) is reared as the major industrial aquaculture marine fish species in North China. In the culture process, members of this species are subject to infection with a variety of pathogens. In 2017, massive death of reared turbot occurred in a farm in Lianyungang City, Jiangsu Province. Externally, no clinical signs were observed for most of the diseased fish. However, after dissection, splenic and renal tubercles were found in all the diseased fish. Homogeneous colonies were isolated from diseased or moribund fish and were named as SM-Myco001. Healthy turbot were subjected to challenge tests by intraperitoneal injection using SM-Myco001. SM-Myco001 was found capable of causing death in turbot, especially at a higher water temperature (22℃). The diseased turbot displayed clinical signs, such as splenic and renal tubercles, similar to those observed in naturally infected fish. SM-Myco001 was identified as Mycobacterium marinum based on bacterial morphology, analytical profile index identification, and 16S rRNA gene sequencing. This study suggests that a strain of M. marinum is the causal agent of splenic and renal tubercle disease in turbot. As a first report, to our knowledge, this study provides a new perspective on disease control in the flat fish aquaculture industry in China.