In 2019, several aquarium-reared fish died at a sea life park in Japan.Necropsy revealed micronodules on the spleen in the dotted gizzard shad (Konosirus punctatus). Seven of 16 fish exhibited microscopic multifocal granulomas associated with acid-fast bacilli in the spleen, kidney, liver, alimentary tract, mesentery, gills, and/or heart. Bacterial cultures yielded isolates from the dotted gizzard shad and a Japanese sardine (Sardinops melanostictus). Microbiological and molecular biological examinations revealed the isolates asMycobacterium pseudoshottsii. To our knowledge, this is the first isolation of M. pseudoshottsii from aquarium-reared fish.

Mycobacterium marinum is a slow-growing, photochromogenic nontuberculous mycobacterium, which can cause mycobacteriosis in various animals, including humans.Several cases of fish mycobacteriosis have been reported to date. Mycobacterium marinum has also been isolated from aquatic environmental sources such as water, sand, biofilms, and plants in the natural environments. Hence, we hypothesized that a wide variety of sources could be involved in the transmission of M. marinum. In this study, we tested this hypothesis by isolating M. marinum from various sources such as fish, invertebrates, seagrass, periphytons, biofilms, sand, and/or water in two aquaria in Japan and conducting a phylogenetic analysis based on single-nucleotide polymorphisms (SNPs) using whole-genome sequences of the isolated strains. The analysis revealed that the strains from animal and environmental sources belonged to the same clusters. This molecular-based study epidemiologically confirmed that various sources, including fish, invertebrates, and environmental sources, could be involved in transmission of M. marinum in a closed-rearing environment. This is the first report where M. marinum was isolated from different sources, and various transmission routes were confirmed in actual cases, which provided essential information to improve the epidemiology of M. marinum.

In 2019, several aquarium-reared fish died at a sea life park in Japan. Necropsy revealed micronodules on the spleen in the dotted gizzard shad (Konosirus punctatus). Seven of 16 fish exhibited microscopic multifocal granulomas associated with acid-fast bacilli in the spleen, kidney, liver, alimentary tract, mesentery, gills, and/or heart. Bacterial cultures yielded isolates from the dotted gizzard shad and a Japanese sardine (Sardinops melanostictus). Microbiological examination, multilocus sequence typing analysis, and variable number of tandem repeats analysis with a newly proposed 6-loci set revealed the isolates as Mycobacterium pseudoshottsii. To our knowledge, this is the first isolation of M. pseudoshottsii from aquarium-reared fish.