Identification of Mycobacterium chelonae from Lined Seahorse Hippocampus erectus and Histopathological Analysis

Abstract

The lined seahorse (Hippocampus erectus) is an aquacultural species in China and has important economic and ornamental value. However, the species is affected by disease, which restricts their large-scale cultivation. In 2021, a disease was observed in cultured seahorses in Tianjin, China, with a cumulative mortality rate of 20%. The symptoms observed in the moribund seahorse included a weak swimming capacity, discolored body surface, enlarged liver and kidneys, and numerous white nodules in the parenchymatous organs. The strains HM-2021-1 and HM-2021-2 were isolated from diseased seahorses and were identified as being responsible for the disease. It demonstrated the potential to infect seahorse, and the cumulative mortalities of the seahorses artificially infected with strains HM-2021-1 and HM-2021-2 were 93.3% and 90.0%. The pathogen was identified as Mycobacterium chelonae based on physiological and biochemical tests, and 16S rDNA, rpoB, and Hsp65 gene sequence analysis. To our knowledge, this study is the first report of M. chelonae associated with diseased seahorses in China.

Two Genotypes of Streptococcus iniae Are the Causative Agents of Diseased Ornamental Fish, Green Terror Cichlid (Aequidens rivulatus)

“…In recent years, the formation of granulomas in visceral tissues has been reported in various marine and freshwater fish, such as turbot Scophthalmus maximus, half-smooth tongue sole Cynoglossus semilaevis Günther, seahorse Hippocampus erectus, and largemouth bass Micropterus salmoides [21][22][23][24][25]. Parasites, viruses, and bacteria have been identified as potential causes of nodules of internal organs in fish [26,27].…”

“…In our study, no parasites or viral particles were observed in the tissues of diseased fish exhibiting nodular symptoms, ruling out the possibility of parasitic or viral infections. It has been reported that bacteria such as Mycobacterium spp., Nocardia seriolae, Renibacterium salmoninarum, Rickettsia spp., Francisella spp., Photobacterium damselae, Aeromonas schubertii, and Aeromonas salmonicida can cause nodules of internal organs in fish [21][22][23][24][25][28][29][30][31]. PCR detection of the first five pathogens was used in the current study, but yielded negative results.…”