Diagnosis of Mycobacteriosis in Cultured Hybrid Tilapia ( Oreochromis spp.) in Trinidad and Tobago

Mycobacteriosis is a significant disease in fish husbandry, with negative impacts on production facilities. Moreover, some Mycobacterium spp. that infect fish have zoonotic potential. Morbidity and mortality events at hybrid tilapia (Oreochromis spp.) farms in Trinidad and Tobago (T&T) associated with mycobacterial infections prompted a broader surveillance investigation across the hybrid tilapia farms within the country. Of the 168 specimens examined by polymerase chain reaction (PCR), 42% were Mycobacterium spp. positive. Among the mycobacteria-positive specimens, clinical signs (lethargy and loss of equilibrium) were observed in 96% (68 of 71), of which gross external abnormalities were evident in 7% (5 of 68) and internal lesions (granulomas) in 22% (15 of 68). Specimens that were mycobacteria-negative showed no clinical signs, gross abnormalities or lesions. Sequence analysis of a partial 723-bp rpoB (region V) fragment confirmed the presence of a consortium of uncharacterised Mycobacterium spp. in 18 hybrid tilapia specimens. These findings suggest that potentially novel species are circulating within and causing clinical and subclinical disease in the local farmed hybrid tilapia population in T&T. The study also revealed that over the period 2020-2021, 75% (9 of 12) of the major hybrid tilapia production facilities in T&T were infected with mycobacteria. This represents the first documentation of a piscine mycobacteriosis outbreak in hybrid tilapia in the Caribbean.