The diagnosis of cutaneous tuberculosis poses a serious challenge due to many skin diseases of different etiology resembling the lesions caused by the TB (tuberculosis) bacillus, and difficulties in confirming the disease. The presented case concerns skin lesions in a hobby aquarist stung in the finger of the left hand by a fish. The resulting inflammatory infiltration was to be cutaneous tuberculosis or mycobacteriosis caused by MOTT (Mycobacterium other than tuberculosis). Laboratory, pathomorphologic, genetic and microbiologic tests of samples obtained from the patient, fish and water in the aquarium gave ambiguous results. A multidisciplinary discussion is presented on the difficulties in the differential diagnosis, problems with a clear interpretation of the results of various conducted tests, and possible ways of transmission of the infection, relevant to the described example.