It doesn’t happen often, but aquarists have acquired infections from their aquaria, specifically granulomatous infections from Mycobacteria.
Mycobacterium (the same genus of bacteria that causes Tuberculosis) species, such as Mycobacterium marinum, exist in many home aquaria. These can gain access through open cuts or scrapes, and cause granulomatous infections. Such infections are often improperly diagnosed, unless a biopsy is done. Subsequent treatment may involve a course of up to several months of antibiotics.
An unpleasant prospect to most of us, at best; a possibly life threatening situation to those whose immune systems are suppressed.
To avoid concern, use rubber gloves when working in your fish tanks.
— G.C.K.A. Newsletter – September 1996