Detection, Disease Characteristics, and Control of Non-Tuberculosis Mycobacteria in Hybrid Devils Hole Pupfish

Non-tuberculosis mycobacteria (NTM) are important pathogens of both humans and aquatic organisms.  Mycobacteriosis of fishes, sometimes termed “piscine tuberculosis” (PT), is a chronic disease of brackish, fresh, and saltwater fishes.  An NTM species was isolated and cultured from hybrid Devils Hole pupfish, Cyprinodon diabolis X C. nevadensis mionectes.  Clinical signs of PT in these fish included spinal curvature, swollen abdomen, emaciation, and lethargy.  In advanced disease, dermal lesions were often present.  PT was uniformly fatal in fish that developed skin lesions.  Pathology showed granulomatous lesions could occur in any organ, but were most common in the spleen, kidneys, and liver.  Vertical transmission of PT occurred despite removal of eggs from parental aquaria for incubation and hatching.  PT was not effectively controlled by surface disinfection of eggs using either iodine at 100 mg/L or formalin at 1,667 mg/L of water.  Incubation of the eggs in water containing the antibiotics chloramphenicol at 50 mg/L or trimethoprim sulfamethoxazole at 25 mg/L resulted in significantly reduced vertical transmission, and was successful in creating mycobacterium-free stocks.  Longevity was also significantly increased in these fish.  The antibiotics cephalexin at 6.6 mg/L and erythromycin at 12.5 mg/L were largely ineffective in preventing vertical transmission.  Disinfection with iodine prior to antibiotic administration further enhanced the effectiveness of chloramphenicol and trimethoprim sulfamethoxazole in elimination of culturable mycobacteria from eggs, but this treatment significantly reduced 15 d survival of larvae.  Neither the number of mycobacterium-positive eggs nor 15 d survival was affected by disinfection with formalin before antibiotic administration.