Abstract

Mycobacteria spp. are ubiquitous bacteria in water supplies that can cause significant morbidity and mortality in aquatic species.³ Leafy seadragons (Phycodorus eques) and weedy seadragons (Phyllopteryx taeneolarus) appear to be particularly susceptible to mycobacterial infection.² Over the past 3 years at the John G. Shedd Aquarium about 50% of the population of leafy seadragons, and 35% of the population of weedy seadragons, presented to necropsy have had histopathology confirm mortality due to mycobacterial infection. The prevalence of mycobacteriosis in wild seadragons is unknown. Mycobacterial infection in seadragon species is presumed to be due to environmental contamination, contamination of the food supply, stress induced immunosuppression, or acquired during importation to the United States.

Mycobacteria chelonae infections were found present hatchery-reared juvenile Pacific salmon fed raw carcasses and viscera of spent fish. The infections were eventually prevented by discontinuation of this feeding practice.¹ A pilot study at John G. Shedd Aquarium was developed to evaluate the mycobacterial load in food stuffs. The first phase of the study was to culture and determine mycobacterial load present in the food supply of mysid shrimp (Americamysis bahia) cultured at the aquarium. The second phase of the study was to evaluate treatment of the mysid shrimp in multiple separate short term (1 day) antibiotic water baths in an effort to reduce the incidence of isolation of Mycobacteria spp. from the foodstuffs. The third phase of the study was to evaluate treatment of mysid shrimp with the bactericidal mycobacterial drug Rifater (rifampin/isoniazid/pyrazinamide) in long term (5 days) and short term (1 day) water baths.

The first phase of the study found in random cultures of the brood stock and holding stock of mysid shrimp, 25% and 50% cultured positive for Mycobacteria spp., respectively. In the single bath trial, mysids treated with ciprofloxacin and doxycycline were culture positive, while the mysids treated with amikacin bath were culture negative. This negative result was achieved with a onetime sample; therefore a long term bath with amikacin was initiated. The shrimp sampled during the long term bath were found positive for Mycobacteria spp. The long term and short term trial with Rifater resulted in 65% and 75% positive cultures respectively, with 33% of the controls for this trial culture positive.

This study reveals that bath treatments with ciprofloxacin, doxycycline and Rifater do not reduce the incidence of isolation of Mycobacteria spp. from live mysid cultures. Further studies with similar design and other antibiotics or combinations of antibiotics will be performed in the future. Further areas of study include the identifying the source of the positive cultures in the breeding and holding stock of mysid shrimp, irradiation treatment of mysid shrimp, or antibiotics sensitivities of the specific cultured mycobacterial species and tailoring trials around those results.

References

1.  Brocklebank J, S Raverty, J Robinson. 2003. Mycobacteriosis in Atlantic salmon farmed in British Columbia. Can. Vet. J. 44: 486-489.

2.  Garner MichaelM, S Frasca, C Bonar, ES Weber, JT Raymond, J Trupkiewicz. 2005. A retrospective study of diseases of sea dragons. AAZV Conference Proceedings: p. 58-59.

3.  Decostere A, K Hermans, F Haesebrouck. 2004. Picine mycobacteriosis: a literature review covering the agent and the disease it causes in fish and humans. Veterinary Microbiology. 99: 159-166.