Abstract

Mycobacterium spp. are ubiquitous bacteria in the environment that can cause significant morbidity and mortality in aquatic species. Mycobacteriosis presents a challenge to fish practitioners due to the typically chronic, subclinical presentation of the disease, the lack of successful treatment modalities, the difficulty disinfecting affected systems, and the zoonotic potential of the bacteria.

An initial survey was distributed to fish health personnel in public aquaria to collate information concerning species affected, clinical presentation and duration, commonly isolated species and methods of identification and isolation (i.e., necropsy, culture, histopathology, and laboratories used), foodstuffs offered to affected species, components of affected systems, environmental stressors, and treatment and disinfection modalities. The results from those surveys were summarized and presented at the Fish Practitioner's Workshop: Mycobacteriosis in Recirculating Systems as a component of last year's IAAAM meeting in Nassau, Bahamas. From a total of forty surveys that were distributed, information was received from ten facilities with one facility reporting no incidence of mycobacteriosis. Of the twenty-three systems with reported high incidence of mycobacteriosis, nineteen (83%) were marine and four (17%) were freshwater. Most commonly reported affected species were found in the Syngnathid family, i.e., Phycodurus eques (leafy seadragon), Phyllopteryx taeniolatus (weedy seadragon), and various Hippocampus species. Signalment, clinical signs, and duration of disease were highly variable. The most common methods of diagnosis were positive benchtop or histopathologic acid-fast stains. While the majority of cases were not diagnosed via bacterial cultures (75.5%), of those that were, the most commonly isolated mycobacterial species were M. chelonae, M. marinum, and M. fortuitum. Two-thirds of facilities reported attempting treatment for mycobacteriosis using numerous antibiotics with two reports of "success" using injectable Amikacin in Phyllopteryx taeniolatus. Reportedly used disinfectants for systems and equipment included sodium hypochlorite, hydrogen peroxide, quaternary ammonium compounds, isopropyl alcohol, povodone, and Virkon®.

The survey helped identify the extent of the problem at these facilities and gave some baseline information with regard to management and areas for improvement. For example, with regard to disinfection, many of the compounds used will not effectively eliminate mycobacteria in systems.

A second updated version of the survey was distributed to fish health personnel in both zoos and public aquaria to collate further information related to the above topics. The responses to these surveys were summarized and are presented. It is hoped that these results will help guide future collaborative mycobacteriosis research, management, and education programs.