Managing mycobacteriosis and associated biosecurity in the care and breeding of threatened freshwater fishes in public aquariums: an overview

Abstract

Management of freshwater fishes in zoos and aquariums for conservation breeding is a key area where much can be achieved with limited facilities and a comparatively modest financial outlay. Some species now survive only in captivity following in situ threats such as habitat loss. Fortunately, short generation length and high fecundity mean that populations of freshwater fishes can be readily maintained in anticipation of ecosystem reinstatement and a reintroduction programme, where conditions are appropriate. However, diseases that occur in captive populations may constrain any species recovery programme. Conversely, any disease not previously found in the wild population should not be present in captive fishes when the animals are reintroduced to the wild. Mycobacteriosis has regularly been identified in episodes of morbidity and mortality in groups of Extinct in the Wild and other threatened freshwater fishes maintained for conservation breeding. It is, therefore, a common impediment to breeding and reintroduction programmes. For any programme to succeed, the issue of disease management needs to be addressed and solutions found to the challenges. An overview of the elements that must be considered when mycobacteriosis is detected in captive populations of threatened freshwater fishes and ways in which these can be managed in aquariums are discussed here.

Investigation and management of an outbreak of multispecies mycobacteriosis in Australian lungfish (Neoceratodus fosteri) including the use of triple antibiotic treatment

“…The absence of AF bacilli on direct microscopy of ZN‐stained tissue impression smears from antemortem lesions or PME material does not preclude the presence of mycobacterial organisms and mycobacterial disease (Yanong et al . ; Routh ). These techniques have poor sensitivity, with more than 50–60% false negatives in some studies (Pate et al .…”

“…Polymycobacterial infections with M. marinum and one of the less common NTM species have been reported by Lescenko et al . () and Routh () in aquarium fish.…”

“…Fomites are known to transfer mycobacterial infection between infected tanks, as do water splashes or aerosol created by aeration of water (Kent et al . ; Routh ) and so could also be a means of infection within the aquarium setting. However, M. peregrinum has previously only been isolated from an amphibian in the Reptile House at ZSL London Zoo and not from any fish species.…”

“…Alternatively, when it occurs in important conservation or laboratory species, control is achieved by managing the disease and fish population with reviews of husbandry protocols, for example reducing stocking densities, separating older and younger stock, separation of breeding stock and optimizing nutrition and water quality parameters (Murray et al . ; Routh ). The question of treatment does arise, however, in individual fish of high value to a collection.…”

“…Treatment is usually not advocated, and instead, mycobacterial disease in fish is typically controlled by culling individuals or by de-stocking entire populations with total disinfection of holding tanks and plumbing (Astrofsky et al 2000;Kent et al 2009). Alternatively, when it occurs in important conservation or laboratory species, control is achieved by managing the disease and fish population with reviews of husbandry protocols, for example reducing stocking densities, separating older and younger stock, separation of breeding stock and optimizing nutrition and water quality parameters (Murray et al 2011;Routh 2013). The question of treatment does arise, however, in individual fish of high value to a collection.…”