Abstract
The amphibian chytrid fungus Batrachochytrium dendrobatidis is a recently emerged pathogen that causes the infectious disease chytridiomycosis and has been implicated as a contributing factor in the global amphibian decline. Since its discovery, research has been focused on developing various methods of mitigating the impact of chytridiomycosis on amphibian hosts but little attention has been given to the role of antifungal agents that could be added to the host's environment. Sodium chloride is a known antifungal agent used routinely in the aquaculture industry and this study investigates its potential for use as a disease management tool in amphibian conservation. The effect of 0–5 ppt NaCl on the growth, motility and survival of the chytrid fungus when grown in culture media and its effect on the growth, infection load and survivorship of infected Peron's tree frogs (Litoria peronii) in captivity, was investigated. The results reveal that these concentrations do not negatively affect the survival of the host or the pathogen. However, concentrations greater than 3 ppt significantly reduced the growth and motility of the chytrid fungus compared to 0 ppt. Concentrations of 1–4 ppt NaCl were also associated with significantly lower host infection loads while infected hosts exposed to 3 and 4 ppt NaCl were found to have significantly higher survival rates. These results support the potential for NaCl to be used as an environmentally distributed antifungal agent for the prevention of chytridiomycosis in susceptible amphibian hosts. However, further research is required to identify any negative effects of salt exposure on both target and non-target organisms prior to implementation.
Highlights
The chytrid fungus Batrachochytrium dendrobatidis is a recently emerged pathogen that causes the fatal disease chytridiomycosis in amphibian hosts and has been implicated as a causal agent in the decline and extinction of over 200 amphibian species [1,2,3]
The results reveal that NaCl exposure has an inhibitory effect on zoosporangia growth, zoospore motility, infection load and host mortality rate
Developing zoosporangia were classified as any stage between a germling, showing visible signs of growth and rhizoid formation, to an enlarged cell with contents defined into individual zoospores but lacking a visibly open discharge tube [4]
Summary
The chytrid fungus Batrachochytrium dendrobatidis is a recently emerged pathogen that causes the fatal disease chytridiomycosis in amphibian hosts and has been implicated as a causal agent in the decline and extinction of over 200 amphibian species [1,2,3]. The chytrid fungus has two distinct life stages, the motile zoospore stage that disperses through water bodies to locate a host and encysts to become the growing zoosporangia stage [4] It infects the keratinized epidermal tissue of post-metamorphic amphibians which disrupts osmoregulatory function, causing electrolyte imbalances and cardiac arrest [5,6]. It infects the keratinised mouthparts of tadpoles which can impede feeding ability and reduce development rates [7], but does not result in disease [2]. As a result, reversing amphibian population declines will not be possible until a way of managing the effect of chytridiomycosis is found
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