Abstract

The mountain chicken frog (Leptodactylus fallax) is the largest endemic amphibian species in the Caribbean. Habitat loss, predation by introduced predators, hunting and the fungal disease chytridiomycosis resulted in the species being listed as ‘critically endangered’ by the IUCN.

Since 1999, efforts have been made to conserve L. fallax across Europe as part of an Endangered Species Programme (EEP) with the hope that this ex situ population will help to repopulate their former range in the future.

In order to maintain a healthy and sustainable captive population of L. fallax, it is important to determine the most common causes of morbidity and mortality. Necropsy reports for 210 individual frogs were received from the four main UK holding institutions (Chester Zoo, Bristol Zoo, ZSL London Zoo and Jersey Zoo) covering the time period, 1999–2018. Of these, 114/210 reports contained information relating to full histological examinations.

Significant causes of morbidity and mortality in adult frogs (>2 years old), where gross and/or histological findings were available, were colitis (40/103) and nephritis (31/103). In addition, analysis showed that 29/90 adult frogs had evidence of colonic adenocarcinoma on histological evaluation of the gastrointestinal tract. Further statistical analysis of the data suggests that these disease processes may be connected. A suggested pathogenesis, whereby colitis causes cystitis and subsequent nephritis, as well as chronic colonic inflammation, metaplasia and neoplasia, is hypothesised.

Further investigations to determine the aetiology of the described disease processes are needed, with the aim of mitigating associated risk factors and improving the health of the captive L. fallax population.

Acknowledgments

The authors would like to thank Dr Gerardo Garcia, coordinator of the L. fallax EEP, for his assistance with this project, plus colleagues from Chester Zoo, Bristol Zoo, ZSL London Zoo and Jersey Zoo for their help producing and compiling the data used in this study.