Chytrid fungi identified from dying frogs in New Zealand

Phil Bishop
phil.bishop@stonebow.otago.ac.nz
Chair
DAPTF Working Group New Zealand.

14 March 2000.

Late last year Bruce Waldman from the University of Canterbury, Christchurch, found a large number of sick and dying frogs (of the introduced Australian species, Litoria raniformis) in a Canterbury pond. The frogs were extremely lethargic but no obvious skin lesions were apparent. Tissues of affected adults and metamorphs were sent to Richard Norman at the Institute of Veterinary, Animal & Biomedical Sciences (IVABS), Massey University, for pathological analyses. Chytrid fungi were found in all affected frogs that were examined. Identifications were confirmed by Lee Berger (CSIRO AAHL, Melbourne).

Despite the large-scale dieoff, numerous apparently healthy frogs remained in the pond throughout most of the summer. Histological examination of the healthy individuals so far has revealed no evidence of chytrid infection. Metamorphosing tadpoles demonstrated a variety of symptoms including skin ulcerations, internal bleeding, and body swellings. To determine possible causal agents, diagnostic samples are being cultured for bacteriological and mycological analyses. Additionally, soil and vegetation samples from the infected pond are being analysed for evidence of chytrids.

Frogs often are collected from this pond by the pet trade. Stock imported into New Zealand is typically held in quarantine facilities on the premises of pet dealers. The possibility thus exists that the fungus was introduced into the pond by collectors. Concern is mounting that commercial trade in frogs may now be spreading the fungus throughout the country. A couple of dead introduced frogs (Litoria ewingii and Litoria raniformis) from different localities on the South Island have recently been examined by myself and chytrids are again suspected. Prepared slides of their tissues have been sent to IVABS for further pathological investigation.

New Zealand has seven species of frog, four indigenous and three introduced (from Australia). New Zealand's four indigenous species are regarded as amongst the most primitive frogs living in the world today. All are considered threatened, one being endangered and another vulnerable following the International Union for Conservation of Nature's Red Data Book categories. Although three of the four indigenous species are mainly terrestrial, Leiopelma hochstetteri may be particularly vulnerable to chytrid infection due to its close association with streams.

All New Zealand Department of Conservation conservancies have been notified of the chytrid fungus finding, and have been asked to investigate, report and sample sick or dead frogs found in their conservancies.

The Ministry of Agriculture and Forestry has offered support for studies delimiting the extent of chytrid spread and determining how the fungus reached the country. To address the latter question, studies are underway by Bruce Waldman and John Klena (University of Canterbury) to assess the genetic similarity of New Zealand chytrids to those that have parasitised frogs elsewhere.

The Department of Conservation would like to receive reports of sites (ponds) where sick/ dying frogs have been observed (please record the date and time of day, location - map reference if possible, and name of observer. Sick or dying frogs, if collected, should be taken as soon as possible (dead frogs decompose rapidly!) to the nearest DOC office. Dead specimens are best preserved in 10% buffered formalin if available. Otherwise use 70% alcohol, or freeze them. With public support DOC and MAF hope to quickly assess the risk this unwelcome threat poses to our unique native frogs.