High Mortality in a Large-scale Zebrafish Colony (Brachydanio rerio Hamilton & Buchanan, 1822) Associated with Lecythophora mutabilis (van Beyma) W. Gams & McGinnis

摘要

Zebrafish(Brachydaniorerio)havebecomeanimportantmodelsystemforstudyingvertebrateembryonicdevelopmentandgenefunctionthroughmanipulationofgenotypeandcharacterizationofresultantphenotypes.Anestablishedresearchzebrafishcolonywithoutsubstantialdiseaseproblemsformorethan7yearsofoperationbeganexperiencingappreciablemortalitiesinNovemberof1997.Youngfish(fry),fromfiveto24daysafterhatching,spontaneouslydevelopedelongatestrandsoforganicmaterialprotrudingfromthemouth,operculum,andanalpore,leadingworkersinthelaboratorytodescribetheinfectedfishas#8220;bearded.#8221;Unliketypicalfreshwaterfishfungalinfections,theskinsurfacedidnothaveevidenceoffungalcolonization.Thediseasewasassociatedwithprogressivelethargy,reducedfeeding,andsubsequentmortality.From10to100%ofthefryinagiventankwereaffected.Initialexaminationindicatedthatthebiofilmaroundtheheadofaffectedfryconsistedofbundlesofseptatefungalhyphae,largenumbersofmixedbacterialpopulations,andprotozoans.Environmentalsamplesofairandwaterinthelaboratorywereobtainedtoascertainthesourceoftheinfectiveagentandtoisolateandidentifythefungus.AfungusidentifiedasLecythophoramutabiliswasisolatedrepeatedlyfrominfectedfishandwatersamplesfrominfectedfishtanks,andfromthemainlaboratorywatersupplytanks,butnotfromlaboratoryair.Somebiofilmbeardsonfishwerefoundtoconsistofrelativelypurebacterialpopulations,andbeardsonoccasionalfishexaminedinthelaterpartofthestudyconsistedofhyphaeandsporesoftheoomycetegenusAphanomyces.Lecythophoramutabilisdidnotinvadetissues;however,eliminationoftheepizooticcorrelatedwithreductioninthenumberofL.mutabilisconidiainthewaterfollowingmodificationofthelaboratorywatersystembyuseofnewfiltrationandsterilizationsystems.WeconcludethatthedensehyphalstrandsofL.mutabiliscomposingthepredominantbiofilmtype,alongwithmixedbacteriaandprotozoa,contributedtothedie-offinyoungfrybyoccludingtheoralcavityand/orgills,leadingtostarvationand/orasphyxiation.