Zebrafishwillmateanddepositfertilizedeggsonthebottomofthetankat"dawn".Theycanbeaccustomedtolayatanyconvenienttimebykeepingtheroomdarkandlightingthetankwithatimer.Themaximumembryoproductionisobtainedwitharatioof1maleforevery2females,withagroupof20-25fish.Thenightbeforeembryocollection,vacuumthetankwellwithasiphontoremovedebrisseveralhoursafterthelastfeeding.Depositalayerofwashedmarblestocovertheentirebottomsurfaceofthetank.Donotdisturbforthefirst30minutesafter"dawn"toallowfishtomate(seebelow).Embryoscanbecollectedonceaweek,withbestresultsfromtankskeptonaregularschedule.Collectembryosandfertilizedeggsfrombetweenthemarbleswithasiphonandcollectwithafinefrynetormeshfilter.Transferthenettoaglassdishfulloftankwaterandexaminetheembryoswithadissectingmicroscopeatlowmagnification.Transferhealthyembryostoacleanglasspetridishcontainingembryomediawithlarge-boreglasspasteurpipets.Discardanythatarecloudyorruptured.Keepembryosat28°C.