In stocks of siluriform and cichlid ornamental fishes imparted from differe
nt locations in tropical Africa and South America. infections with vegetati
ve cysts of a dinoflagellate occurred on skin, fins and gills. In affected
fish the skin was covered with a greyish mucus layer and white spots develo
ped like in infections with Ichthyophthirius multifiliis. The fish stopped
feeding and in some stocks up the 100% of infected Fish died within 7 to 14
days. Treatments with standard procedures against ectoparasites were not s
uccessful. The dinoflagellates were identified based on the presence of a d
inokaryotic nucleus with condensed chromosomes. On fish vegetative cysts bu
t no trophonts were found. The cysts induced an epithelial cell hyperplasia
. The epithelium cells formed a thickend layer which enclosed individual cy
sts or aggregates of cysts.