Ichthyophthirius multifiliis from freshwater fish. This is the
ectoparasite that troubles tropical fish enthusiasts. This is a photo of
the trophozoite sectioned through the cytostome, revealing the forming
pinocytotic vesicles (unlabeled) to the immediate left of the cytostome (CYT).
Secretory vesicles (SV) can be seen being discharged. It is thought these
secretory vesicles contain digestive enzymes which lyse the skin of the fish,
providing nutrition for this ciliate.25,000x.