Ultrastructural and cytochemical study of food vacuoles and primary lysosomes in Ichthyophthirius multifiliis (Ciliophora).

In the trophozoites of the fish parasite Ichthyophthirius multifiliis many food vacuoles can be found in different stages of the digestive cycle. Newly formed food vacuoles are large and contain remains of the fish cells that have been phagocyted by the ciliate. In some food vacuoles it was possible to observe evaginations in the membrane. Primary lysosomes of I. multifiliis are small dense bodies with about 0.2 μn in diameter. Enzyme cytochemistry revealed the presence of acid phosphatase and aryl sulphatase in food vacuoles and primary lysosomes, but trimetaphosphatase was not detected. Since aryl sulphatase activity was observed at pH 4.5 and 6.0 it is possible that two isoenzymes, A and B, are present.