More info about stalked protozoans affecting fish. There are several species of Epistylis that infect the skin, fins, and gills of fish (Esch et al., 1976). The urn shaped organism, which is adorned by a ring of cilia on the distal end, is at the terminus of a dichotomous stalk that, in turn, attaches by a disk to hard surfaces of the host such as spines, scales, or gill covers. Groups of Epistylis form a colony, grouping or cluster. These parasites cause irritation and inflammation of the epithelium of the host at the point of attachment which may provide a site for secondary infections of Aeromonas hydrophila. The parasites feed primarily on bacteria and organic material in the water, but they erode scales and hard spines of fins where they attach. Other than the injury incurred by attachment, they are seldom harmful to the host unless there are large masses of these parasites.
Several other unicellular parasitic ciliates including Trichodina, Tricodinella, Epistylis, Ichthyobodo, Apiosoma, Vorticella and Ambiphrya are common among wild and cultured tilapia, especially when the fishes are farmed at high stocking densities

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