Abstract
This paper gave detailed description of the fine structure of Apiosoma piscicola Blanchard 1885. These parasites were collected from the fry of Tachysurus fulvidraco during parasite surveys of fish at Jiangxia Fish Hatchery in Wuhan, Hubei province in May 2011. Its pellicle, peristomial apparatus, nuclei, trochal band and scopula were described, respectively. The relationship between these peritrich ciliates and their hosts was well discussed herein. The scopula of A. piscicola did not adhere directly to the surface of the host epithelial cells, but by means of a secreted adhesive pad of material according to the present study. Besides, no ultrastructural damage to host epithelial cells could be detected in our work. We concluded that these sessilids should be ectocommensals rather than ectoparasites, but not always harmless. In addition, their great variability of body shape and non-strict host specificity were also discussed.