The ultrastructural histopathological changes of experimentally infected kelp bass were the same as those of spontaneously infected lymphocystis. In the cytoplasm of the cells of skin nodules, lymphocystis cells, there were numerous inclusions that distributed in the form of network of inclusions showing condensed electron dense and coarse granular appearance. The inside and outside of the meshes were closely packed with virus particles. The virus particle attached at first to the surface of the fibroblast cells in the derma, then entered the cells, changed the cells morphology and structure, finally formed the lymphocystis cells. Rupture of the lymphocystis cells on the body surface caused large open ulcerating wound.

Although lymphocystis cells and virus particles were not discovered in the liver, spleen, kidney, heart and intestine of the diseased fish, the ultramicroscopic cell structures of those organs changed in various degrees, i. e. mitochondria had disordered cristae, abundant, endoplasmic reticula enlarged and developed into vesicae, which demonstrated that their function had already been seriously impaired and abnormal fish metabolism could result in final death of the diseased kelp bass.