Pathologic effects of Sphaerospora dicentrarchi Sitjà-Bobadilla and Alvarez-Pellitero, 1992 and S. testicularis Sitjà-Bobadilla and Alvarez-Pellitero, 1990 (Myxosporea: Bivalvulida) parasitic in the Mediterranean sea bass Dicentrarchus labrax L. (Teleostei: Serranidae) and the cell-mediated immune reaction: a light and electron microscopy study.

In the present study, the pathogenic effects of Sphaerospora dicentrarchi and S. testicularis, histozoic and coelozoic myxosporean parasites of the Mediterranean sea bass Dicentrarchus labrax L., respectively, are described. The infection caused by the latter, which usually invades the testes and neighboring tissues, is considered to represent parasitic castration. S. dicentrarchi seems to be harmless except in massive infections, which probably result in organic disfunctions. The cellular host reaction generated by S. testicularis depends on the location of the parasite and is more intense than that produced by S. dicentrarchi. In both sphaerosporoses, macrophages, granulocytes, lymphocytes, plasmacytes, and fibroblast-like cells are involved. The role of the different immune cells is discussed.