Hemagglutination in gill capillaries of sheepshead, Archosargus probatocephalus (Perciformes: Sparidae), infected by a myxosporidean

During a survey Myxozoa, four specimens of the sheepshead (18 ± 1.5 cm and 59 ± 2.5 g) (Archosargus probatocephalus) were collected in the Ipioquinha river (Maceió/AL). Transmission electron microscopy observations revealed erythrocyte agglutinations in gill capillaries located near spherical cysts containing myxospores of the genus Henneguya. This hemagglutination partially or totally obstructed the gill capillaries. Erythrocytes occurred in close adherence to each other, with a closed intercellular space. A few lysed erythrocytes were observed among agglutinated cells. The reduced lumen of the capillaries was partially filled with amorphous dense homogenous material adhering to the erythrocytes. In addition, heterogeneous masses of irregular lower electron density were observed in the reduced channel of the capillary. The agglutinated erythrocytes appeared dense and homogenous, lacking cytoplasmic organelles. The nuclei had the appearance of normal condensed chromatin masses, generally without visible nucleoli. This occurrence of hemagglutination only in the capillaries located in close proximity to the developing myxozoan cysts suggests that parasite development may be a factor triggering erythrocyte agglutination. This is supported by previous experimental studies that showed a probable correlation between parasitic infections and hemagglutination. Nonetheless, further studies are necessary in order to better understand the physicochemical processes involved in this phenomenon.